Fundamentals of Stripe Coating

1.Fundamentals of stripe coating From JPCL, January 2014 More items for Quality Control

Paint failures on bolted connection that had not been stripe coated Photos courtesy of Corrosion Control Consultants and Labs, Inc. Consider the following scenario, which points out one of the worst disappointments in the painting of steel structures. The owner carefully plans a project to include a well-written specification, careful material evaluation and selection, a qualified contractor, and thorough inspection of the work. The project is done on time, within budget, and with no claims for extra work. Two years later, visual inspection of the project reveals that 99% of the painting work shows no signs of failure. Yet, essentially every edge, bolt, and weld is rusting. What happened? The project specification did not require “striping” or “stripe coating” of all edges and welds during the painting work. Is this the problem? Maybe…maybe not. What is ‘Striping’ or ‘Stripe Coating?’ A stripe coat is “a coat of paint applied only to edges or to welds on steel structures before or after a full coat is applied to the entire surface. The stripe coat is intended to give those areas sufficient film build to resist corrosion.”1 Therefore, striping, as it is sometimes called, is the process of “painting the edges of a surface or welds to give them extra protection. Striping is done before priming or before the application of a full coat of paint.”1 (In this article, the terms “stripe coating” and “striping” are used interchangeably.) SSPC-PA 1, Shop, Field, and Maintenance Painting of Steel, includes the following advice about stripe coating.2

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If stripe coating is specified for a project, then all corners, crevices, rivets, bolts, welds, and sharp edges should receive a stripe coating with the priming paint before the steel receives a full coat of primer. The stripe coat should extend at least 1 in. (2 cm) from the edge. To prevent removal of the stripe coat by later application of the primer, the stripe coat should be allowed to set to touch before the full coat of primer is applied. (However, it should not be permitted to dry long enough to allow rusting of the unprimed steel.) Alternatively, the stripe coat may be applied after a complete coat of primer, especially if a long drying period for the stripe coat would allow the uncoated steel to deteriorate.

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Tinting of the stripe coat is advisable to promote contrast.

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Stripe coating is most effective on edges that are rounded by grinding.

The specification notes that stripe coating is advantageous in preventing coating breakdown on edges, etc., in very corrosive surroundings, but it is an expensive operation and may only be justified when it is believed that the cost will be compensated for by extra service life of the coating system. Is Stripe Coating Necessary? Stripe coating of edges, bolts, and welds is often specified because liquid paints tend to flow away from these parts. This is a

result of surface tension in the paint film and shrinkage of the paint film during curing. If this occurs, the paint film at or near the edges will be thinner than elsewhere on the painted surface, and the result can be early corrosion failure in these areas. This can become a critical issue when the paint is failing on the nuts, bolts, rivets, and welds, because these are the items holding the structural pieces together.

Edge failure on stiffener that was not stripe coated

Edge failure evident on yellow angle The benefits of striping are two-fold. First, it tends to fill in small voids, laps, and irregularities in the substrate (such as porosity in welds). Second, if allowed to cure to the point of tackiness, striping tends to retard the next full coat of paint material from flowing away from edges. High-solids paints are less prone to thinning at edges than low-solids paints because they generally have faster setting time, higher viscosity, and lower surface tension. At one time, most structural steel painting work was done with low-solids, relatively slow-curing, oil-based (alkyd) materials. The fact that the industry has moved toward the use of faster setting, higher solids coating materials, which exhibit less tendency to flow away from edges after application, does not mean that stripe coating is not necessary. The corrosiveness of the environment will often determine whether stripe coatings are needed. Stripe coating is often considered most cost-effective in highly corrosive environments such as the insides of tanks and marine or chemical exposures. In moderately corrosive environments such as those frequently wet by fresh water, coating choice and good control of the application without stripe coating may be adequate to protect the structure cost-effectively. In mild environments such as those with low humidity or indoors, striping is not necessary. Stripe Coating Techniques Since the original ATB on stripe coating was published in 2001, SSPC has issued SSPC-PA Guide 11, Guide to Protection of Edges, Crevices, and Irregular Surfaces. Published in 2008, the guide discusses the reasons for employing extra corrosion protection measures on edges, corners, crevices, bolt heads, welds, and other irregular steel surfaces, as well as various

protection options such as edge grinding, chamfering, and application of stripe coats. Some details, including the advantages and limitations of specific methods of obtaining additional coating thickness by stripe coating, are described to assist the specification writer in assuring that the project specification will address adequate corrosion protection. While Guide 11 should be consulted for projects that may include stripe coating application, each specifier and paint applicator must interpret the necessity, means, and methods for stripe coating for each individual project. Therefore, the following information is provided for the reader, based on the author’s experiences and interaction with various paint manufacturers, specifiers, and applicators. This information is not meant to be comprehensive; for more specific questions on stripe coating application, you should refer to Guide 11. When Should Stripe Coating be Specified? Stripe coating should be specified when the history of the structure indicates that edge failure of the paint system has been a problem. Consideration also should be given to specifying stripe coating in a severely corrosive environment, or if the paint manufacturer recommends stripe coating. Is Stripe Coating an Additional Coat of Paint? Owners and contractors have disagreed about whether stripe coating is an additional coat of paint. That depends on what the specification says. The need to cover a blast cleaned surface is paramount in corrosive environments. Therefore, the logical course is to apply the stripe coating after the primer. In this case, the stripe coating is clearly an extra step. On the other hand, in moderate environments or if there are not a lot of edges, it may be possible to apply the stripe coat just prior to the full primer. Then the contractor may have workers applying the stripe coat in front of workers applying the primer, and both of them using paint from the same cans. This process would not necessarily be considered an extra step. Which Generic Paints Warrant Consideration of Stripe Coating? For the most part, low-solids/low-viscosity paints (such as alkyds) tend to benefit from stripe coating. In general, fast-setting paints (such as inorganic zincs) and high-solids/high-viscosity paints (such as epoxy mastics) do not draw away from edges. However, striping does apply additional coating thickness to edges that might not have received enough paint originally. Which Coating Layers Warrant Stripe Coating? Keeping in mind that the primary benefit of stripe coating is compensation for possible reduced coating thickness at sharp edges and irregularities in the substrate, it is reasonable to conclude that only the primer should be striped. After application of the primer, substrate irregularities are covered. Applying stripe coats to all layers of paint can cause more harm than good. Too much paint increases stresses in a coating film, thereby causing cracking or peeling. The tendency of liquid paint to pull away from edges is reduced once a layer of primer has been applied. It is quite common to measure 750 micrometers (30 mils) of paint or more on a surface near edges where a threecoat system of 300–450 micrometers (12–18 mils) was specified with stripe coating of all three layers. Should Stripe Coating Be Applied Before or After the Full Coat of Primer? If a high degree of surface cleanliness is specified, such as SSPC-SP 10/NACE No. 2, Near-White Blast Cleaning (the equivalent of Sa 2½ in ISO 8501-1), the applicator has only a short period of time, depending upon atmospheric conditions, to prime the steel substrate before flash rusting occurs. To preclude flash rusting, the entire substrate probably should be primed first and the stripe coating applied later. The stripe coat should then be tinted so that it is obvious where the stripe coat was applied and if any areas were missed. Is Thinning Required for the Striping Material? If stripe coating with a particular paint material is specified, the application data sheet should be consulted for thinning instructions for the application method selected. For instance, if the stripe coat is to be applied by brush, the thinning instructions for brush application should be followed. No extra thinning should be done. Too much solvent in the paint, especially when the stripe coat is applied before the primer, will require more time for the stripe coating to become tacky. Solvent entrapment, bubbling, or pinholing can occur. Should a Thickness Be Specified for a Stripe Coat? Since irregular surfaces are one of the places stripe coating is used, it may be difficult or impossible to get an accurate dry film thickness reading. Nevertheless, it is important to remember that if total dry film thickness is exceeded by applying both a stripe coat and a full coat, then film defects may result. To achieve a stripe coat that is not excessively thick, the specifier may require that the paint be applied to produce a visual color change on the affected areas and not specify a particular wet or dry film thickness. It should be noted that only a portion of the paint applied directly to an edge flows away, so only a small amount of additional paint is needed to bring the coating on an edge to the same thickness as on flat surfaces. What Application Methods Should Be Used for Stripe Coating? The specifier and applicator must first examine the required qualities of the stripe coating to determine the optimum method of application. In general, the required qualities of stripe coating are

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filling voids and other irregularities in the affected substrate areas;

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providing a tacky surface for subsequently applied full coats of paint to adhere to; and

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not exceeding the optimum dry film thickness for the stripe coat in combination with the full coat.

Two application methods meet the requirements of these three qualities: brushing and spraying with conventional or air-assisted airless equipment. The specifier should permit all of these application methods for stripe coating, depending on specific job conditions. For instance, brushing can be used for stripe coating of small, complex shapes (such as lattice members and bolted connections), whereas conventional spraying is appropriate for the edges of large structural shapes. Application methods that can deposit relatively high volumes of paint (e.g., rolling with a heavy nap roller or airless spraying) should be avoided to prevent excessive dry film thickness and possible film defects. (This assumes that the stripe coating or full layer of primer is being applied while the underlying material is still tacky. More latitude in application methods can be allowed if a full layer of primer is applied and allowed to cure until its dry-to-recoat time. Then, the stripe coating can be thought of as an additional coat of paint being applied to the primer.) Edge Retentive Coatings You have probably also heard of edge retention coatings, which claim to have an edge coating thickness similar to that of a nearby flat plate. The question you’re asking is, can I use one of these coatings, or do I still need to carry out stripe coating? The answer is simple—stripe coating still needs to be carried out, as it serves more than one purpose. In addition to increasing the film thickness at the edge of plates or beams, stripe coating carried out by brush is better at “wetting” the surface and forcing the paint into cracks and crevices, over weld beads and bold heads, and other areas which are subject to premature failure. Conclusion Striping or stripe coating is used to extend the life of certain paint systems in corrosive environments. It compensates for liquid coatings that flow away from edges of steel structures, thus reducing the dry film thickness. For stripe coating to be beneficial and cost-effective, the specifier must consider the configuration of the structure to be painted and the type of paint system to be applied. Stripe coating should be limited to one coat of paint to avoid overly thick coating systems. Proper stripe coating application is needed to avoid defects in the paint film that can cause other problems besides early rusting, for which the stripe coating was applied. Editor’s Note: The original ATB on stripe coating was written by Jon R. Cavallo, P.E., of Corrosion Control Consultants and Labs, Inc. (Eliot, ME) for the May 2001 JPCL. It was slightly updated for this issue by JPCL Technical Editor Brian Goldie. REFERENCES

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SSPC Protective Coatings Glossary (Pittsburgh, PA, USA: SSPC: The Society for Protective Coatings, 2011), p. 201. “SSPC-PA 1, Shop, Field, and Maintenance Painting of Steel” (Pittsburgh, PA, USA: SSPC: The Society for Protective Coatings, April 2000), p. 13. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2014 Technology Publishing Company

Comment from Michael Deaton, (2/26/2014, 7:03 AM) After supervising the 1 million square foot Innerbelt project in Cleveland last year and dealing with the very intense inspection by Mr. Dave Nolan, owner of Quality Control Services, stripe coating was an essential part of the coatings application. There is over a half a million bolts on this project and the finish coat is white, therefore the stripe coat must provide a paint tight seal. Painters utilized 4" cigar or weeny rollers to apply 1st the organic zinc, then macropoxy 646 and finally the acrylic polyurethane to all bolts, edges, welds, etc. The finish coat only required striping where the airless gun could not access, but both the primer coat and the intermediate required full striping. This striping was very time consuming and should be factored into any bid.

Comment from Tom Selby, (2/26/2014, 12:49 PM) It makes more sense to get all blasted surfaces covered with the first coat of paint so that there is no compromising of the quality of the initial blast. After that coat is dry a contrasting color can be used to stripe coat with a brush or weenie roller.

Comment from Billy Russell, (2/26/2014, 4:35 PM)

3.Testing adhesion of multi-coat system

When should the adhesion of an applied coating or lining multi-coat system be tested? From Karen Fischer Amstar of WNY Adhesion testing should be performed for one of two basic reasons:

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if the specification calls for it as a qualifying test for acceptance of the coating system, or if there is a failure or suspected failure in the coating system (material and/or methods) that cannot be evaluated (or fully evaluated) by non-destructive methods.

One must always keep in mind that an adhesion test is a destructive test, so the resulting test area now becomes a repair that could, in itself, fail. This is especially important to keep in mind in the case of linings or any system that will be in immersion service, mechanical service, or a chemical/harsh environmental service. Because it may be necessary to perform adhesion testing in multiple areas (depending on the size of the suspected areas), there will be multiple repairs. Destructive testing should always be the last method employed, not the first method, when evaluating a coating for suspected or obvious failure. From James Albertoni CA Department of Water Resources Some good instances where a multi-coat system should be tested for adhesion include if the re-coat window is missed, if the topcoat is not specifically recommended by the manufacturer to be compatible with the basecoat, if the basecoat and topcoat are from two different manufacturers, or if it is suspected one of the coats was mixed slightly off ratio. Most importantly, the system should always be tested for adhesion if the spec calls for it. From Daniel Liu APC First, it will be up the specifier to decide if an adhesion test is required, and, if so, the specification should include not just the testing requirement but also the acceptance criteria and tester type. From my experience in the field of tank coating, this test is normally not required in the specification because it is a destructive method. Any repair area creates a weak point in the lining, so the more repair areas you have, the more weak spots you have. However, it is quite necessary to make a proper adhesion test recommended by the paint maker when application has or may have deviated from the specification, such as by exceeding the recoat interval, not maintaining the proper level of humidity, or using the wrong mixing ratio for plural-component coatings. Adhesion is quite important for tank coatings that are to be immersed in liquid. But passing the adhesion test does not mean the whole coating system is conclusively qualified for service. The test is only a reference. From Tom Swan M-TEST It’s important to note that if an adhesion test is called for in the specification, the document should specify failure criteria as well as the pull tester to be. All pull testers pull at different rates, and, when I discuss pull tests with most people, they have no idea what the pass/fail criterion is or what adhesion tester to use. If you want to use adhesion testing for pass/fail testing, the specifications should specify the minimum pull required and what test instrument to use. Also note that if you stop the test before the coating fails, there is no guarantee that the pull fixture will not take off the coating when you try to remove the fixture, nor does passing the test guarantee that the adhesion or coating integrity was not affected by the pull. From Manpreet Singh Spiecapag Australia PTY LTD If the client’s specification calls for adhesion testing, the paint system should be simulated on a test specimen of the same material class, 100 mm2 and 6 mm thick. ISO 4624 describes the method of performing the adhesion test. Acceptance criteria, unless specified by the end user, shall be a minimum of 7 MPA at 23 C, and, at 65 C, no more than 40% decrease from pull-off at 23 C. From Atanas Cholakov ACT Adhesion should be tested after the complete cure of the coating system. Information on curing can be acquired from the paint supplier’s technical representative. In the product data sheet, curing is highlighted in a table in accordance with different ambient temperatures and other conditions. From Trevor Neale TF Warren Group Critical service specifications typically call for adhesion testing, so I assume this question relates to field painting where weather and other delays are often unavoidable and formal adhesion testing is not part if the job/project specification. If there is any suspicion that adhesion may be compromised, then the appropriate form of adhesion testing is recommended to ensure the complete system integrity. This is simply a CYA procedure to avoid possible conflicts, or worse, premature failures.

From Bryant Chandler Greenman-Pedersen, Inc. Adhesion testing on coatings must be done after the proper cure time at the correct temperature. This enables the coating to develop the full physical properties. If the coating is tested prematurely, the results often will not meet the specified minimum requirement. The test may or may not be destructive, depending on the thickness of the coating/substrate, and whether or not the test is continued until coating disbondment. As called for in ASTM D 7234 (adhesion testing of coatings on concrete), scoring around the dolly down to the substrate will require a repair even if the test does not go to failure and stops at the minimum test value; a thick coating system (>30–40 mils) on a metallic substrate may require scoring if called for in the specification. If the test can be stopped at the minimum value specified without causing coating failure, than the dolly can be removed, often times by striking the dolly with a sharp blow from the side or carefully inserting a sharp 5:1 tool (putty knife) at the glue line and shearing off the dolly. Repairing the top surface may be required but is much better than having to repair the total coating system. When testing thermal spray coatings, always perform the adhesion tests before application of the seal coat. Tests performed after seal coat application will result in test values that are two to three times the value of virgin thermal sprayed coating. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2013 Technology Publishing Company

4. The case of…bubbles, and pinholes, and blisters, oh my! From JPCL, September 2013 James D. Machen PCS, KTA-Tator, Inc. James D. Machen is a Senior Coatings Consultant with KTA-Tator, Inc., a coatings consulting engineering firm and distributor of inspection instruments, where he has been employed for over 20 years. Machen is an SSPC-certified Protective Coatings Specialist, a NACE-certified Coatings Inspector Level 3 (Peer Review), and a Level II Inspector in accordance with ASTM D4537. He performs coating failure analyses, coating system recommendations, specification preparation, and major project management for a variety of clients in the transportation, water and waste, power generation, chemical processing, and marine industries. He holds a B.A. from the Pennsylvania State University. Richard Burgess KTA-Tator, Inc., Series Editor

This month’s Case from the F-Files describes the problem of bubbles, pinholes, and blisters in a polyurethane finish coat applied to new structural steel members at a coal-fired power generation plant. Many of the pinholes and bubbles were so small that they were difficult to detect with the unaided eye. Many of the largest blisters on the webs of structural members were very flat and shallow and also difficult to detect by eye. These conditions became more difficult to see overtime as thin layers of dirt from normal plant operating processes formed on the surface of the polyurethane finish coat. This case file illustrates that interacting variables, rather than a single cause, can combine to cause a failure. Background The specification required that the structural steel be blast cleaned in the shop in accordance with SSPC-SP 6/NACE No. 3, Commercial Blast Cleaning. Following blast cleaning, a two-coat system, consisting of a moisture cured urethane (MCU) zinc-rich primer and an aliphatic polyurethane finish, was shop-applied. The MCU primer was specified to be applied at a dry film thickness (DFT) of 2.5 to 3.5 mils, and the polyurethane finish was to be applied at a DFT of 4.0 to 5.0 mils. The total two-coat DFT was to be 6.5 to 8.5 mils.

Fig. 1: Sections of newly-coated steel members at a coal-fired power plant displayed blistering and other signs of coating failure. Photos courtesy of James D. Machen, KTA-Tator, Inc. Field touchup work was specified to be SSPC-SP 2, Hand Tool Cleaning, and/or SSPC-SP 3, Power Tool Cleaning, followed by the application of a coat of surface-tolerant epoxy mastic (4.0 to 6.0 mils’ DFT) and a finish coat of polyurethane (4.0 to 5.0 mils’ DFT). The steel was delivered to the project site for sequenced erection. In mid-summer, near the completion of the project, blistering and peeling were observed. At that time, the shop contractor mobilized a field team to make repairs. Repairs were reported to

have been performed using low-pressure water cleaning (4,000–5,000 psi), in conjunction with hand and power tool cleaning, to identify and remove defective areas, which were then touchup repaired. In the spring of the next year, additional coating defects were discovered and field touchup was again performed. However, the same problems reportedly continued to appear. As a result of the continuing problems, an independent investigation of the coating problem was undertaken. Field Investigation

Fig. 2: Close-up of typical concentrations of small, fine blisters in the polyureathane finish coat The tests and inspections performed during the field investigation were those typically associated with failure investigations, and included the following.

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A visual assessment was performed to determine the degree and distribution of coating defects (in this instance bubbles, pinholes, blisters, and peeling). Total coating thickness was measured using a Type 2 electronic film thickness gage operated according to ASTM D7091, Nondestructive Measurement of Thickness of Nonmagnetic Coatings on a Ferrous Base. The number of coatings present and the thickness of each were determined using a destructive coating thickness gage as described in ASTM D4138, Standard Test Methods for Measurement of Dry Film Thickness of Protective Coating Systems by Destructive Means. An integral portable microscope (50X) was used to observe a cross-section of the applied coating. The number of coating layers and thickness of each were measured. Further, evidence of intercoat contamination, voids, underlying rust, mill scale, and pinholes was recorded. Adhesion testing was conducted using Method A (X-Cut) of ASTM D3359, Measuring Adhesion by Tape Test. Method A involves cutting an “X” through the coating to the substrate using a razor knife. Pressure sensitive tape is placed over the X-cut, then rapidly removed. The amount of coating detached by the tape is rated in accordance with the ASTM rating scale. Ratings of 4A and 5A are considered to represent good adhesion, 2A to 3A represent fair adhesion, while 0A and 1A represent poor adhesion. The coating system was removed in small areas, and the substrate was examined for under-film corrosion or mill scale. Active under-film corrosion may be associated with the coating failure and may also contribute to a shortened life of the system.

Coating samples at both failing and non-failing areas were removed for laboratory analysis, and digital images of the typical field coating conditions were obtained. Visual Observations The structural steel consisted primarily of vertical and horizontal I-beam members. Both intact and fractured (peeling) blisters were observed. Blisters were observed on virtually all members inspected. Some of the blisters appeared to be fractured as a result of someone physically scraping the areas, while others appeared to have cracked and fractured on their own. Blistering ranged in size from concentrations of very fine blisters (approximately 1/64 to 1/128 of an inch in diameter) up to single blisters with

diameters of approximately 2 to 3 inches. Both irregularly shaped and circular blisters were observed. The fine concentrations of blisters were located primarily on beam flanges and in the corner areas where the webs and flanges meet. Larger shallow blisters were generally located on the webs of the I-beams. The fine blisters and larger shallow blisters on the webs were more difficult to see, oftentimes becoming visible only when viewed at the proper angle with sunlight hitting the surface after the film of surface dirt and grime was removed.

Fig. 3: Blisters formed in the polyurethane finish coat on a flange Upon scoring around the perimeter of the larger blisters or areas of concentrated fine blisters with a razor knife, the full blister area could be removed. Upon removal, a portion of the zinc-rich primer remained on the steel surface, and a portion remained attached to the backside of the removed blister (cohesive break within the zinc primer). Both faces of the split primer films contained a visible white powder-like residue. Areas that had been repaired by field touch-up were visible across the structure. Blisters were still visible in some touch-up areas. It was not apparent if the blisters had reoccurred in the touch-up area or if some of the blisters were not completely removed and touch-up material was applied over them. Coating Thickness The results of the total system thickness measurements from various locations on the structural steel are summarized below.

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Minimum DFT (mils): 6.3

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Maximum DFT (mils): 15.7

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DFT Average (mils): 13.2

Destructive film thickness measurements most often identified two distinct layers of paint on the steel. In some instances where touch-up repairs had been made, additional coats were apparent, and three to five individual layers were evident. When two coats were present, the first coat was a metallic gray/green and ranged from 4 to 10 mils; the second coat was dark green and ranged from 3 to 7 mils.

Fig. 4: Blisters in the polyurethane finish coat on a lateral brace web Adhesion Adhesion of the coating system in and immediately around blistered areas was rated poor (0A to 1A rating); however, adhesion of the coating system in blister-free areas was rated fair to good (3A to 4A rating). The adhesion test process consistently forced a break within or at the surface of the zinc-rich primer layer. Substrate Examination The substrate was examined at destructive film thickness measurement areas and sample acquisition areas. Because a thin layer of zinc-rich primer remained adherent to the steel surface, a thorough inspection of the underlying substrate was not possible. However, under 50X power illuminated magnification of the destructive coating thickness gage, a roughened bright metal substrate was sometimes visible. This evidence suggests that the steel surface had been abrasive blast cleaned. Laboratory Investigation The laboratory investigation consisted of visual and microscopic examination, infrared spectroscopy and scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDS). The test methods and results are described below.

Fig. 5: Formation of whitish-colored zinc salts on the surface of the zinc-rich primer, beneath

areas where the blistered finish coat was removed Microscopic Examination Microscopic examination of the samples was conducted using a digital microscope with magnification to 200X. The samples had between two and five coating layers. Coating layer thickness measurements, obtained by laboratory microscopic methods, are in Table 1. TABLE 1

Coating Layer Thickness Measurements Sample #

Coating Layers and Thickness (mils)

Sample 1 (Fine Blisters)

Two Layers Green—Top Metallic Gray—Bottom

3.0–6.9 3.8–7.3

Sample 2 (Fine Blisters)

Two Layers Green—Top Metallic Gray—Bottom

2.2–4.4 2.3–3.6

Sample 3 (Fine Blisters)

Two Layers Green—Top Metallic Gray—Bottom

3.8–6.0 5.2–7.2

Sample 4 (Large Blisters)

Two Layers Green—Top Metallic Gray—Bottom

4.9–8.4 5.0–7.9

Sample 5 (Non-Failing)

Two Layers Green—Top Metallic Gray—Bottom

6.9–8.5 2.6–3.9

Sample 6 Five Layers (Non-Failing Repair Area) Green—Top Light Green Green Green Metallic Gray—Bottom

2.0–4.0 2.5–5.5 4.0–6.0 3.0–5.0 5.2–9.9

Sample 7 Four Layers (Non-Failing Repair Area) Green—Top Gray Green Metallic Gray—Bottom

4.0–5.5 3.5–4.0 1.8–3.5 3.9–5.2

Sample 8 (Single Blister)

Three Layers Green—Top Gray Metallic Gray—Bottom

2.9–5.8 3.1–6.8 3.9–8.0

Infrared Spectroscopy Infrared spectroscopic analysis revealed the following.

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The spectrum obtained of the green top-coat was consistent with a urethane. Water (moisture) and crystalline silica were also indicated. The spectrum obtained of the gray primer was most consistent with a zinc urethane. No distinct characteristic bands are associated with zinc coatings although the baseline noise appearance was consistent with a zinc coating (confirmed by elemental analysis).

SEM-EDS SEM-EDS analysis revealed that the white powdery substance on the gray surface of the primer was primarily zinc. Other elements detected included magnesium, aluminum, and silicon. Conclusions The field investigation and laboratory analysis identified multiple variables that contributed to the blistering coating problems on the structural steel.

Fig. 6: Close-up of zinc salt formation on the zinc-rich primer surface, beneath the removed blistered finish coat The zinc-rich primer used on the project was a MCU material. MCUs react with moisture (atmospheric humidity or other moisture source) to cure. During the curing reaction with moisture, carbon dioxide gas (CO 2 ) is liberated as a reaction product. The CO 2 gas escapes from the coating film in a process commonly referred to as “out-gassing.” When a lot of moisture is available, MCUs cure at an accelerated rate, and CO 2 formation and out-gassing increase. When an additional paint layer is applied while the MCU is still out-gassing, the release of CO 2 from the MCU can be inhibited. The gas must now pass out of the MCU and through the newly applied layer. Depending on the state of drying and curing of the newly applied layer, some CO 2 gas may escape, and some may become trapped in the new film. The CO 2 that escapes produces pinholes or craters when the topcoat has begun to gel, while CO 2 that is trapped creates sufficient pressure to form bubbles through the cross-section and at the surface of the new film. Laboratory microscopic examination of the paint samples consistently revealed that pinholes and bubbles were present in the green topcoat layer applied over the MCU primer. This evidence indicates that the MCU zinc-rich primer was top-coated with the polyurethane before the primer had sufficiently cured. Infrared spectroscopic analysis of the green polyurethane finish coat identified bound moisture within the film. In order for moisture to become bound within this layer, the moisture would have had to have been present on the MCU zinc-rich primer layer over which the polyurethane finish was applied. This evidence indicates that the surface of the MCU zinc-rich primer where defects occurred (i.e., bubbling, pinholes) was damp when the polyurethane was applied. Field thickness measurements and laboratory microscopic measurements revealed that the MCU zinc-rich primer was often applied above the specified DFT range of 2.5 to 3.5 mils. Destructive thickness measurements and laboratory microscopic measurements indicated DFTs of up to 7 mils and 9.9 mils respectively. Excessive primer thickness prolongs the dry and cure time of the primer; as a result, the CO 2 out-gassing is also prolonged, serving to increase the likelihood of pinholes and bubbling. The polyurethane finish coat was also applied above the specified DFT range of 4.0 to 5.0 mils, with measurements up to 8.7 mils in some instances. These thicker films could slow the escape of the CO 2 or trap it, possibly contributing to increased bubble and pinhole formation. The white powdery residue on the backside of the detached blister area and on the substrate was identified as zinc oxide in the laboratory. Zinc oxide (“white rust”) is produced as the zinc dust in the primer oxidizes. This finding indicates that the MCU zincrich primer layer was performing as designed: providing galvanic/sacrificial corrosion protection to the carbon steel substrate. Moisture (rain, condensing moisture) was gaining access to the MCU zinc-rich primer through the voids (i.e., pinholes, fractured bubbles) in the polyurethane finish coat. The moisture served as the electrolyte, allowing the MCU zinc-rich primer to oxidize. Moisture condensing on the steel was likely contaminated with sulfides from the coal-fired power generating station. Water-soluble salts such as sulfides, in combination with moisture, increased the corrosivity of the exposure environment. Recommendations The defective areas (i.e., bubbles, pinholes) were identified and removed by high-pressure water cleaning. Industry experience has shown that water pressures in excess of 4,000 psi are usually effective for revealing and removing defective coatings. However, because each individual project is unique, some experimentation is needed to arrive at the optimal cleaning pressure. It was ultimately determined that the best removal method involved the use of a zero-degree, rotating tip on the pressure washer gun, with careful observation to maintain the equipment manufacturer’s gun-to-work-piece distance and dwell times. In areas

where pressure washing was not entirely effective, supplemental mechanical cleaning with power tools (i.e., power sanding) was used. Once the defective coating was completely removed, any coating that remained was probed with a dull putty knife as described in SSPC-SP 2 and SSPC-SP 3, Hand Tool and Power Tool Cleaning, respectively. Remaining coating that passed the dull putty knife test criteria was considered “tightly adherent” for touchup repairs. The periphery of touchup areas was featheredged to provide a smooth transition from the repair area to surrounding intact coatings. Once surface preparation was accomplished, touchup proceeded using the field touchup system, consisting of a coat of epoxy mastic followed by a matching green polyurethane finish coat. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2013 Technology Publishing Company

5. Measuring Dry Film Coating Thickness According to SSPC-PA 2 From JPCL, April 2013 William D. Corbett PCS, KTA-Tator, Inc. Bill Corbett is the Vice President and Professional Services Group Manager for KTATator, Inc., where he has been employed for 33 years. He chairs SSPC committees C.3.2 on Dry Film Thickness and C.6 (Education). He is an SSPC-approved instructor for four SSPC courses, and he holds SSPC certifications as a Protective Coatings Specialist, Protective Coatings Inspector (Level 3), and Bridge Coatings Inspector (Level 2). He is also a NACE Level 3-certified Coatings Inspector. He was the co-recipient of the SSPC 1992 Outstanding Publication Award, co-recipient of the 2001 JPCL Editors’ Award, recipient of SSPC’s 2006 Coatings Education Award, and recipient of SSPC’s 2011 John D. Keane Award of Merit.

William D. Corbett PCS, KTATator, Inc.

