Caltex Materials of Construction
March 10, 2017 | Author: glazetm | Category: N/A
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SECTION 1
MATERIALS OF CONSTRUCTION
CALTEX REFINERY MATERIALS MANUAL
October 1999
SECTION 1 MATERIALS OF CONSTRUCTION
TABLE OF CONTENTS 1.0
1.1 1.2 1.3 1.4 1.5 1.6
MATERIALS OF CONSTRUCTION CONSTRUCTION................................ ................................................................ ......................................... .........1 1
CARBON STEEL ............................................................................................................................1 LOW ALLOY (CARBON - 0.5MO) ..................................................................................................1 LOW ALLOY (CR-MO ALLOYS) (1.25CR-0.5MO - 9CR-1MO) ........................................................1 LOW ALLOY (AISI 4140, 4340) ....................................................................................................1 LOW ALLOY (2.5NI, 3.5NI)..........................................................................................................2 STAINLESS STEELS ........................................................................................................................2 1.6.1 Ferritic/Martensitic ...............................................................................................................2 1.6.2 Austenitic ............................................................................................................................2 1.6.3 Duplex Ferritic/Austenitic .....................................................................................................3 1.6.4 A286 ....................................................................................................................................3 1.7 NICKEL ALLOYS............................................................................................................................3 1.7.1 20Cb3 (Alloy 20).................................................................................................................3 1.7.2 Alloy 800.............................................................................................................................3 1.7.3 Alloy 825.............................................................................................................................3 1.7.4 Alloy 600.............................................................................................................................4 1.7.5 Alloy 625..............................................................................................................................4 1.7.6 Alloy B..................................................................................................................................4 1.7.7 Monel 400 ...........................................................................................................................4 1.8 COPPER ALLOYS...........................................................................................................................4 1.8.1 Admiralty Brass.....................................................................................................................4 1.8.2 Aluminum Brass...................................................................................................................5 1.8.3 Naval Brass...........................................................................................................................5 1.8.4 Copper-Nickel Alloys (70-30 and 90-10).............................................................................5 1.8.5 Aluminum Bronze..................................................................................................................5 1.9 TITANIUM ....................................................................................................................................5 1.10 ALUMINUM .................................................................................................................................6 1.11 HARD FACING ALLOYS (Stellite)..................................................................................................6
2.0
2.1
COATINGS ................................................................ ................................................................................................ .................................... .... 11
FUNDAMENTALS OF COATING TECHNOLOGY ..........................................................................11 2.1.1 Coating System Composition .............................................................................................12 2.1.2 Coating Composition ........................................................................................................12 2.1.2.1 2.1.2.2
2.2
The Pigment............................................................................................................................ 12 The Vehicle ............................................................................................................................. 13
2.1.3 Methods Of Cure .................................................................................................................15 PROPERTIES OF PAINTS ..............................................................................................................17 2.2.1 Oil Paints............................................................................................................................17 2.2.2 Oleoresinous Paints ..............................................................................................................18 2.2.3 Alkyd Paints..........................................................................................................................18 2.2.4 Phenolic Paints .....................................................................................................................18 2.2.5 Epoxy Paints.........................................................................................................................18 2.2.6 Lacquer Type Paints............................................................................................................19
CALTEX REFINERY MATERIALS MANUAL
October 1999
2.8
2.2.7 Vinyl Paints.........................................................................................................................19 2.2.8 Chlorinated Rubber Paints ..................................................................................................19 2.2.9 Latex Paints ........................................................................................................................19 2.2.10 Epoxy-Coal Tar Paints.........................................................................................................20 2.2.11 Silicones..........................................................................................................................20 2.2.12 Polyurethane or Urethane Paints .....................................................................................20 2.2.13 Silicone Alkyd Paints........................................................................................................20 2.2.14 Vinyl Alkyd Paints ............................................................................................................20 2.2.15 Acrylic Paints...................................................................................................................20 2.2.16 Wash Coat Pretreatment .................................................................................................21 2.2.17 Bituminous Paints............................................................................................................21 2.2.18 Mastics and Cements ......................................................................................................21 2.2.19 Special Purpose Paints .....................................................................................................21 COATING SELECTION ................................................................................................................22 2.3.1 Service Exposures................................................................................................................22 2.3.2 Selection of Paints...............................................................................................................22 INSPECTION ..............................................................................................................................25 TYPES OF COATING PROBLEMS AND CAUSES............................................................................26 2.5.1 Lifting .................................................................................................................................26 2.5.2 Blushing..............................................................................................................................26 2.5.3 Orange Peeling ...................................................................................................................26 2.5.4 Checking, Crazing ..............................................................................................................26 2.5.5 Fisheyes ..............................................................................................................................27 2.5.6 Cracking .............................................................................................................................27 2.5.7 Embrittlement.....................................................................................................................27 2.5.8 Softening............................................................................................................................27 2.5.9 Chalking .............................................................................................................................27 2.5.10 Undercutting ..................................................................................................................27 2.5.11 Blistering.........................................................................................................................27 PAINT COST...............................................................................................................................28 TEMPORARY PROTECTION .........................................................................................................29 2.7.1 Grease Preventives ..............................................................................................................29 2.7.2 Oil Preventives ....................................................................................................................29 2.7.3 Solvent Cut Back Preventives...............................................................................................29 2.7.4 Strippable Plastics ...............................................................................................................30 GALVANIZING............................................................................................................................30
3.0
PLASTICS ................................................................ ................................................................................................ ....................................... ....... 33
4.0
REFRACTORIES ................................................................ ................................................................................................ ................................ 37
2.3 2.4 2.5
2.6 2.7
3.1 THERMOPLASTICS .........................................................................................................................34 3.2 THERMOSETTERS..........................................................................................................................34
4.1
MATERIAL CLASSIFICATION .......................................................................................................37 4.1.1 Castable and Gunning Mixes ..............................................................................................37 4.1.2 Vibration Castable...............................................................................................................38 4.1.3 Plastics................................................................................................................................38 4.1.4 Ramming Mixes..................................................................................................................39 4.1.5 Chemical Setting Mixes ......................................................................................................39 4.1.6 Fiber Linings .......................................................................................................................39 4.1.7 Bricks/Formed Shapes .........................................................................................................40 4.2 MATERIAL SPECIFICATIONS........................................................................................................40 4.2.1 Chemical Composition........................................................................................................40
CALTEX REFINERY MATERIALS MANUAL
4.3 4.4 4.5 4.6 4.7
October 1999
4.2.2 Bulk Density........................................................................................................................40 4.2.3 Cold Crushing.....................................................................................................................41 4.2.4 Permanent Liner Change ....................................................................................................41 4.2.5 Thermal Conductivity .........................................................................................................41 4.2.6 Abrasion Resistant ...............................................................................................................41 4.2.7 Temperature.......................................................................................................................41 4.2.8 Porosity ..............................................................................................................................41 MATERIAL TESTING ....................................................................................................................43 DESIGN ......................................................................................................................................43 ANCHORING SYSTEMS AND STEEL FIBERS .................................................................................44 INSTALLATION ...........................................................................................................................44 CURING AND DRYOUT ..............................................................................................................45
TABLE OF TABLES Table 1-1a NOMINAL COMPOSITION ...................................................................................................7 Table 1-1b COMMON ASTM SPECIFICATIONS FOR FREQUENTLY USED ALLOYS ....................................9 Table 1-2 CLASSIFICATION OF COATINGS BY METHOD OF CURE ......................................................16 Table 1-3 OVERCOATING TIMES OF SELECTED PAINTS .......................................................................17 Table 1-4 PRINCIPLE ADVANTAGES/DISADVANTAGES OF FREQUENTLY USED INDUSTRIAL COATINGS23 Table 1-5 RECOMMENDED COATING TYPES ........................................................................................25 Table 1-6 AVERAGE JOB BREAKDOWN ..................................................................................................28 Table 1-7 GENERAL TYPES OF REFRACTORY MATERIAL FOR CHEMICAL PROCESS INDUSTRY (CPI) USE......................................................................42 Table 1-8 SELECTION OF REFRACTORIES FOR REFINERY USAGE ............................................................42
CALTEX REFINERY MATERIALS MANUAL
October 1999
CALTEX REFINERY MATERIALS MANUAL
1.0
October 1999
MATERIALS OF CONSTRUCTION
1.1
CARBON STEEL Carbon steel is the basic material used in refinery construction. It is selected based on cost, availability and suitability for general service. At higher temperatures above 800oF (427oC) and in corrosive environments, other materials are usually more economical. Carbon steel's strength decreases rapidly above 800oF (427oC) as well as its resistance to graphitization. Oxidation resistance above 1000oF (538oC) and sulfidation resistance above about 500oF (260oC) are problems. Other problems include resistance to hydrogen attack in hydrogen environments at temperatures over about 450oF (232oC) and problems with environmental cracking in aqueous sulfide, caustic and amine solutions in welded equipment. Depending on chemistry and steel making practice, some carbon steels may be susceptible to brittle failure as high as 100oF (38oC) while others are satisfactory down to approximately -50oF (-46oC). As more alloying elements are added, overall cost for all product forms goes up.