Coating thickness shall be measured in accordance with SSPC: The Society for Protective Coatings Paint Application Standard No. 2 (SSPC-PA 2) is a simple enough statement, yet this common specification requirement is often misinterpreted or regarded as a document that simply states how to measure the dry film thickness (DFT) of coatings, something we already profess to know how to do. Yet the requirements of SSPC-PA 2 regarding gage calibration, verification of gage accuracy and adjustment procedures, the number of measurements to obtain, and the tolerance of the measurements are complex and should be fully understood by the specification writer before invoking PA 2 in a contract.

iStock On more than one occasion, I have heard the question, “When did SSPC-PA 2 and dry film thickness measurement become so complicated?” In fact, when you take a close look, measuring DFT isn’t that complex. We have allowed it to become more technologically complex while making the data easier to analyze. We can gather hundreds of gage readings in a relatively short time; batch the measurements; print the data or upload it to a computer for graphing; report the highest, the lowest, the mean, and standard deviation of the collected data; incorporate digital images of the structure or coated area; and even program the gage to produce an audible signal if a spot measurement is outside of the tolerance range. I am no doubt leaving out other bells and whistles, but my point is that while we are able to do a lot with the readings obtained, measuring DFT involves four or five basic steps.

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Step 1: Instrument Calibration

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Step 2: Verification of Gage Accuracy on Certified Coated Standards or Certified Shims

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Step 3: Base Metal Reading Acquisition or Gage Adjustment (using certified or measured shims)

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Step 4: Measurement of Coating Thickness

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Step 5: Correction for Base Metal Reading (if acquired).

After a brief review of the history of SSPC-PA 2, this article will describe each of the five steps, based on the 2012 edition of SSPCPA 2. Special attention will be given in the article to how PA 2 addresses the required number of coating thickness measurements;

the acceptability of gage readings, spot measurements, and area measurements; nonconforming thickness; measuring DFT on coated edges; and measuring DFT on pipe exteriors. Some History SSPC-PA 2 was originally published as a temporary standard 40 years ago in 1973 (73T) as “Measurement of Dry Coating Thickness with Magnetic Gages.” The standard referenced gages like the one shown in Fig. 1, which are now all but obsolete. The standard has been updated on multiple occasions. Until 2012, the most recent technical changes were published in May 2004, with a minor editorial revision in 2009 to one of the appendices (regarding measurements on test panels). The SSPC Committee on Dry Film Thickness Measurement began revising and updating the 2004 version in 2007. The revisions took five years to complete. The latest edition of the standard (“Procedure for Determining Conformance to Dry Coating Thickness Requirements”) is dated May 2012 and was made available to the industry in July 2012.

Fig. 1: One type of magnetic gage referenced in original SSPC-PA 2 for measuring dft Figures courtesy of the author except where otherwise indicated In nearly the same timeframe, the 2005 version of ASTM D7091, “Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to NonFerrous Metals” was being revised and updated. It, too, was published in 2012. The most current version of the ASTM standard focuses on proper gage use, while SSPC-PA 2 focuses primarily on the frequency of measurements and the acceptability of the acquired measurements. References to the frequency of measurements were removed from the ASTM standard. The two documents are designed to be used together. It is important to note that both documents address the measurement of the DFT of coatings on ferrous and non-ferrous metal substrates. Before 2012, SSPC-PA 2 addressed measurement of coatings only on steel, a ferrous metal. (The sidebar on p. 32 in this article summarizes the key changes made to PA 2 in 2012.) Summary of Changes to SSPC-PA 2: 2004 Version and 2012 Version 2004

2012

“Measurement of Dry Coating Thickness with Magnetic Gages”

“Procedure for Determining Conformance to Dry Coating Thickness Requirements”

Addressed measurement of coatings on steel only

Addresses measurement of coatings on ferrous and non-ferrous metal surfaces

No referenced standards section

ASTM D7091 and SSPC Guide 11 included by reference

Definitions section included Calibration; Verification; Adjustment; Coating Thickness Standard; Shim (foil); Dry Film Thickness Reference Standard; Accuracy; Structure.

Definitions section includes Gage Reading, Spot Measurement and Area Measurement only. All definitions related to gage calibration, accuracy and adjustment are incorporated by reference in ASTM D7091. Spot measurement definition was expanded.

No. of “Area Measurements” based on the size of the No. of “Area Measurements” based on the size of the area of coated structure surface Isolation of nonconforming areas required measurement of each 100 square foot area painted during the work shift.

The magnitude of nonconforming thickness assessed by obtaining spot measurements in eight equally spaced directions radiating outward from the nonconforming area

Recommended specifying minimum & maximum thickness range; if no range was specified, thickness value was considered minimum (with no maximum)

If a single value is specified and the coating manufacturer does not recommend a range, the minimum and maximum thickness range is established at ±20% of the stated value

Contained a minimum gage accuracy requirement to qualify for use

No minimum gage accuracy requirement to qualify for use

Conformance to Specified Thickness: Gage Readings: Unrestricted Spot Measurements: ± 20% of specified range Area Measurements: Per Specification

Conformance to Specified Thickness: Five different Coating Thickness Restriction Levels established. If no Restriction Level is specified, default is based on 2004 conformance requirement.

Notes section contained principles of gage operation Notes section includes Overcoating and Correcting for Low/High Thickness and various substrate/surface conditions that may only ASTM D7091 describes principles of gage operation and various affect measurements; overcoating; and correcting for substrate/surface conditions that may affect measurements. low/high thickness. Contained 6 appendices

Contains 8 appendices. Six appendices from 2004 version included. Added two:

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Method for Measuring DFT of Coating on Edges

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Method for Measuring DFT of Coated Steel Pipe Exterior

Gage Types SSPC-PA 2 addresses two types of DFT gages, both of which are supplied by a variety of manufacturers. Magnetic pull-off gages are categorized as Type 1 (Fig. 2).

Fig. 2: Example of magnetic DFT gage categorized as Type 1 in SSPC-PA 2 These gages were designed in the 1950s. While their use has declined, they are still readily available and used by some. For these gages, a permanent magnet is brought into direct contact with the coated surface. The force necessary to pull the magnet from the surface is measured and converted to coating thickness, which is displayed on a scale on the gage. The operating principle is simple. Less force is required to remove the magnet from a thick coating, while more force is required to remove the magnet from a thinner one. The scale is not linear, as will be discussed below. Electronic gages are categorized as Type 2 (Fig. 3). These gages use electronic circuitry to convert a reference signal into coating thickness and are more popular than Type 1 gages. They are typically regarded to be faster, more accurate, and easier to use.

Fig. 3: Example of electronic DFT gage categorized as Type 2 in SSPC-PA 2 Gage Calibration, Accuracy Verification, and Adjustment To help assure the reliability of the coating thickness measurements, ASTM D 7091 describes three operational steps that must be performed before taking the measurements. These steps are (1) gage calibration, (2) verification of gage accuracy and (3) gage adjustment. The steps are incorporated by reference in SSPCPA 2 and are completed before obtaining coating thickness measurements to determine conformance to a specified coating thickness range. The steps to verify the accuracy of the gage are based on the principle that you check the gage by measuring a known thickness before you use the same gage to measure an unknown thickness. Verification of gage accuracy is typically performed using certified coated thickness standards (for Type 1 or Type 2 gages) or certified shims (Type 2 gages). Adjustment of Type 2 gages to compensate for substrate characteristics (described later) is typically performed using certified shims. Measured shims (individually labeled with a stated thickness value) commonly supplied with Type 2 gages can also be used for gage adjustment. Dry film thickness gages are calibrated by the equipment manufacturer, its authorized agent, or an accredited calibration laboratory (under controlled conditions). A test certificate or other documentation showing traceability to a national metrology institution is required. While there is no standard time interval for re-calibration, an interval can be established based on experience, the work environment, and/or the internal equipment calibration procedures of the company using the gage. A one-year calibration interval is a typical starting point suggested by gage manufacturers. Verifying Gage Accuracy To guard against measuring with an inaccurate gage, SSPC-PA 2 requires that gage accuracy be verified (at a minimum) at the beginning and end of each work shift according to the procedures described in ASTM D 7091. If a large number of measurements are being obtained, the user may opt to verify gage accuracy during measurement acquisition (for example, hourly). If the gage is dropped or suspected of giving erroneous readings during the work shift, its accuracy should be rechecked. Verifying the Accuracy of Type 1 Gages The accuracy of Type 1 (magnetic pull-off) gages is verified by placing the gage probe onto a certified coated thickness standard (Figs. 4 and 5). A one-point or two-point accuracy verification procedure can be performed; typically, the two-point verification provides greater accuracy. If a one-point verification procedure is adopted, the coated standard should be selected based on the intended range of use. For example, if the intended use is between 4 and 6 mils, then a five-mil coated standard is appropriate. Using the same example, if a two-point verification procedure is adopted, then a two-mil and an eight-mil set of coated standards (slightly below and above the intended range of use) is appropriate.

Fig. 4: (top) and 5 (bottom) Verifying the accuracy of Type 1 gages using certified coated thickness standards The final step in the process is to obtain a set of base metal readings (BMRs) to compensate for substrate characteristics including (but not limited to) substrate metallurgy, geometry, thickness/thinness, and roughness (Fig. 6). These readings represent the effect of the substrate conditions on the coating thickness measurement device. SSPC-PA 2 states that a minimum of 10 (arbitrarily spaced) locations should be measured (one reading per location) and then averaged. This average BMR is then deducted from subsequent coating thickness measurements to remove any effect of the base metal surface and its conditions.

Fig. 6: Obtaining base metal readings with Type 1 gage Because Type 1 gages cannot be adjusted, some gage operators believed that a “correction value” could be applied to the coating thickness readings to compensate for the inaccuracy of the gage. For example, if a gage reading was 5.7 mils on a five-mil coated standard, a 0.7-mil “correction value” could be deducted (by the gage operator) from subsequent coating thickness measurements. However, because Type 1 gages are non-linear, one cannot assume a linear (mil-for-mil) correction value across the full range of the gage. While the gage may be out of tolerance by 0.7 mils at 5 mils, it may be out of tolerance by more or less than 0.7 mils at a different thickness. Accordingly, SSPC-PA 2 states that the practice of using a linear correction value is not appropriate. However, Note 6 in the standard states, “A correction curve can be prepared by plotting the actual gage readings against the stated values on the (coated) test blocks (standards). Subsequent coating thickness measurements can be “corrected” by plotting the measurements along the correction curve. The correction curve may or may not cover the full range of the gage, but should cover the intended range of use. The Base Metal Readings (BMR) described in 6.1 may also need to be plotted on the correction curve.” This requirement makes Type 1 gages very difficult to use. While some gage operators may simply subtract a fixed amount (for example, 0.5 mils) from any reading, such a practice is not in compliance with SSPC-PA 2. Verifying the Accuracy of Type 2 Gages The accuracy of Type 2 (electronic) gages can be verified by placing the gage probe onto a certified coated thickness standard (described for Type 1 gages) or certified shims (Figs. 7 and 8). The certified shim should be placed onto a smooth, uncoated metal surface to remove any effect of the surface roughness during this process. A one-point or two-point accuracy verification procedure can be performed (as described earlier for Type 1 gages).

Fig. 7: Verifying accuracy of Type 2 gage on a certified coated standard

Fig. 8: Verifying accuracy of Type 2 gage using a certified shim Adjusting Type 2 Gages The final step in the process is to adjust the gage on the surface to which the coating will be applied. Adjustment is accomplished by placing a certified or measured shim (or shims) onto the prepared, uncoated metal surface and adjusting the gage (when feasible) to compensate for substrate characteristics including (but not limited to) substrate metallurgy, geometry, thickness/thinness, and roughness (Fig. 9). The gage reading is adjusted to match the thickness of the shim, which effectively removes any influence from the underlying surface.

Fig. 9: Adjusting Type 2 gage using a measured shim on the surface to which the coating will be applied This step sounds reasonably straightforward but poses several hidden challenges. First, once the surface is coated (for example, with a primer), an uncoated surface may no longer be available for subsequent gage adjustments, so the user may want to have a similar uncoated surface prepared and reserved for future gage adjustments on a given project. Naturally, this surface must be representative of the metallurgy, geometry, thickness/thinness, and roughness of the actual surface, which can be a challenging requirement. Second, some Type 2 gages cannot be adjusted. In such cases, the user will need to obtain BMRs from the prepared, uncoated substrate (described earlier for Type 1 gages). While many Type 2 (electronic) gages have a “zero-set” function, the gages should never be adjusted to zero unless the surface is smooth. Required Number of Coating Thickness Measurements The section of SSPC-PA 2, “Required Number of Measurements for Conformance to a Thickness Specification,” causes many users

confusion, which can result in either under- or over-inspection. Arguably the most critical section in the document, Section 8, describes how many areas to check, the size of the areas, the number of measurements to obtain in each area, and the steps to take if spot or area measurements do not conform to the specification. SSPC-PA 2 contains three definitions that are critical to understanding this next area of discussion.

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Gage Reading: A single instrument reading.

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Spot Measurement: The average of at least three gage readings made within a 4-cm (≈1.5-inch) diameter circle. Acquisition of more than three gage readings within a spot is permitted. Any unusually high or low gage readings that are not repeated consistently are discarded. The average of the acceptable gage readings is the spot measurement.

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Area Measurement: The average of five spot measurements obtained over each 10 m2 (≈100 ft2) of coated surface, or increment (portion) thereof.

An area is defined as approximately 100 square feet. Within each area, five randomly spaced spots are selected. Each spot consists of a 1.5-inch diameter circle. A minimum of three gage readings is obtained in each spot, culminating in a minimum of 15 gage readings within an area. Unusually high or low gage readings that cannot be repeated consistently are discarded. The average of the three acceptable gage readings is the spot measurement; the average of five spot measurements is the area measurement. Figure 10, from Appendix 1 in SSPC-PA 2, depicts an approximate 100-square-foot area containing gage readings and spot measurements.

Fig. 10: Approximate 100-square-foot area containing gage readings and spot measurements, as depicted in Appendix 1 of SSPC-PA 2. Courtesy of SSPC The number of areas that must be measured for coating thickness varies, depending on the size of the coated area. There are three categories of coated area: less than 300 square feet; 300 to 1,000 square feet; and greater than 1,000 square feet. For areas containing less than 300 square feet of coated surface, every 100-square-foot area must be measured for coating thickness. For areas of coating 300 to 1,000 square feet, three random areas are selected and measured. For areas of coating exceeding 1,000 square feet, three random areas are selected from the first 1,000 square feet, along with one additional area for each additional 1,000 square feet. Because areas of coating often exceed 1,000 square feet, our example will be based on this third tier (>1,000 square feet). Let’s assume that the total coated area (perhaps the area coated during a work shift, although SSPC-PA 2 does not equate coated area with work shift) is 12,500 square feet. A total of 15 areas must be measured (three in the first 1,000 square feet and one additional area in each of the 12 remaining 1,000-square-foot areas or portions thereof). This culminates in a total of 75 spot measurements (15 x 5) and a minimum of 225 gage readings (15 x 5 x 3). If spot measurement variances result in area measurements that do not meet the specification, then additional spot measurements are acquired (radiating outward in eight directions from the nonconforming area) to determine the magnitude of the non-conforming thickness. This process is described later in this article. Acceptability of Gage Readings, Spot Measurements, and Area Measurements

While individual gage readings that are unusually high or low (and cannot be repeated consistently) can be discarded, there are limitations on the thickness values representing the spot measurements (the average of three gage readings). A minimum thickness and a maximum thickness are normally specified for each layer of coating. However, if a single thickness value is specified and the coating manufacturer does not provide a recommended range of thickness, then the minimum thickness and maximum thickness for each coating layer are established by SSPC-PA 2 at ±20% of the stated value. For example, if the specification requires 3 mils’ DFT and the coating manufacturer does not provide any additional information regarding a recommended thickness range, then, by default, the specified range is established as 2.4–3.6 mils. Because the coating may not perform at the lower thickness, it is important for the specifier to indicate an acceptable range for each coating layer. To assist the specifier, the 2012 edition of SSPCPA 2 incorporates a Restriction Level Table (Fig. 11). The Table enables the specifier to select from five different restriction levels related to spot and area measurements.

Fig. 11: Coating Thickness Restriction Levels (as shown in Table 1 of SSPC-PA 2, Section 9) Courtesy of SSPC Level 1 is the most restrictive and does not allow for any deviation of spot or area measurements from the specified minimum and maximum thickness, while Level 5 is the least restrictive. Depending on the coating type and the prevailing service environment, the specifier can select the DFT restriction level for a given project. The specifier may also invoke a maximum thickness threshold for Level 5 Spot or Area Measurements for a generic product type and/or service environment that will not tolerate an unlimited thickness. If no Restriction Level is specified, then the default is Level 3, which is based on the 2004 version of SSPC-PA 2 (what many users of the standard have become accustomed to). For the purpose of final acceptance of the total DFT, the cumulative thickness of all coating layers in each area must be no less than the cumulative minimum specified thickness and no greater than the cumulative maximum specified thickness. For example, assume that the specification requires a four- to six-mil application of primer. The actual minimum and maximum spot and area thickness requirements are shown in Fig. 12 for each of the five restriction levels.

Fig. 12: Coating Thickness Restriction Levels Based on a Four-to-Six-Mil Requirement Derived using the 2012 edition of SSPC-PA 2, “Table 1, Coating Thickness Restriction Levels” Determining the Magnitude of Nonconforming Thickness Another change in the 2012 version of the standard is the procedure for identifying nonconforming areas (Fig. 13). In the 2004 edition, if spot or area measurements were out of conformance, each 100-square-foot area coated during the work shift had to be measured, and nonconforming areas had to be demarcated. On a larger structure with multiple applicators, the measurement and documentation process could be extensive, so the approach was changed in the 2012 revision. If a nonconforming area is identified, spot measurements are made at five-foot intervals in eight equally spaced directions radiating outward from the nonconforming area, as shown in Fig. 13.

Fig. 13: Depiction of procedure for identifying nonconforming areas, as described in the 2012 edition of SSPC-PA 2. Courtesy of SSPC If there is no place to measure in a given direction, then no measurement in that direction is necessary. Spot measurements are obtained in each direction (up to the maximum surface area coated during the work shift) until two consecutive conforming spot measurements are acquired in that direction, or until no additional measurements can be made. Acceptable spot measurements are defined by the minimum and maximum values in the contract documents. No allowance is made for variant spot measurements (for example, ±20%), which is consistent with the practice followed when determining the area DFT. On complex structures or in other cases where making spot measurements at five-foot intervals is not practical, spot measurements are taken on repeating structural units or elements of structural units. This method is used when the largest dimension of the unit is less than 10 feet. Spot measurements are obtained on repeating structural units or elements of structural units until two consecutive units in each direction are conforming or until there are no more units to test. Non-compliant areas are demarcated using removable chalk (or another specified marking material) and documented. All of the area within five feet of any non-compliant spot measurement is considered non-compliant. For a given measurement direction or unit measurement, any compliant area or unit preceding a non-compliant area or unit is designated as suspect, and, as such, is subject to re-inspection after corrective measures are taken. Appendices to the Standard There are eight appendices in the 2012 version of SSPC-PA 2. Two of the eight appendices were added in 2012 (the remaining were in the 2004 edition) and are highlighted below. The appendices to SSPC-PA 2 are not mandatory but may be invoked by contract documents. Appendix 6: Method for Measuring the Dry Film Thickness of Coatings on Edges For decades, the industry was cautioned about taking coating thickness measurements within one inch of an edge, let alone on an edge. However, several Type 2 (electronic) gage manufacturers offer a variety of probe configurations, some of which are less affected by proximity to edges and are designed to better measure the thickness of coatings on edges (Fig. 14). Obviously, the gage operator should consult the gage manufacturer’s instructions before measuring coating thickness on edges.

Fig. 14: One of a variety of Type 2 gage probe configurations designed to better measure DFT of coatings on edges Before measuring coating thickness on edges, the user should verify the gage and probe for accuracy by placing a thin, flexible shim (certified or measured) onto the prepared, uncoated edge. Adjustments to the gage may or may not be required. This procedure also verifies that the probe configuration will accommodate the edge configuration before acquiring coating thickness data. Once verification of accuracy and adjustments are made, a minimum of three gage readings are taken within 1.5 linear inches of coated edge. The average of the gage readings is considered a spot measurement. The number of spot measurements along the edge will vary, depending on the total length of the coated edge. Appendix 7: Method for Measuring Dry Film Thickness on Coated Steel Pipe Exterior Appendix 7 was added to accommodate pipe coaters that need to determine coating thickness conformance on non-flat (or nonplate) areas, including smaller pipe sections on a cart or rack and longer pipe spools. Pipe sections loaded onto a cart or rack can be considered a complete unit (Fig. 15). The total number of spot and area measurements is based on the total square footage of pipe on the cart or rack. The square footage is calculated as shown on p. 35.

Fig. 15: (top and bottom): Appendix 7 of the 2012 edition of SSPC-PA 2 describes a method for measuring DFT on non-flat steel, such as pipe sections that can be loaded on racks or carts. Photos courtesy of Turner Industries Group, L.L.C.

Some carts may have several small pipe sections, and the total coated surface may exceed 100 square feet. In this case, a Pipe DFT Frequency Factor shown below may be invoked.

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Pipe DFT Frequency Factor 2 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 2 Pipe DFT Frequency Factor 3 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 3 Pipe DFT Frequency Factor 4 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 4 Pipe DFT Frequency Factor 5 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 5 Pipe DFT Frequency Factor 6 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 6

Based on the example above, if “Pipe DFT Frequency Factor 4” was invoked, 20 spot measurements would be taken (5 spots x Frequency Factor 4) Pipe spools that are not loaded onto a rack or cart are typically measured individually (Fig. 16). The number and locations of spot measurements are based on Appendix 7’s Table A7 (Fig. 17). Three sets of four circumferential spot measurements should be obtained on pipe spools less than 10 feet in length.

Fig. 16: DFT of pipe spools not loaded on cart or rack are typically measured individually.

Fig. 17: Number and Locations of Spot Measurements—Pipe Spools (Table A7 from 2012 edition of SSPC-PA 2, Appendix 7) Courtesy of SSPC Conclusion SSPC-PA 2 has undergone significant changes in an attempt to make it more complete; more in concert with ASTM D7091; easier to use in the shop and field; and more flexible in providing the specifier with options for coating thickness restrictions based on the type of structure, the coatings to be applied, and the service environment. SSPC-PA 2 and ASTM D7091 are both undergoing additional technical and editorial changes to bring them into even greater alignment with one another. Get the Latest Standards on Dry Film Thickness of Coatings The 2012 edition of SSPC-PA 2, “Procedure for Determining Conformance to Dry Coating Thickness Requirements,” is available from the SSPC: The Society for Protective Coatings through sspc.org, under the “Standards” tab at the top of the home page. The 2012 edition of ASTM D7091, “Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to NonFerrous Metals,” is available from ASTM International through astm.org under the “Standards” at the top of the navigation bar on the site. Change is never easy…. Communicating the new requirements of this standard to the industry is challenging but essential. One conduit is through training and education. For example, SSPC offers a short course, “Using SSPC-PA 2 Effectively,” that was recently updated to reflect changes made to the standard. Free webinars are available through SSPC/JPCL for those who cannot participate in instructor-led training. Updates to SSPC and other industry-provided inspector training and certification courses (and the associated instructor education) will be critical to fully understanding and effectively communicating the requirements of this highly regarded industry standard. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2013 Technology Publishing Comp

6.Testing the cure of IOZ From JPCL, April 2013

Is the MEK rub test a conclusive test to check the cure of inorganic zinc coatings? From Rob Francis Consultant The solvent rub test for cure of ethyl silicate inorganic zinc (IOZ) coatings, as described in ASTM D4752, is the accepted test for checking if such a coating is cured. This is especially critical before overcoating, but even a single coat system can dry without curing if applied under low humidity conditions. Other tests that are used include scraping with the edge of a coin (the “Quarter test” in the USA) or simply a fingernail. If significant zinc powder is produced with either test, the coating is considered uncured. However, these tests are considered more subjective than the solvent rub test. An uncured coating will result in considerable zinc removal with a few double rubs, while a cured coating will be little affected with the 50 double rubs required. It should be noted that even a fully cured coating will show some zinc discoloration on the white rag. While as with any test, it may be possible to get ambiguous results, this test, in most situations, will be definitive, and certainly superior to any other simple field test. If there is any doubt regarding the cure, leave the coating (if the humidity is high enough) or water mist it and retest. From Simon Hope BIS Salamis (M&I) The MEK rub test is only subjective as proof of cure for IOZ coatings. The test is only valid for the actual area tested and can be applied to the whole item only by extrapolation of the result. Confidence in the result can vary wildly, depending on time, humidity, and temperature, because the curing mechanism of IOZ is totally dependent on the integration of water into the silicate precursor to create the matrix to support the metallic zinc. Hence, the best advice is that once touch dry, fresh water washing enhances the cure mechanism. High humidity and water washing will give confidence, and MEK rub then gives verification. From Gary Hall Consultant I am answering the question about the MEK test as it relates to testing a coating in the field. The ASTM test method that pertains to measuring cure of inorganic zinc coatings/primers by solvent resistance is ASTM D4752, “Standard Practice for Measuring MEK Resistance of Ethyl Silicate (Inorganic) Zinc-Rich Primers by Solvent Rub.” This method has been shown to correlate well with the results obtained with an analytical chemical test called diffuse reflectance infrared spectroscopy, by which the degree of cure of inorganic zinc (IOZ) primers can be accurately determined. It should be noted that the results of D4752 might not indicate when full cure has been achieved because the coating may become resistant to MEK before full cure occurs. A hardness test may also be used if the coating manufacturer can provide the appropriate hardness data. One such test is ASTM D2240, which uses a Shore durometer. The Shore durometer test gives the amount of indentation made by a specific needle. Because the ASTM D2240 test will deform the coating surface under the needle, this type of test is best performed on a companion piece of substrate coated and cured in the same manner as the coating on the substrate on the actual project. Problem Solving Forum questions and answers are published in JPCL and its sister daily electronic publication, PaintSquare News. Upcoming questions in JPCL include the following.

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Whose responsibility is safety on a bridge coating site? If an inorganic zinc (IOZ) coating has not fully cured because of low humidity, can water be sprayed onto the IOZ-coated surface to accelerate the cure?

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What action should be taken if an inorganic zinc coating fails the MEK (methyl ethyl ketone) rub test?

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What causes “amine blush” in epoxy topcoats?

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Do water treatment processes to stop the transfer of invasive marine species in ballast water affect the performance of ballast tank coatings? How soon does metallizing need to be sealed after it is applied to concrete on bridges?

Responses to JPCL questions can be submitted to [email protected]. Readers may also propose questions. Readers can also respond to PSF questions posted on PaintSquare News and can propose questions on PaintSquare News at paintsquare.com/psf.

7. Basics of corrosion of steel for applicators From JPCL, January 2013 Joe Pikas

A good coating job requires the right steps to be performed to achieve the protection needed. It is important to know why things are done, as well as how the various steps are performed. A primary reason for using protective coatings is corrosion protection. For the purposes of this series, corrosion of steel is defined as “the destruction of steel by an electrochemical process that is characterized or recognized by the formation of rust or pits.” To understand how protective coatings protect a steel surface, the nature of corrosion must be understood— why it occurs and how it can be prevented. Steel is manufactured by taking the mined ore and adding a large amount of energy to it in the blast furnace. This produces an unstable metal. Nature does not like all that energy stored in the steel. So upon exposure to the atmosphere, especially moisture and oxygen, this energy is released, and the iron returns to its natural stable state—iron ore. Rust, therefore, is nothing more than a pure form of iron ore (oxides). Protection of steel from corrosion involves methods to retard this natural release of energy (Fig. 1).

Fig. 1: One approach to slowing the natural corrosion of steel and appearance of rust is the use of protective coatings. Courtesy of JPCL To understand how coatings protect steel, we must understand the four conditions required for corrosion to occur. Unless all four of these conditions are present, corrosion will not occur. These four conditions are:

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a positive pole (a cathode),

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a negative pole (an anode),

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an electrical conductor, and

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an electrolyte.

The terms “anode” and “cathode” have technical definitions in electrochemistry, but for our purposes, we will use them to refer to areas on a substrate or materials of different electrical potentials. The “electrical conductor” is a means of conducting electricity, similar to the copper wiring in your house. An “electrolyte” is a liquid solution (usually water) that also can conduct electricity. To help illustrate these terms and how corrosion happens, let’s look at the dry cell (battery). A battery represents a beneficial use of corrosion, though the process is the same as corrosion that occurs with steel. A battery has two terminals. Typically, one is connected to a carbon rod running down the center of the battery, while the other is connected to the outer casing, which is made of zinc. These are the two dissimilar materials of different electrical potential, which serve as cathode and anode. If you have ever taken a battery apart, you would have seen that there is a pasty material between the casing and the carbon rod. This substance is the electrolyte. If you wanted to use the battery, you would connect the wires to something such as a flashlight. The wires are the electrical conductor. Once the wires are connected, the flashlight will keep on glowing until the battery has become corroded. In the battery, it is actually the zinc casing that is consumed and corroded. How does this example of a battery relate to corrosion of steel? You would see that steel is not a smooth, uniform material if you looked at it under high magnification (Fig. 2). It actually consists of very small grains or grain boundaries. This means that steel has spots on it with slightly different electrical potentials.

Fig. 2: Peaks and valleys of profiled clean steel Courtesy of KTA-Tator Adding stresses to the steel also creates areas of different electrical potential. This normally occurs by such processes as differential heating of the steel during treatment, bending or cutting the steel, or even hitting it with a hammer. Any of these processes adds small amounts of energy to the steel. So by its very nature, steel contains spots of different electrical potential, or anodes and cathodes. What about the electrical conductor? This was the wire in the example of the battery. Does steel conduct electrical current? It certainly does, so wires are not needed. As you can see from this explanation, steel contains anodes and cathodes, and is an electrical conductor. It already contains three of the four conditions necessary for corrosion. The fourth condition needed is the electrolyte or liquid that can conduct electricity. Where does it come from? Normally, atmospheric moisture that condenses on the surface serves as an electrolyte. It can be in the form of rain, dew, or simply humidity in the air. Some structures either are used to hold water or are used in water. They are constantly exposed to an electrolyte. Our atmosphere is laden with moisture at all times, even in desert areas, although to a esser degree. Most steel surfaces are exposed to dew at night and water vapor during the daytime hours in addition to the normal rainfall. In highly industrial areas such as Houston, Los Angeles, and New York, airborne chemical contaminants contain substances called ions. The point to be made is that steel (like most other manufactured metals) contains three of the four conditions needed for corrosion. The most common way to slow down corrosion is to isolate the steel from the electrolyte. Therefore, the major function of the coating is to keep moisture off the steel. Some coatings, such as zinc primers, perform other functions, which will be discussed in subsequent Bulletins. There are a few common forms of corrosion that a painter will see regularly: general corrosion, galvanic corrosion, pitting corrosion, and crevice corrosion. General corrosion takes place fairly evenly over the metal. Usually, it begins as spots or freckles and becomes progressively worse. Galvanic corrosion occurs when dissimilar metals are in contact. The more active metal (the anode) corrodes to protect the less active metal (the cathode). For example, if a brass valve were connected to a steel pipe, the steel would corrode to protect the brass. The steel at the fitting would be consumed rather quickly, first appearing as a thinning of the metal and ultimately resulting in penetration. Another example of galvanic corrosion is mill scale on steel. Steel is more active than mill scale, so when corrosion conditions are present, the steel will corrode to protect the mill scale. Pitting corrosion occurs when the corrosion forces are concentrated in a small area. Metal loss is into the steel rather than over the surface. The rust pits that form have serious consequences because the pits represent metal section loss. This can result in perforation if the structure is a tank or a vessel, and loss of structural integrity no matter what the structure is. Crevice corrosion (Fig. 3) is another common form seen on structures, and occurs when there is a small space between structural elements, be they metal-to-metal or metal-to-non-metal. Examples of places where crevice corrosion can occur are back-to-back angles, where steel plates overlap, around rivets and bolts, near tack welds, and any other place where a small opening is present. What happens is that moisture gets into the crack and completes the corrosion circuit. The moisture gets trapped in the crevice and accelerates the corrosion compared to the surrounding area. The corrosion reactions are greatest at the bottom of the crevice, so metal loss is concentrated in that area.

Fig. 3: Severe corrosion is seen at a weld seam. Courtesy of KTA-Tator There are many other forms of corrosion that a painter may see, including microbiologically influenced corrosion (deep isolated pitting as shown in Fig. 4), cavitation corrosion, or erosion corrosion, to name a few. In most of these cases, the corrosion reaction is accelerated by another factor beyond the general corrosion reaction explained above.

Fig. 4: Microbiologically influenced corrosion on piece of steel pipe Courtesy of the author To stop corrosion, all that is needed is to eliminate one of the factors that produce the reaction. It is impossible to eliminate the environment, and it is cost-prohibitive to make steels that corrode at a slow rate. Therefore, coatings are often used to prevent corrosion by eliminating contact between the environment (electrolyte) and the steel substrate. Coatings are therefore a barrier material. A coating may also be applied to enhance appearance. However, to protect against corrosion for a period of time, it is necessary for coatings to possess features that make them effective barriers. By isolating steel from the electrolyte, a good protective coating can prevent corrosion for extended periods of time. The better the application, the longer the coating will serve its useful purpose. On the other hand, a poor coating job may lead to the expense of premature failure, which requires reblasting and recoating. On large projects, such premature failure can cost hundreds of thousands of dollars or more. Good coating work can also save steel structures from unnecessary and costly deterioration. It is estimated that the cost of corrosion in the U.S. each year runs in the billions of dollars. Your work as an applicator can help significantly to reduce these losses. Upcoming Applicator Training Bulletins The following are among the upcoming Applicator Training Bulletins. Basics of Corrosion and Coatings

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How Coatings Protect Steel

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Basics of Concrete Deterioration for Applicators

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How Coatings Protect Concrete

Surface Preparation

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Why Surface Preparation Is Important

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Introduction to Surface Preparation of Concrete

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Mechanical Methods of Preparing Concrete

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Chemical Cleaning of Concrete

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Power Tool Cleaning for Steel

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Using Paint Strippers on Steel and Concrete

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Setting Up Air Abrasive Blasting Systems

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Techniques of Air Abrasive Blasting

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Containing Dust and Debris during Air Abrasive Blasting

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Setting Up and Operating Wet Blasting Equipment

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Using High Pressure Waterjetting

Application

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Product and Application Data Sheets

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Mixing and Thinning Paint

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Basic Training in Brush and Roller Application

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The Basics of Conventional Air Spraying

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Using High Volume, Low Pressure Spray Equipment

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Using Airless Spray Equipment

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Introduction to Plural Component Spraying

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Applying Two-Pack Epoxies and Polyurethanes

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Applying Zinc-Rich Coatings

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Applying Water-Borne Coatings

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Applying High Solids Coatings

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Applying Polyureas

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Applying Floor Coatings and Toppings

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Special Concerns about Applying Coatings in the Shop

Quality Control

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The Effects of Weather on Cleaning and Coating Work

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Conforming with Job Requirements

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Records of Work and Working Conditions

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Why Good Housekeeping Is Important

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Assessing Surface Cleanliness and Profile

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Assuring Quality during Abrasive Blasting

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Assessing Quality of Wet Methods of Surface Preparation

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Computing Film Thickness and Coverage

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Measuring Dry Film Thickness

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Measuring Adhesion of Coatings

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Recognizing and Correcting Paint Application Deficiencies

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Quality Control in Coating Concrete

Safety and Health

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Safety Considerations for Abrasive Blasting

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Anticipating Job Hazards

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Respiratory Protection: Hazards and Equipment

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Fit Testing Procedures for Respirators

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Job Hazards during Climbing and High Work

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An Introduction to Confined Spaces

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Identifying and Controlling Job Hazards When Working around High Voltage

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Using Lighting Safely

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Protection against Worker Exposures during Hazardous Paint Removal

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Safety for Applicators Working near Process Equipment

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Safety with Solvents and Paint Strippers

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Where To Get Help in Safety and Health

Editor’s Note: This article marks the return of JPCL’s Applicator Training Bulletin, a series first published from 1988 to 1992. The series was intended to help industrial contractor firms train blasters and painters. The original series was developed and written by the Coatings Society of the Houston Area in collaboration with SSPC, and Lloyd Smith edited it. The series was subsequently collected in one volume. From 1992 to 1993, a separate series on safety was developed and written under the direction of KTATator. In 1997, the series was updated and expanded. Beginning this month, the series will again cover the basics of corrosion, surface preparation, application, quality control, and safety. The series will be updated and expanded where necessary. Because the basic theory of corrosion, how coatings protect steel, and the importance of surface preparation have changed little since 1988, some of the original articles will also appear with minor revisions, including this first one on what applicators need to know about corrosion. Written by Joe Pikas, with Transco Corporation at the time, the article was first published in the July 1988 JPCL, then updated and re-published in the April 1997 JPCL.

8. Can in-process QC prevent premature coating failures? From JPCL, January 2013

PCS, KTA-Tator, Inc. Bill Corbett is the Professional Services Business Unit Manager for KTA-Tator, Inc., where he has been employed for 31 years. He is an SSPC-approved instructor for three SSPC courses, and he holds SSPC certifications as a Protective Coatings Specialist, Protective Coatings Inspector, and Bridge Coatings Inspector. He is also a NACE Level 3-certified Coatings Inspector. He was the co-recipient of the SSPC 1992 Outstanding Publication Award, co-recipient of the 2001 JPCL Editors’ Award, recipient of SSPC’s 2006 Coatings Education Award, and recipient of SSPC’s 2011 John D. Keane Award of Merit. Richard Burgess Series Editor, KTA-Tator, Inc.

William D. Corbett, PCS, KTA-Tator, Inc.

For decades we have heard that the incidence of premature coating failure would decline by explicitly requiring the contractor to control the quality of workmanship (via contract document language) using properly trained (and equipped) quality control personnel. In this Case from the F-Files, we’ll take a brief look at five case history failures and assess whether quality control inspection of the work as it proceeded could have prevented the failure from occurring, or whether it would have happened despite the efforts of knowledgeable quality control personnel.

Defining Quality Control The ISO definition states that quality control is the operational techniques and activities that are used to fulfill requirements for quality.1 This definition could imply that any activity, whether serving the improvement, control, management, or assurance of quality could be a quality control activity. Quality control is a process for maintaining standards and not for creating them. Standards are maintained through a process of selection, measurement, and correction of work, so only the products or services that emerge from the process meet the standards. In simple terms, quality control prevents undesirable changes in the quality of the product or service supplied. The simplest form of quality control is illustrated in Fig. 1. Quality control can be applied to particular products; to processes that create the products; or to the output of the whole organization, by measuring its overall quality performance.

Fig. 1: The generic control process Figure and photos courtesy of KTA-Tator Quality control is often regarded as a post-event activity, that is, a means of detecting whether quality has been achieved and taking action to correct any deficiencies. However, one can control results by installing sensors (e.g., inspection check points) before, during, or after the results are created. It all depends on where you install the sensor, what you measure, and the consequences of failure.1 The Joint Certification Standard for Shop Application of Complex Protective Coating Systems (AISC SPE/SSPC-QP 3 420-10) defines quality control as the inspection of work. Inspection includes but is not limited to confirming that procedures are met; workers are properly qualified; equipment is appropriate and in acceptable working order; and the proper materials are used and are in compliance with inspection criteria. Let’s take a look at a few case studies to see whether implementation of a quality control program using trained, properly equipped inspectors makes a difference. Case Study No. 1: Mirror, Mirror… Background: A contract was awarded to remove and replace the existing coating system on a large riveted structure. The specification required abrasive blast cleaning to achieve a Near-White blast (SSPC-SP 10/NACE 2), followed by two coats of a polyamide epoxy (standard gray) and one coat of polyurethane topcoat. Six months after the contract was completed, corrosion was observed (Fig. 2).

Fig. 2: Corrosion products on the back sides of the rivets and edges after six months’ service Cause: Corrosion products remained on the back side of the rivets that were not subjected to direct impact by the abrasive stream during blast cleaning. The coating was also applied from one direction, causing thin areas of coating on the back side of the rivets and the adjacent flat areas of the steel plate. Inadequate attention was given to the coating along the edges. Avoidance Through Quality Control Inspection? The QC inspector should have carefully examined the “difficult access” areas after surface preparation and application of each coating layer. As a general rule, if the quality control inspector has difficulty accessing the areas, then the coating applicators likely had difficulty as well. Verifying coverage on an abrasive blast-cleaned surface with a gray coating can be challenging. Good lighting and the use of an inspection mirror would likely have revealed the missed areas. The specifier could have selected a contrasting color for the primer and may have required stripe coating in these areas (in accordance with SSPC-Guide 11) to help protect the edges. Case Study No. 2: The Fix is in, and That’s the Problem! Background: The project specification required abrasive blast cleaning to achieve a Near-White blast (SSPC-SP 10/NACE 2), and the application of a single coat of an inorganic zinc primer to piping. Surface preparation and coating application were performed in the shop. Once the piping was installed in the field, damaged areas (caused by the installation) were abrasive blast cleaned and touched up with an organic (epoxy) zinc-rich primer. All of the touch-up areas performed well. However, within one year, portions of the piping showed extensive pinpoint rusting and rust-through. A closer examination of the pipe (Fig. 3) shows one of the rusted areas, with the edge of a repair area also shown (left portion of Fig. 3). As illustrated, the repair area is performing well, but the surrounding area is exhibiting rusting. Cause: When repairing damaged areas, the blaster failed to start and stop the flow of abrasive from the blast nozzle when moving from one damaged area to another. Instead, the blast nozzle was moved to the next location while the abrasive was still flowing at maximum pressure, which caused considerable damage to the coating. This is apparent in Fig. 3, where a round patch of coating had been effectively removed by the abrasive impact, with the surrounding area nicked by the abrasive.

Fig. 3: Close-up of rusted area, with the edge of a repair area also shown on above Because the zinc primer is essentially the same color as the steel, the damage went unnoticed until the electrolyte (water) contacted the surface and caused the formation of corrosion. Avoidance Through Quality Control Inspection? Many would point to a misplaced repair procedure as the culprit in this case; and perhaps, even with diligence, the overblast damage may have been unavoidable. However, during the start-up of the repair procedures, the QC inspector should have observed the abrasive blast cleaning operations, recognized the potential for overblast

damage, and discussed the issue with the owner/specifier before work continued. The owner and inspector could have discussed alternative methods of preparation. Anticipating potential problems and proposing resolutions before a widespread problem occurs are intangible values that quality control inspection can bring to a project. Case Study No. 3: You Know What They Say: Dry Heat Is More Comfortable Background: The project specification required abrasive blast cleaning to achieve an SSPC-SP 10/NACE 2 Near-White blast and the application of an inorganic zinc primer to structural steel components in the fabrication shop. Application of the intermediate coat was also performed in the shop, while the topcoat was scheduled for application in the field after erection and bolting of the steel. The work was done in the winter, and the shop was heated. The fabricator’s quality control specialist kept documentation revealing that the shop coating had conformed to the thickness and recoat times recommended by the coating manufacturer’s technical representative, who visited the shop during coating application. The steel was loaded onto trucks and shipped to the site. When the coated steel arrived at the construction site, spontaneous cracking of the coating along the fillet weld (where the web and flange are joined) was discovered (Fig. 4). Figure 5 illustrates the spontaneous cracking and lifting along the fillet, and the poor adhesion of the coating system on the top of the bottom flange. Examination of a disbonded coating chip revealed the presence of zinc primer on the back side of the chip and on the steel surface, indicating that the location of break was cohesive within the zinc primer.

Fig. 4: Spontaneous cracking of the coating along the fillet weld

Fig. 5: Poor adhesion of the coating on the top of the bottom flange Cause: Ethyl silicate inorganic zinc-rich primers require moisture to cure. In this case, insufficient time was allowed before the application of the epoxy midcoat. Once the epoxy was applied, no more moisture could react with the primer because the epoxy sealed off the primer. The zinc primer remained in a dry but uncured (and weakened state). The solvents from the epoxy midcoat penetrated the uncured primer, and the contractive curing stresses imparted by the epoxy caused the zinc primer to cohesively split. Because a web and flange are adjacent to one another, the thickness of the epoxy was slightly higher along the fillet weld area. The higher thickness exacerbated the problem and resulted in the cracking and detachment. When other areas were evaluated, it became evident that the entire system was at risk for failure. Avoidance Through Quality Control Inspection? Inorganic zinc-rich primers dry very quickly (especially in a heated environment); however, they may not cure for many hours or even days if the humidity is too low within the prevailing environment. The key is to verify that temperature and humidity (listed on the product data sheets) are present in the shop before application and to verify the cure has been achieved, rather than relying on cure time tables provided by the coating manufacturer, or assuming that drying and curing are synonomous. Quality control inspection by the fabricator should have included a curing test. In fact, there is one specifically designed for the primer in this case study (ASTM D4752, Measuring MEK Resistance of Ethyl Silicate (inorganic) Zinc-Rich Primers by Solvent Rub). Once a resistance rating of “4 or 5” is achieved (after 50 double rubs), the zinc-rich primer can be considered cured and ready for recoating. Some manufacturers rely on pencil hardness data instead of solvent resistance to

assess cure. Either way, a competent QC Inspector knows how specific coating types cure, the conditions necessary for the reactions to occur, and the tests available to verify coating film properties before applying the next coating. Case Study No. 4: A Picture’s Worth Thousands of $$$ Background: The project specification required abrasive blast cleaning to achieve a Commercial Blast (SSPC-SP 6/NACE No. 3) and the application of a single coat of alkyd primer in the joist fabrication shop. The joists were shipped to the project site, where they were stored outdoors (on the ground) for six months. Corrosion was visible within six months (Fig. 6). Cause: SSPC-SP 6/NACE No. 3 requires removal of all mill scale. The surfaces may have staining from mill scale (provided it does not exceed 33% of each 9 square inches). In this case, the “pock marks” in Fig. 6 clearly indicate that mill scale was left on the surface and coated over. The “hollow” areas represent those locations where the mill scale was removed, while the surrounding areas contain mill scale. The areas containing mill scale exhibit corrosion products. In a mild environment (and with the proper thickness), this system should have lasted longer than six months. However, the application of a thin (3- to 5-mil) film alkyd primer combined with damp storage conditions led to water permeation of the alkyd. The result was the formation of a corrosion cell at the mill scale/steel interface. Mill scale is cathodic to steel, which means that the base steel becomes the anode in the corrosion cell and begins to deplete, generating the corrosion products. Ironically, had the joists been stored indoors (or installed upon receipt), the lack of quality may have never been revealed, because it is unlikely that corrosion would have occurred due to the lack of electrolyte. Avoidance Through Quality Control Inspection? Careful visual inspection of the steel surfaces by the quality control inspector after surface preparation (including the use of SSPC-VIS 1) would have revealed the presence of mill scale, which is not permitted by the specified cleanliness standard. That is, quality control personnel need to know industry standards and need to use tools (in this case, visual guides) for help in making intelligent decisions. While additional surface preparation before application of the primer would have required additional labor and more abrasive, it would have been done at a significantly lower cost than the cumulative costs associated with the failure investigation, transportation of the joists back to the fabrication shop (and then back to the project site once the rework was done), the material and labor costs associated with re-application of the primer, and potential for liquidated damages due to project schedule delays.

Fig. 6: Corrosion of steel beneath alkyd primer evident within six months Case Study No. 5: Hey! I Followed the Spec; It Wasn’t My Fault. Background: The underside of a viaduct containing an aged lead alkyd coating was brush-off abrasive blast cleaned to remove loosely adhering corrosion and paint (SSPCSP 7/NACE No. 4), followed by the application of an epoxy mastic overcoat. Figure 7 illustrates the condition of the coating prior to abrasive blast cleaning. Figure 8 illustrates lifting of the old alkyd by the epoxy mastic overcoat. The number “10” written on the coating in Fig. 8 is in an area where the epoxy mastic was applied directly to the steel, rather than the aged lead alkyd. Directly beneath that area is an area where the mastic had lifted the alkyd, and was removed by scraping during the failure investigation. The area beneath the hand in the same photo represents epoxy mastic applied over the aged lead alkyd. This area was not probed during the investigation.

Fig. 7: Condition of the coating on the underside of the viaduct before brush-off blast cleaning Cause: The aged lead alkyd coating was in poor condition, as illustrated by Fig. 8. While brush-off abrasive blast cleaning removed the loosely adhering materials, the impact of the abrasive on the “intact” alkyd weakened (fractured) it, but did not affect it enough to consider it “loose” by the dull putty knife test. Application of the epoxy mastic imparted curing stresses that weakened the cohesive strength of the aged lead alkyd, causing it to lift and disbond from the surface.

Fig. 8: Area where epoxy mastic was applied directly to the steel rather than the aged alkyd Avoidance Through Quality Control Inspection? Because the QC inspector does not have the authority to change the specification, this project was doomed from the minute the work was awarded. Even though the QC inspector may have questioned the specification, it is doubtful that that owner would have altered the spec unless the fracturing of the aged lead alkyd had been visible to the unaided eye and the inspector had informed the owner of the damaged coating. Inspection personnel cannot use magnification (according to the SSPC Surface Preparation Standards). So while it appears that controlling quality as the work is performed reduces the opportunity for coating failure, quality control cannot be a substitute for a well-written specification, quality coating materials, and quality workmanship.

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THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2013 Technology Publishing Company

9.New SSPC Standard Helps Determine Compliance with Profile Requirements From JPCL, December 2012 Aimée Beggs SSPC: The Society for Protective Coatings Aimée Beggs is SSPC’s standards development specialist as well as SSPC’s technical committee liaison. She has worked for SSPC for 32 years. She has written and co-written articles for JPCL on SSPC surface preparation and visual standards. Aimée was the recipient of the SSPC Executive Director’s award in 2010. Heather Stiner SSPC: The Society for Protective Coatings Heather Stiner is the staff technical expert on protective coatings at SSPC. She also performs technical writing, contributes articles to the JPCL, responds to scientific inquiries, and acts as a technical resource for SSPC members. Heather is a graduate of the University of Pittsburgh, and is a member of the American Chemical Society, ASTM, and NACE.

Heather Stiner

Steel surface profile, sometimes referred to as “anchor pattern,” is the textured surface (resembling a series of peaks and valleys when viewed under magnification) that results from abrasive blast cleaning or power tool cleaning to bare metal. The peaks and valleys of the profile provide additional surface area to enable a protective coating to mechanically bond to the substrate. To enable the coating to adhere to the substrate as well as provide a continuous protective film, the depth between peaks and valleys, along with the number of peaks in a given area, must be carefully controlled. Most coating manufacturers provide a recommended surface profile range on their product data sheets. Project specifications may also contain these requirements, or reference those provided by the coating manufacturer. A recently issued (September 2012) SSPC standard, SSPC-PA 17, “Procedure for determining conformance to Steel Profile/Rough Roughness/Peak Count Requirements,” complements existing ASTM standards for measuring surface profile and roughness. SSPC-PA 17 does not replace the existing ASTM standards. This article will review current standards for measuring surface profile features and describe the development as well as the use of SSPC-PA 17 to determine compliance with project specifications.

ASTM Standards for Measuring Steel Surface Profile or Surface Roughness Over the years, a number of instruments have been developed to measure surface profile. ASTM Committee D01 has issued two standard test methods describing instruments and their proper use to measure steel profile.

Courtesy of KTA-Tator

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ASTM D 4417, Standard Test Methods for Field Measurement of Surface Profile of Blast Cleaned Steel, describes 3 methods and provides procedures for use of each. Method A describes the use of a profile comparator, a metal replica containing several segments representing degrees of roughness that can be visually or tactilely compared with the surface being evaluated. This method requires reporting the range of results from an unspecified number of locations on the surface as the surface profile. Method B describes the use of a depth micrometer, a gage that contains a pointed probe to measure the distance between a single valley and the peaks of the profile. The mean of ten gage readings is recorded. The mean of all locations (number is unspecified) measured on the surface is reported as the profile of the surface. Method C describes use of a special tape containing a compressible foam attached to a non-compressible uniform plastic film. The tape is pressed onto the steel surface to create a negative impression of the surface. The impression is then measured with a specially designed micrometer. One gage reading is taken on each of three pieces of tape, and the mean of the three readings is determined for that location. The mean for all locations measured (number is unspecified) is reported as the surface profile. ASTM D 7127, Standard Test Method for Measurement of Surface Roughness of Abrasive Blast Cleaned Metal Surfaces Using a Portable Stylus Instrument, describes the use of a portable stylus instrument (often referred to as a “profilometer”). The stylus is used to determine the number of peak and valley pairs, as well as the distance between the highest peak and the lowest valley encountered during each of five traces over the surface being assessed. Averages of each measurement parameter are reported, but the standard does not contain requirements for reporting surface profile measurement.

Rationale for Development of the SSPC Standard

Although both of the above ASTM standards provide recommendations for the number of instrument readings required to characterize the surface profile, neither standard provides acceptance criteria to determine whether the profile over the entire prepared surface is within the specified range. The frequency, location, and number of measurements to determine compliance, as well as the method of profile measurement, are left to the specifier. In 2008, SSPC formed a technical committee, chaired by Heather Stiner, SSPC Protective Coatings Professional, to develop a standard that defined a procedure for determining compliance with specified profile ranges and that complemented the information in the ASTM D4417 and D7127 standards. The SSPC committee consisted of representatives of coating manufacturers, painting contractors, manufacturers of profile measurement gages and equipment, facility owners, inspectors, and protective coating consultants. Members of the ASTM committees that developed D4417 and D7127 also participated. Options for Determining Compliance The “Process Control” Method The committee recognized that many production factors contribute to the size and angularity of surface profile, including: equipment used; size, hardness, and shape of abrasive media; type of steel; and accessibility of the surface, among others. Because any of these variables can change frequently during the production process, the first drafts of the proposed standard were based on “process control” requirements. The process control requirements call for the contractor

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to produce a four-foot square “field standard” that meets the project specification,

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to measure the profile of the field standard, and

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to verify compliance of the field standard with project requirements.

Example of portable stylus instrument that measures surface roughness and peak count as described in ASTM D7127. Courtesy of KTA-Tator. Following the owner’s acceptance of the “field standard,” the contractor must verify continued compliance with project requirements by taking an additional profile measurement each time any of a number of specified processes changes occurs during the project. A final profile measurement is taken following completion of production to verify compliance.

Compressible tape and micrometer described in ASTM D4417 Method C. The burnishing tool is used to compress the emulsion on the underside of the polyester film. Courtesy of KTA-Tator. However, some committee members argued that the “process control” method would create unacceptable levels of documentation and work stoppages because of the number of production factors requiring verification of continued compliance. Other committee members argued that specific requirements for frequency, number, and location of measurements to verify compliance were needed, and suggested a different approach, based on SSPC-PA 2: Procedure for Determining Conformance to Dry Film Thickness Requirements. The approach based on SSPC-PA 2 was adopted by the committee, and the “process control” method was moved out of the body of the standard into an appendix, giving specifiers the option of substituting it for the “PA-2 Method” below.

Surface profile comparator as described in ASTM D 4417 Method A. Courtesy of KTA-Tator. The “PA-2 Method” The SSPC-PA 2 standard requires averaging three dry film thickness gage readings within a 1.5-inch circle to obtain a “spot” measurement, then averaging five “spot” measurements within a 100-square-foot coated area to determine compliance. The number of 100-square-foot areas measured to ascertain compliance is determined by the size of the total area coated. Modifications for PA 17 Because various methods of surface preparation may be used on a substrate during a given work shift, and each method will generate profile in a different way, the PA 17 standard requires that the profile created by each piece of equipment during a single work shift (12 hours or less) be verified in three locations, regardless of the size of the area prepared.

Electronic depth micrometer as described in ASTM D4417 Method B.

Courtesy of Elcometer. The PA 17 standard requires averaging individual instrument readings within each of three randomly selected 6x6-inch locations on the prepared surface to generate a “location average” for that location. PA 17 requires reporting the highest and lowest location averages, and the average of the three location averages. Each location average must fall within the specified profile range.

Electronic depth micrometer as described in ASTM D4417 Method B, showing probe. Courtesy of KTA-Tator. Using PA 17 to Determ ine Compliance with Specified Profile Step 1: Identify the method used to take readings from the surface. This could be any of the three methods in ASTM D 4417, or ASTM D 7127 could be specified. ASTM D 4417 Method C (tape) will be used for this example, as it is one of the most frequently specified methods. Step 2: Identify the pieces of equipment used to prepare the surface during a particular shift. If nozzles from Blast Pot A and Blast Pot B were used to prepare the majority of the surface, and a power wire brush was used to clean several areas that could not be reached by nozzle blasting, verification of the profile in areas prepared by Blast Pot A, Blast Pot B, and the power wire brush must be performed separately. Step 3: Select three 6x6-inch locations (L1, L2 and L3) on an area prepared by Blast Pot 1 during the work shift. Step 4: Within each location, prepare and read 3 tapes in accordance with ASTM D 4417 Method C. Step 5: Add the readings from Tapes 1, 2, and 3 and divide the result by 3 to generate the “location average” for L1. The “location average” for L1 must be within the specified profile range. Step 6: Perform Steps 3 through 5 in locations L2 and L3 within the area prepared by Blast Pot 1. If the L2 and L3 location averages are also within the specified profile range, the area prepared by Blast Pot 1 is compliant. Step 7: Report the highest and lowest location average, as well as the “measurement” (the average of L1, L2 and L3 values) for the area prepared by Blast Pot 1. Step 8: Perform Steps 3 through 6 in the area prepared by Blast Pot 2, and again in the area prepared by the power wire brush to verify the areas prepared by each piece of equipment are also in compliance with the specified profile range. Steps 1 through 8 are performed at a minimum of once per work shift. This frequency is intended to minimize work stoppages while at the same time periodically verifying conformity with project requirements during the course of production. Identifying Non-Conforming Areas If any “location average” is outside the specified profile range, you must select four additional locations equidistant from each other and 5 feet away from the non-compliant location, and obtain “location averages” for each of the four locations. Each of these four location averages must comply with the specified profile range, or the process of selecting additional locations at five-foot distances from the non-compliant location must repeat. If there is no room to take a measurement in a given direction, no measurement is required. You must mark and report any non-compliant locations.

Summary SSPC-PA 17 was developed to provide specifiers, inspectors, and contractors with a standard set of acceptance criteria to determine compliance with steel profile requirements in industry project specifications. In many ways it is similar to the SSPC-PA 2 standard, which has been widely specified since its initial publication in 1996. As with all SSPC standards, PA 17 is subject to periodic reapproval or revision at least every five years. Revisions may be made within that period if the committee agrees that they are necessary. The committee anticipates that refinements will be proposed as the PA 17 standard becomes more generally specified and used, and welcomes suggestions to improve the usefulness and clarity of this, and all other SSPC standards. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2012 Technology Publishing Company

10.Temperature and Humidity Monitoring for Industrial Coating Application From JPCL, November 2012 Don Schnell DRYCO Don Schnell is the national strategic accounts manager for DRYCO, which is based in Downers Grove, IL. He has worked in the protective coatings industry since 1977 and has more than 20 years of experience with dehumidification and temporary climate control. He has had an important role in the development and expansion of climate-control innovations used in the protective coatings industry.

It has long been known that temperature and humidity have a significant impact on proper surface preparation and application of liquid-applied coatings. High humidity near the surface of dry abrasive-blasted steel increases corrosion rates and therefore causes flash rusting before the prime coat can be applied. Surface temperatures impact the rate of polymerization and the evaporation rate of solvents in the coatings as they are applied and cured. A quality coatings application can occur only when these conditions are within the tolerance of the product being applied.

Don Schnell, DRYCO

To assure that these conditions are maintained, the contractor and the inspector must employ good practices to measure, monitor, and record these conditions. This attention to climatic conditions is important on interior and exterior applications and with or without climate control measures. The accuracy and completeness of this measurement and documentation not only assures a quality application, but also protects all parties from culpability should a premature coating failure occur. This article reviews good practices for measuring, monitoring, and recording ambient conditions during coating operations.

iStock Objectives of Measuring, Monitoring, and Recording Conditions To help ensure that the coating project is successful and that the service life of the coating is maximized, it is imperative that the conditions be monitored from the time surface preparation begins until final cure is achieved. On the industrial coating project, the facility owner should demand that regular readings be taken and recorded. To be sure that this occurs, a well-written specification must be in place and followed. The owner’s representative should demand this documentation throughout the project, avoiding the disappointment of learning after the fact that the readings were not taken or documented. Any reconstruction of condition data is only supposition and a guess at best. Current practice usually includes gathering readings for dry bulb temperature, surface temperature, relative humidity, wind speed, and dew point temperature. (See the sidebar, “Psychrometric Definitions,” for more on the meaning of these different readings.) The measurement and monitoring should include at a minimum, surface temperature and dew point temperature. Although relative humidity is also important, the true relative humidity at the surface can be determined only by using the surface temperature and dew point temperature. (See the sidebar, “Calculating Relative Humidity at the Surface.”) These readings should be taken in all areas that are in the process of surface preparation, coating application, or coating cure. The specifier and inspector also need to consider that conditions vary on different areas of the project. Here are some examples. Psychrometric Definitions Dew Point Temperature: The temperature at which moisture condenses from the air. A common example is when the air is cooled adjacent to a cold beverage and condensation forms on the outside of the glass. Dew point temperature is important on the coating job as condensation on surfaces causes flash rusting and coating cure problems. As mentioned in this article, dew point temperature is also a useful metric when determining appropriate environmental conditions. Dry Bulb Temperature: The temperature of the air as measured by a dry thermometer. On the coating job, dry bulb temperature impacts surface temperatures, relative humidity, and material temperatures.