1.2
LOW ALLOY (CARBON - 0.5MO) Carbon-0.5Mo has better elevated temperature strength than carbon steel and was thought to have increased resistance to hydrogen attack in hydrogen environments. Unless chemistry, steel making and fabrication procedures are strictly followed, carbon-0.5Mo steels can have very poor notch toughness (resistance to brittle failure) in thicker sections greater than 3/4 inch. Because of variable hydrogen attack resistance, carbon-0.5Mo has not been used for new construction, although a considerable amount of equipment is in service. "GPS A-9 Selection of Metallic Materials" prohibits the use of carbon 0.5Mo steel.
1.3
LOW ALLOY (CR-MO ALLOYS) (1.25CR-0.5MO - 9CR-1MO) Increasing Cr content gives better high temperature strength than carbon steel, increasing oxidation resistance and hydrogen attack resistance. Sulfidation resistance in environments with no hydrogen is considerably improved over carbon steel. Notched toughness can be considerably improved over carbon steel with proper chemistry and heat treating controls. In service ductility problems leading to serious cracking can be reduced with chemistry and heat treating controls. These alloys have good hardenability and must be pre and postweld heat treated to have acceptable ductility for service. Many reactors and other heavier wall equipment greater than one inch can have serious cracking and/or ductility problems after service above roughly 650oF (363oC). Chemistry and heat treating restrictions can minimize these potentially serious problems on new equipment. Special inspection and startup/shutdown handling procedures may be required for existing susceptible equipment.
1.4
LOW ALLOY (AISI 4140, 4340) These alloys are hardenable by heat treatment and offer the high strength at temperatures up to about 800oF (427oC) needed for bolting, compressor and pump shafts and sometimes impellers. The alloys are weldable with special procedures and proper heat treatment. However, because of the high strength levels, they are very susceptible to sulfide stress corrosion cracking in wet sulfide environments. Special heat treatments can minimize the cracking potential.
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CALTEX REFINERY MATERIALS MANUAL
October 1999
1.5
LOW ALLOY (2.5NI, (2.5NI, 3.5NI) The low nickel alloys are used because of their improved notch toughness at lower temperatures if properly fabricated and heat treated. While certain carbon steels can be used down to -50oF (-46oC), 3.5Ni can develop good notch toughness down to -150oF (-101oC). Proper heat treatment is necessary to develop the desired properties. The low nickel alloys may require more careful temperature control during postweld heat treatment/tempering than the Cr-Mo steels to develop desired properties.
1.6
STAINLESS STEELS
1.6.1
Ferritic/Martensitic Chromium contents in the 11 to 18 percent range give these steels good resistance to sulfide corrosion with or without hydrogen in the environment, good oxidation resistance and good resistance to chloride stress corrosion cracking. The ferritic stainless steels generally are not hardenable by heat treatment but can develop very low ductility because of grain growth during welding. Type 430 is susceptible to sigma phase formation at temperatures over 1050oF (566oC). However, it is rarely used at temperatures this high because of strength considerations . Types 405 and 409 are susceptible to service induced ductility problems at 650o - 1050oF (343 - 566oC). This is commonly referred to as "885oF embrittlement". The loss of ductility may show up as welding or tray straightening problems and can generally be solved, at least temporarily, with an embrittlement erasing heat treatment at 1100oF (593oC) to allow welding or straightening. The ASTM A240 Grade 26-1 alloy has very good sulfide, oxidation and chloride stress corrosion cracking resistance. However, it has ductility problems as welded because of grain growth and is vulnerable to 885oF (474oC) and sigma phase embrittlement problems. The martensitic stainless steels can be hardened by heat treatment and can reach hardness levels (generally greater than 200 Brinell hardness) that make them susceptible to sulfide stress corrosion cracking in wet sulfide environments. Welding requires preheat and postheat treating to guarantee usable service properties. CA6NM is used for castings because it is easier to cast than the standard 12Cr (CA15) material. CA6NM requires a difficult double temper to minimize high hardness that would make it very susceptible to sulfide stress corrosion cracking. Carbon and silicon must be limited to 0.3% and 0.05% respectively in order to meet HRC22 even after a double temper. Type 410S has lower carbon and will generally be less susceptible to developing high hardness during welding. All of these alloys may be vulnerable to pitting problems due to underdeposit or oxygen concentration cells.
1.6.2
Austenitic The austenitic stainless steels are nominally 18Cr - 10Ni with various other elements added for specific reasons. They have good overall resistance to oxidation [up to about 1500oF (816oC)] and sulfidation in both hydrogen and hydrogen free environments. They have good elevated temperature strength [up to roughly 1400oF (760oC)]. The molybdenum bearing grades (types 316 and 317) have good resistance to naphthenic acid corrosion with resistance increasing with higher molybdenum content. Types 321 with titanium and 347 with niobium (columbium) are very resistant to sensitization and intergranular polythionic acid cracking if properly heat treated during product form manufacture. The L or low carbon grades can usually be welded without
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CALTEX REFINERY MATERIALS MANUAL
October 1999
sensitizing (forming grain boundary carbides) that makes the alloy susceptible to intergranular cracking. If service temperatures are low enough [below 750oF (399oC)], they will not sensitize during service. The alloys in this group are all susceptible to chloride stress corrosion cracking in aqueous conditions, although the molybdenum alloys have better pitting resistance. The nonstabilized (i.e. no titanium or niobium added) grades are susceptible to sensitization and intergranular corrosion in many refinery environments after fabrication and/or service exposure above about 750oF (399oC). The niobium stabilized grade type 347 is sensitive to hot short and other weld cracking problems in sections over about 3/4 inch thickness. Type 347 corrosion protection overlay often used on heavy wall reactors is susceptible to hot short and sigma phase formation problems if the proper chemistry is not laid down. The titanium stabilized alloy, Type 321, has shown poor stress rupture properties above about 1100oF (593oC) so type 347 has been used for heater tubes. 1.6.3
Duplex Ferritic/Austenitic The duplex stainless steels have the good overall corrosion resistance of the austenitic stainless steels but are not as susceptible to chloride stress corrosion cracking. The duplex stainless steels are generally more resistant to pitting problems. They are not as easy to weld as the austenitic stainless steels and will embrittle above about 650oF (343oC) because of the extensive ferrite phase present in the microstructure.
1.6.4
A286 A286 is an iron based Ni-G superalloy alloy used primarily for its high temperature strength and thermal expansion characteristics similar to austenitic stainless steels. Its ductility is very dependent on proper heat treatment and does not have much of a strength advantage over the austenitic stainless steels over about 1300oF (704oC). It has been used for high temperature bolting such as the internal bolting in FCCU slide valves.
1.7
NICKEL ALLOYS
1.7.1
20Cb3 (Alloy 20) 20Cb3 is an Fe-Ni-Cr-Cu-Mo-Cb alloy that is used for resistance to sulfuric acid in alkylation units. It is also more resistant to chloride stress corrosion cracking than the 300 Series stainless steels. It is difficult to weld (hot short) and can be difficult to cast without defects for pumps and valves.
1.7.2
Alloy 800 Alloy 800 is an Fe-Ni-Cr alloy that has generally good resistance to sulfidation, oxidation and better high temperature strength than the 300 Series stainless steels. Although not immune to chloride stress corrosion cracking, it has better resistance than the 300 Series stainless steels. It will sensitize and be vulnerable to polythionic acid cracking when furnished coarse grained. Typical of nickel alloys, cleaning sulfide scales from the surface when repair welding is necessary to prevent cracking due to formation of a low melting Ni sulfide phase in the grain boundaries.
1.7.3
Alloy 825 Alloy 825 is an Ni - Fe - Cr -Mo - Cu - Ti alloy similar to 20Cb3 except it has more nickel making it very resistant to chloride stress corrosion cracking. Alloy 825 has very good general corrosion resistance and generally will not sensitize. Alloy 825 is sensitive to sulfide problems during repair welding but is easily welded with proper precautions. Alloy 825 has good resistance to
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CALTEX REFINERY MATERIALS MANUAL
October 1999
ammonium bisulfide corrosion and along with Alloy 800 is used for tubes in hydroprocessing reactor effluent air fan coolers. 1.7.4
Alloy 600 Alloy 600 is an Ni-Cr-Fe alloy with good high temperature strength. The high nickel content and lower chromium level makes the alloy vulnerable to sulfide corrosion above about 750o-800oF (399oC-427oC)) particularly in hydrogen environments. Alloy 600 has good oxidation resistance but will sensitize and be vulnerable to intergranular cracking problems. Being a high nickel alloy, it is very sensitive to sulfur or sulfides when being repair welded and very strict cleaning procedures are necessary to prevent intergranular cracking due to nickel sulfide formation.
1.7.5
Alloy 625 Alloy 625 is a Ni-Cr-Mo-Cb alloy that has good resistance to sulfide corrosion, oxidation, a high resistance to pitting and good high temperature strength. It has been used for expansion bellows on FCC units. Alloy 625 will embrittle at temperatures over about 1050oF (566oC) and lose considerable ductility. Alloy 625 is very resistant to chloride stress corrosion cracking. The high Mo content makes the alloy very resistant to naphthenic acid corrosion.
1.7.6
Alloy B Alloy B is a Ni -Mo alloy that has good high temperature strength but is best known for its corrosion resistance to reducing acids such as HCl. It is resistant to chloride stress corrosion cracking but can be sensitized and is therefore vulnerable to intergranular corrosion problems. Alloy B-2 has a modified chemistry and will not sensitize. Both Alloy B and B-2 can suffer catastrophic corrosion when exposed to certain oxidizing species.