Relative Humidity: The moisture content of the air as a percentage of what it can hold when the air is saturated at that same temperature. When the air is saturated, it is at 100% relative humidity. Specific Humidity: Also called the humidity ratio. This is the ratio of the actual water that is in the air to the weight of the air itself. Specific humidity is expressed in grains of water per pound of air. A grain is a simple unit of measure and there are 7,000 grains in a pound. This is another way of expressing dew point temperature. Wet Bulb Temperature: The temperature of the air as measured by a thermometer surrounded by a wetted wick. The wick draws heat from the sensing bulb as the water evaporates. The rate of evaporation is dictated by the amount of moisture in the air, therefore, the resulting temperature indicates the amount of moisture in the air. This is only valuable on the coating job when a psychrometer is used. The wet bulb must be compared to the dry bulb temperature to determine the relative humidity or dew point temperature. Calculating Relative Humidity at the Surface At 100% relative humidity, the dew point temperature equals the dry bulb temperature and condensation begins to occur. If we can keep the relative humidity (at the surface) below 50%, we can keep dry abrasive-blasted steel clean for some time. The relationship between relative humidity and surface temperature is often misunderstood and misinterpreted on the jobsite. On the coating jobsite, the only conditions that matter are those occurring adjacent to the surface being worked on. This is an important point to make because condition readings taken elsewhere in the space can be misleading. As an example, consider a bridge project that exhibits the following conditions:

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dry bulb temperature: 70 F;

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relative humidity: 60%; and

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surface temperature: 60 F.

The observer measuring relative humidity may be satisfied that 60% is acceptable. In reality, the air at the surface of the bridge steel is cooled down to 60 F, raising the relative humidity to 85%. This condition represents a dew point temperature of 55.5 F. When compared to the surface temperature, this is a difference of only 4.5 degrees. Typical coating application guidelines call for a maximum of 85% RH and a minimum difference of 5 F between the surface temperature and the dew point temperature. This condition can easily occur at dusk on a clear night or in the morning before the sun can heat the steel. The author has experienced many situations during tank work where panic calls come in from the jobsite regarding high humidity in the tank when the cooling equipment may be maintaining a very acceptable relative humidity at the surface. The reverse also occurs where the observer measures a nice low relative humidity in a heated tank while the cold tank surface is about to condense. The solution is to forget about relative humidity. It changes with temperature and does nothing but confuse things. Dew point temperature will equalize in a well-contained space and is very consistent from one end of the bridge to the other. If the monitoring focuses on dew point temperature and surface temperature, we can all deal with accurate and meaningful metrics. Most measurement tools now also display dew point temperature so conversions are rarely needed. To make the leap from relative humidity at the surface to dew point spread, a little work with a psychrometric chart tells the observer the following.

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The often-specified maximum relative humidity of 85% equates to a surface temperature that is 5 degrees above the dew point temperature. To preserve dry abrasive-blasted steel (often referred to as “holding the blast”), the surface temperature should be at least 20 degrees above the dew point temperature. This varies a little as temperatures fluctuate, but a 20-degree spread is a safe middle ground. Surfaces heat up when exposed to sunlight. Surfaces cool when exposed to the night sky, particularly on clear nights. It is typical to experience surface temperatures well below the ambient air temperature on a clear, still night.

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Surface temperatures are highly impacted by exposure to wind or air movement.

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Hot air rises.

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Buried surfaces, surfaces on the ground, and surfaces below the water line react much differently than those exposed to the atmosphere. Dew point temperature equalizes very quickly throughout a space. Dew point temperatures will be fairly consistent in an enclosed space unless the space is compartmentalized or elongated, or if there is excessive air flow or infiltration of outside air.

(See the Sidebar, “Sample Specification for Environmental Conditions.”)

Sample Specification for Environmental Conditions 3.01 ENVIRONMENTAL CONDITIONS A. Do not apply coatings, under the following conditions, unless otherwise recommended by the coating manufacturer: 1.

Under dusty conditions, unless tenting, covers, or other such protection is provided for items being coated.

2.

When light on surfaces measures less than 15 foot-candles.

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When ambient or surface temperature is less than 45 degrees Fahrenheit.

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When relative humidity is higher than 85 percent.

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When surface temperature is less than 5 degrees Fahrenheit above the dew point.

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When the surface temperature exceeds the manufacturer’s recommendation.

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When ambient temperature exceeds 95 degrees Fahrenheit, unless manufacturer allows a higher temperature.

B. Provide fans, heating devices, dehumidifiers, or other means recommended by manufacturer to prevent formation of condensate or dew on surface of substrate, coating between coats, and within curing time following application of topcoat. C. Provide adequate continuous ventilation and sufficient heating facilities to maintain minimum 45 degrees Fahrenheit for 24 hours before, during, and for 48 hours after application of topcoat. Courtesy of Russell Spotten, Corrosion Probe Manual Readings Before the surge in electronic measurement equipment, ambient conditions were obtained in the field using a sling psychrometer (Fig. 1), and surface temperature was taken with a magnetic surface thermometer.

Fig. 1: Sling psychrometer Courtesy of Bacharach, Inc., and KTA-Tator, Inc. Infrared thermometers offer a much more convenient and accurate method for reading surface temperatures while giving the inspector the ability to get readings on surfaces several yards away from the instrument (Fig. 2).

Fig. 2: Infrared thermometer Courtesy of Raytek The psychrometer is a device that holds two thermometers in an air stream. The end of one thermometer is covered with a cotton wick that is wetted with distilled water. When the air passes over the wetted wick, it is cooled by evaporation until it reaches the wet bulb temperature. By comparing the dry bulb and the wet bulb temperatures, one can determine the dew point temperature or the relative humidity using a psychrometric chart, tables, or special software designed to make these calculations. There are two common versions of the psychrometer, aspirated and sling-type. The aspirated psychrometer is housed in an enclosed case where a small fan passes the air across the wetted wick at the prescribed 600 feet per minute. The more common tool on the job-site is the sling psychrometer, which holds the thermometers in a tube that is spun around to create the air flow. When read properly and if the water and the wick are clean, the psychrometer can be accurate within 5%, and it does not need calibration. The author prefers an aspirated psychrometer over all devices for field measurements. A common error in reading these instruments is taking average readings or spinning the thermometers too long or not long enough. The most accurate reading is the lowest wet bulb reading the user reads. The wet bulb reading should be monitored as it drops and then begins to rise again while the wick begins to dry out, with the lowest observed reading recorded. It may take five or more tries to reach the lowest possible reading. Magnetic surface temperature thermometers get the job done but can lose accuracy with use. It is not uncommon to see these devices in use with cracked lenses, damage from falling to the floor of the tank, or paint overspray or steel grit caked on them. Today, it is much more common to see electronic measurement instruments on the coating jobsite. These include instruments that measure dry bulb temperature, relative humidity, and surface temperature while calculating and displaying the dew point temperature. With on-board logging features, these devices are capable of logging the data collected with time stamps to later download to spread sheets or other formats. These instruments are very convenient and can allow the user to take many readings rapidly (Fig. 3). It is important to calibrate these devices regularly, particularly when exposed to extreme conditions.

Fig. 3: Electronic dewpoint meter Courtesy of Elcometer Data Logging Another approach to monitoring and recording conditions is to use some kind of electronic device that automatically takes readings and records them on paper or in digital format (Fig. 4). Simple chart recorders have been around for decades and have been used successfully on painting jobs. This mechanical technology uses a bundle of human hair or a polymer strand that expands and

contracts with humidity to move a pen on a revolving disk or drum chart. Another pen will record the air temperature simultaneously. These devices must be calibrated every 6 to 12 months and are very susceptible to dust and physical damage that is quite likely on a blast cleaning and painting site. (See the sidebar, “Calibration.”) Calibration It is important that all instruments be calibrated properly and at regular intervals. This can be done by comparing the device to an electronic condensation-based hygrometer. These hygrometers use a chilled mirror to make a very accurate determination of exactly what temperature moisture begins to condense in an air sample. Quick field calibration can be done with an aspirated psychrometer. Keep in mind that the psychrometer’s error margin will always be to the high side. Because the wet bulb thermometer can only cool down to the wet bulb temperature, the psychrometer cannot give a humidity reading that is too low.

Fig. 4: Electronic data logger for temperature and relative humidity Courtesy of Onset Computer Corporation Electronic data loggers offer a fairly low-cost alternative to the chart recorder. Loggers add the ability to record the conditions into commonly used spreadsheet files and email the data. Typically, these loggers are very small and battery powered. The data can be downloaded to a computer with a cable link, or “shuttle” devices on some models allow the collector to capture the data in the field and upload it to a computer later. These units can be quite durable but still must be protected from the very aggressive environments typical to our industry. Hand-held monitoring tools also have logging capabilities. Readings can be stored with a date/time stamp and the ability to download to a file for processing later. The modern hand-held electronic hygrometers also have a surface temperature sensor, which was a big step in the evolution of condition monitoring. To be able to read the surface temperature, relative humidity, and dry bulb temperature in the same location is the most accurate and meaningful way to gather this information. (See the sidebar, “Calculating Relative Humidity at the Surface.”) It is also important to take these readings where the work is occurring. Although chart recorders and electronic data loggers can (and should) include surface temperature sensors, they are generally stationary, taking readings in one location. Enhanced Monitoring It is important to know if climatic conditions were not acceptable at some point during a coating project, but a completely different value is attached to being able to avoid adverse conditions. In the past decade, a significant improvement in monitoring technology has emerged. The introduction of remote monitoring allows the contractor, inspector, and owner’s representative to monitor and record site conditions in real time and to see these conditions online (Fig.5). In addition, it becomes possible to set up alarms that will contact a party when conditions deteriorate past a pre-defined point or to have an alarm go off when there is an equipment failure. These features offer the ultimate in documentation while adding the security of knowing immediately if the conditions on the project have reached a critical point.

Fig. 5: Remote monitor for checking jobsite conditions while off-site Courtesy of DRYCO Now, with a secure password, the interested party can check the jobsite conditions from anywhere—home, a coffee house, the office, etc.—using a laptop, tablet, or other electronic device with Internet access. When a climate control provider is used, the technician is notified when conditions are approaching the limits of the specification and can react to repair or adjust the climate control system before things become critical. To get the most value from remote monitoring, the user should specify that the device can provide the following.

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• • • •

The device should allow the user the ability to view current readings and historical data on site without the use of a laptop. The contractor or inspector should be able to walk up to the jobsite in the morning and quickly view what had occurred overnight. Data should be stored on the device and on the website for redundancy. This protects the data from loss due to website failure or device failure. Data should be available online in graph or tabular formats, with the date range sortable and downloadable into a spreadsheet or tab-delimited format at any time with the correct password. The system should be capable of reading and recording humidity and temperature in two locations and surface temperature in four locations. The data should include relative humidity, dry bulb temperature, dew point temperature, surface temperature; the difference between the dew point temperature and the surface temperatures should also be clearly displayed.

Conclusion The methods used for measuring, monitoring, and recording the climate conditions on industrial coating projects have advanced significantly in the past decade. There are fast, accurate hand-held devices that can log the readings for later download. These instruments should be calibrated and interpreted properly to get the full value from their use. Older technologies may be less accurate and more cumbersome, but do not require calibration. The latest technology available includes remote monitoring that measures and records conditions as well as sends them to a website where they can be viewed or downloaded in real-time. This technology also allows the users to receive alarms by email or text message when conditions on the job deteriorate. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2012 Technology Publishing Company

11.The Ideal Coating Inspector From JPCL, November 2012 Brendan Fitzsimons Pyeroy Brendan Fitzsimons has nearly 30 years of experience in the protective coatings industry with over two thirds of this at Senior Level with International Coating Contractors. He is a divisional director at Pyeroy, an international coatings contractor. Fitzsimons has a Master’s Degree in Materials Engineering, is a Chartered Scientist and a Fellow Member of the Institute of Corrosion. He is a NACE Protective Coating Specialist, Coating Inspector, and Peer Reviewer.

Surface treatments and application of protective coatings are generally expensive and essential processes, and they are critical tasks when surfaces are exposed to hostile environments. Inspectors, therefore, are used extensively to check the quality of the work and reassure clients and customers that each task has been conducted in accordance with the coating specification, international standards, and/or the manufacturer’s product data sheets. The profession may be known as coatings inspector, painting inspector, or paint inspector. Whatever phrase is used in the protective coatings industry, the term “Inspector” is used in this article to reflect many activities and locations globally. Inspectors are used at various levels during a project and may be employed by the painting contractor, fabricator, engineering organization, or ultimate customer. It is not uncommon to have inspectors who have worked at all levels and thus gained the experience of such to make the first and final decision on inspections. Brendan Inspectors work in virtually every industry including nuclear, offshore, marine, petro-chemical, infrastructure, Fitzsimons, Pyeroy pipeline, and general construction. Some inspectors remain specialized within a specific industry such as offshore while others move from industry to industry depending on the length and extent of the project and location.

Photo of splashzone Courtesy of the author photo: iStock Because of various recent regulations in the corrosion control industry, such as the IMO PSPC requirements in the marine industry, there has been an increased need for qualified inspectors. Some of these regulations have certainly produced a number of training courses and newly qualified inspectors who are now equipped with their ‘ticket’ to conduct their inspection duties in their chosen industry. This article will review the various qualifications and training requirements of the inspector and try to establish whether the ideal inspector really does exist. For the purpose of this article, we will refer to the ‘coating inspector’ because this is the most commonly used phrase in most of the industries discussed. Lifetime Experience Having been in the coatings industry for almost 30 years, I can say in all honesty that I have met a lot of coating inspectors who do an excellent job of maintaining the credibility of the training, qualifications, and good name of the profession as a whole. Unfortunately, I have also encountered some coating inspectors who, in my opinion, should not be employed in the protective coatings industry at the inspector level. At a recent conciliation between a painting contractor and a bridge owner who hired an ‘independent’ coating inspector, the conciliator concluded: “The coatings inspector can make or break a job.” Unfortunately, in this particular case, the conciliator was correct, and the painting contractor was awarded many thousands of Euros for the instructions given by the coatings inspector that breached the terms of the contract. Unfortunately, some inspectors can be overzealous, difficult, or both. There are many examples where the coating inspector has created problems on a contract through lack of experience, lack of knowledge, or an intention to build a reputation for the wrong reasons. Common problems created include the following:

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imposing particular tests that are not specified; increasing levels of quality above those required in the specification and not being pragmatic, resulting in an increase in the length of a contract and a corresponding increase in personal remuneration; and

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creating a poor working relationship with the contractors, such as the ‘us vs. them’ approach.

There are also a few coating inspectors who are ‘frustrated’ contract managers and believe they could manage the contract better. In most cases, the coating inspector has been trained in quality issues but has little concept of planning, costs, practicalities, and completing a project on schedule. Coating inspectors have limited legal obligations within a contract and will not generally have professional indemnity insurance. That said, inspectors should recognize the financial impact of recommendations and advice, and limit their recommendations to areas within their field of experience and qualifications. More importantly, coating inspectors should recognize that they provide recommendations, and not direction. Generally, the client should make the decisions, choosing whether or not to follow the inspector’s recommendations. There are also many examples in which a coating inspector has passed on his or her wealth of experience and knowledge during a contract and, by so doing, has benefited all parties, including the painting contractor. An engineer once said, “a good coatings inspector is worth his [her] weight in gold.” Coating systems may have been designed and tested for certain hostile locations, and, without the correct level of quality control, premature coating failure is always a possibility. There are generally good reasons why high-performance systems are specified. The coating inspector should make himself or herself fully familiar with any specified product. Product training may also be a requirement. Industry Qualification Schemes Various credible coating inspection qualification training schemes are used globally. • Institute of Corrosion (ICorr; UK) The Institute of Corrosion is a professional body in the UK and has an established training scheme for paint and coating inspectors. The scheme also has training and qualifications for inspecting metallic coatings, pipeline coatings, cathodic protection, and thermal insulation. The paint and coating inspector scheme has three Levels: 1, 2, and 3. There is no pre-requisite for attending Level 1; however, qualifications and experience are required for Levels 2 and 3. Closed book specific and general examinations are conducted for all levels along with practical essays for Levels 2 and 3. Practical assessments are also conducted. The scheme is conducted and governed in accordance with the Institute of Corrosion Document ICORR REQ DOC. • SSPC: The Society for Protective Coatings The SSPC is based in the U.S. and is a non-profit organization focused on the protection and preservation of concrete, steel, and other industrial and marine structures and surfaces through the use of high-performance protective, marine, and industrial coatings. The SSPC has a Protective Coating Inspector scheme (PCI) with three levels, similar to the Institute of Corrosion’s scheme. There are no pre-requisites for the entry level, but qualifications and experience are necessary for Levels 2 and 3. Level 3 consists of a four-part examination that includes creating an inspection test plan based on a coating specification. The training program is well established and specified globally. SSPC provides many other courses aimed at painting applicator skills, supervisor training, and other aspects of protective coating work. • NACE International NACE International is a professional organization for the corrosion control industry and has a large membership in over 100 countries. NACE has an established coatings inspector program (CIP) that has gained worldwide recognition; it has been available for over 25 years and has some 19,000 certified Inspectors. The CIP course consists of three levels. The first two levels are similar to other training schemes for coating inspectors; however, the third level is a Peer Review. The Peer Review consists of a two-hour verbal examination in front of three experienced coating experts who have many years of coating inspection experience as well as being NACE-qualified coating inspectors. As with other training schemes, there is no entry pre-requisite for the course entry level. • FROSIO The Norwegian Professional Council for Education and Certification of Inspectors for Surface Treatment (FROSIO) acts through formulation of quality demands for surface treatment in accordance with the Norwegian Standard NS476. FROSIO deals only with examination and certification, not training. A number of training bodies are used to deliver the training, which consists of 80 hours of theoretical and practical training in accordance with NS476 as the syllabus. There are three levels of qualification, with no experience required for Level 1 (white certificate). Level 2 (green certificate) candidates must have two years of experience, and Level 3 (red certificate) candidates must have five years of experience, two of which are to be documented inspection practice. Certification at Level 1 and 2 is achieved by examination. Level 3 is achieved by Level 2 plus documented evidence. • TWI CSWIP & BGAS

The Welding Institute (TWI) is a worldwide organization and a reputable expert in welding techniques, training, testing, investigation, and related areas. TWI has a Painting Inspector training scheme that consists of three levels, Grades 3, 2, and 1. No pre-requisites are required for Grade 3, and candidates must have obtained Grades 3 and 2 to attempt Grade 1. Grade 1 is an advanced qualification that specifically deals with offshore practices. The scheme was initially developed for personnel wanting to work for British Gas only and, thereafter, other clients and locations as well. Table 1 represents the various levels between the main global training schemes for coating inspectors. The writer recommends that a light Internet reading on the various schemes and levels should be conducted before specifying one or all. TABLE 1

Levels in Main Global Training Screens ICorr

SSPC

NACE

FROSIO

Level 1 Level 1-Basic

Level 1

Level 1-White Grade 3

Level 2 Level 2-Certified Level 2

Level 2-Green Grade 2

Level 3 Level 3-Certified Level 3 Level 3-Red Peer Review

TWI CSWIP & BGAS

Grade 1

All of the above training schemes have one thing in common—no experience is required for a candidate to attempt the first level of the scheme. One scheme provider states, “No formal entry qualifications required, but knowledge of dry abrasive blast cleaning or industrial paint application techniques would be advantageous.” Some of the above schemes do not issue ‘certification’ for the entry Level, so it is worth checking on the specific scheme and type of certification. It is important to specify the scheme along with the required Level, e.g., NACE CIP Level 2, not just NACE CIP. Unless specifically requested, the trained coating inspector, regardless of the training scheme, should:

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observe the work,

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assess the work,

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document the work, and

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report the work.

All of the above tasks should be conducted in accordance with the contract Inspection Test Plan. This author is not averse to new recruits entering the coatings industry. However, in the age of new and sophisticated coatings, highrisk projects, and customer reliance on technical advice from the ‘coatings inspector,’ the question arises about whether a newly trained and qualified coatings inspector, who has possibly never been involved in the protective coatings industry, is a suitable choice, given the potential exposure to extreme environments and the probability of working with contractors who have vast experience in most types of surface treatments and protective coatings. It is clear that there is a difference between highly experienced individuals who are acting almost as consultants to their customers, and trained but inexperienced inspectors who should be regarded as quality control technicians and perhaps no more. Customers should be, and are often not, aware that the provision of detailed technical advice is not appropriate for novice inspectors. The question of comparing qualification levels from scheme to scheme is often raised and debated. It would not be politically correct for this writer to give views on the schemes and what the equivalence between levels is. However, this writer would recommend that the specifier review the syllabuses of the different schemes, the recommended experience required per level, and the type of examinations to select the scheme best suited to a particular contract. ISO Standard An ISO standard for the qualification or certification for inspectors is under review. Certain European countries have expressed a desire to certify inspectors who could then work in other countries, with that certificate being accepted by all other countries. What the standard should be has not been defined, e.g., guidelines, qualifications, certification, or minimum course requirements. Because no agreement could be reached at the initial meeting and in order to report back to TC35/SC14, it was agreed to send out a questionnaire to national mirror committees for their views. The discussions were planned to continue when the questionnaires were complete; however, it may be some time before an agreement is reached on what the ISO standard should address. Online Training A recent change in the training of coating inspectors is with the use of online training through the Internet (Fig. 1). There are potential advantages and disadvantages with online training.

Fig. 1: Typical page in a web-based training program. Courtesy of the author Here are three significant advantages:

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training can be conducted at any time to suit the student;

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training is conducted at home or work, so there are no hotel bills or expenses; and

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the training is updated easily and can be used as an ongoing source of information.

Here are two significant disadvantages:

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the instructor has no direct interface with the student; and

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a practical session is still required to cover the use of inspection equipment, etc.

Some of the schemes currently use the Internet for online training, and this approach to training is expected to increase dramatically over the next few years. One paint company is using online training to educate and qualify over 600 staff. There is no doubt the use of online training will increase. A balance of online training and practical training before examinations is the recommended process. This will ensure that students are able to train with and demonstrate on the inspection equipment. Minimal industrial experience is essential for the online training. Online use for general corrosion education is also set to significantly increase in the coming years. Ongoing Technology Technology is forever changing in the coatings Industry. Standards are amended and updated at specific anniversaries (Fig. 2). Recertification of coating Inspectors usually consists of a CV, a possible questionnaire, and fees. The writer believes that coating inspectors should

Fig. 2: Inspectors should keep up with changing standards, such as those for adhesion testing. Courtesy of the author • be aware of new technology, including instrumentation, regulations, and standards, on an ongoing basis, possible through an IT hub; and • prepare more concise information relating to what experience and knowledge they have attained.

Some of the scheme providers interrogate the coating inspector considerably more than others on re-certification. The process could possibly be included in the proposed ISO standard. Consideration should be given to requiring the coating inspectors to compile and continually update a “CPD”—Continuing Professional Development—which demonstrates that their knowledge and professional skills are kept up to date. The coating inspector should be able to keep up to date with coating technology, inspection equipment, new standards, etc. A coating hub would be of great benefit to the industry. All scheme providers would, however, have to contribute and agree upon the contents and updates, etc. Alternatively, an independent Internet hub could be approved by all training providers. Health and Safety All the above training schemes for coating inspectors cover aspects of health and safety. The regulations for health and safety in the coatings industry have increased over the past few years. There is now a greater need for all personnel to have specific Health and Safety training. All coating Inspectors should be able to write risk assessments and method statements. The aforementioned is not generally covered in the coating inspectors’ training. This writer would strongly recommend additional health and safety training to that which is usually afforded by the painting supervisor or painting manager. The coating inspector should be generally fit and used to working at heights; in confined spaces; and in poorly lit, potentially dusty, and hazardous environments. Any intake of medication, poor eyesight, or other health conditions should be declared before starting the work or whenever the worker’s health status changes. Inspection Test Plans Inspection test plans that describe the methodology of the preparation and coating process step by step are an ideal tool for agreeing upon the inspection activities in advance of the work. This writer is convinced that the use of agreed inspection test plans that detail the level of inspection, type of test, and equipment (including exact details with regard to pass/fail criteria) would greatly assist contracts and ensure disputes are resolved quickly. The contractor should be fully familiar with the painting specification as well as where and how the inspection test plan is used. All parties must agree upon the hold (h), witness (w), and surveillance (s) points for all levels of activity. All the above should be covered at the pre-contract meeting, which must have the contractor and coating inspector present. One scheme provider has the development and use of Inspection Test Plans as part of the training course. Other scheme providers have a cursory review while still others do not discuss the Plans at all. Documentation The coating inspection industry could benefit from standardization of documentation. This writer has witnessed over 50 types of daily inspection forms, logs, weekly reports, and other inspection documents. Internationally agreed-upon inspection reports could be approved and placed on the coating inspection Internet hub approved by all scheme providers. Some scheme providers do give a list of key forms used to document coating work and quality monitoring but these are suggestions only and not acknowledged by other scheme providers. Some coating specifications stipulate the details that should be contained within the documentation and some give specific examples. Experience and Attitude Experience is invaluable. If you are going to line a vessel with a specialty coating or work on a complex project, an experienced coating inspector is essential. You should follow up on a CV submitted by an agency to ensure it is correct, and ask for references wherever possible. What you will not find on a CV is the attitude of the coating inspector. Most coating inspectors have a good attitude toward the work they inspect and desire to achieve a high-quality job. There are, however, a few coating inspectors who wish to enforce the painting specification overzealously because they think they have the power to do so and do not understand that the coating inspector should also be pragmatic and understand the costs of doing the work and possible program implications. The writer would prefer a coating inspector who has limited but adequate experience with a good attitude rather than an experienced coating inspector with a bad attitude. The importance of obtaining and checking references cannot be overemphasized. Conclusion So does the ideal coating inspector really exist? If you can find a coating inspector who is mature, qualified, experienced in the specific contract or product, has a good attitude toward helping the contract, is aware of the costs implications if wrong decisions are made, is safety conscious as well as flexible and firm, has a good reputation, and is in good health, then the answer is a definite yes. I would say, however, that the chances of finding such a coating inspector could be very low (30–40 mils) on a metallic substrate may require scoring if called for in the specification. If the test can be stopped at the minimum value specified without causing coating failure, than the dolly can be removed, often times by striking the dolly with a sharp blow from the side or carefully inserting a sharp 5:1 tool (putty knife) at the glue line and shearing off the dolly. Repairing the top surface may be required but is much better than having to repair the total coating system. When testing thermal spray coatings, always perform the adhesion tests before application of the seal coat. Tests performed after seal coat application will result in test values that are two to three times the value of virgin thermal sprayed coating. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2013 Technology Publishing Company

22.The Crude Truth about Lining Tanks for Oil Transport From JPCL, September 2013

Michael McGlamry Hempel USA Michael McGlamry is the Americas Protective Product Manager for Hempel, USA. McGlamry is highly experienced in the coatings world, with almost 20 years in the Protective and Lining Segments. He has worked in a variety of roles including Product Manager, Lining Technical Manager, Technical Service Manager, and Upstream Offshore Engineering Sales. He is NACE Level 1 certified and also holds an international certification for Project Management.

Courtesy of Hempel USA In the past, tank cars carrying crude oil had no protective linings for corrosion protection. Cargoes of light sweet crude (containing less than 0.5% sulfur) have a passivating effect on the steel of the cars, and very little corrosion was ever identified during routine inspections. Why is there now significant concern about corrosion in rail cars, when the industry has a track record (pun intended) of over 100 years with very low corrosion rates in unlined cars? What has changed? Is crude becoming more corrosive? Are fracking chemicals mixing with the oil and corroding our steel? Before we answer these questions, let’s consider some numbers about the rail business concerning crude shipments from a May 2013 report from the Association of American Railroads: The 2013 report noted that whereas five years ago (2008), “U.S. Class I railroads originated just 9,500 carloads of crude oil,”1 the number of carloads originated had increased to 234,000 in 2012, and in the first quarter of 2013, the number was 97,000. Given the 2013 first quarter number, the report predicted another large increase in carloads of crude originated by U.S. Class I railroads.1 Given the above numbers, maybe we are seeing more corrosion on tanker cars just because we have a whole lot more steel exposed. Or maybe we are carrying crude that’s not only crude. The answer to our problem can be found by understanding oil production and the constituents in crude. For this discussion, we are focusing on the developments in the unconventional onshore oil market in North America, which is pushing the overall rail crude oil tank requirement capacity.

We must understand that there are several advanced completion techniques within the unconventional market, including, to name a few, traditional welling/fracking, in situ mining, steam-assisted gravity drainage (SAGD), and cyclic steam stimulation (CSS). For this article, we will focus specifically on the fracking completion technique. There has been a lot of discussion in the unconventional oil and gas market and in the media about fracking, so we won’t go into great detail here, but the fact is, there are corrosive chemicals used in the fracking process. The presence of corrosive chemicals in fracking raises a question about transporting oil: When those chemicals are pumped into the formation, do they return to the surface with the oil extracted and with enough corrosion potential to cause problems? The answer is “No.” While the chemicals can be found in the produced crude, the concentrations are so low that they are not seen as problematic. It’s important to note that with traditional extraction methods, crude oil also contains water, chlorides, oxygen, and up to 0.5% sulfur for sweet crude or higher for sour crude. What about bitumen produced from mining oil sands? Oil sands are a naturally occurring mixture that typically contains 10–12% bitumen, 80–85% minerals (clays and sands), and 4–6% water. Bitumen is a mixture of large hydrocarbon molecules containing sulfur compounds (equivalent to up to 5% elemental sulfur by weight), small amounts of oxygen, heavy metals, and other materials. Now that we are starting to get a clear picture of the composition of the cargo, we should take a closer look at the water, sulfur, and oxygen. When we do, the “ah-hah” moment comes. Bitumen is extremely viscous at ambient temperatures, but crude can be just as viscous in extremely cold temperatures, such as those occurring in North Dakota winters. In an effort to make the bitumen or crude flow into the tank cars, it is heated. This heating causes the water, sometimes with high levels of chloride, to naturally separate from the oil and sink to the heel, or bottom, of the rail car. So, we’ve created an environment that contains sulfur, high chloride levels, and hot water, an environment ideal for supporting corrosion. To put this environment into perspective, even at ambient temperatures, wet elemental sulfur has been shown to corrode mild steel up to 1 mm/yr (0.04 in./yr), with localized pitting rates of up to 7 mm/yr (0.27 in./year). With the addition of chlorides, the corrosion rates have been shown to double and even triple, in research conducted by Fang, Young, and Nešić.2 Now that we have a better idea of what we’re fighting, another question arises: How do we protect the interiors of tank cars carrying crude oil or bitumen from oil sands? We’ll need an interior lining that must be resistant to high temperatures, and, since highpressure steam is often used during the cleaning of the tank cars, with steam temperatures that can be as high as 330 F (166 C), the lining also must be resistant to thermal shock. In addition, during crude loading in the winter, the steel temperature could be -40 F (-40 C), while the crude temperature will be around 160 F (71 C). This condition leads to an immediate 200-degree F (111-degree C) temperature swing, resulting in thermal expansion of the steel as well as the lining material. So the lining will also need to have some level of flexibility to cope with the flexing of the tank car during loading and unloading operations, as well as the general movement associated with transportation. This is a tall order, even before adding the chemical resistance requirements of hot chloride water and the low pH environment associated with sulfur compounds. The good news is that advanced technology phenolics and thick-film epoxy novolac linings on the market can withstand the environment. Coating manufacturers focused on the rail industry have long, successful track records for this type of service. The real question becomes, should you risk an unscheduled release and loss of an asset because the tank car wasn’t lined? REFERENCES 1. 2.