1.7.7
Monel 400 Monel 400 is a Ni-Cu alloy that has good resistance to caustic and HCl at low concentrations. It has been used as cladding for atmospheric column top section corrosion protection. Monel 400 is very sensitive to nickel sulfide formation during repair welding. Monel will stress corrosion crack in ammonium chloride. Monel is used in HF alkylation service because of its good corrosion resistance to HF. In general, the nickel based or high nickel alloys offer much better corrosion and chloride stress corrosion cracking resistance than the 300 Series stainless steels. They are considerably more expensive and may be vulnerable to some side issue degradation problems.
1.8
COPPER ALLOYS
1.8.1
Admiralty Brass Admiralty is a Cu-Zn-Sn alloy used as condenser and/or cooler tubes because of its good resistance to brackish water. It has reasonable resistance to process side sulfide corrosion but will stress corrosion crack in solutions containing ammonia, and/or ammonium chloride and oxygen. It will dezincify in aggressive waters under deposits even though it has dezincification inhibitors As, Sb or P. Admiralty has marginal resistance to sea water corrosion but is the standard refinery condenser material in fresh and/or brackish water. In some services, water wash ammonium chloride deposits off of bundles before opening to the atmosphere to minimize stress corrosion cracking.
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CALTEX REFINERY MATERIALS MANUAL
October 1999
1.8.2
Aluminum Brass Aluminum brass is very similar to admiralty with the same good features and problems. It is better than admiralty in sea water.
1.8.3
Naval Brass Naval brass is a Cu-Zn alloy that is generally used for tubesheets in condensers and/or coolers. As a high zinc copper alloy it is vulnerable to dezincification. The dezincification is usually not a serious problem for tubesheets because of their thick section size.
1.8.4
Copper-Nickel Alloys (70-30 and 90-10) The two Cu-Ni alloys are generally very corrosion resistant in sea water as well as fresh and brackish water. The lower nickel alloy does not have as good a resistance to sulfide on the process side as the 30 percent nickel alloy. Both alloys are susceptible to under-deposit attack but handle higher velocity waters better than admiralty and aluminum brass. The Cu-Ni alloys are very resistant to ammonium chloride stress corrosion cracking. The cost of these alloys is high and they have been replaced with titanium in some services. The Cu-Ni alloys are weldable.
1.8.5 Aluminum Bronze This alloy is used in sea water for pumps and condenser/coolers for channels and floating heads. It can be furnished as plate or cast. Aluminum bronze is weldable with difficulty. 1.9
TITANIUM Titanium, usually Grade 2, is used for exchanger, condenser and/or cooler tubing in sea water or brackish water service. Titanium is very corrosion resistant in many refinery type services but is vulnerable to hydriding and crevice corrosion in chlorides. The thin wall titanium tubes need more support than regular TEMA R design. Vibration can be a major tube bundle problem. When the tube wall temperature exceeds about 170oF (77oC), Grade 2 will pit under sodium chloride and/or ammonium chloride deposits or in crevices. Grade 12 has better chloride pitting resistance [up to about 350oF (177oC)]. Titanium is very susceptible to hydriding above 180oF (82oC). Temperature increases hydrogen solubility while stress decreases solubility. Hydriding by hydrogen pickup from service or by being cathodic to most other metals will seriously embrittle titanium and cause very low ductility, making handling a problem. The allowable stress drops off rapidly with temperature even at 100oF (38oC). It is important, therefore, to accurately specify the design temperature for a solid tubesheet where there is a differential temperature. Titanium is cathodic to most other materials so Cu-Zn alloy tubesheets will corrode with titanium tubes. Aluminum bronze does better but may require coating to minimize corrosion. The disadvantage of coatings is that pinholes can accelerate attack (large cathode, small anode). There is little driving force for galvanic corrosion with CuNi (70-30) or Monel with titanium tubes. CuNi (90-10) has low strength as a tubesheet and will cause problems when rolling the stronger Grade 2 titanium tubes. Titanium will salt plug with low velocities in sea water. Titanium is not as sensitive to impingement problems as copper based alloys. Do not bell tube ends; titanium tends to split or push out of the roll in the tubesheet. Titanium tubing needs to be treated to minimize biofouling.
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CALTEX REFINERY MATERIALS MANUAL
October 1999
1.10
ALUMINUM Aluminum has been used in refinery service particularly in sour water stripper units because it is very resistant to wet hydrogen sulfide corrosion. However, aluminum is very vulnerable to heavy metal ion pitting problems and will deteriorate very rapidly in a caustic environment. Aluminum melts at a low temperature [approximately 1100oF (593oC)] and is considered a hazard for pressure containment under fire conditions.
1.11
HARD FACING ALLOYS (STELLITE) These alloys are generally Co-Cr-W alloys with various other carbide formers present. As deposited they form hard wear resistant carbides. The principal use is for high temperature wear resistance for sliding surfaces on slide valves and stems. There are refractories available that offer better erosion resistance for large areas on slide valves such as discs and throats. These alloys are crack prone and generally are accepted for service with minor cracking.
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CALTEX REFINERY MATERIALS MANUAL
Table 1-1a
October 1999
NOMINAL COMPOSITION
Page 1
Material
UNS Number
Fe
Cr
Ni
Mo
Cu
Zn
OTHER
Carbon Steel Low Alloy Carbon-0.5 Mo
(A516-70) K02700
Base
-
-
-
-
-
-
K12822
Base
-
-
0.5
-
-
-
1.25 Cr-0.5 Mo
K11597
Base
1.25
-
0.5
-
-
-
2.25 Cr-1 Mo
K21590
Base
2.25
-
1
-
-
-
5 Cr-0.5 Mo
K41545
Base
5
-
0.5
-
-
-
9 Cr-1 Mo
K90941
Base
9
-
1
-
-
-
AISI 4140
G41400
Base
1
-
0.25
-
-
0.4C
4340
G43400
Base
1
2
0.25
-
-
0.4C
Low Temperature Alloy Steels 2.5 Nickel
K22103
Base
-
2.5
-
-
-
-
3.5 Nickel
K32018
Base
-
3.5
-
-
-
-
Stainless Steel Ferritic/Martensitic Type 405
S40500
Base
13
-
-
-
-
0.3AI
Type 409
S40900
Base
11
-
-
-
-
0.5Ti
Type 410S
S41008
Base
13
-
-
-
-
0.08C
Type 410
S41000
Base
13
-
-
-
-
0.15C
Type 430
S43000
Base
17
-
-
-
-
-
CA6NM
S41500
Base
13
4
1
-
-
-
26-1
S44627
Base
26
-
1
-
-
0.01C
18-5-3
S31500
Base
18
5
3
-
-
0.03C
22-6-3
S31803
Base
22
6
3
-
-
0.03 C
Type 304
S30400
Base
18
10
-
-
-
0.08C
Type 304L
S30403
Base
18
10
-
-
-
0.03C
Type 316
S31600
Base
17
12
2.5
-
-
0.08 C
Type 316L
S31603
Base
17
12
2.5
-
-
0.03 C
Type 317
S31700
Base
19
13
3.5
-
-
0.08 C
Type 317L
S31703
Base
19
13
3.5
-
-
0.03 C
Type 321
S32100
Base
18
10
-
-
-
0.5 Ti, 0.08C
Type 347
S34700
Base
18
10
-
-
-
1Cb, 0.08C
A286
S66286
Base
15
26
1.5
-
-
2Ti, 0.3V, 1Cb
Ferritic/Austenitic
Austenitic
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CALTEX REFINERY MATERIALS MANUAL
October 1999
Table 1-1a Page 2
Material
UNS Number
Fe
Cr
Ni
Mo
Cu
Zn
Other
2 Cb 3
N08020
36
21
35
3
4
-
1Cb
800
N08800
46
21
33
-
-
-
-
825
N08825
30
22
42
3
2
-
1Ti
600
N06600
8
16
76
-
-
-
-
625
N06625
3
22
62
9
-
-
4Cb
B
N10001
2
1
69
38
-
-
-
400
N04400
2
-
68
-
30
-
-
Nickel alloys
Nickel Welding Electrodes/Wire 182
W86182
8
16
67
-
-
-
7Mn, 1Ti, 2Cb
A
W861133
8
15
70
2
-
-
3Mn, 2Cb
112
W86112
4
22
61
9
-
-
3.7Cb
82
N06082
3
20
70
-
-
-
3Mn,2.5Cb, 0.8Ti
625
W86625
5
22
60
9
-
-
3.8Cb, 0.4Ti
C44300
-
-
-
-
70
29
1Sn, As
C44400
-
-
-
-
70
29
1Sn, Sb
C44500
-
-
-
-
70
29
1Sn,P
Aluminum Brass
C68700
-
-
-
-
77
21
Naval Brass
C46500
-
-
-
-
62
37
1Sn
Copper Nickel (90-10)
C70600
1
-
10
-
89
-
-
C71500
1
-
30
-
69
-
-
Aluminum Bronze
C61400
2
-
-
-
91
-
Titanium Grade 2
R50400
99 + Ti
Aluminum Alloy 3003
A93003
AL base, 0.1Cu, 1.25Mn, 0.6Si
Stellite 1 (1)
W73001
2.5C, 30Cr, 12W, 54Co
(1)
W73006
1C, 29 Cr, 4W, 66Co
Copper Alloys Admiralty
(70-30)
Hard Facing Alloys Stellite 6
Wallex 50
(2)
0.8C, 21Cr, 17Ni, 10W, 44Co, 3Si, 3.25B
(1)
Trademark Cabot (2) Trademark Wall Colmonoy
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2AL
7 AL
CALTEX REFINERY MATERIALS MANUAL
Page 1
Table 1-1b COMMON ASTM SPECIFICATIONS FOR FREQUENTLY USED ALLOYS
Material
Structural Carbon Steel Pressure Equipment Carbon Steel Low Temperature Carbon Steel Low Alloy Carbon-0.5Mo 1.25Cr-0.5Mo 2.25Cr-1Mo 5Cr-0.5Mo 9Cr-1Mo AISI 4140
October 1999
Heat Exchanger Tubing
Pipe/
A283
-
A53
A285 A515 A516 A516
A214 A179
A53 A106 API 5LB A333 Gr1,6
A105 A181
A2334 WPB
A216 WCB
A193 B7 A194 2H
A350 GrLF2
A420 GrWPL6
A352 LCB
A320 GrL7
A204
A209
A387 Gr11 A387 Gr22 A387 Gr5 A387 Gr9 -
A199T11 A213T11 A199T22 A213T22 A199T5 A213T5 A199T9 A213T9 -
A335P1 A161T1 A335P11 A200T11 A335P22 A200T22 A335P5 A200T5 A335P9 A200T9 -
A182F1 A336F1 A182F11 A336F11 A182F22 A336F22 A182F5 A336F5 A182F9 A336F9 -
A182F1 A234WP1 A182F11 A234WP11 A182F22 A234WP22 A182F5 A234WP5 A182F9 A234WP9 -
A217 WC1 A217 WC6 A217 WC9 A217 C5 A217 C9 -
A193-B7 A194 2H,7 A193-B7 A194 2H,7 A193-B7 A194 2H,7 A193-B7 A194 2H,7 A193-B7 A194 2H,7 A193-B7 B16 A194-2H,7
A333 Gr7 A333 Gr3
A350-LF9 A350-LF3
A420-WPL9 A420-WPL3
A352-LC2 A352-LC3
A320-L7 A320-L7
A268 A268
A336 F6 A182 F6NM A182 FXM27 A336 FXM27 A182 A336 A182 A336 A182 A336
A182 F6 A182 F6NM A182 FXM27
A217 CA15 A352
A193-B6 A194-Gr6 -
A182 A403 A182 A403 A182 A403
A351 CF8 A351 CF8M A351 CF3M
A193-B8 A194, 8 A193-B8M A194-8M
Plate
A334 Gr1,6
Low Temperature Alloy Steels 2.5 Ni A203B A334 Gr7 3.5 Ni A203E A334 Gr3 Stainless Steel Type 405 A240 Type 410S A240 Type 410 A240 A268
Flanges
Fittings
Castings
Bolting
Tubing
Type 430 CA6NM
-
A268 -
-
26-1
A240
A268
A731
Type 304
A240
A249
Type 316
A240
A249
Type 316L
A240
A249
A312 A271 A312 A271 A312
A307
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CALTEX REFINERY MATERIALS MANUAL
Page 2
October 1999
Table 1-1b COMMON ASTM SPECIFICATIONS FOR FREQUENTLY USED ALLOYS
Material
Plate
Heat Exchanger Tubing
Pipe/Tube
Flanges
Fittings
Castings
Type 317
A240
A249
A312
A182
A182
A351
A403
CG8M -
Type 321 Type 347
A240 A240
A249 A249
Bolting
A312
A182
A182
A271
A336
A403
A312
A182
A182
A351
A193--B8C
A271
A336
A403
CF8C
A194-8C
A182-FS1
A182-FS1
22-6-3
A240
A789
A790
A286
-
-
-
A193-B8T A194-8T
A453 Gr660
Nickel Alloys 20Cb3
B463
B468
B464
B462
B366
A351
B473
CN7M 800
B409
B163
B407
B564
B564
-
B408
825
B424
B704
B423
B564
B564
-
B425
B167
B564
B564
A494
B166
B163 600
B168
B163
CY40 625
B443
B704
B444
B564
B564
B
B333
-
-
B366
B366
400
B127
B163
B165
B446 A494
B467
N12M
B468
B564
B564
A494
B467
B366
B366
M35
B468
Copper Alloys Admirality
B171
B111
-
-
-
-
-
Aluminum Brass
-
B111
-
-
-
-
-
Copper Nickel
B171
B111
B469
-
-
-
-
B466 Naval Brass
B171
-
-
-
-
-
-
Aluminum Bronze
B171
-
-
-
-
B148
-
Titanium
B265
B338
B337
B381
B363
B367
Aluminum
B209
B234
Alloy
Alloy
3003
3003
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CALTEX REFINERY MATERIALS MANUAL
2.0
2.1
October 1999
COATINGS
FUNDAMENTALS OF COATING TECHNOLOGY Paints have been used by man from the dawn of civilization. Painted, lacquered, and varnished artifacts created by early man for decoration, religious expression, and teaching or storytelling are exhibited in museums around the world and are in remarkably good condition. They attest to the ability of paints to protect as well as beautify. Through the years, there have been greater demands for paints to provide protection in a variety of conditions. The paint chemist has responded to these demands and has developed a wide variety of paint materials that can resist severe chemical environments. The World War II search for synthetics to replace the cut off natural rubber supply, led to the discovery of a number of synthetic resins, used today in coatings to impart chemical, abrasion, and moisture resistance to paints. With the development and use of these exotic paints, it is possible for an engineer to specify lower cost structural materials, such as carbon steel and concrete, in environments that otherwise would require more durable and expensive construction materials. Paints continue to serve multiple functions in modern industrial and architectural applications. The sophistication of paint chemists has created formulations which make paints suitable for: • • • • •
corrosion protection anti-fouling chemical resistance decoration/identification heat resistance camouflage noise control fire retardation
While paints serve these multiple functions, it is the ability of the cured paint film to act as a barrier between the substrate to which it is applied and the surrounding environment, thereby providing corrosion/erosion control and preventing structural damage, that is of fundamental importance in selecting coating systems for industry. The properties of paint which define its useful performance in service include: • • • • • • • • • • •
Abrasion resistance Chemical resistance Moisture resistance Hardness Brittleness Color retention Chalking characteristics Hiding power Gloss Flow Applicator requirements (e.g. temperature limitations, required surface preparation)
A review of the generic paints in common industrial use today with reference to these properties and service limitations, is the topic of this section.
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October 1999
Paints vs. Coatings. The terms 'paint' and 'coating' are both widely used and often interchanged. In the most narrow sense, paint is used when referring to pigmented liquids such as wall paint, exterior architectural paint, traffic paint, and masonry paint. Other paint type products, such as sealers, varnish, lacquer, stains, and primers are commonly called coatings or finishing materials. Elastomeric coatings, synthetic organic coatings, flame spray metal coatings (more recent additions to the paint chemists' line) have expanded the use of the term coatings. In general, paint is used to refer to the less chemically sophisticated materials of alkyds, enamels, and latexes; and, coatings to the more exotic high performance industrial products. The practice of engineers and field applicators of employing the term coating or referring to a particular generic coating type will be adopted here. 2.1.1
Coating System Composition PRIMER:
Holds to the metal substrate and protects the substrate and the topcoat. Primers contain corrosion inhibitors
TOPCOAT: Protects the primer from the environment. 2.1.2
Coating Composition The manufacturing of coatings is an important segment of the chemical industry. Technically, it is one of the most complex, employing more kinds of raw materials than any other division of the industry. Paints incorporate almost the complete range of commercial organic polymers including the chemical counterparts for most types of plastics, rubbers, adhesives and synthetic fibers. A paint manufacturer may stock 500 to 600 different raw materials and intermediates in order to produce a complete line of coatings. Coatings have two basic components; the pigment and vehicle. The pigment, finely ground solid material, is dispersed in the vehicle which is a liquid containing two parts, the solvent and dissolved resin or binder.
2.1.2.1 The Pigment Pigment solids are used in coatings for a variety of purposes. (i) Protective Pigments - provide corrosion control or chemical resistance in three ways: •
Barrier Protection
Laminar pigments reduce permeability, and help the binder to form coating film which is impervious to water, oxygen, and salts that accelerate deterioration.
•
Galvanic Protection
Metallic zinc dust provides galvanic protection by combining with oxygen in preference to the anodic steel substrate. The zinc is sacrificed forming a zinc salt which appears as a white dust on the surface of the coated steel.
•
Inhibitive Protection
A large number of pigments exert a chemical physical effect which serves to protect steel from corrosion. Included here are red lead, zinc chromate, zinc phosphate, calcium plumbate, and metallic lead. The mechanism of protection is complex. While several theories exist, the mechanism is not well understood.