Association of American Railroads, “Moving Crude Oil by Rail,” May 2013,https://www.aar.org/keyissues/Documents/Background-Papers/Crude-oil-by-rail.pdf Haitau Fang, David Young, and Srdjan Nešić, “Elemental Sulfur Corrosion of Mild Steel at High Concentrations of Sodium Chloride,” 17th International Corrosion Congress, Paper #2592, Las Vegas, NV, October 6–10, 2008. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2013 Technology Publishing Company

23.QA/QC: Some Things Are Old; Some Are New

Warren Brand Chicago Coatings Group, LLC Warren Brand is the founder of Chicago Coatings Group, LLC, a consulting firm he formed in 2012. Before opening his consultancy, Brand was the president of Chicago Tank Linings. He has more than 25 years of experience as a coatings contractor, is an SSPCcertified Protective Coatings Specialist and a NACE-certified Level 3 coatings inspector, and holds an MBA and a BA in Journalism. When JPCL’s editor invited me to write a piece about changes in quality assurance and quality control (QA/QC) in the industry over the past 30 years, I was honored and motivated. I love our industry and enjoy writing and learning as much about it as I am able to. The editor also suggested that the piece not be a “year-by-year account, but something that will be a review to veterans and an easy introduction to newcomers.” And I liked that challenge. As I was thinking about the article, my mind wandered to what was really fundamental to QA/QC for coatings. There are, of course, all the cool tools of our trade: gages, meters, electronics, comparators, etc. But I wanted to know what was really, really fundamental, which led me to evaluate how I work for my clients. What if I were being paid by a client to provide this type of presentation? One of the things I try to focus on in my consulting business is root-cause analysis. That is, let’s say we’ve been hired to design a coating for the inside of a sulfuric acid tank. Instead of just picking a coating system, we would also look into keeping moisture out of the carbon steel tank. If we could set up a dehumidification system, the tank would not actually need to be lined. A better and real-life example of looking at corrosion (which is why we’re all here in the first place) from a truly fundamental lens is the dome being built to cover the nuclear reactor at Chernobyl. As some of you might recall, Chernobyl was the single worst nuclear power reactor disaster in history.

Chernobyl nuclear reactor: The decision to use air conditioning instead of coatings to prevent corrosion of steel in the extraordinary dome that will protect the reactor was based on root analysis, fundamental to QA/QC for all coating issues. iStock Dozens of countries contributed to the development of the “new safe confinement” (NSC). This is an unimaginably huge arch, measuring 110 meters high, 250 meters wide, and 150 meters long, and weighing in at 30,000 tonnes. The NSC is being built 600 meters away from the damaged reactor and will be slid in place, over it, in 2015. The NSC is designed to last for at least 100 years and to cost an estimated $1.2 billion dollars. The arch is made of carbon steel and is hollow—in order to provide monitoring of the interstice in case there should ever be an internal breach. Well, the question was, how do you internally protect this interstice from corrosion? Painting, of course, is an option, but too dangerous in this situation, because of the proximity of deadly radiation and access. How did they solve the problem? Easy. Engineers are going to keep the interstice air-conditioned—through dessicant dryers—to keep the humidity below 40%, below which carbon steel cannot corrode, due to the absence of the electrolyte, humidity. So in thinking about my current task of what is new, I first started thinking about what was old and what was really fundamental to, or at the root of, all coating issues. Way Back Then and Now: Coatings and QA/QC I thought about a video I had recently seen on the design of ancient byzantine floor mosaics. These mosaics, many of which are thousands of years old, were designed to last well, for thousands of years. They were on floors, so they were, for example, walked on, rained on, and cleaned (one presumes). And many of them are in excellent condition today. What’s different about an ancient mosaic and a modern-day floor coating application? Fundamentally, not a darn thing.

The basic processes for laying ancient floor mosaics and modern day epoxy broadcast flooring are similar; QA/QC for the mosaic was largely qualitative, while for modern flooring QA/QC is largely quantitative. iStock The video showed that the mosaic surface, which is all we see, is actually on a bed of layered terra-cotta and other fill, in order to provide a sound base. This would correspond to our concrete floor or secondary containment today. Then a thick plaster of lime, plaster dust, water, and other materials was mixed and troweled onto the bed, and small pieces of glass and other durable materials were placed, by hand, into the parge coat. The plaster was designed to take a long time to cure, so that the artist would have plenty of time to place the mosaic tiles into the material. How is this different, say, from an epoxy broadcast floor system? Well, again, it’s not. In both cases we’re dealing with a solid substrate. With the mosaic, it would be a layered bed of stone with a solid parge coat. Today, the solid substrate would be our concrete floor. (We are assuming that both are new and clean.) Then, a material (today, a clear epoxy resin—then, a plaster parge coat) is applied—and aggregate placed inside the uncured material. Did the artisans and contractors thousands of years ago have the tools that we do today to conduct inspections? Of course not. Did that prevent them from successful coating applications? Same answer—of course not. But let’s look back even further, say, 40,000 years. According to a June 14, 2012 National Geographic News article (news.nationalgeographic.com), “World’s Oldest Cave Art Found—Made By Neanderthals?” there are some caves along Spain’s northern coast that contain paintings that are more than 40,000 years old—so far, the oldest in the world. Located at El Castillo, these paintings were made by some type of “mineral-based paint.” (Don’t even get me started on Roman frescoes, or ancient cisterns and viaducts that are as water-tight today as they were when they were first specified and built, by contractors wielding camel-hair brushes and wooden trowels, and wearing loin cloths, and of course, baseball caps.) There are even products that have their ties to these same types of products used thousands of years ago. A company out of Europe has been making a product to protect and beautify masonry since 1878. When I was working on a project not too long ago, I asked the technical rep what the anticipated service life was, and he said something like, “I think there’s a church in Southern Italy that’s about 110 years old that’s still in good shape.” There are hundreds of similar ancient examples, but suffice it to say that we humans have been in the business of painting and coating for quite a while. After all, when the pyramids were built, they were originally lined and covered with marble. So, in looking back and obsessively thinking about this topic, I’ve concluded that, fundamentally, the only shift in the past 40,000 years has been from one of qualitative QA/QC to quantitative. That shift continues today, and, certainly, is the biggest difference in the past 30 years as well. We are simply honing our quantitative tools and training. Was there QA/QC during the time of the pyramids and before? Of course. But back then, it was, for the most part, qualitative. It was the legacy of the tradesman-apprentice relationship that maintained the quality. It was the pride one took in his work. Or, if slavery was a part of the mix, it was the fear of the repercussions for shoddy workmanship. Not Nearly as Far Back and Now When I first started out in the coatings industry at 15 (1977), a gentleman named Vic Johnson worked in our company. His nickname was “Rail” because of the unusually elongated shape of his head. Vic was large and kind. (In fact, he took me to pick up my first car—an AMC Gremlin—from a junkyard when I was 16.) And Vic knew coatings as well as anyone. He could barely read but when it came time to abrasive blast, Vic could tell by looking and touching the surface whether or not it had the right mil-profile and correct visual appearance for proper coating. I’m certain if Vic were around today, he could tell the difference between a 1 mil profile

and a 2.5 mil profile by touch. I know there are people reading this article who could do the same. So if qualitative inspection was sufficient for so many thousands of years, what’s all the fuss, rush and research pertaining to quantitative inspections? (For those seasoned folk reading this, yes, there are still qualitative aspects to some of our testing protocols, such as the use of comparators and SSPC-VIS standards) It’s about one thing, and one thing only: consistency. Today, you don’t have to have an apprentice painting contractor with thirty years of experience to apply a challenging tri-coat system. Because of advanced training techniques and highly effective testing tools and techniques, we can apply coatings around the world, in the most challenging of environments and situations in a consistent, predictable, and quantifiable manner. What Vic had learned from blasting millions of square feet of every material possible, we can now deduce and measure by using visual standards, comparators, replica tape, and electronic as well as mechanical gauges to determine what Vic knew in an instant. And yet, with all of our tools and training, we still get situations like the Sable Offshore Energy Project in Canada. The offshore oil platform had a coating failure so profound that it was mentioned in a March 8, 2011 article on PaintSquare News (www.paintsquare.com) as, “What may be the world’s priciest botched paint job [that] could cost hundreds of millions dollars to repair.” Back in the day, when I was spraying thousands of gallons of different paints and coatings, I was able to tell, within a couple of mils, the WFT by appearance. As I applied the coating (either conventionally or airless), I could see the profile of the substrate disappear and the sheen, texture and appearance of the coating change. Of course I would use a wet mil gage to ensure my instinctual hunches, but more times than not, I was spot on. So, for beginners, I think it is critical to understand why we inspect. And for the more seasoned of us, I am hoping this was an interesting read and, perhaps, put what we do in a different perspective. So, now that we’ve established what we do (quantitative inspection protocols) and why (for consistency), let’s discuss what has changed over the past 30 years. And, in keeping with the theme of fundamentals, we’re going to talk about two dimensions: Training and Equipment. First, let me explain why we’re sticking with the fundamentals and painting the changes with very broad brush strokes (pun intended). The reason is that any attempt to speak specifically about either Training or Equipment will fall far short of doing either topic justice. For example, let’s take a look at the April 2013 issue of JPCL. There is an excellent and informative article entitled “Measuring Dry Film Coating Thickness According to SSPC-PA 2.” The article is roughly 10 pages long and more than 4,000 words—and it’s just about checking the thickness of a coating after it has cured. The primary focus of the article is on SSPC-PA 2, the intellectual and training aspect of the duo, but, of course, it deals with the tools of our trade. But without even discussing the difference between a Type 1 gauge (magnetic or banana gauge) and a Type 2 gauge (an electronic gauge), the article goes into exquisite and appropriate detail about all of the fundamentals of testing a cured coating.

For the ancient pyramids, QA/QC was a matter of pride in craftmanship or fear of retribution for poor work (or both). iStock

So, speaking too specifically about either aspect will dilute the importance of either. Training When I asked Pete Engelbert, a well-qualified inspector, what had changed the most in the past thirty years, he did not hesitate: “Smarter inspectors. The biggest change has been with the level of sophistication of the inspection—not the equipment,” Engelbert said. Engelbert has a keen understanding of the industry, and he teaches NACE courses around the world. (His credentials include CSP, RPIH, CHST, CET, CIT, CSSM, NACE Certified Coatings Inspector—Level 3 [Nuclear/Bridge], BIRNCS Senior Nuclear Coatings Specialist #12 NACE Protective Coating Specialist, NACE Corrosion Technician, and NACE instructor.) I asked him to describe a typical inspection scenario from thirty years ago until today. So, we started with a pipe inspection job (which Pete is currently handling). “Thirty years ago there were very few standards to measure conformance. Now we have multiple standards,” Engelbert said. He also said that thirty years ago during a pipe coating project, it would not be uncommon for an inspector to stand at the top of a the excavation and watch the contractor slop on some “stuff.” It would not be uncommon to have a contractor brush on petrolatum, tar, or other materials; wrap it with heavy paper; and bury it. Often, the inspector wouldn’t even look at the bottom portion of the pipe to see if it had been addressed. Surface prep wasn’t even on the radar. Today, pipes come shipped, typically, pre-coated with fusion-bonded epoxy (FBE). The inspector’s job is to monitor the joint coating process. Engelbert said that there are roughly 15,000 to 16,000 NACE 1 inspectors worldwide. And the demand for inspectors, particularly overseas, is huge, with SSPC rapidly growing as well. “Training has taken off overseas,” he said. “The next standard (for inspectors) will shift from NACE 1 to a NACE 2 or NACE 3.” Training and development of new standards and guidelines are universal. There are, of course, SSPC and NACE, but there are also IMO, ISO, ANSI, STI, and subsets to all of these. I am currently working on a project for a major oil company pertaining to CUF (corrosion under fireproofing) and related issues. There is a whole universe of guidelines, standards, nomenclature, and tools that are different for the CUF job than, say, a bridge coating project, even though the common denominator remains corrosion. Another broad example of improved training is SSPC’s cutting-edge Quality Programs (QP) and the Painting Contractor Certification Programs (PCCP). As summarized on SSPC’s website (sspc.org), the training is relevant to all aspects of a coating project.“…the selection of suitable materials is just one aspect of a successful coating project. It is critical that work is done according to sound specifications, with correct surface preparation and proper application techniques. Facility owners need to find top quality people to provide these services— trained people who know the current standards and practices and have a proven track record of success.” SSPC’s QP series is extensive and has modules for contractors, owners/specifiers, and inspection companies. The trend toward smarter inspectors is profoundly obvious in the introduction to the SSPC-QP 5smprogram, “Certification for Coating and Lining Inspection Companies.” “QP 5 is a certification for Inspection Companies whose focus is the industrial coating and lining industry. QP 5 evaluates an inspection company’s ability to provide consistent quality inspection of coatings & linings for its clients.” Engelbert said another major shift in terms of training has been documentation. Thirty years ago, there was very limited documentation and even less that was standardized. “Many of the daily forms we use today are an offshoot, a progeny, of one of the originals, which was an ANSI standard for coatings in nuclear power plants.” In fact, one of the hallmarks of the SSPC-QP certification programs is an emphasis on documentation. I think most would agree that the intellectual advances in guidelines, standards, practices, recommendations, etc., move at a relatively slow, predictable pace. That is, a two-mil profile is a two-mil profile. But not so for the tools of our trade. In contrast, there are changes in technology that will change more in the next ten years then they’ve changed in the last 40,000. Tools When speaking with Engelbert about tools, I mentioned that I thought the biggest advance was the ability of the electronic gauges to gather and store data and then network the data directly to other devices. He laughed and quipped, “Hey, I was just happy when they came out with batteries.” He said that thirty years ago it was unlikely to get a trained coating inspector on a job in the first place. Very often, “inspection” work was designated and assigned to an individual who might be an inspector for another trade, perhaps a welder, or structural engineer.

“You had welding inspectors or others signing off on coatings almost as an afterthought.” He said if a job was fortunate enough to have a coating inspector on site, and he was tasked, say, to measure DFTs, “You’d have one inspector taking measurements with a banana gauge and another walking behind him with a clipboard taking notes.” Now, modern gauges can store almost limitless inspection points and then download them for evaluation. “Fundamentally, it means the inspector has to get smarter. You have to know how to use a computer and, if you don’t, find an eightyear-old to teach you,” he said. Suffice it to say that the fundamental focus of inspection tools in the past thirty years has been in ease of use, storage capacity, and data sharing (USB, Blue-Tooth, wireless), etc. But the most exciting and most important advances are the cutting edge developments we are seeing now. The breadth is breathtaking. I attended a conference about eight years ago in conjunction with the National Center for Manufacturing Sciences (NCMS). One of the latest (at the time) technologies for surface preparation of aircraft was the use of lasers to remove paint. With wings being designed to unimaginable tolerances, the use of an abrasive was impossible because it might damage or warp the wing. The typical means of paint removal was through highly toxic and dangerous paint removers, oftentimes methylene chloride. The technology was in its infancy at the time but is now being widely used to remove paint from aircrafts. Then there’s a November 30, 2011 article from the United States Naval Research Laboratory entitled, “NRL Researchers Develop ‘Streamlined’ Approach To Shipboard Inspection Process” (http://www.nrl.navy.mil/media/news-releases/2011). The article talks about inspecting the condition of exterior shipboard coatings. In the case study reported, the work was performed on the USS Aircraft Carrier, the Nimitz. In a quote from the article, “The manual method required a 65-man-day effort to perform the inspection of the entire topside coating with results taking an additional four weeks to complete. By contrast, we were able to perform the same inspection using digital hand-held cameras with the new process in less than four days including immediate access to over 3,000 images depicting the ship’s surface condition for in-depth inspection.” Briefly, the new process includes highly-detailed photographs downloaded and analyzed by algorithms used to quantify the condition of the existing coating. Going even a step further, we haven’t even touched upon the changing technologies pertaining to coatings and how those changes will interact with, and change, technologies for inspection services. For example, it is not uncommon to use a conductive primer on concrete in order to be able to use a holiday detector on the subsequent topcoat. There are talks of nanoparticles that may communicate with various devices, the use of fluorescent additives to indicate DFT, etc. Conclusion Are we far from the day when new coating systems will work in concert with new technologies to speed and improve our ability to quantify and control coating applications? “I am working with an engineering company that is developing a visor that, using different light frequencies, can see the depth of profile, DFTs, number of coats, wet and dry. After that, who knows? A paint ball gun that could paint an entire water tower tank? It’s only a matter of time,” said Mr. Engelbert. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2013 Technology Publishing Company

24.The “No Big Bang” Theory: An Introduction to Risk- Based Inspection Systems for Mitigating CUI in Process Equipment and Piping From JPCL, August 2013

Peter Bock Capital Inspectors Peter Bock is Inspection Sales Manager for Capital Inspectors, The Woodlands, TX. He is an Air Force veteran and has degrees from Tulane and the University of Northern Colorado. Bock has 36 years of experience with sales, management, and technical service in oilfield and petrochemical heavy-duty coatings in the U.S., Canada, Mexico, Venezuela, Indonesia, and Taiwan. He has experience with on- and offshore production, drilling and workover rigs, shipyard work, natural gas and LNG, pipelines, terminals, refineries, and chemical plants. He is a specialist in elevated temperature systems and CUI mitigation. The author gives special thanks for the photographs to Mr. Lawrence “Joe” Bordelon, Senior Coatings & Linings Technologist, Site SME/Technical Support/Paint Operations, Global Paint/ Linings TRN Member, The Dow Chemical Company, St. Charles Operations. Steelwork at all levels of industry in the United States is corroding despite our best efforts to stop it.1 Unexpected atmospheric corrosion damage (including corrosion under insulation—CUI) causes tens of billions of dollars in losses annually from unanticipated shutdowns of equipment; loss of production; unplanned maintenance; unexpected cleanup costs; and, in more severe cases, damage to adjacent equipment, injuries to operating personnel or surrounding residents, toxic chemical releases, environmental damage, and other long-term effects. Moreover, this unexpected corrosion damage affects everything from the largest and most sophisticated refineries down to small local waterworks and sewage plants. While the damage can take many forms, one of the most challenging is CUI, the focus of this article. Our news media regularly report “big bangs”—fires, explosions, chemical spills, toxic releases and other similar “events.” Many of these are caused by CUI. CUI is as likely to be found on the boiler feed lines in a local hospital or food processing plant as in a coal-fired electrical generating plant or a major petrochemical facility, where hot process equipment and pipeline are common. The larger and more complex a manufacturing facility is, the more likely it is to suffer from CUI and unexpected atmospheric corrosion damage. In addition, the larger and more complex a plant is, the more likely it is that a corrosion-related failure during operation will have major consequences. Chemical and petrochemical plants can be quite complex, and the damage to them (and the surrounding area) from CUI can be quite severe because CUI is usually well under way before it is detected. Unfortunately, it is often “detected” after it has caused significant damage. Finding CUI before the damage occurs is challenging. This article describes using risk-based inspection (RBI) to detect and mitigate CUI in chemical and petrochemical process equipment and pipeline before severe damage is done. The article also illustrates a successful in-house CUI-RBI program in Figs. 1a and 1b; Figs. 2a, 2b, 2c, and 2d; and Fig. 3.

Fig. 1a: Vertical process vessel after complete reblast and recoat with thermal spray aluminum. Thermal spray is used under insulation on large, flat, easy-to-access surfaces.

Fig. 1b: Vertical process vessel coated with thermal spray aluminum after insulation and cladding have been replaced, and before removal of scaffolding. Photos courtesy of The Dow Chemical Company, St. Charles Operations, Hahnville, LA 70057

Fig. 2a: Sphere being abrasive blasted prior to recoating and re-insulation. Maximum operating temperatures are low enough that an epoxy system can be used.

Fig. 2b: Newly applied epoxy primer and stripe coats on the sphere. Each step of the coating application process is closely inspected before the next step is allowed to start.

Fig. 2c: Epoxy topcoat of the sphere. After the epoxy had passed inspection and was fully cured to accept insulation, the sphere was insulated and cladding was installed.

Fig. 2d: After work is complete and scaffolding has been removed, the newly recoated, insulated and clad sphere is seen at the left of the picture in the plant’s sphere tank area.

Fig. 3: Five-year-old liquid-applied elevated temperature coating exposed for RBI inspection. Liquid-applied coating is used under insulation on complex or hard-to-reach surfaces. CUI: The Back Story Most oil refining and petrochemical manufacturing processes are simply advanced forms of cooking—crude oil or intermediate chemicals are “cooked,” heated under specific conditions or in specific temperature and pressure environments, to produce more desirable end products. Process vessels and piping are usually insulated to conserve process heat and reduce the fuel required, to reduce process temperature variations, to stabilize stored intermediates or end products, and to protect workers from exposure to hot equipment. Insulation is normally covered with unpainted aluminum or stainless steel sheet metal “cladding” to protect the fragile insulation. It is this sheet metal cladding over insulated piping and vessels that gives a refinery or chemical plant’s process units a shiny, misleading “good-to-go” appearance. But don’t be fooled—beneath that shiny exterior cladding and the insulation it covers, there usually beats a hidden heart of rusty steel. And in many cases, no one has any idea of how rusty the steel really is. Once corrosion eats into the steel, wall thickness is lost, and the vessel or pipe is no longer capable of resisting the temperature and pressure it was originally rated for. Normally, there is a “corrosion allowance” of extra thickness in the steel. When the thickness of corrosion exceeds this allowance, the pipe or vessel becomes unsafe. If corrosion continues, cracking, leakage, or catastrophic failure during operation becomes more and more likely. Until the 1970s, carbon steel under insulation for elevated temperature service was often left unpainted. It was thought that the high operating temperatures would keep the steel from rusting, and there were no effective paints for high temperatures. There were two major problems with this concept. 1. Nothing stays hot forever—most elevated temperature equipment actually cycles hot-cold fairly frequently. Even equipment that runs hot almost continuously is cooled down for maintenance turnarounds and corrodes during those “cool” times if not protected. 2. CUI is normally invisible. The insulation and cladding hide the steel, and even if it was properly painted with a temperatureresistant coating, there is usually no quick and inexpensive way to check that the coating is protecting the steel. To make matters worse, most cladding leaks, and most insulation holds water to some degree, so the steel under insulation is exposed to a severe immersion corrosion environment whenever it is operating below the boiling point of water. Today, there are effective coating systems available for elevated temperature CUI service, but problems 1 and 2 continue.2Corrosion under insulation tends to be invisible, and no coating system gives 100% protection for tens of years under such severe conditions. The cost of removing cladding and insulation is time consuming and very expensive; replacing cladding and insulation is even more expensive. Most insulated equipment receives only periodic spot checks of tiny areas during normal operation. Most of the steel under insulation is not seen for the expected life of the coating system or the expected life of the uncoated steel. When the “expected life” matches real life, cladding and insulation are removed, and the steel beneath is inspected, re-prepared, re-coated, re-insulated, and re-clad. But real life becomes much shorter than “expected life” and catastrophes can occur when unexpected moisture or chemical contaminants get beneath the insulation; when the steel is damaged; or when operating conditions change, allowing increased corrosion under the insulation. The currently circulating draft of API RP 583, “Corrosion Under Insulation and Fireproofing,” lists nearly a dozen different electronic

methods of checking remaining wall thickness of insulated and clad steel pipe or vessels.3 These methods range from simple X-rays to complex real-time systems using the latest nuclear technology. Many of these methods do not require the insulation and cladding to be removed while doing the electronic testing, but none has been found reliable enough to completely eliminate removal of insulation and cladding and visual inspection of the surface at problem areas indicated by the electronic test. Risk-Based Inspection Systems for CUI Other than the expense of removing and replacing cladding and insulation, a large part of the reason for unexpected atmospheric corrosion damage from CUI or other sources is a lack of qualified plant inspection personnel and a lack of planning. All U.S. industries now run with extremely lean staffs of qualified personnel. Even some major refineries and chemical plants may have only one corrosion manager or corrosion engineer, and a few technicians at most. Moreover, the corrosion engineer is usually in charge of all types of corrosion mitigation, not just atmospheric corrosion or CUI and not just mitigation through protective coatings. Mid-sized facilities may have only a maintenance manager or maintenance engineer, for whom corrosion mitigation is only a secondary duty. Very few successful, cost-effective facilities have enough people, time, and money in their maintenance budget to do thorough, complete CUI inspections regularly without outside help. Because of their limited staffing and budgets, smaller plants may actually operate on an “inspection by perforation” philosophy, which can be costly and dangerous. One effective (and cost-effective) method of CUI mitigation that has been known and used successfully for a couple of decades is a Risk-Based Inspection (RBI) Program. Unfortunately, RBI is a complex program that requires support and cooperation of the entire company, from top-level management to field-unit operators. Initial setup of an RBI program requires extensive in-house work, a fairly generous budget, and lots of time even for just the insulated piping and equipment in a plant.4 Operation of a successful RBI program also requires a multi-year commitment. For CUI-RBI, a successful program may require a multi-decade commitment because scheduled major maintenance programs on insulated piping and equipment can be at 10- to 15year intervals. Many companies shy away from setting up meaningful RBI programs because the programs seem too complicated and too costly, the time horizons are beyond the companies’ normal planning ranges, and the companies’ plants do not have skilled people or budgets big enough to do the required initial baseline surveys. Setting Up an RBI Program Setting up an RBI program requires an initial investment of time and thought by the company’s top management, who need to identify their company’s concept of “risk” and to rank their company’s sensitivity (and aversion) to the different types and levels of risk they may encounter in operating their plants. Fortunately, this type of assessment needs to be done only once for the entire company, or, at most, once for each type of operating unit and possibly each country the company operates in. The Exploration and Production, Americas, division of one global oil and petrochemical producer has worked with the RBI concept for more than two decades. On the one hand, the division has distilled the basic concept and philosophy of RBI into a simplified matrix printed on two sides of one sheet of paper. On the other hand, the petrochemical division of the same company has expanded it to a level where, for some process units in its South Louisiana petrochemical plants, every valve, every flange, and sometimes even every set of bolts and nuts have been analyzed and given an individual “criticality” rating and inspection frequency requirement. We can draw on both divisions’ use of the matrix to amplify our discussion of setting up an RBI program. Producing a Risk Assessment Evaluation requires identification of potential events and their potential consequences, estimating their potential severity and likelihood, and then estimating the level of risk based on the combination of severity and likelihood of the event happening. A Risk Assessment Evaluation is required for every location. For the exploration and production division of our model company, “location” is defined as the smallest individual unit assessed, down to each production platform offshore or each flow station onshore. For a refinery or petrochemical plant, a “location” may be defined as one production unit within a larger plant, or even one specialized portion of the plant (such as “raw materials storage and handling”). A simplified typical Risk Assessment Evaluation Chart (Table 1) examines possible consequences of an unexpected event and their effect on the following.

•

Neighbors: People, buildings, and land in the area of the affected plant

•

Equipment in the plant itself

•

Environment both in the immediate area and in general

•

Reputation of the owner or parent company, locally and worldwide

TABLE 1 Risk Assessment Evaluation Chart INCREASING LIKELIHOOD OF AN EVENT >>>>

EFFECTS OF AN EVENT ON:

A

B

C

D

E

Has

Occasionally

Frequently

Occurred

Occurs

Occurs

Possible Possible But NEIGHBORS

EQUIPMENT

ENVIRONMENT

REPUTATION

(0) No Injuries

No Damage

No Effect

No Effect

(1) Minimal

Minimal

Detectable Effect Short-Term

Injuries

Damage

Unlikely

RISK

>

Local Effect INCREASES

(2) Few minor

Easily

Measurable

Short-Term

injuries

Repaired

Effect

Regional Effect

>>>

Damage (3)

Serious

Slight Short-Term Longer,

Hospitalizations Damage

Effect

Regional Effect

(4) Death

Long-Term

Serious Short-

National Effect

Damage

Term Effect

Total Loss

Long-Term Effect Long-Term

(5) Multiple Deaths

>>>>>

>>>>>>>

>>>>>>>>>

National Effect

Severity of consequences is rated from Zero—No injuries, no damage, no environmental or reputation effect—to Five— Multiple fatalities, massive damage to the facility, and a huge long-term impact on the environment and on the company’s reputation. A “Serious” effect, Three on the consequences scale, would be an event that produces many days of absence from work for affected employees, or that results in long-term disabilities; a release of large amounts of crude oil or of any reportable quantity of a hazardous chemical; an event that triggers an environmental fine; an event that incurs very high repair and mitigation costs; or an event that causes partial shutdown of a facility and generates extensive regional media coverage. The likelihood of such an event occurring is also rated in five steps, from “Possible but unlikely,” as the lowest rating to “Occurs Frequently” for the most likely to occur. A simple chart of severity versus likelihood of an event produces the risk rating for that particular event. The higher the likelihood of an event is and the more serious its consequences are, the more closely and more frequently the equipment involved must be monitored to keep the potential event from happening. The purpose of the RBI program is to reduce all such risks to a minimum “ALAP” (“As Low As Practical”), that is, to a level at which the cost and effort of further risk reduction are unaffordable or disproportionate to the risk reduction achieved. Once the Risk Assessment for all potential events has been completed, the actual evaluation of operating equipment begins in order to determine the required Risk Based Inspection process for assuring that operation of the equipment will not produce negative events beyond the “ALAP” level. The second half of an initial RBI assessment involves personnel actually operating and maintaining the equipment being rated. These are the people who actually live with the equipment day-in and day-out; they are most qualified to identify portions of the unit or piece of equipment most likely to fail, and whose failure is most likely to cause damage. They also are most likely to know what coincidental or collateral damage one failure might cause to other parts of the plant. This process allows a whole series of possible “events” to be evaluated from each potential failure. Plant maintenance records and equipment design blueprints are analyzed to determine the portions or pieces of equipment most likely to corrode and cause an “event.” Then, potential events are rated for their effect on plant operation and production, and the same potential events are rated against the company’s Risk Assessment charts. This initial survey can be done by outside consultants, but, ultimately, it is the plant operating personnel who are familiar enough with plant components to know which are the most likely to fail, and local plant management who are best able to determine what and how severe damage such a failure will cause. Commitment to an RBI Program The engineer or manager chosen to design and implement a CUI-RBI program faces a daunting task. First, he or she must be assured of buy-in from upper management and from the field people who will be doing the site evaluation. After everyone

understands and agrees that an RBI program is a multi-year, continuing effort, not a one-time inspection, there comes the question of return on investment (ROI). On the one hand, the initial survey and risk assessment are expensive and time-consuming. On the other hand, preventing one “Moderate” event from the Risk Evaluation chart can mean a savings of $1,000,000; preventing a “Major” event can save ten times as much. In comparison, the cost of the initial plant RBI survey may seem reasonable. For a refinery or oil production facilities, and for many petrochemical plants, the in-plant risks—such as a vapor cloud explosion, petroleum jet fire, petroleum pool fire, or major toxics release—can all do grievous harm to the plant, to the surrounding environment, and to the company’s bottom line as well as to its reputation. The in-plant survey needs to identify specific high-risk areas or pieces of equipment whose failure might raise the severity of consequences on the “Equipment” column of the risk chart. Of course, such equipment should already be closely monitored as part of the plant maintenance program, but identifying (or reidentifying) key high-risk items helps the RBI initial survey become a defined risk-mitigation process. Existing plant data on performance of unit vessels, piping, operating equipment, controls, and even electrical and electronic subsystems can be used to develop an RBI continuing inspection schedule and calculate its expected cost in terms of dollars per square foot or dollars per linear foot of pipe per year of the RBI program. Remaining service life of an older unit, expected upgrades or replacement, and the part one unit plays in the overall operation of the plant all need to be evaluated against the risk evaluation for that particular unit. Once data is collected, the proposed RBI program needs to be prioritized, based on highest possible event consequences, age and replacement cost of equipment, turnaround schedules, and the ability to incorporate the RBI program into existing inspection procedures (if any exist). Because there is not enough budget for 100% frequent inspection of all insulated areas, a priority ranking program is set up, with the “riskiest” vessels, piping, and equipment receiving the most frequent and most thorough spot inspections, and lower-risk equipment being inspected less often, or with less of the insulation and cladding actually removed as part of the scheduled inspection. Lowest-risk or no-risk equipment may receive only the minimum required electronic wall thickness tests annually. Some critical refinery areas may require 100% removal of cladding and insulation and 100% visual inspection. A key factor in the frequency of visual inspections is the equipment owner’s confidence in the CUI coating systems used on equipment included in the CUI RBI program. Where quality surface preparation, a suitable proven coating system, good application, and thorough inspection have been done on equipment under insulation, the number of inspection spots may be reduced to areas of known breakdown, and the inspection intervals may be extended. Table 2 shows a major global petrochemical company’s “confidence level” for length of service life of coatings under insulation, where operating temperatures never exceed the maximum service temperature of the applied coating system.5

TABLE 2 Expected Service Life Performance of Typical CUI Systems System

Service Life Required Repair

Clad, insulated, uncoated bare steel (Lose entire wall thickness corrosion allowance)

6 years; 100% re-do

Clad, insulated, organic coating without abrasive blast (Lose entire coating system, portion of wall thickness)

12 years; 100% re-do

Clad, insulated, organic coating with SSPC-SP 10 abrasive blast (Lose portion of coating system, portion of wall thickness)

16 years; 100% re-do

Clad, insulated, thermal spray aluminum with SSPC-SP 5 abrasive blast (Lose small portion of TSA, small portion of wall thickness)

40 years; 25% re-do

Continuing the RBI Program After the base plant (or unit) RBI survey has been done, and the risks and hazards have been agreed upon, quantified, and ranked by plant personnel, then the actual annual (or otherwise recurrent) field surveys can be done by an outside survey firm that has experienced, qualified inspectors, and follows the base survey. Many existing RBI programs actually combine electronic nondestructive testing (NDT) with insulation and cladding removal and visual inspection of selected small areas. Both parts of the survey may be done by the same firm, or NDT can be done by a specialist, and the results can be verified by a paint inspection company. The findings of these recurrent surveys are summarized in electronic format, incorporating electronic testing results, digital photographs, and the field contract inspector’s “eyeball on the steel” evaluations. The plant’s corrosion engineer or maintenance manager now can examine the corrosion state of his facility on a computer monitor in his or her office, at his or her convenience. Management personnel can review the survey results, match them against expected results based on the initial RBI survey, and decide on an appropriate course of action.