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October 1999
(ii) Hiding Pigments - Sunlight has a marked degrading effect on the organic resins in a coating film. The ultraviolet and infrared ranges of the spectrum cause the film to lose elasticity. Hiding pigments shield the film from the sun's rays, and reflect much of the solar radiation. Aluminum flake and titanium dioxide, which is snow white in color, are typical of hiding pigments. (iii) Tinting Pigments - Color is imparted to a coating by adding the appropriate tinting pigments. Iron oxide is used to obtain yellows, reds, and browns of subtle, dullish hue. White paints contain large quantities of titanium dioxide, a very stable, non-reactive pigment, and, in addition to providing hiding and color, Ti02 will offer good control over chalking. Carbon, or lampblack, is used to obtain black. (iv) Extender Pigments - These pigments are generally referred to as extenders or fillers because of their low cost and high bulking value. However, they may add valuable properties such as decreased permeability and enhanced film build. Calcium carbonate (chalk), mica, and silica quartz are common extender pigments. 2.1.2.2 The Vehicle The vehicle is the liquid medium in which the pigment is suspended and is comprised of the volatile or solvent portion which totally evaporates as the film dries, and the non-volatile, vehicle solids, resin or binder portion which remains on the surface of the substrate to form the film encapsulating the pigment matrix. The volatiles, or solvents, control consistency, dissolve the solids so that they can be applied, and promote leveling. The non-volatile, or resin, is composed of one or more polymers or prepolymers that form the coating film, determine the method of cure, and to a large degree define the corrosion and chemical resistant properties of the coating. For these reasons, coatings are generally classified by the type of resin used, for example, alkyd, vinyl, epoxy, coal tar, phenolic and urethane resin bearing coatings. (i) Vehicle Volatiles - Solvents in the coating serve a variety of functions. The primary role of the solvent is to permit easier application, or to dissolve the resin which will dry to form a film, after the coating has been applied and the solvent volatilizes. Solvents which are added to the coating after the can has been opened in the field are called thinners. Thinning solvents promote ease of application and assist in the flow-out and leveling of the film. It is good practice to avoid thinning except as is necessary to achieve the desired workability when applying the coating. Spraying usually necessitates a certain amount of thinning, and additional thinning may be necessary in warm or windy weather. The most frequently encountered solvents for identical coatings fall into the following general categorization: • • • •
aromatic hydrocarbons (toluene, xylene, benzene) aliphatic hydrocarbons (mineral spirits) Ketones (methyl ethyl ketone [MEK], methyl isobutyl ketone [MIBK]) esters and alcohols (ethylacetate, isopropanol)
Drying oils are a class of solvent obtained from plants and certain fish. They dry to form films by absorbing oxygen and by polymerization. Drying oils may be used as the sole ingredient in the solids portion of the vehicle or may be fortified with resins.
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October 1999
Varnish, is a term used to describe the product resulting from cooking a drying oil with resin. Upon exposure to air, varnishes will dry to form a smooth, durable elastic film. The degree of elasticity is affected by the types and proportions of oil and resin used and the cooking procedure used. Until relatively recently Lead-In-Oil paint, a lead pigmented raw linseed oil formulation, was about the only type of house paint sold. Linseed oil is the most commonly used drying oil in paints. It makes an excellent vehicle for paints for wood and structural steel, especially under mild atmospheric conditions. Though its moisture penetration resistance is only fair, this quality can be enhanced by further processing the oil. (ii) Vehicle Non-volatiles - The resin or binder is considered the heart of the coating, for it binds the pigment particles together and to the surface of the substrate forming a rough, durable film. In nonpigmented, or clear, coatings, the binder is the total film forming agent. Resins exist in two broad classifications, natural and synthetic. Resins are solid or semisolid, water insoluble, organic substances, evidencing little tendency to crystallize. Resins are often added to drying oils to decrease their permeability. A dried resinous vehicle tends to be brittle, but this effect can be mitigated by combining the resin with drying oil. A natural resin is defined as a solid organic substance, originating in the secretion of certain plants or insects and dissolves in certain solvents, but not water (ASTM D16, Definitions Relating to Paint). Though there are many natural resins available, most are not used in metal protective coatings. Rather, their main use is in furniture varnishes. Shellac is one of the most common natural resins. Synthetic, or manmade, resins are manufactured by polymerizing organic chemical compounds of many types, and form the backbone of the protective coating materials used in industry today. Their types and classifications are many and varied, and seem to be increasing at an exponential rate. Furthermore, resins are frequently chemically blended in combinations of two or more resins to obtain a synergistic effect, i.e., to provide coating materials with qualities superior to those which could be provided by any of the constituent resins used singularly. While all the solvent is lost upon curing of a coating, the proportion of resin and pigment remains the same. The ratio of pigment to resin is related to the gloss of the coating. Flat coatings expose more pigment than high gloss coatings. Gloss is related to the fineness of grind of the pigment, the smaller the size of the pigment particle, the greater the gloss. (iii) Additives - Other materials such as driers, plasticizers, ultraviolet light absorbers, emulsifiers, anti-skinning agents, anti-flocculation agents and anti-mildew agents are added to coatings to impart special properties. Depending upon their solubility, they may be considered part of the vehicle or pigment component. Driers are a particularly important coating additive. They fall into two general classes: chemical compounds, added to shorten the drying time, or catalysts. Driers: Metallic soaps. Metallic soaps are formed by mixing metallic oxides with oils. These insoluble soaps promote faster drying, act as thickening agents, and provide a flat hand-rubbed appearance for certain product finishes. Soaps of lead, cobalt, manganese, calcium, tin, zirconium, aluminum and zinc are common. Lead promotes drying throughout the coating film, and is frequently used in combination with cobalt. Where environmental controls restrict the use of lead, zirconium is frequently substituted. Tin, a fast drying agent, is usually used in combination with other metallic soaps for a more controlled reaction.
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October 1999
(iv) Catalysts - Technically speaking, a catalyst is a substance which effects a reaction, but does not enter into, or become part of, the reacted material. In coatings, chemical catalysts are used to speed up the cross-linking of molecules. Reactive urethanes, thermosetting polyesters, and amine, polyamide, and amine adduct-cured epoxies are frequently used as catalyzed, high performance coatings. 2.1.3 Methods Of Cure Coatings cure in three basic ways: (i) Solvent evaporation (ii) Oxidation The process by which oil or resin molecules combine with oxygen in the air to effect cure; Driers are used to initiate or accelerate this reaction. (iii) Polymerization The linking of free molecules in the resin to form long chains of high molecular weight. Cross linking may be activated by the presence of heat (e.g., baking enamel) chemically, by the addition of a catalyst (e.g., reactive epoxy, urethane and polyester), or by exposure to radiation, gamma rays, x-rays, ultraviolet rays. (NOTE: Radiation cures are being experimented with for various types of product finishing, especially automobile exteriors. They have not yet found real commercial acceptance.) Complete curing of a coating is essential in order to obtain promised service life and may be a critical factor in the adhesion of a multicoat system. Curing and drying, while often used interchangeably, are not synonymous. A dry film is one which is dry to touch. When the thumb is pressed with moderate pressure on a dry film and rotated 90 degrees, the coating film will not distort, sag, or retain an imprint. A coating may be dry to touch, but may not be cured. Solvents may be trapped in the interior of the coating film (i.e., only the surface has dried and the hard skin has entrapped solvents which may form blisters or cause lifting of the film, or oxidation or polymerization within the film may be incomplete). The manufacturer's data sheet will indicate time to cure, but this is affected by ambient conditions, and time adjustments may need to be made for a particular job. A classification of generic coating types by their method of cure is found in Table 1-2. Typical overcoating times of commonly used paints are shown in Table 1-3.
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CALTEX REFINERY MATERIALS MANUAL
Table 1-2 - CLASSIFICATION
SOLVENT EVAPORATION
OF COATINGS BY METHOD OF CURE
water thinned
water soluble coatings "emulsion" coatings
solvent thinned
shellac lacquers solution vinyls polyvinyl chloride chlorinated rubber T/P acrylics oil phenolic varnish oleo resinous varnish alkyds chlorinated alkyds silicone alkyds epoxy esters acrylic enamels urethanes (oil modified)
OXIDATION
POLYMERIZATI
October 1999
heat conversion
chemical conversion "catalyzed"
silicone (crosslinked with oil material) phenolics aminos, urea and melarnine formaldehydes alkyds, vinyls, or oils) T/S acrylics Polyurethane
(crosslinked with
reactive or "two-pack" vinyl esters furon linings coal-tar epoxies coal-tar urethane polyurethane polyester epoxy, polyamide cured epoxy, amine & amine adduct cured epoxy polyester PVB (wash primer)
moisture conversion
ethyl silicate zinc rich primer urethene
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CALTEX REFINERY MATERIALS MANUAL
Table 1-3
October 1999
OVERCOATING TIMES OF SELECTED PAINTS
NAME
OVER COATING TIME
COMMENTS
Alkyd Resin Paints
12-48 hrs.
if the interval greatly exceeds 48 hrs. there is risk of poor intercoat adhesion.
Chlorinated Rubber Paints
2-4 hrs. (normal)
No upper limit for overcoating time drying of these paints. Least likely to be affected by low temperature. High build types best finished with normal types.
Vinyl Resin paints
1-2 hrs. (normal)
48-72 hrs.(high build 48 hrs (high build)
Epoxy Resin paints
4 hrs.
Intervals greater than 24 hrs. incur risk increasing with delay, of poor intercoat adhesion. Curing time 7 days (for max. resistance).
Epoxy/Pitch paints
4 hrs.