In simplified form, the recurrent RBI survey can have four possible results for a particular unit or piece of equipment.

•

• •

•

Less corrosion is found than was expected. This result is noted in the survey. If the result is found to repeat in the next scheduled survey of this unit, the unit or piece of equipment may be re-evaluated for lower risk or less frequent inspection. Some owners also use such a finding to re-evaluate related equipment, working on the sound theory that if one unit or piece of equipment is rusting less than expected, something else related to the equipment may be acting as an anode and rusting more than expected. Corrosion is as expected. The survey is submitted and repeated as scheduled. A small increase in corrosion is noted over expectation. Additional portions of the unit are inspected at the same time to confirm the increase in corrosion. For CUI work, inspecting additional portions means removing additional small areas of cladding and insulation. The unit or area is marked, and the next scheduled re-inspection will determine whether unscheduled corrosion-preventive maintenance may be necessary. A large or unexpected increase in corrosion is noted. Additional portions of the unit are inspected at the same time to confirm the increase in corrosion, and plant personnel are brought in to try to determine a cause. Budget and scheduling are rearranged to give priority to corrosion-preventive maintenance on this unit or piece of equipment. The recurrent survey schedule is rearranged to closely monitor this problem until corrosion-preventive maintenance is done, and then afterward to determine whether the maintenance resolved the problem.

RBI programs for plants with large amounts of insulated piping and equipment require additional input during the initial set-up of the program to assure that the spots selected for recurrent survey are actually representative of the “worst case” areas of each unit or piece of equipment. The first few recurrent surveys done by a contract inspection or survey firm may actually include additional, redundant spot inspection points, which can be phased out later if survey results are as expected. Where electronic testing or thermal imaging produces reliable results and matches destructive spot testing over several recurrent survey cycles, the destructive testing spots may be reduced, thereby reducing the overall survey costs without affecting reliability. Figures 1-3 that accompany this article show an in-house RBI program in action at a petrochemical plant in South Louisiana. The facility is an older plant, but equipment is meticulously maintained, and a very thorough RBI program is in place. Sections of insulated piping, vessels, and equipment are inspected annually on a rotating basis, with a typical section being re-inspected every three years on average. The plant uses a combination of organic coatings and thermal spray aluminum for CUI work; annual survey results tend to confirm the plant’s RBI base surveys and the service life expectations for the systems used. Confidence is high that the CUI-RBI program is working as it should. A Houston-area industrial gas facility, which produces various gases by cryogenically refrigerating air and then separating its components, has an entirely different approach to RBI for the company’s piping for transfer, storage, and loading. The facility doesn’t do any RBI. Analysis of maintenance and operating records on these low-temperature piping systems in the plant has shown that failures are always due to cracking of piping in cyclic service from cryogenic to ambient temperatures. A failed pipe is quickly discovered through unexpected pressure loss; the insulation and cladding over the pipe act as an effective containment over the ruptured pipe; and the only loss is of the product in the pipe, which, as a gas component of air, is inherently non-polluting. The plant has been designed to allow effective isolation of failed pipe run sections, so when such a failure occurs, the affected pipe run is shut in, insulation and cladding are removed, and the failed pipe section is replaced. Loss of product and loss of productivity are minimal. The plant runs several parallel air separation trains, so the downtime required to replace a fractured length of pipe in the transfer, storage, and loading piping produces only a small reduction in plant output and does not require other shutdowns. Corporate management has determined that for these portions of the plant, this policy of neglect presents low enough risk and is more cost effective than an intense RBI program. Conclusion Unfortunately, a great deal of corrosion-mitigation plant maintenance, both for CUI and for atmospheric corrosion damage, is done reactively, rather than proactively. There is an “Oh Sh**” moment that comes in almost every unscheduled CUI inspection. That’s when the plant corrosion engineer or maintenance manager looks at the large area of newly exposed corroding steel where insulation and cladding were removed after serious corrosion was seen in a smaller exposed area, and the engineer says “Oh Sh**. Fixing this is going to take my entire maintenance budget for the year.” For these plants, CUI repair work is scheduled and done only after a serious problem is unexpectedly found. This work often involves unscheduled shutdowns; loss of production; manufacturing bottlenecks or backlogs; and, occasionally, even fires, explosions, or toxic product releases. This maintenance process is unnecessarily costly and can be easily improved. Improvement requires only a small increase in budgets and no long-term increase in plant personnel, using RBI with an initial survey by plant personnel and recurrent inspections by outside contract inspectors or surveyors. Although commitment to a CUI-RBI program requires a substantial initial investment of time and effort, and a multi-year continuing commitment, the relative security, peace of mind, and confidence in the plant corrosion state offer a positive return on investment even before factoring in the cost savings of not having an unexpected event that might shut down the plant, pollute the neighborhood, and irreparably injure the company’s reputation.

REFERENCES 1. 2. 3. 4.

5.

George F, Hays P. E . “Now is the Time,” White Paper, World Corrosion Organization, Houston, TX,corrosion.org, 2007. “Control of Corrosion Under Thermal Insulation and Fireproofing Materials, a Systems Approach,” NACE SP 0198-2010, NACE International, Houston, TX, nace.org, 2010. “Corrosion Under insulation and Fireproofing,” Currently circulating draft of API RP583, First Edition, First Ballot, American Petroleum Institute, Washington, DC, api.org, 2012. Keith E. McKinney, Fred J. M. Busch, Andre Blaauw, Andrea M. Etheridge . “Development of Risk Assessment and Inspection Strategies For External Corrosion Management,” Paper No. 05557, NACE Corrosion 2005, NACE International, Houston, TX, nace.org, 2005. William C. McRae, Nalton Thompson . “CUI Project Development,” Bring on the Heat 2013, NACE International, Houston, TX, nace.org, 2013. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2013 Technology Publishing Company

25.Tools and methods of hand tool cleaning From JPCL, September 2013 Hand tool cleaning is one of the oldest methods of preparing steel surfaces. It is widely used for preparing small areas and for areas that cannot be blast cleaned. A hand tool-cleaned surface is one that is free of loose rust, loose paint, and loose mill scale. Tight rust, tight mill scale, and tight paint are allowed to remain on the surface. Before you start hand tool cleaning, remove dirt and grease from the surface by solvent or detergent cleaning. A hand tool-cleaned surface is achieved with wire brushes, sanders, chipping hammers, and other hand tools listed below. Industry Standards The SSPC specification for hand tool cleaning is SSPC-SP 2, defined as follows: “Hand tool cleaning removes all loose mill scale, loose rust, loose paint, and other loose detrimental foreign matter. It is not intended that adherent mill scale, rust, and paint be removed by this process. Mill scale, rust, and paint are considered adherent if they cannot be removed by lifting with a dull putty knife.” However, SSPC-SP 2, Hand Tool Cleaning, requires you to remove all visible deposits of oil and grease in accordance with SSPC-SP 1, Solvent Cleaning, before starting the process of hand tool cleaning. Photographs that illustrate the appearance of an SSPC-SP 2 (Figs. 1 and 2) surface are found in the publication, SSPC-Vis 3. These photographs were developed by SSPC. In Europe and other parts of the world, the industry standard is ISO 8501-1 (Preparation of Steel Substrates Before Application of Paints and Related Products—Visual Assessment of Surface Cleanliness— Part 1: Rust Grades and Preparation of Uncoated Steel Substrates and of Steel Substrates After Overall Removal of Previous Coatings), which uses photographs developed by the Swedish Standards Institute.

Fig. 1: (Left) Unpainted steel, pitted and rusted. (Right) The same steel specimen after hand tool cleaning to SSPC-SP 2. Courtesy of SSPC. Note: Fig. 1 and Fig. 2 are not equal in photographic quality to the actual reference photographs in VIS 3 and should not be used as substitutes for the actual standard.

Fig. 2: (Left) Previously painted steel with rust and several layers of deteriorated coating. (Right) The same specimen after hand tool cleaning to SSPC-SP 2. In ISO 8501-1, the color and appearance (metallic sheen) of a surface after thorough hand tool (or power tool) cleaning are shown as St2. The color and appearance of a surface after very thorough hand tool or power tool cleaning are shown as St3. The end result will vary depending on the condition of steel before it is cleaned. The four initial conditions or grades of steel in the ISO specification are:

•

Grade A: Adherent Mill Scale;

•

Grade B: Rusted Mill Scale;

•

Grade C: Rusted; and

•

Grade D: Pitted and Rusted.

For example, if a bid specification calls for a steel surface to meet C SA2, it tells the applicator that the initial condition of the steel is rusted and it must be hand tool cleaned and have a faint metallic sheen, as shown in the photo depicting C SA2. SSPC recognizes Grades A–D but also recognizes three additional grades of steel.

•

Grade E: light-colored paint (mostly intact) applied to blast cleaned steel;

•

Grade F: zinc-rich paint (mostly intact) applied to blast cleaned steel; and

•

Grade G: painting system (thoroughly weathered, blistered, or stained) applied to steel with mill scale.

Therefore, the pictorial standards must be used with care—those of ISO only depict uncoated steel, whereas those of SSPC additionally depict pre-coated steel. Description of Tools Common tools used for hand tool cleaning are sandpaper, non-woven abrasive pads, wire brushes, chipping hammers, scrapers, and hammers and chisels. The type of equipment selected depends on the condition and location of the surface. A chipping hammer or hammer and chisel are used in areas of heavy rust scale, deep rust pits, or thick build-up of paint. Various types and styles of chisels are available for use, depending on the surface to be cleaned. There are many types of wire brushes. Within each type, brushes are classified by wire stiffness and the size, number, and rows of wire. The following are a few types of wire brushes.

•

Shoe Handle Scratch: all-purpose wire scratch brush for brushing pipe threads and removing paint and rust scale

•

Wire Scratch and Scraper: for removing loose, scaling paint and varnish

• •

Hand Wire Scraper: curved wire face for removing paint, varnish, and wax from large flat surfaces (The curved face enables better brushing control because fewer wires are in contact with the surface at one time.) Flat Block Wire Scratch: longer and more flexible wires to remove paint, rust, and grease from large, flat surfaces

Sandpaper and non-woven pads are used to remove loose paint and rust and to achieve a feathered edge on well-bonded paint, allowing touch-up paint to be applied consistently. Assuring Quality Work Hand tool cleaning is laborious and tiring. The quality of work can suffer as the day wears on. A worker must realize this and be more aware late in the day that the specification is followed. Before you begin hand tool cleaning, make sure that dirt, grease, and oil have been removed from the surface. This can be achieved by solvent or detergent cleaning. Some hand tools, such as chipping hammers, can cause a steel surface to burr. Special care must be taken because burrs may protrude through the protective coating, causing a rust bloom and premature coating failure. After a surface is cleaned and is suspected to have burrs, it should be wiped with a rag, and if burrs are found, they should be sanded smooth. A chipping hammer should have a blunt edge. The intent is to remove rust, paint, and mill scale, and not to gouge the steel. Safety Proper safety procedures should be observed when hand tool cleaning a surface. Because these tools can create respirable dust, flying paint chips, rust, and other contaminants, NIOSH-approved cartridge respirators, safety glasses or goggles, gloves, and other protective equipment should be used. These dangers may seem trivial, but they can cause serious injuries. Responsibility for the correct safety equipment should be based on the following guidelines.

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The Contractor—Should provide proper safety equipment for the job being performed; ensure that the workers are trained to correctly use the equipment; and ensure that they do use the equipment. The Worker—Should be familiar with the safety equipment provided; maintain it in proper condition; and notify the owner if a replacement is required. The Owner—Should assure that proper safety practices are followed; and not allow questionable materials on the jobsite.

When to Use Hand Tool Cleaning A coating on a metal surface that has been abrasive blast cleaned to White Metal or Near-White Metal generally is expected to last much longer than a coating on a surface that has been prepared by hand tool cleaning. Therefore, considerations of coating life expectancy should be determined before a job is specified. Hand tool cleaning can provide an important alternative to other means of surface preparation in a maintenance-painting program. As areas of corrosion failure occur on a structure, hand tools are used to remove rust and failing paint selectively so that only the

areas affected are prepared. In this instance, hand tool cleaning can be accomplished quickly and inexpensively to maintain the life of a coating system. Other benefits of hand tool cleaning are that it can be done in confined areas and that it produces a very small amount of dust. Therefore, hand tool cleaning may be appropriate near sensitive equipment or in areas where people are working. For small areas, it is often less expensive per square foot to use hand tools, but on larger jobs, hand tool cleaning becomes very slow and labor intensive compared with other means of surface preparation. The most proven coating for a hand tool-cleaned surface is a slow drying, oil-based paint. This type of paint will provide for good coverage over uneven surfaces and will adhere adequately. This is important when applying paint on a failed area that has been hand tool cleaned, because hand tools can scar the surface, leaving it with high and low areas. Epoxy mastics are also quite popular for hand tool-cleaned surfaces. A hand tool-cleaned surface is desirable for applications where a low-cost cleaning method is required and a short-life paint system can be tolerated. Remember to be thorough in hand tool cleaning operations, and don’t let fatigue lower the quality of your work. Always clean the surface with solvent to get rid of grease and oil before you begin hand tool cleaning, and avoid creating burrs on the steel. This article is the ninth in JPCL’s updated Applicator Training Bulletin Series. The Series was first published from 1988 to 1992. It was expanded in 1993 and updated the first time starting in 1997. The current update began in January 2013. The series is intended as an introduction to protective coatings work, with topics divided into five categories:

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Basics of Corrosion and Coatings,

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Surface Preparation,

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Application

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Quality Control, and

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Safety and Health.

Editor’s Note: The original version of this article, written in 1989 by Craig Henry (with Service Painting Company of Texas at the time) and Burke Bennett (with Clemtex at the time), was published in the February 1989 JPCL as part of the original Applicator Training Bulletin Series developed by the Coating Society of the Houston Area. The article was subsequently updated and published in the February 2006 JPCL, and updated again for publication this month. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2013 Technology Publishing Company

26.Recent Developments in SSPC Surface Prep Standards From JPCL, Three Decades of Change in the Coatings Industry 2013 - Special Issue The JPCL Staff

In the past five years, SSPC has added, replaced, and revised several standards for surface preparation and abrasives in response to changes in the industry. The documents cover power tool cleaning; blast cleaning galvanized steel, stainless steels, and non-ferrous metals; water jetting of metals; mineral and slag abrasives; and encapsulated abrasives. The information below was provided by SSPC. Power Tool Cleaning SSPC revised two power tool cleaning standards in 2012: SSPC-SP 11, Power Tool Cleaning to Bare Metal, and SSPC-SP 15, Commercial Power Tool Cleaning. The types of power tools described by SP 11 and SP 15 have been reorganized and reclassified into grinding and impact categories. The impact category now includes wire bristle impact tools, which were introduced to the U.S. market after the earlier SP 11 and SP 15 were developed. In both standards, the default method for measuring profile is ASTM D 4417, Method B (depth micrometer) unless otherwise specified. Other methods (replica tape or portable stylus instrument) may be used if permitted by the project specification. Feathering of remaining intact coatings is required unless otherwise specified. Compressed air used in power tool cleaning must be verified to be free of oil and water in accordance with ASTM D4285, Standard Test Method for Indicating Oil or Water in Compressed Air. Non-mandatory notes have been added to both standards to caution against damaging surfaces, and to alert users that characteristics of individual tools and variations in the steel may affect the appearance and depth of resulting profile. For both standards, what did not change is as noteworthy as what did change, according to SSPC. The 2012 revisions have not changed existing requirements for surface cleanliness and minimum surface profile in either standard. Surface Preparation and Abrasives In 2010, SSPC issued SSPC-SP 16, Brush-Off Blast Cleaning of Coated and Uncoated Galvanized Steel, Stainless Steels, and NonFerrous Metals. According to SSPC, this standard covers surface preparation of coated or uncoated metal surfaces other than carbon steel before application of a protective coating system. Surface preparation in this standard is used to uniformly roughen and clean the bare substrate and to roughen the surface of intact coatings on these metals before coating application. Substrates that may be prepared by this method include, but are not limited to, galvanized surfaces, stainless steel, copper, aluminum, and brass. For the purpose of this standard, the zinc metal layer of hot-dip galvanized steel is considered to be the substrate, rather than the underlying steel. This standard is intended for use by coating specifiers, applicators, inspectors, or others who may be responsible for defining a standard degree of surface cleanliness. SSPC-SP 16 is not to be used for cleaning coated or uncoated carbon steel substrates. The standard represents a degree of cleaning similar to that defined for carbon steel substrates in SSPC-SP 7/NACE No. 4, Brush-Off Blast Cleaning, except that SSPCSP 16 requires a minimum surface profile depth on the bare metal surface. SSPC-AB 1, Mineral and Slag Abrasives, was revised in 2013, its first revision in 22 years. The standard was developed to establish quality benchmarks for non-metallic abrasives and to provide a classification scheme that would allow users to select the appropriate size distribution (work mix) for a given project. Key changes to the standard begin with the scope. It has been expanded to include manufactured, non-metallic abrasives that meet the requirements of the standard, such as silicone carbide and other abrasives that are neither naturally occurring minerals nor slag byproducts. The revision also clarifies the responsibilities for testing the abrasives to determine initial qualification to the standard, conformance testing for continued compliance, and testing for field quality control. The supplier is responsible for third-party testing to determine initial qualification. The requirements for documentation of initial qualification testing include requirements for the credentials of the laboratory performing the qualification testing of the abrasive. The supplier is also responsible for conformance testing of material for continued compliance when such testing is required by the purchaser. The contractor is responsible for field testing for oil and soluble salt contamination of delivered new media before initial use, and, if the use of recycled work mix is permitted by project specification, the contractor is responsible for testing the work mix before field use. The standard calls for the latter testing to be done once every work shift or eight-hour period, whichever is shorter. Also new to the standard is an appendix with additional requirements for non-metallic abrasives used by the U.S. Navy. This appendix is non-mandatory unless specified by the purchaser, and it includes additional requirements for friability, radioactivity, and inspection that are currently required by MIL-A-22262(SH). In 2009, SSPC issued a new abrasive standard, SSPC-AB 4, Recyclable Abrasive Media (in a compressible cellular matrix), developed to help those who use these composite abrasives to reduce dust generation and ricochet damage when blast cleaning steel and other surfaces. The standard includes requirements for selecting and evaluating the encapsulated media (e.g., steel grit, aluminum oxide) as well as requirements for quality control of new and recycled encapsulated media.

Four Waterjetting Standards Replace Existing Standard The 2012 revision of the 2002 version of SSPC-SP 12/NACE No. 5 standard, Surface Preparation of and Cleaning of Metals by Waterjetting Prior to Coating, replaced the single standard with four separate documents, each addressing a different level of surface cleanliness. There were several reasons for the changes, according to SSPC, but much of the material in the new standards was drawn from SSPC-SP 12/NACE No. 5. The organization of the four resulting standards has been revised to more closely parallel the organization of the dry abrasive blast cleaning standards, and allows the specifier to specify levels of cleanliness for waterjetting by use of separate standards, as is done when specifying levels of dry abrasive blast cleaning. The titles of the new standards are:

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SSPC-SP WJ 1/NACE WJ-1, Waterjet Cleaning of Metals—Clean to Bare Substrate (WJ-1);

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SSPC-SP WJ 2/NACE WJ-2, Waterjet Cleaning of Metals—Very Thorough Cleaning (WJ-2);

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SSPC-SP WJ 3/NACE WJ-3, Waterjet Cleaning of Metals—Thorough Cleaning (WJ-3); and

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SSPC-SP WJ 4/NACE WJ-4, Waterjet Cleaning of Metals—Light Cleaning (WJ-4).

The definitions of the four surface cleanliness levels have changed very little from the definitions in the 2002 version of the standard. Clarification that permissible staining or tightly adherent matter must be evenly distributed over the surface has been added to WJ-2 and WJ-3. In addition, a clarification of “tightly adherent” (cannot be lifted with a dull putty knife) has been added to WJ-2, WJ-3 and WJ-4 definitions. As in the original standard, descriptions of three degrees of flash rusting are provided in each of the revised waterjetting standards. These descriptions are based on the degree to which the rust obscures the carbon steel substrate and the degree of adhesion to the substrate. The color of the rust is no longer addressed. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2013 Technology Publishing Company

27.Surface Preparation: A Continuing Evolution From JPCL, Three Decades of Change in the Coatings Industry 2013 - Special Issue Charles Lange JPCL

If you’re in the coatings industry, then you’re well aware of just how vital surface preparation is to any protective coatings-related endeavor. Whether it’s a matter of removing and containing existing lead-based paint from a structure, or providing a clean substrate and a uniform surface profile to ensure proper coating adhesion, surface preparation is every bit as important as the actual coating application, and it requires strict attention to detail, clear and concise regulations and standards, and the most up-to-date equipment to get the job done right. According to Fred Goodwin, from an article in the July 2012 JPCL, “Proper surface preparation is one of the most important stages in achieving successful coating installation.” (p. 45) The 25th Anniversary issue of JPCL (August 2009) provided a general summary of surface preparation practices, equipment, and standards dating back to the publication of JPCL’s first issue in 1984. Industry growth hasn’t ceased since then; in fact, surface preparation methods and equipment continue to develop. In conjunction with these developments, SSPC has adapted its standards along the way, providing a clear point-of-reference to surface preparation work and resulting in better execution of the work. This article will take a look at some of the advances in surface preparation, with particular attention paid to the last four years. While it is not intended to be comprehensive, this article can serve as a framework for some of the trends and continuing developments in the surface preparation field. Trends identified are based on product developments reported by JPCL, PaintSquare News, and individual companies. 1984–2009: A Brief Review The August 2009 JPCL summarized and detailed the ongoing developments in surface preparation practices, equipment, and standards between 1984 and 2009. Trends highlighted in the summary include the advances made in abrasive blast cleaning, as well as the establishment of new standards to ensure quality during blasting operations and selection of abrasive materials (pp. 56– 57). Advances in standards for power tool cleaning (pp. 58–59), as well as the emergence of visual standards (p. 61), were also explained. The August 2009 summary also touched on the emergence of waterjetting, an alternative to dry blasting, and the establishment of the original SSPC waterjetting standard in 1995 (pp. 59–60). Wet abrasive blasting methods were also discussed (p. 60), as were techniques and standards for preparing concrete surfaces (pp. 62–63). The equipment and practices covered in the August 2009 JPCL haven’t disappeared, just changed to adapt with technological advances and the constant need for corresponding standardization. Some of the trends discussed in the 25th Anniversary summary are still prevalent in the industry today. While there has certainly been plenty of new innovation in the surface preparation field, it is more common that past methodology is developed and tweaked for use in the future. Pay attention to how some of these older methods have been modified to reflect the changes in the industry, while others have been outright replaced by the new tools of the trade.

High-tech equipment like robotic units offer many advantages, but surface preparation still needs that human touch. iStock Equipment & Practices: 2009–Today Robotics Revolution One of the most visible trends in surface preparation equipment and practices is the automation of surface preparation processes through the emergence of new robotic equipment. Debuted primarily during marine coating endeavors, robotics usage has expanded across several different industries, and few technologies have had such far-reaching effects in these industries as robotics. These new components have a wide range of benefits, helping contractors increase efficiency; reduce negative environmental impacts; and, because robotics equipment can prepare dangerous or nearly inaccessible areas, often keep workers out of harm’s way. Over the past five years, we’ve seen a number of robotic waterjetting machines put to use for surface preparation jobs on vessels and storage tanks. These machines include features such as increased coatings removal rates, mobile or radio-controlled operation, magnetic attachment systems for horizontal or vertical surfaces, both vacuum effluent and vacuum-less containment systems, and various safety devices. Robotics aren’t just for waterjetting. Some new robotic gritblasting machines are designed to store blast process parameters for different blasting operations, ensuring an even profile and consistent stand-off distances, nozzle angles, and surface speeds. In addition to enhanced productivity, these features are intended to ensure quality control and consistency, as well. Better Ways to Waterjet JPCL’s 25th Anniversary review of surface preparation techniques was published as waterjetting started gaining ground as a preferred technique. As contractors looked for alternative preparation methods for jobs in which dry abrasive blasting was not the best option, ultra-high pressure (UHP) waterjetting emerged as a suitable substitute. The first waterjetting standard, published by SSPC and NACE in 2002, was expanded a decade later to reflect the technical and practical changes and developments that took place. (For more information on the revised waterjetting standard, take a look at the Surface Preparation Standards article, p. 44.) To go hand-in-hand with the revised waterjetting standards, equipment and practices have been modified, with increased efficiency and user ease taking the lead as the driving forces behind new innovation. Some of the aforementioned robotic waterjetting machines have the ability to tackle a variety of surfaces and substrates. But a thorough surface preparation job can’t be completed by robots alone—it needs that human touch, so to speak. Recent manpowered waterblasting machines have been designed with a keen eye on ergonomic design and other considerations that could help increase efficiency and productivity, as well as more portability and better access for usage across a variety of structures. The past five years have seen several new versatile waterjetting components introduced, including water jet pumps that contain multiple operating pressures and engines that run up to 1,000 hp. Others include new convertible waterjet units; new multi-gun valves; new ergonomic equipment designed to make waterjetting easier; and revamped control gun handles, designed to be easier to hold and operate, helping the worker complete the job in the most efficient manner possible.

Concrete needs surface prep and coating application tailored to its unique makeup. iStock Conquering Concrete If you’ve ever picked up and read a copy of JPCL, chances are you don’t need to be reminded that concrete surfaces require different methods of surface preparation than steel and other materials—but we’ll mention it, anyway, just to drive the point home once more. Concrete demands a surface preparation and coatings application plan tailored for its unique composition, porosity, and possible surface defects. The 25th Anniversary JPCL described some early steps to establishing more tried-and-true concrete surface preparation methods, including the establishment of and revamping of SSPC-SP 13/NACE No. 6, Surface Preparation of Concrete. With this standardization as the foundation, surface preparation equipment and practices for concrete continue to develop. Tracy Glew authored an article in the January 2013 JPCL, “Preparing Concrete Floors for Coatings,” which highlighted some of the most common techniques for preparing concrete floors before coatings application. The methods Glew touched on include multistripping, planing, grinding, and shotblasting—which Glew says is one of the most cost-effective methods of preparing concrete, given proper conditions (p. 32). Not surprisingly, there have been plenty of developments in the equipment aiding these processes, such as new self-propelled or walk-behind shotblasting machines intended to strip previous coatings and compounded residues from concrete at high production rates. Other developments include new multi-level grinding kits and upgraded pneumatic surface planers, designed for use in marine and other industrial settings. Going Green Nowadays, it’s impossible to ignore the negative impacts that industry has had on the environment. Among pollution, depletion of natural resources, and the negative health effects on humans, it has become increasingly obvious that every industry needs to rededicate itself to making sure the harm to the environment and people is kept to an absolute minimum, and the coatings industry is no exception. Some of the aforementioned technological developments have environmentally friendly features, such as vacuum blasters, and so on. Indeed, preparing surfaces that leave large quantities of blasting dust and residue, or removing existing lead-based paint, always poses a risk to the environment and requires the use of containment and other measures to make sure these harmful byproducts do not enter into the ecosystem.

Protecting workers and the environment during surface prep is as important as properly cleaning and profiling the substrate. iStock While water jetting to avoid abrasive dust and waste has become an increasingly popular method of avoiding said byproducts, dry blasting hasn’t gone by the wayside. Instead, manufacturers have been hard at work developing more “green” abrasives that leave behind less debris and pose considerably fewer threats to the environment. In the October 2012 JPCL, David Dorrow answers the question, “What is a Green Abrasive?” Dorrow describes the different kinds of recyclable abrasives, including steel, garnet, glass, and others. Dorrow says that these recycled, green abrasives can reduce the overall waste generated by a project, and advises contractors not only to consider cost and convenience considerations when selecting an abrasive material, but to also think about sustainability and effects on the environment. He also explains the ways of producing abrasives from industrial byproducts, such as mineral aggregates (or “slags”), and post-consumer materials like recycled household plastic and glass waste. The “green” abrasive products on the market today reflect Dorrow’s school of thought—putting environmental considerations at the forefront of the selection process. Abrasives aren’t the only surface preparation materials that have been modified for better sustainability and less environmental impact. Machines that use heat to remove coatings have been around for many years and continue to be developed, with focuses on features such as reduced environmental harm, improved portability, and ease of access. Paint strippers also continue to evolve. Old solvent-based versions had put workers and the environment at risk. Today, paint strippers come to market in formulations free of solvents and other hazardous compounds.