Intervals greater than 24 hrs. incur risk, increasing with delay, of poor intercoat adhesion. -
Zinc Silicate
5-7 days
Allow 4 hrs. before curing paints with acid wash and wash with (inorganic) water before recoating
Zinc Silicate
1-2 days
Cure is hastened by washing down after 2 hrs, using clean water.
Polyurethane Resin paints
paints (organic)
2.2
PROPERTIES OF PAINTS PAINTS Specific properties of some types of paints have been mentioned, but general advantages and disadvantages have not been discussed. Each type of paint has properties that make it suitable for particular uses. Of course, there are large variations in properties within each type, and it is seldom possible to select a suitable paint by type alone.
2.2.1
Oil Paints Oil paints have drying oil vehicles that cure by oxidation and polymerization. Raw and bodied linseed oil are the most commonly used drying oils. Raw linseed oil paints have excellent wetting ability, but are slow drying. Bodied linseed oil paints are faster drying, have increased water resistance and decreased permeability, but their wetting properties for rusted or dirty steel are inferior. A mixture of raw and bodied linseed oil is frequently used, especially for primer paints. Oil paints are used extensively because of their excellent weathering characteristics. In normal atmospheric exposure, oil paints gradually erode by deterioration of the surface until the undercoats are exposed. At that time, they should be recoated with a finish paint, priming any rusted areas if necessary. Films of oil paints are elastic and flexible and have good adhesion. However, they have poor resistance to abrasion and conditions of high humidity and their resistance to alkaline environments is very poor. Films of oil paints are too porous to be generally satisfactory for underwater surfaces.
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October 1999
2.2.2 Oleoresinous Paints Oleoresinous paints are those that have both drying oils and resins in their vehicles. Natural varnish resins are sometimes used but synthetic resins are more commonly used in metal protective paints. These paints are better than linseed oil paints for severe service conditions because of their decreased permeability and increased chemical and abrasion resistance. Films of these paints are more brittle than those of linseed oil paints, and they must be formulated carefully to avoid a brittle film that fails by checking and cracking. The most widely used classes of oleoresinous paints contain alkyd, phenolic or epoxy resins. 2.2.3 Alkyd Paints Most alkyd paints formulated for painting structural steel are oleoresinous paints. The vehicles of these paints are referred to as oil-modified alkyds to indicate that the resin has been combined with a drying oil. Properties of the alkyd paints are controlled primarily by the amount and type of oil incorporated in the resin. However, a limited variation in wetting and drying properties is possible through the selection of alkyd resin. Long oil alkyd paints, which contain a high proportion of drying oil to alkyd resin, have good wetting and slow drying properties similar to those of oil paints. Short oil alkyd paints, which contain only a small proportion of drying oil, have properties approaching those of unmodified alkyds, that is, rapid drying, extreme hardness, good durability, relative insolubility in mineral spirits, and poor wetting of rusted or dirty steel. The quick drying, unmodified alkyds have poor adhesion, and thorough blast cleaning is recommended before application of these paints as primers. In general, alkyd paints are less permeable and have better chemical resistance than oil paints and, therefore, are better suited for severe environments. However, they are too permeable to be satisfactory for continuous immersion in water. 2.2.4 Phenolic Paints Like the alkyds, most phenolic paints formulated for painting structural steel are oleoresinous. They contain oil soluble phenolic resins modified by the addition of drying oils. And their properties depend, to a large extent, on the amount and type of drying oil used. In general, oil modified phenolic paints are quick drying and have low permeability, good water resistance, and good chemical resistance. They are not, however, resistant to alkalis. Their adhesion is only fair, and blast cleaning is the recommended minimum surface preparation. Oil modified phenolic paints are particularly suitable for fresh water immersion and atmospheric exposure in severe industrial or marine atmospheres. 2.2.5 Epoxy Paints Air drying epoxy paints are formulated with epoxy resins that have been esterified with a drying oil acid. They are referred to as esterified epoxies, epoxy esters, or modified epoxies. As with other oil modified synthetic resin paints, the properties depend largely on the type of drying oil acid reacted with epoxy resin. In general, they are suitable for severe industrial and marine environments. Esterified epoxy paints are relatively quick drying and have low permeability, good water resistance and good chemical resistance. In these respects, they are better than the alkyds and comparable to the air drying phenolics. They have excellent adhesion, and surface preparation is usually no problem, though blast cleaning is always recommended where practical. Unmodified epoxies, or 100% epoxies, that require the addition of a catalyst just before application have excellent acid and alkali splash resistance. They are suitable for immersion in hydrocarbons, mild acids and alkalis, but blistering may be a problem in sea water, aqueous ammonia and fertilizer solutions.
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CALTEX REFINERY MATERIALS MANUAL
2.2.6
October 1999
Lacquer Type Paints Lacquers are usually considered to be pigmented or unpigmented solutions of cellulose esters, or ethers that cure to a solid film solely by solvent evaporation. In recent years, however, several non-cellulosic, solvent drying resins have been developed, and these are used by themselves or combined with cellulose derivatives to give coatings of improved properties. The term lacquer type paint can be used to distinguish cellulose lacquers (nitrocellulose automobile lacquers, for example) from other classes of solvent drying resin paints such as the vinyl and chlorinated rubber paints. As previously mentioned, oleoresinous and oil paints cure by reaction with oxygen from the air, but lacquer type paints do not require oxygen. The resin that is in solution at the time of application is deposited on the surface with the pigment and becomes a solid film when the solvent evaporates. High molecular weight resins, suitable for this type of coating, are difficult to put into solution and high solvency power solvents are required. A low solids content paint generally results and the dry film thickness per coat of applied paint is low. Several coats may be required to obtain desired film thicknesses. However, the use of hot spray processes permits a high build per coat.
2.2.7
Vinyl Paints Vinyl paints and lacquer type paints are formulated with vinyl resins in alcohol, ketone or ester solvents. The most common resins used are copolymers of vinyl chloride and vinyl acetate with a small amount of another constituent, such as maleic anhydride, to improve adhesion. Poor adhesion is the principal disadvantage of these paints and the minimum surface preparation required is abrasive blasting to white metal. However, they have outstanding resistance to severe environments, particularly for submerged surfaces. Vinyl paints are quick drying because low boiling solvents (for example, methyl ethyl ketone) and they must be sprayed. Using recently developed hot spray techniques, vinyls may be applied in film thicknesses comparable to oleoresinous or oil paints.
2.2.8
Chlorinated Rubber Paints Chlorinated rubber paints are lacquer type paints containing, in addition to pigments, chlorinated rubber resin, plasticizers, stabilizers and aromatic solvents. A plasticizer is required to decrease the brittleness of the film. A stabilizer, usually an epoxide compound, is required because the resin has a tendency to liberate small quantities of hydrogen chloride. Chlorinated rubber paints have outstanding resistance to acids and alkalis and are used extensively where acid fumes are present. Their adhesion is better than that of the vinyls, but their wetting ability for dirty or rusted steel surfaces is only fair and blast cleaning is recommended. The aromatic solvents used (for example, toluene and xylene) provide relatively quick drying properties but are slower drying than the vinyls.
2.2.9
Latex Paints Latex paints are usually based on aqueous emulsions of three basic types of polymers; polyvinyl acetate, polyacrylic and polystyrene butadiene. They dry by evaporation of the water followed by coalescence of the polymer particles to form tough, insoluble films. They have little odor, are easy to apply, and dry rapidly. Latex films are somewhat porous so that blistering due to moisture vapor is less of a problem than with solvent thinned paints. They do not adhere readily to chalked, dirty or glossy surfaces. Therefore, careful surface preparation is required.
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CALTEX REFINERY MATERIALS MANUAL
October 1999
2.2.10 Epoxy-Coal Tar Paints Coal tar is often added as an ingredient of epoxy paints, resulting in a significant decrease in cost with relatively minor effect on corrosion resistance. Color choice is limited because of the black color of the coal tar. It is used primarily for interior and submerged surfaces. 2.2.11 Silicones Silicones are used for water repellents and for heat resistant coatings. (i) Water Repellents Dilute solutions (5% solids) are used to reduce water absorption on unpainted concrete or masonry. They usually do not affect the color or appearance of the treated surface. (ii) Heat Resistant Coatings These contain a high concentration of silicone resins. When properly formulated and applied, they can withstand temperatures as high as 1500oF. (816oC) 2.2.12 Polyurethane or Urethane Paints There are two general types of polyurethane coatings; oil modified and moisture curing. (i) Oil Modified These are similar to phenolic varnishes, although more expensive. They have better color and color retention, dry more rapidly, are harder, and have better abrasion resistance. They can be used as exterior spar varnishes or as floor finishes. (ii) Moisture Curing These are unique in having the performance and resistance properties of two component finishes, yet are packed in single containers. Moisture curing urethanes are used in a manner similar to other one-package coatings except that all containers must be kept full to exclude moisture during storage. If moisture enters or is in the container, they will gel. 2.2.13 Silicone Alkyd Paints The combination of silicone and alkyd resins results in an expensive, but very durable, coating for use on smooth metal. 2.2.14 Vinyl Alkyd Paints The combination of vinyl and alkyd resins offers a compromise between the excellent durability and resistance of the vinyls with the lower cost, higher film build, ease of handling and adhesion of the alkyds. They can be applied by brush or spray and are widely used on structural steel in moderately severe corrosive environments. 2.2.15 Acrylic Paints Cross-linked acrylic resins with styrene and other materials provide a very durable and attractive line of lacquer and enamel coatings used for automotive and appliance finishes. These coatings require baking at temperatures of 300-400oF (149oC-204oC) after application. Water based acrylic latex emulsion paints are used widely for wood, plaster, and masonry coatings.
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2.2.16 Wash Coat Pretreatment The wash coat pretreatment, also called a wash primer treatment, is a surface preparation step rather than a paint because a chemical reaction with the surface is involved. However, a thin, 0.3 to 0.5 mil, film is left on the surface. Essentially, the material is a two part composition that consists of an alcohol solution of polyvinyl butyral resin and phosphoric acid, pigmented with zinc tetroxy chromate. When it is applied to a blast cleaned steel surface, an adherent film is formed by reaction with the steel. The film improves the bond between the steel and poorly adherent paints, such as the vinyls. The wash coat pretreatment is used to improve adhesion of paints on such smooth metals as galvanized steel, stainless steel, magnesium and aluminum. 2.2.17 Bituminous Paints Bituminous paints are solvent solutions of bituminous materials; that is, asphalt, coal tar, gilsonite or vegetable pitch, with or without added fillers. These paints normally do not exhibit inhibitive properties and metal protection is derived from a mechanical barrier obtained by applying thick coats of 1/8 inch or more. Film thickness per coat is increased by the addition of inert fillers, such as calcium carbonate, mica, silica, asbestos and others. Solvents used, vary from aliphatic hydrocarbons for asphalts to aromatic hydrocarbons for coal tar materials. Good protection is obtained with these coatings if applied in sufficiently thick films. One of the disadvantages is the number of coats required to obtain the thickness desired. In severe exposures, a rust inhibitive prime coat is recommended and this introduces the problem of lifting of the undercoat by the aromatic solvent in coal tar base paints. The bituminous paints are not resistant to longterm exposure to sunlight and weather and they must be protected when used outdoors. The use of asbestos is not acceptable environmentally in many countries. 2.2.18 Mastics and Cements As the result of surface tension effects on drying films, coatings are usually too thin on sharp edges, over rivet and bolt heads, etc., to prevent corrosion. These are the places coatings breakdown first. This, however, can be easily overcome when using vinyls or by applying vinyl mastic on all sharp edges, rivets, bolt heads and nuts and in cracks where two or more members are jointed. This will effectively prevent rapid coating failure. The mastic may be applied by trowel, putty knife, brush or high pressure spray equipment. 2.2.19 Special Purpose Paints Film forming materials other than oils and resins can be used for special coating requirements. Zinc dust is used in an inorganic vehicle containing sodium silicate to produce a paint that requires a chemical hardening agent. Portland cement and casein are used in water base coatings. Water base paints consisting of water emulsions of many types of coating materials are being used for wood and masonry surfaces but they are seldom used in metal protective paints. Some water emulsions may be heavily pigmented and applied as very thick coats. These are the so-called mastics. Water emulsions of polyvinyl acetate or acrylic resins are used extensively for painting masonry surfaces. They have greater tolerance for alkaline surfaces than previously used oleoresinous paints. Water emulsion paints are gaining wide acceptance for interior paints because they eliminate the odor of organic solvents indoors.
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2.3
COATING SELECTION SELECTION
2.3.1
Service Exposures In industrial maintenance coating, more than any other coating area, it is important to choose that paint, of the many available types, whose resistance properties best coincide with the demands of the service environment. A paint that performs perfectly well under one set of conditions, may fail miserably under others. Or, a less resistant paint may be completely satisfactory in areas where high performance coatings are sometimes used. Table 1-4 shows the principle advantages/disadvantages of frequently used industrial coatings. Table 1-5 shows the recommended type of coatings for refineries and terminals (inland and coastal.)
2.3.2
Selection of Paints The following criteria should be used in selecting a coating: • • • • • • • • • • • •
Abrasion resistance Adhesion Impact resistance Flexural qualities Resistance to a given media Resistance to sunlight Temperature resistance Drying time Appearance Wetting time Applied cost Antistick properties
The coating, or coatings, having the best properties for a given set of conditions should be selected, providing the cost is not prohibitive. Top quality coatings should be compared generically. However, it is important to keep in mind that identification, by generic name per se, is no guarantee of quality. Coatings should be purchased on specifications from reliable coatings manufacturers. It is false economy to purchase a protective coating without knowing its solids content and the resin content of the solids. Heavy bodied vinyls and other materials are now available that can be applied from 6 to 8 mils thick/coat with an ordinary spray gun. Where no large crevices are to be filled, this is superior to mastic because they can be applied much faster and with regular paint-spray equipment. Mastic or heavy bodied vinyl and some of the other materials should be applied after the prime coat is applied. When coated structures have large numbers and lengths of cracks and crevices, especially when these are subject to fading action as is the case in bridges, priming preliminary caulking will not only save time, but will insure a longer lasting job. Vinyl and phenolic mastics have been tested with good results on steel pilings in sea water. There are epoxy compounded cements, which may be used in conjunction with epoxy coating systems just as vinyl mastic is used with vinyl systems.
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Table 1-4 PRINCIPLE ADVANTAGES/DISADVANTAGES OF FREQUENTLY USED INDUSTRIAL COATINGS GENERIC TYPE AND CURING MECHANISM
PRINCIPAL ADVANTAGES
PRINCIPAL DISADVANTAGES
DRYING OILS
Very good application properties Fair exterior durability Outstanding wetting and penetration qualities Excellent flexibility Good film build per coat Relatively inexpensive
Slow Drying Soft films - low abrasion resistance Poor water resistance Fair exterior gloss retention Poor chemical and solvent resistance
One-package coating Fair exterior durability Moderate cost Excellent flexibility Excellent adhesion to most surfaces, including poorly prepared surfaces Easy to apply Good gloss retention
Poor chemical and solvent resistance Fair water resistance Poor heat resistance
Excellent exterior durability Good film build per coat Very good chemical resistance Excellent water resistance Extremely hard film
Very brittle Critical recoat intervals Poor gloss retention Yellows on aging
One-package coating -unlimited pot life Hard, durable film Good chemical resistance Good water resistance High film build per coat Moderate cost
Fair gloss retention Not applicable over inorganic zinc
Rapid drying Excellent durability, gloss and color retention Good heat resistance Moderate cost
Poor chemical resistance Low film build per coat Thermoplastic at elevated temperatures Blasted surface desirable.
Rapid drying and recoating Excellent chemical resistance Excellent water resistance Excellent durability Very good gloss retention Applicable at low temperatures
Poor solvent resistance Poor heat resistance Low film build per coat Requires white metal blasted and primed surface
Rapid drying and recoating Excellent chemical resistance Excellent water resistance Excellent durability Good gloss retention Applicable at low temperatures
Poor solvent resistance Poor heat resistance Blasted surface desirable questionable over inorganic zincs
Excellent chemical and solvent resistance Excellent water resistance Very good exterior durability Hard, slick film
Two-Package coating -- limited pot life Curing temperature must be above 50oF (10oC) Poor gloss retention Film chalks on aging Sandblasted surface desirable Topcoating may require blasting
Oxidation
ALKYDS Oxidation
PHENOLICS Oxidation
EPOXY ESTERS Oxidation
ACRYLICS Evaporation
VINYLS Evaporation
CHLORINATED RUBBERS
EPOXIES Polymerization
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Excellent chemical and solvent resistance Very good acid resistance Excellent water resistance Good heat resistance Extremely hard film Excellent abrasion resistance High film build per coat
Not for exterior use Critical recoat intervals Required white metal sandblasting Two-package coatings - limited pot life.