More equipment is coming to the market to improve the efficiency, quality, and safety of preparing ship hulls. iStock Portability & Access: It’s All in Reach Not all surface preparation jobs are created equal. While some jobs require one or two straightforward processes to clean uniform, easily accessible surfaces, others present more complicated and challenging areas to prepare. Coating jobs often require especially small or large surfaces, or hard-to-reach areas, to be prepared and coated with the same attention to detail and quality as the easier parts of the structure. If these surfaces do not receive adequate preparation before coating application, the performance of the entire structure’s coating system is put at risk. With this in mind, several new innovations in the industry have been designed with the intent of helping contractors cover these crucial areas. New blasting machines, designed to prepare surfaces of steel and concrete storage tanks, ship hulls, and other horizontal or vertical surfaces, can disassemble to fit inside of a tight storage tank access hole, keeping workers out of dangerous areas. There have also been developments in handheld units for dry and wet surface preparation. Such tools are designed to remove coatings from steel structures that are too large for manual surface preparation, but too small for fully-automated equipment. From the tools and machines created for small spaces where access is difficult, to self-attaching units that prepare large, vertical surfaces at extreme heights and hand-held tools aimed at completing medium-sized preparation jobs, surface preparation equipment is changing to meet the demands of the industry. What’s Next? So where does surface preparation go from here? It’s hard to predict innovation—if we could, we’d all be millionaire inventors, after all. It is, however, possible to study the trends we’ve discussed in surface preparation equipment and practices, and try to make an educated guess as to what developments the future may hold.

Waterjetting, once a novel method of surface preparation, has become much more popular, and development of its standards, practices, and equipment continues to meet new demands. iStock Take a look back on the past five years. We’ve seen the emergence of new robotic surface preparation machines, versatile, multifaceted waterjetting units, cleaner recycled abrasive materials, and new methods and machines for cleaning concrete. The vast majority of the new products we’ve seen popping up in the marketplace now come equipped with features that increase efficiency and productivity, allow for maximum portability, lessen harmful impacts on the environment, and keep workers safe. It’s safe to say that these goals will continue to drive innovation in the surface preparation field. Efficiency and productivity, in a certain sense, will always be one of the top motivations for development, but they can’t come at the expense of any of the other benefits contractors strive for. It will certainly be interesting to see which considerations will take front and center as the development of surface preparation equipment and practices continues. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2013 Technology Publishing Company

28.Why surface preparation is important From JPCL, May 2013 Coatings experts often say that surface preparation of a steel surface is the most important part of a coating system. By this they mean that surface preparation affects the performance of the coating more than any other variable. Given that the proper coating system has been selected, if the surface preparation is poor, coating performance will often be compromised, even when the application is perfect. If surface preparation is good, then the coating applied over it is likely to perform well. For you, the applicator, it is useful to know why surface preparation is so important, because knowing why can help you do a better job. The following discussion focuses on the preparation of steel, but the concepts apply to other substrates as well. Surface Preparation Is a Foundation First, we can express the reason for the importance of surface preparation in a broad, general way, with the help of an analogy or comparison. Surface preparation is to a coating system what a foundation is to a building. If a building has a poor foundation, it can list or lean, as the famous Leaning Tower of Pisa does, or it can collapse altogether. If a coating system has a poor foundation (surface preparation), it will fail sooner than expected (say, after five years rather than ten years), or it can fail catastrophically, within the first year of application. In both instances, reduced service life and catastrophic failure can result in great financial losses to a facility owner. The contractor may be held responsible for these losses if the surface preparation work is found to be faulty. As a professional painter, you have a responsibility to your employer to make certain that the surface preparation work you provide complies with the specification requirements—to provide the solid foundation necessary for the proper performance of the coating system. When speaking about the function of surface preparation, it is important to go beyond the general concept of a foundation, and look to specific attributes. Surface preparation creates a foundation in two important ways: a mechanical way, by providing an anchor for the coating; and a chemical way, by allowing intimate contact of coating molecules with the steel surface. These elements of foundation are best understood by their opposites—the negative or detrimental conditions of slipperiness and debris on the surface. Overcoming the Negative of Slipperiness When a surface is very smooth, coatings have a difficult time adhering strongly. Imagine a coating on glass, for instance, and the ease with which it can be removed by a scraper or even a fingernail. Imagine, on the other hand, a rough surface like sandpaper on the same piece of glass, and how difficult it would be to remove a coating film from it. Steel, when it is abrasive blasted, has a surface that is rough like sandpaper, with a series of tiny peaks and valleys called surface profile (Fig. 1).

Fig. 1: Scanning electron microscope photo of a steel cross-section. The steel substrate is the shiny, smooth part toward the bottom—the granular, crystalline lighter gray layer is inorganic zinc. The darker gray top layer is a high-solids epoxy, complete with a large burst bubble in the middle. Photo courtesy of International Paint Co./John Cozine Coatings anchor themselves to the valleys of the profile, and the peaks are like teeth. This is why surface profile created by blasting is sometimes called an “anchor pattern” or “mechanical tooth.” This article was first published in October 1988, as part of the original Applicator Training Bulletin series, and in January 2005, when the series was revisited. The authors of the original article are Robert Barnhart (now deceased), then of Devoe Coatings (now International Paint); Debbie Mericle (no longer in the coatings business), then of Sline Industrial Painters (now part of K2 Industrial Services, which has partnered with the Halifax Group); Chuck Mobley, Mobley Industrial Painters (now Mobley Industrial Services, Inc.); Tom Hocking, Sullair of Houston; Jeff Bogran, then with Bob Schmidt, Inc. (now Axxiom), and now working for Energy Clean; and Ernestine McDaniel, then with Stan-Blast (now U.S. Minerals) and now working for GMA Garnet. Overcoming the Negative of Debris Debris on a steel surface can be comprised of many different materials. They include dirt, dust, grease, oil, rust, moisture, and in some cases, millscale. When materials such as these are painted over, they interfere with both mechanical and chemical adhesion of the coating to the substrate and make it likely that the coating will fail prematurely. On the other hand, when all debris is removed, the coating can achieve complete and continuous contact with the steel substrate, thus assuring the best possible adhesion. When a coating adheres well, it will create a more effective barrier, minimizing the moisture that reaches the steel substrate and that helps corrosion.

Non-Visible Contaminants Other forms of debris, not visible to the naked eye, are chemical contaminants. The most dangerous forms of chemical contaminants are soluble salts such as chlorides and sulfates. When such contaminants are painted over, they have the power to draw the moisture through the coating to cause blistering, detachment, and accelerated corrosion of the underlying steel. When structural steel is going to be repainted, areas that were previously rusted and pitted may contain soluble salt contamination, especially in the bases of the pits. Dry abrasive blasting typically does not remove these salts, so it is wise to check for their presence with specially-designed field test kits before painting, and then to take additional cleaning steps to remove the salts, if they are present in detrimental amounts. Testing for and removal of soluble salts will be discussed in detail in a later lesson. Degrees of Separation In any job specification, the degree of cleaning (Fig. 2) required for a given steel substrate before painting depends on a number of factors. The service environment of the coating system is perhaps the most important and, normally, is the first consideration when determining the degree of surface preparation. Generally, the more severe the environment, the better the surface preparation required. Severe service environments include immersion in liquids, exposure to aggressive chemicals or environments, high temperatures, or combinations of these conditions.

Fig. 2: Samples of degrees of blast cleaning on steel covered with rust and millscale, from SSPC’s VIS-1, Guide and Reference Photographs for Steel Surfaces Prepared by Dry Abrasive Blast Cleaning. Courtesy of SSPC. Not to be used in place of the actual visual standard. A second consideration is the generic kind of coating used. Some coatings, such as oils and alkyds, because they flow out and wet the surface well, can tolerate application over minimally-prepared or hand-cleaned surfaces. In addition, some epoxy mastics and other “surface-tolerant” coatings are formulated to be applied over hand-and power tool-cleaned surfaces. Coatings such as inorganic zincs, however, are at the other end of the spectrum. They require a higher degree of cleaning than many other types.

Cost is another factor in selecting the degree of surface preparation. Blast cleaning to SSPC-SP 5 (White Metal) is about 4–5 times more costly than to SSPC-SP 7 (Brush-Off) or SSPC-SP 3 (Power Tool). In some severe environments and with some coating types, rigorous cleaning is necessary, but in other instances, the cost and cost-benefit of higher grades of cleaning relative to increased coating lifetime will become an important factor in selecting the degree of surface preparation. Finally, regulations may have an impact on the degree and method of surface preparation. In residential or congested urban environments, open blasting may be prohibited; in addition, where lead- or chromate-based paints are being removed, environmental and hazardous waste regulations may require containment and use of special surface preparation methods. Determining the degree of surface preparation, as described above, is the job of a specifier or engineer. The task of doing the work is the contractor’s. No matter what degree of surface preparation is required, it must be done thoroughly. If hand-tool cleaning is required, then all of the surface area specified must be hand-tool cleaned, after it has been first cleaned by water or solvent according to SSPC-SP 1 to remove dirt, oil, or grease. If SSPC-SP 5 is specified, then conformance with the written description of SP 5 must be achieved on all designated surfaces. In cleaning steel, it is also important to follow the proper sequence (Fig. 3). First, you must remove dirt and other debris. It is a lot easier to sweep mounds of dirt and other loose material off a surface with a broom (or by vacuuming in the case of leadcontaminated debris) than to try to remove it with surface preparation tools. The next step is removing visible oil and grease by solvent cleaning. Then you must conduct the operation of hand tool, power tool, or blast cleaning.

Fig. 3: Observe the proper sequence when cleaning steel. If you reverse these steps, particularly with blast cleaning, the force of the blasting abrasive may drive the debris into the roughened steel surface or profile, or spread it around as is the case with grease and oil. Then it is not easy to remove, and it may interfere with coating adhesion. In addition, it is important to achieve the surface profile required by specifications. When the profile is too rough, the coating may not cover the peaks of the profile, and the result will be pinpoint rusting. When the profile is not rough enough, the coating may not anchor well to the surface, and the result will be loss of adhesion. Upcoming ATBs The following are among the upcoming Applicator Training Bulletins. Application

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Product and Application Data Sheets

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Mixing and Thinning Paint

Quality Control

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The Effects of Weather on Cleaning and Coating Work

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Conforming with Job Requirements

Safety and Health

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Safety Considerations for Abrasive Blasting

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Anticipating Job Hazards

To make sure that a coating system will perform well as a barrier to prevent corrosion, you must roughen the steel surface for mechanical adhesion and make sure that all debris is removed so that the coating contacts the entire surface of the steel. In achieving these two conditions of cleanliness and profile, you will have assured that a proper foundation has been created for application of a coating system. This good foundation should help to provide many years of service life for the coating. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2013 Technology Publishing Company

29.Preparing Concrete Floors for Coatings From JPCL, January 2013 Tracey Glew Group Managing Director, The Preparation Group, UK

The successful application and durability of resins, coatings, and screeds on concrete floors depends on a sound surface. The key to success is in the preparation. When selecting the correct equipment and methods, consideration must be made for potential problems such as uneven joints, high spots, contaminants, worn coatings, sticky residues, old tiles, and friable substrates, which all need to be tackled to achieve a clean, profiled surface suitable for the application of the specified coating or covering. There is a wide range of surface preparation machines and accessories on the market and a vast array of techniques that can be employed, with each unit and technique producing a different result. The model, size, and power requirements of the machine, together with the accessories selected and the type, thickness, and composition of the material to be removed, will determine production rates achievable. Other important factors to consider are area size; location and accessibility; the power supply available; and, critically, the profile required for the coating specified. It is important to note that surface preparation machines are also designed to work with dust collection and filtration units to minimize the dust contamination common in the preparation of concrete surfaces. When concrete is not finished correctly, or if it has been broom finished/tamped (packed down and having a light rippled effect), the surface may have a large degree of laitance. To achieve a sufficient bond for the specified material to be applied, this laitance must be removed. This article describes common techniques and equipment for preparing concrete before applying a coating or other system. Multi-Stripping The multi-stripping method is used to remove material from a surface or to clean it. Often, multi-stripping is selected when there are no other effective options available. There are 110-volt, hand-operated, walk-behind machines for clearing small areas, and large, ride-on, three-phase electrical or propane-powered machines for clearing large areas. Blades or picks are attached to the front of the machine and their type, weight, and position affects the removal of the designated surface. A flat blade should be selected to scrape off tiles, latex, adhesives, and elastomeric systems, while a curved blade cuts material into manageable lengths as it strips, so it is ideal to lift up membranes, carpet, and sheet vinyl. Picks are employed to break up hard materials such as ceramics and terrazzo tiles. The operator positions the machine to cut or lift the material as the machine drives forward. In this way, multi-strippers can remove floor coverings such as waterproofing membranes, epoxies, polyurethanes, sticky residues, thermoplastic materials, asphalt, bituminous materials, adhesives, and the various other coverings such as wood, vinyl, carpets, ceramic tiles, latex, and screeds. Once the floor is stripped, additional techniques for floor preparation are often specified in order to provide a suitable surface for application of the resin or screed, etc., such as the following. Planing You would select planing to remove materials in excess of 2 mm in thickness, when there are multiple layers of coatings, and when a rippled profile is required. Applications include removing old screeds, asphalt, latex, and adhesives, and reducing tamped surfaces and levels. Machines range from small 110-volt, single-phase, to larger three-phase electrically powered petrol or diesel walk-behind models and ride-on versions for large-scale projects and heavy-duty applications. The planing operation is based on a drum rotating at high speed within the body of the machine. The profile or texture is created by the accessories fitted to the drum known as flails (Fig. 1), or picks in the case of ride-on models (Fig. 2). Once contact is made with the surface being treated, the flail configuration cuts with a downward rotary action.

Fig. 1: Underside of small planing machine showing milling flail drum Photos

courtesy of the author

Fig. 2: Profile created by ride-on planing machine fitted with pick drum There are different shapes and sizes of flails and picks available for specific tasks and they can be arranged on the drum for light cleaning applications through to heavy-duty grooving. Generally, milling flails are for the removal of thermoplastic line markings (Fig. 3), bituminous materials, and rubber deposits; tungsten carbide-tipped flails are for cleaning, texturing, and roughening concrete; and star flails and beam flails are for removing soft material compositions.

Fig. 3: Walk-behind planing machine removing thermoplastic line markings Picks can remove and reduce materials in excess of 2 mm and up to 25 mm. It is important to note that hard surfaces may be a problem for smaller planing machines because there is not enough weight to cut into the surface. This can result in the machine malfunctioning and becoming a hazard to the operator. Grinding Grinding would be selected when a flat, level, and smooth concrete surface is required. It is used for removing surface contaminants, adhesives, paint (Fig. 4), sealers, and coatings, and for cleaning.

Fig. 4: Paint removal by a single-head, three-phase grinding machine Grinding models are available in single-phase or three-phase electric and in single-head, double-head, and multi-head versions. There are also diesel- and petrol-powered alternatives and variable speed models that can be fitted with provisions for wet grinding and polishing applications. Grinding is achieved by diamond (Fig. 5), tungsten, or resin-bonded plates or discs that are secured to the single or multiple rotating heads. There is a wide range of grades of diamond, resin-bonded, and PCD (Polycrystalline Diamond) shoes for removing adhesives and coatings, and for grinding, smoothing, and polishing decorative screeds and concrete screeds.

Fig. 5: Underside of grinding machine showing diamond plate As a general rule, hard composition surfaces will require a soft bond diamond segment or disc, and soft compositions will require a hard bond. The correct diamond accessory is important because incorrect selection will either simply glaze over the surface without creating the profile or wear out extremely quickly in the initial stages of the operation. Grinding is not recommended if the surface is uneven or if the concrete has been tamped. Shotblasting In the correct conditions, shotblasting is one of the most cost-effective methods of preparation. It is often selected to clean and profile power-floated concrete, to remove laitance (Fig. 6), coatings, and light surface contaminants. Surfaces to be shotblasted must be sound and hard. Shotblasting is not suitable for removing or treating soft compositions or materials thicker than 2 mm.

Fig. 6: Shotblasting machine removing surface laitance Shotblasting machines are available in walk-behind, 110-volt single-phase and three-phase electric and ride-on versions, and all offer different operating widths. The process involves propelling steel shot or abrasive at high velocity (by a rotating wheel contained in the body of the machine) onto the surface to produce the desired profile. The debris removed is then collected in a dedicated vacuum/filtration unit for disposal upon completion of the process, and the shot is recycled. Many profiles can be achieved; each profile is determined by the size or grade of shot or abrasive selected and the speed at which the machine is propelled. Shotblasting will also highlight surface defects in the substrate being prepared, and cannot be carried out in wet or damp conditions. For optimum results, the process requires a smooth, even surface; otherwise, the shot will escape from the machine. Summary Selecting the correct technique for the nature of the concrete surface to be prepared is essential for obtaining the optimum substrate for coating or further treatment. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2013 Technology Publishing Company

30.On static electricity and abrasive blasting From JPCL, December 2012

What causes static electricity during abrasive blasting? What risk does it pose, and how can it be controlled? From Simon Hope Salamis Static electricity is produced by the active transport of electrons to create a potential difference or charge (the classic example being the Van de Graff generator), which then discharges back to earth when the voltage is great enough to ‘jump’ as a spark. The spark will take the shortest and easiest track to earth. In abrasive blasting using compressed air, it is possible to charge up the blast nozzle with static electricity. Dry air, rather than damp air, helps maintain the charge that builds up as the abrasive transports electrons to the nozzle and deposits them there. Eventually, the charge becomes so great that the electrons jump to the nearest earth, which will be either the operator, if not wearing suitable rubber-soled boots, or the substrate. Sparks can be over one foot (300 mm) long and have relatively high energy. Sparks themselves do not pose a particularly high risk in normal operations such as in blast pens of general construction sites. They do, however, become a problem in explosive or potentially explosive environments, where a spark becomes an ignition source. An adjacent spray shop may have enough solvent vapor to be within the explosive concentration limits for the material. Similarly, in petrochemical sites, there are ‘zoned’ areas where equipment producing sparks or having a spark potential must be controlled by a permit-to-work system due to the risk from hydrocarbons. Systems such as flour mills that produce fine dust likewise are high-risk areas for static-producing equipment because the spark can cause ignition of the dust, with catastrophic consequences. Control of the static is quite simple to achieve. The first and simplest thing to do is to provide a controlled discharge path without permitting a spark. This path can be provided either by directly earth-bonding the nozzle using an earth wire from the nozzle straight to earth or by using conductive blast hose with continuity to the blast pot, which is then earthed to a suitable point. Another alternative control is the use of a wet abrasive slurry. It creates continuity with the nozzle and substrate, thus completing the earth circuit. The air from the nozzle can act as a purge to remove flammables from the vicinity of any discharge, although this practice is not a substitute for proper earthing. In Europe, static discharge comes under the ATEX (ATmosphere EXplosive) regulations, so any equipment with the potential to generate static that is used in a zoned area must be built to be compliant with these regulations and must be certified accordingly. In the U.S., OSHA should be consulted for regulations, standards, and guidance on explosive environments and static discharge (osha.gov). Also, for work in high-risk areas, the use of suitable gas monitors set to pick up any potentially explosive situations is a must. Editor’s Note: This Problem Solving Forum was also posted on JPCL’s sister publication,PaintSquare News. Online responses to the question as well as other Problem Solving Forum questions and answers can be found at paintsquare.com/psf/. Problem Solving Forum is an interactive column on PaintSquare News and on JPCL. Additional answers to this month’s question may be submitted to PaintSquare News or to JPCL. You can also submit questions for Problem Solving Forum on PaintSquare News, or you can submit questions to Karen Kapsanis, JPCL, [email protected]. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2012 Technology Publishing Company

31.Preparing stainless steel for atmospheric salt service From JPCL, October 2012

What is the proper surface preparation for stainless steel before coating to resist a salt-laden atmosphere? From William Slama International Paint/Ceilcote Products Over the years, there have been many of these applications in which the original alloy was found to be inadequate for the operating conditions (usually chloride fluoride chemistry) of the vessel or equipment. In some cases, the inadequacy was identified even before the structure was placed in service; other times, the inadequacy was identified when the alloy didn’t perform as expected. A recurring recent case is the many FGD vessels (absorbers and other vessels) constructed of Alloy 2205. Apparently, buildup of scale creates a concentration of chlorides/fluorides under the scale buildup, which results in extreme pitting of the alloy. The surface preparation, not surprisingly, is not much different than that needed for lining carbon steel. Basically, the alloy requires a clean surface with a sharp profile with the required blast profile (depth) for the system being applied. For most high-build linings or coatings, a 3-mil profile is needed. For most alloys, adjacent unlined surfaces should be protected during abrasive blasting to ensure that the surfaces are not contaminated by iron. The protection is needed because the most commonly used slag abrasives contain iron. In some cases, that possibility is avoided by using a blast abrasive that does not contain iron. Garnet or aluminum oxide abrasives are suitable, providing they are able to produce the required sharp profile. As with carbon steel, the surface must be tested for salt contamination and cleaned if necessary to the lining manufacturer’s requirements. One differing feature is that the surface must be coated or primed soon after blasting, unless dehumidification (DH) control holds the relative humidity (RH) to less than 40-50% because the surface will not show the typical discoloration due to surface oxidation as carbon steel does. From Derek Righinni Certified Coating Inspection Ltd There is no clear consensus on a cleanliness standard that stainless steel is required to meet before the application of coatings to protect it from chloride-induced pitting or stress corrosion cracking. Here is the question that should be asked: Is the chromium oxide passive layer that forms rapidly on the surface of stainless steel tightly adherent and suitable for painting? The answer to the question dictates the time allowable between the start of blasting to the maximum time the stainless steel substrate can be left before coating. It would be helpful if NACE, SSPC, ISO, and ICORR would give the industry some clear guidance on the preparation of stainless steel for painting with protective coatings and linings. Editor’s Note: This Problem Solving Forum was posted on JPCL’s sister publication,PaintSquare News. Answers have been edited to conform to JPCL style and space limitations. For more Problem Solving Forum questions, go to paintsquare.com/psf/.Problem Solving Forum is an interactive column on PaintSquare News and on JPCL. Additional answers to this month’s question may be submitted to PaintSquare News or toJPCL. You can also submit questions for Problem Solving Forum on PaintSquare News, or you can submit questions to Karen Kapsanis, JPCL, [email protected]. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2012 Technology Publishing Company

32.What is a Green Abrasive? From JPCL, October 2012

Do YOU consider a “green” abrasive when planning for your surface preparation project? David Dorrow Mineral Aggregates Inc. David Dorrow is the president of Mineral Aggregates Inc., which develops marketing solutions for mineral co-products from the steel, smelter, and other industries. With more than 30 years of experience in the abrasive markets, he is a member of SSPC and has served on its Abrasive Steering Committee; Surface Preparation Steering Committee; and Development Committee for SSPC-AB 1, Mineral Abrasive Specification.

Photo courtesy of the author On the market today are a multitude of abrasives that are described as “green,” but what actually is a green abrasive? Generally, the use of “green” is a kind of shorthand term referring to the effect of the abrasive on the environment. More specifically and practically, the question that really should be asked is: “What environmental impact and sustainability of our natural resources will my selection of abrasive for my next surface preparation project produce?” Our society has become more and more focused on how we are affecting the world we live in with our everyday behavior as our population continues to grow. We should all be accountable to future generations for decisions we make today, including our activities in the surface preparation industry. Our focus should be on using the best practices available that prevent pollution of our environment, use sustainable technologies, and eliminate waste that crowd our already brimming landfills. The surface preparation industry has made some tremendous strides over the past two decades in improving the environmental footprint of a blasting and painting project. Some of these changes have centered on the abrasive blasting segment of the project. Increased use of containment, improved engineering controls and a focus on proper abrasive waste characterization and reduction have all produced significant environmental strides in the right direction. With today’s multitude of abrasives and surface preparation technologies, making a choice can often be confusing. Coupled with all of the different claims about reduced environmental impact that manufacturers are making about their surface preparation products, decision makers may become overwhelmed. If the abrasive you have selected can reduce waste generated, be recycled, be produced from an industrial byproduct or a post-consumer waste stream, or be beneficially reclaimed, should it be considered a sustainable abrasive technology with reduced environmental impact? Of course, the answer is “yes,” depending on the perspective one is taking. Recyclable Abrasives The ability to recycle an abrasive for more than one use can be viewed as an environmentally sensitive technology because of the reduction in waste generation. If an abrasive has the characteristics that result in limited breakdown after the initial use, it should be collected and processed for reuse as an abrasive. Steel abrasives have been used for many years in fixed site facilities—fabrication and paint shops—that are set up to recycle the

abrasive hundreds of times. In the early 1990s, with the increased awareness of protecting the environment from the impact of lead paint removed from structures, the development of portable/mobile recycling equipment expanded the use of steel abrasives to projects in the field such as bridges and water towers. A project using recyclable steel abrasives reduces the amount of total waste that is generated. This abrasive recycling process may also produce a potential waste concern because the removed paint waste is concentrated during the cleaning of the abrasive. Proper characterization and handling of the collected waste product with the intention to protect the environment is a prerequisite to maintaining an environmentally responsible position. High-quality garnet is also an environmentally responsible abrasive selection because it can fall into the recyclable abrasive category. Along with recyclability, the fast cutting rates and low consumption rates achieved when using garnet abrasives can also reduce their environmental impact. Producing Abrasives from Industrial Byproducts The focus of the industry on developing additional market applications for byproducts generated during production processes continues to increase. Industrial byproducts are evaluated for chemical and physical characteristics and targeted for corresponding markets that can beneficially use the materials as abrasive as an alternative to immediately disposing of them after they are produced. Coal-fired power plants, metal smelters, and steel mills generate byproduct mineral aggregates (slags) that have been successfully used as abrasives. Sometimes the generation processes of these byproduct minerals are engineered to produce enhanced byproduct characteristics. The use of these materials to produce abrasives can be viewed as a green application because a material originally destined for a landfill can be used to add value to the surface preparation industry. Other byproduct minerals are generated during the mining and recovery process of valuable earth minerals. The use of the mineral staurolite is a co-product separated during the refining process of mineral deposits containing high value metals and minerals. This material is a sought-after abrasive for certain blasting applications and can also be viewed as green. Producing Abrasives from Post-Consumer Materials Many of us participate in recycling of our household waste: paper, plastic, or glass. These materials that were originally destined for a landfill are now finding beneficial uses in various products. Several companies in the surface preparation market are offering postconsumer recycled glass as an abrasive product. The glass bottles that we leave at our curbside are collected, crushed, cleaned, and processed, enabling the green label to be applied to this reuse technology. What’s Next? It can be noted that once the value as an abrasive is used up, the used abrasive and accompanying paint and rust debris from the blasting project typically become a waste and will likely end up in a landfill. Sometimes the waste is hazardous and will have to be treated before disposal; other times, the waste will not be hazardous but will still require disposal. There are, however, some in the industry taking the next step by beneficially using the spent abrasives as raw materials for alternate industries. This additional green step is regionally dependent, and this technology has not yet been developed to its full potential. In parts of the country, the lead-bearing paint debris from steel grit recycling systems has been successfully introduced back for beneficial reuse to the smelter industry. Slag abrasives continue to have value even after use as abrasive because they have a chemistry desirable to the Portland cement industry. Perhaps because of economics or logistics or indifference to being green, this final important step in closing the loop has lost momentum in the abrasive market. Closing Thoughts Making the correct decision in selecting a green abrasive technology reminds me of the following fable. Three blind monks were walking down a familiar path when they happen upon a sleeping elephant that was blocking their way. Having never experienced an elephant before, the three eagerly spread out and began to touch different parts of the elephant. One wrapped his arms around the sleeping elephant’s front leg; the second grabbed a hold of one of the elephant’s ears, while the third took hold of the elephant’s trunk. Sensing that the elephant was beginning to wake, the three quickly ran off. When they stopped to rest, the three monks began to talk about the elephant and what the elephant looked like. The first man said, “An elephant is round like a tree trunk with no branches.” The second man said, “No, an elephant is flat and leathery like a drum skin.” Then the third man said, “No, no, no—you are both wrong! An elephant is long and thick and strong like a snake.” Each individual has his or her own perspective when it comes to selecting a green abrasive, and each of us has assigned a different importance associated with each abrasive technology. The significance for all of us as an industry is increasing our awareness of and focus on future sustainability by using the best available technology and minimizing our environmental impact. The abrasive selection should not be based solely on cost, convenience, or what we have always done in the past, but should also include an evaluation of how we are affecting our environment for future generations. THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2012 Technology Publishing Company

33.Preparing Surfaces at Wastewater Plants: An Overview of Substrates, Practices, and Standards From JPCL, September 2012 Vaughn O’Dea Tnemec Company, Inc., Kansas City, MO Vaughn O’Dea is director of sales—water & wastewater treatment for Tnemec Company, Inc., where he is responsible for strategic sales, marketing, and technical initiatives. He has written numerous technical reports and articles for various waste-water industry journals. He is active in the technical committees of NACE, SSPC, and ASTM and is a member of AWWA, WEF, ACI, ICRI, NASSCO, and NAPF. He is a contributing editor for JPCL, was awarded the JPCL Editors’ Award in 2008 and 2010, and received aJPCL Top Thinker award this year.

Our valued wastewater infrastructure has been underfunded, under maintained, and under attack for many decades. Corrosion and deterioration are winning the battle. Wastewater infrastructure in the United States is clearly aging, and the required investment is not able to keep up with the need. The 2009 Report Card for America’s Infrastructure issued by the American Society of Civil Engineers (ASCE) assigned wastewater infrastructure a “D minus.”1 In accompanying comments, the ASCE indicated that as much as 900 billion gallons of combined sewer overflows are released yearly because of the poor state of our sewerage infrastructure. To complicate matters, a 2011 ASCE report titled Failure to Actdetermined that the investment gap has significantly increased because of our failure as a nation to respond.2

Vaughn O’Dea

According to the ASCE report, the Environmental Protection Agency (EPA) estimated the cost of the capital investment required to maintain and upgrade waste-water treatment systems across the U.S. in 2011 was $58.3 billion. However, only $16.1 billion was funded, leaving a capital funding gap of nearly $42.2 billion. By 2020, the predicted deficit for sustaining waste-water treatment infrastructure will be $60 billion, a staggering 42 percent increase in less than 10 years. The funding gap is expected to widen by 2040.

These statistics are nothing short of alarming. Perhaps we can look to Adam Smith and his “diamond-water paradox” to explain why our wastewater infrastructure has deteriorated to such perilous conditions. In his epic book, The Wealth of Nations, Smith notes that although water is essential for life while the value of diamonds is mostly aesthetic, the price of water has always been far lower than that of diamonds. Consequently, our tendency to place little economic value on water has arguably resulted in the neglect on our water and wastewater infrastructure. What’s more, it is said that the sustainability of a community is directly related to its waterworks system. Overburdened or failing wastewater infrastructure not only has a negative economic impact, but, worse, conditions caused by the result in unsanitary conditions increase the likelihood of public health problems. Recognizing that investments made now have a profound impact in the long-term, the EPA issued the Clean Water and Drinking Water Infrastructure Sustainability Policy as part of its effort to ensure robust and sustainable waterworks systems moving forward.3 The overarching goal of thisPolicy is to encourage the adoption of sustainable practices, such as embracing the philosophy of capital asset management. Simply put, sustainability is effectively maintaining a desired level of service life at the lowest life-cycle cost. This forward-thinking management of our infrastructure assets minimizes the total cost of owning and operating them while delivering the desired service levels. Asset management is the framework to achieve effective wastewater management. The use of high-performance protective linings contributes to the sustainability of wastewater infrastructure. Let’s take a look at how the protective coatings industry can support the sustainability concept beginning with surface preparation. This article discusses the prevailing views and current practices—from the author’s perspective—for the surface preparation required for the common substrates found within severe wastewater environments: concrete, carbon steel, ductile iron, and stainless steel. Background The term severe wastewater environment is used colloquially in this article to describe any confined-space wastewater environment, whether a sewer pipe or enclosed structure, containing a headspace (or vapor area above the flow of sewage). The Useful Lives of Wastewater System Components

Component

Useful Life (Years)

Collections

80–100

Treatment plants—concrete structures

50

Force mains

25

Pumping stations—concrete structures

50

Interceptors

90–100

Source: EPA (2002, Table 2-1, adapted) Wastewater headspaces are areas susceptible to corrosion from biogenic sulfide attack.4 These areas are typified by elevated concentrations of hydrogen sulfide and other sewer gases. Despite a useful design life in excess of 25, 50, or even 80–100 years,5 many of these structures commonly experience significant corrosion that ultimately requires replacement in dramatically less time. One such example is that of a lift station in Florida where the concrete, ductile iron, and stainless steel material were all severely corroding in less than five years of service (Fig. 1). The lift station is scheduled for complete replacement (a far cry from the

50-year design life). Not surprisingly, the coal tar epoxy on the concrete and ductile iron in Fig. 1 is clearly unable to withstand the elevated headspace exposure and therefore certainly not able to provide the requisite corrosion protection. The wastewater industry is now recognizing that high-performance lining systems with low-permeation properties to sewer gases and acids are paramount to achieving the service life expected of these structures.6 Equally important, and often overlooked, is the proper surface preparation of the construction materials to maximize the service life of the lining system. Although sound in principle, surface preparation is fraught with challenges and met with resistance because of the variety of surface preparation techniques offered in the wastewater marketplace.

Fig. 1: A wastewater lift station experiencing significant corrosion of concrete, ductile iron, and stainless steel materials. Note the failing coal-tar epoxy that was applied to the concrete and ductile iron materials. Photos courtesy of Tnemec. Concrete Concrete is inherently durable and is used extensively in wastewater construction. The alkaline nature of concrete, however, makes it—relative to other substrates discussed in this article—most susceptible to the effects of biogenic sulfide corrosion. Sewer pipes, manholes, lift stations, screening structures, grit chambers, equalizations basins, junction boxes, and many additional headspacecontaining structures are commonly constructed of concrete and require corrosion protection by high-performance protective linings to achieve the anticipated service life of the structures. Preparing concrete surfaces appropriately to maximize the performance offered by high-performance protective linings is, in this author’s view, the most commonly overlooked aspect of coating concrete. Unfortunately, the wastewater industry sees a myriad of preparation recommendations, including the proverbial “pressure wash” or “sand blasting” techniques. With no standard of quality, the outcome often leads to premature failures—most commonly resulting in disbondment because of improper removal of the laitance layer (Fig. 2) or insufficient substrate rugosity—or profile (Fig. 3).

Fig. 2: Delamination failure due to inadequate removal of laitance layer

Fig. 3: Delamination failure due to insufficient substrate anchor profile So how do you ensure consistent preparation on what is unquestionably considered an inconsistent substrate? First, follow industry consensus standards and practices such as the SSPC-SP 13/NACE No. 6, Surface Preparation of Concrete7 and NACE (Standard Practice) SP0892, Coatings and Linings over Concrete for Chemical Immersion and Containment Service.8Both documents detail standardized and reproducible methods for inspection, surface preparation, and sample acceptance criteria to ensure that current preparation methods and coating system design requirements are achieved. Specifically, SSPC-SP 13/NACE No. 6 defines a standard degree of cleanliness, strength, profile, and dryness of prepared concrete surfaces while NACE SP0892 sets forth guidelines for the selection and installation for concrete surfaces that will be exposed to immersion conditions or chemical splash and spillages. Second, it is important to specify the appropriate anchor profile to ensure a satisfactory mechanical profile is created for the lining specified. A tactile method for determining a substrate’s profile is by using the ICRI Technical Guideline 310.1R9 concrete surface profile (CSP) comparators. It is the author’s experience that for severe waste-water exposures, the substrate profile should be equal to an ICRI-CSP5; a lesser profile may not provide sufficient mechanical interlocking of the system to the substrate to resist the lifting forces exerted on the film from exposure to the severe sewer environment. Third, it is important that all voids, gouges, bugholes, and other surface anomalies on the substrate be repaired with the appropriate patching materials before applying a coating system.10 Repairing new and existing concrete levels the substrate and creates a paintable surface (Fig. 4). Concrete substrates—including new, cast-in-place and pre-cast structures—should be repaired to allow the topcoat to achieve a continuous, monolithic film.

Fig. 4: Properly prepared concrete (above) and concrete repair via a cementitious resurfacing material (below) Ferrous Metals Ferrous metals, such as carbon steel and ductile iron, are also commonly used in wastewater construction for a variety of components including tanks, pipes, fittings, valves, and structural members. Ferrous metals are subject to microbiologicallyinfluenced corrosion and direct molecular attack from hydrogen sulfide gas, so they require barrier protection in severe wastewater environments. Carbon Steel It is well understood that the surface preparation of carbon steel is the key foundation to achieving long-term performance of heavyduty, high-performance protective liners. Carbon steel members are typically abrasive blasted to achieve a prescribed degree of substrate cleanliness and to achieve a suitable anchor profile (waterjetting is occasionally used for rehabilitation where a satisfactory profile exists). Similar to concrete, proper surface preparation is consistently achieved by following industry consensus surface preparation standards. SSPC-SP 5/NACE No. 1, White Metal Blast Cleaning,11 with a minimum 3.0-mils (76.2-microns), angular anchor profile ensures optimum surface cleanliness and adhesion of the protective coating system in severe sewer environments. Ductile Iron Pipe Ductile iron (DI) is also a common material for many appurtenances, including pipe and fittings found in severe sewer exposures. Although inherently more corrosion resistant than concrete and carbon steel, ductile iron nonetheless requires a high-performance protective lining to achieve the useful design life when exposed to sewer environments. Similar to carbon steel, ductile iron surfaces require attention to surface preparation to make the substrate suitable for topcoating. While ductile iron and carbon steel are both ferrous metals, there are inherent metallurgical and manufacturing differences between the two metals that preclude ductile from meeting certain parts of the SSPC/NACE surface preparation standards. But there is an industry consensus standard to provide consistency in surface preparation: the National Association of Pipe Fabricators developed NAPF 500-03, Surface Preparation for Ductile Iron Pipe and Fittings in Exposed Locations Receiving Special External Coatings and/or Special Internal Linings.12 The NAPF 500-03 contains several standards that can be selected based on whether the piece is a pipe or fitting, what surface—interior or exterior—is to be prepared, and what exposure conditions are expected (See box). For example, the method in 500-03-04, Abrasive Blast Cleaning–External Pipe Surface, is selected if a ductile iron pipe exterior is scheduled to receive a high-performance protective coating for heavy-duty exposures (Fig. 5). This standard is written specifically for exterior DI pipe because unlike carbon steel surfaces, it is possible to “overblast” the external surfaces of DI pipe, causing slivering of the substrate. NAPF 500-03 Standards NAPF 500-03-01 Solvent Cleaning NAPF 500-03-02 Hand Tool Cleaning NAPF 500-03-03 Power Tool Cleaning NAPF 500-03-04 Abrasive Blast Cleaning of Ductile Iron Pipe NAPF 500-03-05 Abrasive Blast Cleaning of Cast Ductile Iron Fittings

Fig. 5: Ductile iron pipe exterior prepared in accordance with NAPF 500-03-04 External Pipe Surface High-Velocity Jet Sewer Cleaning: No Flushing Matter Sanitary sewer overflows caused by blocked or corroded pipes result in the release of as much as 10 billion gallons of raw sewage yearly, according to the ASCE.1 Interruptions in sewer service are thought to be avoided by strict enforcement of sewer ordinances and timely cleaning and inspection of sewer systems. This is commonly accomplished using what the sewer cleaning industry refers to as high-velocity jet cleaning techniques (aka jetting or hydrocleaning) with pressures commonly 2,500–3,000 psi (172–207 bar; Fig. 9).14 Jetting is a hydraulic cleaning method that removes grease buildup and solids debris by directing high velocities of water against the interior pipe walls at various angles.15, 16 As the procedure connotes, hydrocleaning is extremely aggressive on high-performance linings applied to sewer interceptors. For context, visualize a 2,500 psi pressure washer with the 0-degree tip (jet) operating at a distance of 2 in. (51 mm) from the lined surface. The hydrodynamic forces (stresses) produced by high-velocity jet cleaning are considered extreme by any measure.

Fig. 9: High-velocity jet cleaning a ceramic epoxy-lined ductile iron pipe An extremely durable, low pigment-volume-concentration (PVC) coating formulation with excellent adhesion is certainly a requisite to withstand hydrocleaning. In the author’s experience, certain specialty, ceramic-modified amine epoxies have demonstrated their ability to withstand high-velocity jet cleaning. Additionally, it may be said that the foundation for success— the surface preparation—plays a significant role. Assuming that the coating achieves certain physical properties, what exactly allows this lining to withstand the hydrodynamic stresses? An objective observer cannot rule out superior adhesion to the substrate. Further, it is well understood that a uniform, angular anchor profile directly contributes to maximum adhesion. Therefore, the author submits that, in addition to a high-quality coating film, the ability to withstand high-velocity jet cleaning is a function of the quality of surface preparation—in this case, thorough rotary blasting of carbon steel or ductile iron sewer pipe. Conversely, the interior surface preparation of DI pipe is defined by the method in NAPF 500-03-04, Abrasive Blast CleaningInternal Pipe Surface. The standard requires that the entire surface to be lined shall be uniformly struck by the blast media. And like carbon steel pipe diameters of less than 42–48 inches, the interior preparation can only be accomplished adequately by employing rotary blasting equipment. Rotary blasting establishes a 90-degree angle of impact of the abrasive media to the interior surface to ensure removal of the annealing oxide layer on DI pipe as well as to properly profile the surface for optimum adhesion (Fig. 6). Otherwise, the annealing layer and other foreign contaminants may not be satisfactorily removed from the center section of the pipe, causing potential delamination or undercutting of the coating film. Damage from overblasting to the interior DI pipe normally does not occur.

Fig. 6: Rotary abrasive blasting the interior surfaces of ductile iron pipe Ductile (Cast) Iron Fittings NAPF 500-03-05, Surface Preparations Standard for Abrasive Blast Cleaning of Cast Ductile Iron Fitting, details four degrees of

abrasive blast cleaning. The selection depends on the type of service for which the DI fitting is intended and on the type of coating/lining specified. (Typical abrasive blasting of DI fittings is shown in Fig. 7.) Briefly described, the four degrees of blast cleaning are

Fig. 7: Uniformly abrasive blasting the interior surfaces of cast iron fittings using an angular abrasive

•

Blast Clean #1: no staining;

•

Blast Clean #2: no more than 5% staining;

•

Blast Clean #3: no more than 33% of staining; and

•

Blast Clean #4: no limit on staining that may remain on the surface, provided it is tightly adherent.

The Blast Clean #1 condition is the recommended degree of cleanliness, with a minimum 3.0-mil (76.2-micron), angular anchor profile for high-performance linings for severe wastewater environments (Fig. 8).

Fig. 8: Internally lining a ductile iron fitting following a Blast Clean#1

condition, 3.0 mils anchor profile Stainless Steel Stainless steel, a non-ferrous metal, is often selected as a construction material for sewer exposures because of its general corrosion resistance to these environments. This corrosion resistance is primarily attributed to a thin, inert, chromium-rich, transparent oxide film on the surface—the result of a process called passivation. However, some types/grades of stainless steel succumb to the aggressive nature of severe sewer environments and eventually corrode. A high-quality, high-performance lining system with low permeation properties to sewer gases can significantly extend the service life of stainless steel in these environments. As with ferrous metals, surface preparation is the key to achieving optimum adhesion—and ultimately protection—on stainless steels. Stainless steels should be uniformly abrasive blasted in accordance with SSPC-SP 16, Brush-Off Blast Cleaning of Coated and Uncoated Galvanized Steel, Stainless Steels, and Non-Ferrous Metals, again with a minimum 3.0-mil (76.2-micron),13angular anchor profile (Fig. 10). (Some manufacturers may require greater anchor profile.) Exercise care when selecting an abrasive material to ensure that it will not embed into the substrate, potentially causing bi-metallic corrosion. Generally, it is preferable to use only extremely hard mineral abrasives, such as garnet, aluminum oxide, and stainless steel grit, of suitable particle size. Also, given the reactive nature of stainless steels, this author suggests top-coating as quickly as possible after surface preparation, generally within 2 to 4 hours.

Fig. 10: Stainless steel surface following uniform abrasive blasting Summary Capital spending has not been keeping pace with the needs for wastewater infrastructure. While today’s sewerage systems have become more severe, municipal owners and engineers are expecting increasing performance—it is imperative these structures meet their anticipated design expectancy. This tenet also applies to the protection offered by high-performance lining systems. To maximize the service life of quality lining products it is critical that all substrates in the sewerage systems be prepared in the very best manner. The use of industry consensus standards and prevailing industry practices are paramount to achieving optimum protection of our critical wastewater assets with high-performance protective lining systems. Editor’s Note: This article, by Vaughn O’Dea, is part of the series of Top Thinker articles appearing in JPCL throughout 2012. Mr. O’Dea is one of 24 recipients of JPCL’s 2012 Top Thinkers: The Clive Hare Honors, given for significant contributions to the protective coatings industry over the past decade. The award is named for Clive Hare, a 20-year contributor toJPCL who shared his encyclopedic knowledge of coatings in many forums. Professional profiles of all of the award winners, as well as an article by Clive Hare, were published in a supplement to the August 2012 JPCL. REFERENCES

1. 2. 3. 4. 5.

American Society of Civil Engineers (ASCE), 2009 Report Card for America’s Infrastructure March 2009. American Society of Civil Engineers (ASCE), Failure to Act: The Economic Impact of Current Investment Trends in Wastewater Treatment Infrastructure, 2011. U.S. Environmental Protection Agency (EPA), Clean Water & Drinking Water Infrastructure Sustainability Policy, http://water.epa.gov/infrastructure/sustain, Washington, D.C. (2010). O’Dea, Vaughn, “Understanding Biogenic Sulfide Corrosion” Materials Performance, November 2007, pp. 36–39. U.S. Environmental Protection Agency (EPA), The Clean Water and Drinking Water Infrastructure Gap Analysis, EPA/816-R/02/020, Washington, D.C. (2002).

6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

O’Dea, Vaughn, Caleb Parker, and Rémi Briand, “Testing Permeation Resistance in Coatings for Wastewater Service,” Journal of Protective Coatings & Linings (JPCL), September 2010 pp. 16–28. SSPC-SP 13/NACE No. 6 (latest revision), “Surface Preparation of Concrete,” (Pittsburgh, PA: SSPC, and Houston, TX: NACE). NACE International (NACE) SP0892 (latest revision), “Coatings and Linings over Concrete for Chemical Immersion and Containment Service,” Houston, TX. International Concrete Repair Institute (ICRI) Technical Guideline No. 310.2, “Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, and Polymer Overlays,” (Rosemont, IL: ICRI). O’Dea, Vaughn, “Protecting Wastewater Structures from Biogenic Sulfide Corrosion,” JPCL (October 2007), pp. 52–56. SSPC-SP 5/NACE No. 1, “White Metal Blast Cleaning,” (Pittsburgh, PA: SSPC, and Houston, TX: NACE). National Association of Pipe Fabricators (NAPF) 500-03, “Surface Preparation Standard for Ductile Iron Pipe and Fittings in Exposed Locations Receiving Special External Coatings and/or Special Internal Linings,” Edmond, OK. SSPC-SP 16, “Brush-Off Blast Cleaning of Coated and Uncoated Galvanized Steel, Stainless Steels, and Non-Ferrous Metals,” (Pittsburgh, PA: SSPC) National Association of Sewer Service Companies (NASSCO), “Jetter Code of Practice,” (Owings Mills, MD: NASSCO). U.S. Environmental Protection Agency (EPA), Collection System O&M Fact Sheet: Sewer Cleaning and Inspection, EPA/832-F/99/031, Washington, D.C. (1999). U.S. Environmental Protection Agency (EPA), Sewer Sediment and Control: A Management Practices Reference Guide, EPA/600/R-04/059, Washington, D.C. (1999). THE JOURNAL OF PROTECTIVE COATINGS & LININGS ©2012 Technology Publishing Company

34.Influence of UHP Waterjetting on Shop-Primed Steel in New Construction, Part 3 From JPCL, August 2012 Philippe Le Calvé DCNS, France Philippe Le Calvé is responsible for R&D, paint technology, for DCNS, a military shipyard in France, where he has worked for 25 years. For the past 10 years, he and his co-workers have been involved with, and have written articles on, the use of UHP waterjetting as a surface preparation technology. Jean-Pierre Pautasso Direction Générale de l’Armement, France Nathalie Le Bozec French Corrosion Institute, France

Philippe Le Calvé

Surface preparation processes influence the performance and lifetime of coating systems applied to steel substrates. The state of the steel surface immediately before painting is crucial. The main factors influencing the performance are the presence of rust and mill scale; surface contaminants including dust, salts, and grease; and surface profile. For aggressive environments such as marine atmospheres of C5M corrosivity category and for high-performance coatings that require cleaner and/or rougher surfaces, blast cleaning is often the preferred method of surface preparation. However, it is well known that abrasive cleaning can produce a considerable amount of waste, mainly containing blasting media, old removed paint, and rust products. As an alternative to abrasive cleaning for maintenance work or complete renovation, ultra-highpressure (UHP) waterjetting is becoming common as long as the performance of the coatings on steel structures is not affected. UHP waterjetting technology has been described intensively in previous papers.16 There are, however, questions about its suitability for new (naval) constructions.

Courtesy of DCNS. Due to these questions, a project was started with the purpose of reinforcing the knowledge about the behavior of different paint systems for highly corrosive marine environments (C5M) and, more particularly, for assessing UHP waterjetting performance in relation to abrasive blasting on steel coated with a zinc-rich shop primer (ZRP).7-10

All other images and figures are courtesy of the authors. Courtesy of DCNS. In the first stage of the study, the characterization of surfaces after UHP waterjetting of shop primed steel surfaces was reported in the April/June 2011 issue of PCE as well as the May 2011 JPCL, and in the second part (reported in July/Sep 2011 issue of PCE and September 2011 JPCL), the performance of seven paint systems applied on UHP (DHP4) treated ZRP-coated steel flat panels and welded panels was studied in laboratory and field tests.10 The results were compared with conventional abrasive blasted (Sa 2.5 MG) surfaces. It was concluded that UHP waterjetting was a promising technique for steel surface preparation within the scope of new constructions (on ZRP-coated steel). The results showed behavior of UHP waterjetting comparable to standard surfaces after abrasive blasting. Despite a slight difference in the roughness compared to abrasive blasting, coating performance did not seem to be affected. However, some results remained inconclusive regarding welded panels as a consequence of inhomogeneous weld area.

In this article, the authors describe the third and final part of the study, which involved testing three paint systems over UHP waterjetted ZRP panels, including more representative welded panels, compared to conventional grit blast-treated panels. Experimental Conditions In this study, an effort was made to design an appropriate welded sample, including a mixed zone at the periphery of the weld seam cleaned by UHP waterjetting to get a surface cleanliness DHP4. Partially cleaned ZRP-coated steel flat panels, treated with UHP to get a DHP1 cleanliness, were also considered. These were compared to conventional blasted surface (Sa 2.5 MG). Three different paint systems were applied on the various panel designs and roughnesses, and they were exposed to cyclic corrosion tests and natural weathering. Test Panels, Surface Preparation, and Coating Test panels of DH36 steel, commonly used in naval constructions, with different surface preparations representing the different practices used on a newbuild structure, were selected. As shown in Table 1, the steel plates had first been grit blasted (metallic abrasives) to grade Sa 2.5 and coated with a zinc-rich shop primer (zinc silicate, 10-15 μm) to create the initial conditions (i.e., steelmaker delivery standard). Two designs of test panels were considered: flat panels (100 x 175 mm) and welded panels (320 x 250 mm). TABLE 1

Description of Steel Samples Test Piece Reference

T1

Steel Grade Initial State Test Piece Configuration 6-Month Natural Aging

T3

DH36 Cleaning up to Sa 2.5 (grit and shot mixed) + zinc rich primer (10-15 μm) Welded panel (320 x 250 mm, 10-mm thick)

Flat panel (175 x 100 mm, 5.5mm thick)

Yes

Yes

Yes

Surface Preparation Grit blasting UHP waterjetting Sa 2.5 (ISO 8501-1) ; MG DHP4: complete ZRP cleaning and oxide removal in the (ISO 8503-1) mixed zone at weld area periphery

UHP waterjetting DHP1: partial ZRP cleaning

The flat test pieces were then cleaned by UHP waterjetting on only one side, to treatment degree DHP1, light cleaning according to NF T 35-520 standard (“surface shall be free from oil, mud, grease, caking, poorly adhering former paint, poorly adhering rust and mill scale, former coatings and any foreign matter. At this treatment degree, 70% of the surface is still partially covered by former coatings”). Details on the UHP waterjetting parameters are given in Table 2. TABLE 2

Selected UHP Waterjetting Parameters (According to NF T 35-520) UHP Waterjetting – Requirement NF T35 520

DHP4

DHP1

Test Piece Configuration

Welded test pieces

Flat test pieces

Cleaning Parameters

Pressure: 2400 bars Progression: 1 m/min Distance: 50 mm Rate: 13 l/min

Pressure: 1125 bars Progression: 1.5 m/min Distance : 70 mm Rate: 17 l/min

The welded samples consisted of two panels assembled by conventional welding for ship construction. At the center of the welded panels, a 120-mm-wide strip at right angles to the weld was machined, as shown in photographs in Fig. 1. Then, in order to mimic shipyard conditions when the ZRP is depleted during construction phases, the welded panels were exposed outdoors for six months in the shipyard at Lorient before secondary surface preparation and painting (The site is classified C2 on steel: corrosion rate, 195.8 +- 4.6 g/m2 per year, i.e., 24.9 +-0.6 μm/year).

Fig. 1: Photographs of the welded panels (A-D) as a function of surface preparation stages and flat test panel DHP1 (E). (from left to right) Welded test piece before natural aging; Welded test piece after outdoor exposure; Welded test piece after DHP4, OF1 UHP cleaning; Welded test piece after grit blasting Sa 2.5; and Flat test piece DHP1 A B Then, half of the panels were abrasive blasted to Sa 2.5 grade while the other half were cleaned by UHP waterjetting on one side to get a surface cleanliness DHP4, OF1 according to the NF T 35-520 standard (“surface shall be free from oil, mud, grease, caking, poorly adhering former paint, poorly adhering rust and mill scale and any former coatings or foreign matter. The exposed steel must be uniform and have an “original metallic colour”). Photographs of the different steps in the preparation of welded samples are shown in Fig. 1. The roughness of the different areas of the welded panels was measured after the UHP waterjetting (DHP4) and is summarized in Table 3. It should be remembered that after abrasive blasting to Sa 2.5 MG, the measured roughness Ra ranged from 9 to 12 μm while the machined area roughness (after machining and before rusting) was from 0.3 to 0.7 μm (Ra). TABLE 3

Surface Roughness of Pre-Rusted Welded Panel Location on Welded Panel

Ra (μm)

Area 1: Machined steel (central section) 4.4 ± 1.1 Area 2: ZRP DHP4

7.1 ± 0.9

Area 3: Machined weld

6.4 ± 1.9

Once cleaned by either UHP waterjetting or blasting, the flat and welded samples were painted using three different commercial paint systems selected from the preliminary phase of this study.10 As indicated in Table 4, two of them were based on an inhibiting protection mechanism, while the other operated on the barrier effect. TABLE 4

Paint and Category Protection System Protection Category Primer Nature Barrier Effect Inhibitor Effect S1 S2 R

X X

Dry Film Thickness, μm 350 350

X

240

Before testing, scribes down to the steel substrate were made using a scribing tool equipped with a rectangular blade of 0.5 mm. On flat samples, a vertical scribe parallel to the longest side of 100 x 0.5 mm was made in compliance with the previous phase of the study.10 For the welded test panel, several areas were considered, and, therefore, a scribe was made in each of the five areas being considered (Fig. 2).

Fig. 2: Position of the scribes and pull-off test dollies on the welded test panel (dimensions are given in mm) Artificial Ageing Test and Field Test The corrosion performance of the paint systems as a function of surface preparation was carried out in the laboratory according to the C5M test cycle described in Fig. 3, a test that was implemented during the study preliminary phase.11 The duration of the test was 4,200 hours.

Fig. 3: Basic artificial weathering cycle used in the study Outdoor exposure was carried out at the marine site at Brest (classified C5M on steel, according to ISO 9223). Two duplicate samples per system, except abrasive-blasted welded samples, were exposed at 45 degrees facing south. The minimum duration of the test will be four years with intermediate inspections, and, at the time of writing this article, two years’ evaluations were available. Assessments Visual Assessment ISO 4628-2 to -6 standards have been used to assess paint defects, such as blistering, rusting, cracking, and chalking. For delamination measurement from the scribes, two methods have been used as described and illustrated in Fig. 4.

Fig. 4: Assessment of scribe creep. Left: M1=(V-scribe width)/2 This measurement method has been used for intermediate measurements in particular. Right: M4=(C’-scribe)/2 where C’ = ΣC’n/n This measurement has been used after removal of the coating once C5M test was completed. Pull-Off Adhesion Test The pull-off adhesion tests were carried out according to ISO 4624 standard using a hydraulic pull-off device on unexposed references and after completion of the C5M cycle. Twenty-millimeter diameter dollies glued to the coating were used, and the tests were carried out in laboratory conditions (23.8 C – 45.1% RH). Figure 2 indicates the position of the dollies as a function of the area on the welded test pieces. Assessment Requirements For accelerated corrosion tests, the assessment of test pieces cleaned by UHP waterjetting was carried out according to the acceptance requirements defined in ISO 20340 (Table 5) and compared to abrasive blasting performance. TABLE 5

Assessment Criteria According to ISO 20340 Criteria

Standard Acceptance Thresholds Established at the End of the Ageing Cycle (ISO 20340)

Defects before and after aging

ISO 4628- 0 (S0) 2 Ri 0 ISO 46283

Peeling-corrosion around the scribe

ISO 4628- Max < 8 mm for the coating system with zinc-free primer 8 and ISO 20340

Adhesion before C5M weathering test

Minimum pull-off test value: 4 MPa for the coating system with zinc-free primer No adhesion ISO 4624 defect between the substrate and the first layer except if pull-off values exceed or equal 5 MPa

Adhesion after C5M

ISO 4624 Minimum pull-off test value=50% of the initial value with a minimum value of 2 MPa No

weathering test

adhesion defect between the substrate and the first layer except if pull-off values exceed or equal 5 MPa

Results Cyclic Corrosion Test C5M Flat test panels: No degradation such as blistering, rusting, cracking, and chalking was observed on any of the paint systems. However, a loss of brightness was seen on S2 paint system. Visible degradations for all test pieces were red rust runs from the scribes. Regarding flat test panels of DHP1 surface preparation grade, a variable degree of creep from the scribe line was observed with the different paint systems, as shown in Fig. 5. Thus, paint system S1 was clearly less efficient than the other two systems, S2 and R. This has already been observed in a previous study where the same system (except for the first layer) was tested.10 For the other two paint systems (S2 and R), the results were comparable between UHP-treated DPH4 and grit-blasted Sa 2.5 surface states.

Fig. 5: Delamination from the scribes on flat test pieces after 6 months of C5M test. Paint system adhesion results are summarized in Table 6. These show satisfactory behavior of paint systems S2 and R on a ZRP UHP-waterjetted DHP1 surface state. The behavior was the same as for the abrasive-blasted surface (data from a previous study), indicating no alteration of the coating performance on ZRP completely (DHP4) or partially (DHP1) cleaned steel surfaces. Nevertheless, the results highlighted the poor behavior of system 1. TABLE 6

Pull-Off Test Values on Flat Samples after Six Months of C5M Cycle Corrosion Test* Paint System

Pull-Off Test Value, MPa T1 (Sa 2.5)

T3 (DHP1)

S1

15.7±1.1

11.0±2.3

S2

12.2±3.2

14.6±1.2

R

12.8±1.9

9.4±1.9

*T1: Sa 2.5, T3: DHP1. Data on T1 surface state from Ref 10 Welded test panels: As with the flat test panels, no degradation such as blistering, rusting, cracking, and chalking was observed on any of the paint systems. Only corrosion from the scribes was present.Figure 6 (p. 50) presents the scribe creep measured on the welded test panels after six months of C5M test for both Sa 2.5 abrasive-blasted surface (T1) and DHP4 UHP-treated samples (T3). As mentioned in the experimental section regarding the design of the welded samples, five scribe lines were applied to assess the coating performance on the surface properties. From the results, abrasive blasting gives satisfactory behavior whatever the locations on the welded sample, in particular when considering systems S2 and R. It is interesting to note that the weld area periphery (scribes 2 and 5) or machined area (scribe 3, 4, and 5) are not significantly more affected than the reference surface (scribe 1).

Fig. 6: Influence of surface preparation (left: abrasive blasting Sa2.5 - T1; right: UHP watterjetting DHP4 – T3) of welded test pieces on the delamination from the scribes after 6 months of C5M cycle test. The labels 1 to 5 refer to the 5 scribes as shown on the scheme in the right-hand graph. This test also clearly highlights the difference in behavior between the three paint systems applied on abrasive-blasted samples. Only system S1 did not satisfy the aging resistance criteria defined in Table 5. Indeed, the average scribe creep after coating removal of the five scribes gives the following values per paint system: S1 = 11 mm; S2 = 7.8 mm; S3 = 2.2 mm. Regarding UHP-waterjetted (DHP4) samples, system S1 again gave unsatisfactory results, even worse than the abrasive-blasted surface. Nevertheless, for the two other paint systems, S2 and R, there was no significant difference between the two surface preparation modes. The average scribe creep after coating removal of the five scribes was the following: S1=17.4 mm; S2=7.6 mm; S3=3 mm. It should be noted, however, that on paint system S2, an unsatisfactory value of scribe creep was measured at scribe 2, located on the as-fabricated weld area with an average value of 13 mm. This may be observed on the photographs in Fig. 7. They also clearly highlight the degree and extent of corrosion upon the surface state, with an obvious remarkable behavior of the UHP DHP4 machined area in the center of the samples.

Fig. 7: Photographs of test panels S2T3 (DHP4) after six months of C5M test – (left): before coating removal around the scribe, (center): details of scribe 3 and (right): after coating removal. Paint system R presented a marked and constant behavior regardless of the scribe location, whereas extremely different roughness and surface profile levels were tested. The scribe creep was far below the requirements (