Very good chemical and solvent resistance Hard, abrasion resistant film High film build per coat Excellent adhesion - - particularly to aged, intact coatings Easily topcoated after extended periods of time with a variety of coating types May be applied directly to clean, dry concrete surfaces
Two-package coating -- limited pot life Curing temperatures above 50oF (10oC) Sensitive to early rain or dew
Excellent heat resistance Good water resistance and water repellency
Must be heat cured Very high cost Poor solvent resistance Requires blasted surface
Excellent exterior durability Good chemical resistance Good heat resistance Excellent adhesion to most surfaces Excellent gloss and color retention Excellent flexibility Very good moisture resistance
Poor solvent resistance Relatively high cost
Excellent gloss or color retention at elevated temperatures Excellent heat resistance Excellent durability
Poor solvent resistance Moderate chemical resistance High Cost
Offers one coat protection under many service conditions Excellent exterior durability Excellent heat resistance Excellent abrasion resistance Hydrocarbon insoluble Provides "galvanic" protection properties Provides "permanent" primer capability when used in conjunction with proper topcoats and/or maintenance practices Self-curing (some types) Selected ability to accelerate cure - depending on type used
High cost Requires excellent surface preparation-relative to many other types of coatings Spray application only-- skilled applicators required for successful job Not suitable for acidic or caustic service unless properly topcoated Requires careful selection of tie coats and topcoats for service involved. Selected temperature and humidity effects-depending on type used
POLYURETHANES
Excellent gloss retention (aliphatic types)
Gloss drop with high humidity
Polymerization
Can be applied at low temperatures
Limited pot life
Excellent chemical and solvent resistance
High cost
High hardness
Good clean, dry surface required
Excellent durability
Two-component
Excellent flexibility
Isocyanate sensitivity
EPOXY PHENOLICS Polymerization
EPOXY EMULSIONS Evaporation Polymerization
SILICONES Polymerization (Heat Required) SILICONE ALKYDS
SILICONE ACRYLICS INORGANIC ZINC EvaporationPolymerization
Regular to high film build recoatable
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Table 1-5
October 1999
RECOMMENDED COATING TYPES
REFINERIES AND TERMINALS - INLAND TYPE OF UNIT
GOOD
BETTER
BEST
Tanks - Cone Roof
Alkyd
Epoxy Ester
Acrylic
Tanks - External Floating Roof
Shell: Alkyd
Shell: Epoxy
Shell: Acrylic
Roof: Zinc/Vinyl
Roof: Zinc/Vinyl
Roof: Zinc/Vinyl
Structural Steel
Alkyd
Epoxy Ester
Amine Epoxy
Control Equipment
Alkyd
Alkyd
Alkyd
Piping
Alkyd
Epoxy Ester
P.A. Epoxy
Zinc/ Silicone Acrylic
Zinc/ Silicone Acrylic
Zinc/ Silicone Acrylic
Silicone
Silicone
Silicone
Stacks and Breeching to 500 oF (260oC) o
o
to 1000 F (538 C)
REFINERIES AND TERMINALS - COASTAL INDUSTRIAL ENVIRONMENT TYPE OF UNIT
GOOD
BETTER
BEST
Tanks - Cone Roof
Alkyd
Epoxy Ester
Acrylic
Tanks - Shell and External
Zinc High Build
Zinc High Build Vinyl
Zinc High Build Epoxy
Structural Steel
Epoxy Ester
Epoxy Ester
Zinc High Build Epoxy
Control Equipment
Alkyd
Chlorinated Rubber
P.A.Epoxy
Piping
Alkyd
Epoxy
P.A. Epoxy
Zinc/ Silicone Acrylic
Zinc/ Silicone Acrylic
Zinc/ Silicone Acrylic
Silicone
Silicone
Silicone
Floating Roof
Stacks and Breeching to 500 oF (260oC) o
o
to 1000 F (538 C)
2.4
INSPECTION The tightest specifications and the most corrosion resistant coating systems are money wasted without competent inspection. Because maintenance painting is not critical for the immediate operation of an existing plant, and because a good paint job is not necessary for starting up a new plant, their priority levels are very low. Maintenance foremen, maintenance engineers, and unit inspectors are in the field already; therefore, one of them is usually asked to "inspect" painting as part of his daily routine. Assistant project engineers or craft inspectors are assigned the task on new construction. Though these men might be eminently qualified in their own field, often they are not familiar with the coatings, equipment, inspection tools, or specifications necessary for making the intelligent decisions required in a good inspection effort. Equally important as the qualifications of the inspector are his methods of carrying out the program. An inspection procedure should be written and included in the specifications and contracts. It is important for both the customer and contractor to have this in writing. It allows the contractor know exactly what to expect and protects the customer from complaints or harassment because the job is being held up.
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It is advisable to include the following steps in the procedure: 1. Surfaces to be inspected for oil, grease, or any other contaminant which will not permit proper surface preparation. 2. All surface preparation to be inspected and approved before any coatings are applied. 3. Each coat to be inspected and approved before ensuing coats are applied. It is desirable to stipulate that areas be kept squared up as the work proceeds. This reduces the chances of the inspectors missing poorly cleaned areas or skippers in the paint. The inspector must be careful that the contractor does not use him as a tool for his own benefit. An inspector who is not careful will find himself pointing out every little discrepancy and then waiting while it is repaired. This is the paint foreman's job, not the inspector's. When the inspector is called to approve an area, he should assume the paint foreman has already inspected and corrected the deficiencies. If a significant number of deficiencies are found, the entire area under consideration should be rejected and the inspector recalled when it is ready for approval. Taking an engineering approach toward painting, using qualified people who can write concise specifications, select appropriate coating systems and ensure proper application by diligent inspection, can reassure management that money spent on painting is not wasted money.
2.5
TYPES OF COATING PROBLEMS AND CAUSES
2.5.1
Lifting Lifting is defined as softening of an undercoat by application of a topcoat. It can be recognized by a swelling or rising of the wet coating film and occasionally a shriveled surface. Peeling occurs as this film dries or cures. It is principally caused by incompatibility of the two coats - solvents attacking the previous coat.
2.5.2
Blushing The appearance of blushing will be that of a mist of milky haze and loss of gloss on the surface. It can be caused by the condensation of moisture in the wet coating film due to the cooling effect produced by evaporation of solvents or incompatible thinner. Blushing can be corrected by reducing humidity, using a retarder or slow/dry thinner, or proper thinners.
2.5.3
Orange Peeling This condition is easy to identify as the surface will have a dimpled appearance resembling an orange peel. It is caused by droplets of coating drying prematurely due to a solvent which is too fast, an improperly handled spray gun, or an air temperature which is too high.
2.5.4
Checking, Crazing Checking has the appearance of a parallel pattern of cracks and checks. It is generally caused by excessive film thickness. An irregular pattern of tiny splits, scales or cracks is referred to as 'crazing' and can result from the solvents softening the previous coat. Extreme temperature changes can cause both problems.
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2.5.5
Fisheyes When small openings, holes or deep depressions form in wet film exposing previous coating or substrate they are designated as fisheyes. This problem is traced to surface contaminants, such as silicone, that repel the wet coating.
2.5.6
Cracking Cracking is a splitting or disintegration of coating by breaks through film. This results from expansion and contraction when a heavily pigmented coating is applied over a more flexible undercoating that has greater extensibility. Inorganic zinc coatings also may crack when applied at excessive thicknesses. This is commonly referred to as 'mud-cracking'.
2.5.7
Embrittlement As coatings cure, they become harder and generally more impervious. Certain coatings, particularly most epoxies, embrittle on aging. Exposure to sunlight or alkali environment accelerates this process. The coating, at some stage, is vulnerable to cracking and chipping should the steel substrate flex or be subjected to physical abuse.
2.5.8
Softening Softening results from two causes: (1) coating is not resistant to corrosive environment and is being attacked and (2) lack of cure caused by poor formulation, manufacturing or improper mixing of two component materials. When a coating softens, it often stains, indicating a reaction with corrosives.
2.5.9
Chalking Organic coatings deteriorate by oxidation resulting in wearing away of the film and continues until the binder is completely destroyed. Heavy chalking tends to accelerate erosion Measuring yearly film loss with a thickness gauge tells when recoating is necessary.
2.5.10 Undercutting Undercutting results when a corrosive penetrates the coating film through the pinholes or damaged areas. Corrosion proceeds under the film with a lifting force that separates the film from the substrate. In many cases, undercutting cannot be detected without cutting into suspected areas with a knife. Primers having good adhesive properties and chemical resistance will prevent or retard subfilm corrosion. With inorganic zinc coatings, undercoating does not occur; corrosion is localized, and damaged areas are easily repaired. 2.5.11 Blistering Blistering is defined as 'bubbling' in dry or partially dry films. Water found under blisters indicates that the coating was applied over a moist surface. Application of topcoats before undercoat solvents have been released will cause solvent blistering. Certain inorganic zinc coatings are prone to cause topcoat blistering because of water soluble alkali residues that remain in the film and are dissolved out in a wet atmosphere.
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2.6
October 1999
PAINT COST When talking to users or potential users of blast cleaning equipment, the universal question is always asked, "What is it going to cost to clean a specific surface?" There are six obvious reasons why no one can give an accurate answer to this type of question. 1. The Type of Surface to be Cleaned - No one can look at a surface and determine what is on that surface. It might be easy to see that a green coat of paint is facing you; however, you have no knowledge of what is under the surface coat. There may be three or four mils, or 3/16" of old paint that have been applied over the many years the surface has been standing. Beneath, may be the original rust and mill scale which caused the initial coating to fail. There is no visual way of determining these factors and, even if there were, they could vary considerably over different areas of the surface. 2. The Type of Abrasives Being Used - The type, particle size, shape and hardness have a large influence on both the rate and degree of cleaning. Another prime consideration is the delivered cost of the abrasive. Prices on abrasives can range from a locally available sand at $4.oo per ton to products costing as high as $800.oo per ton for specially manufactured metallic types. 3. What Is Clean? - The surface preparation required must be clearly specified, for obviously, a white metal blasted surface requires a more thorough job than does a brush-off blasted surface. If you have five inspectors in a room, you could probably secure five different decisions as to what constitutes a clean surface to match the particular specification. 4. Air Pressure Available at Nozzle - The nozzle air pressure has a tremendous effect on job efficiency and the rate of production can be seriously hampered if the nozzle pressure is too low. 5. Operator Efficiency - The ability for the operator to perform an efficient job is one of the largest variables. 6. The Type and Efficiency of the Blast Cleaning Equipment - Using properly balanced blasting equipment can increase production two- or three-fold and has a great reflection on reduced costs. Table 1-6 AVERAGE JOB BREAKDOWN Cost
% of Total Costs
Surface Preparation Coating Material Cost Application Accessory Products Clean Up
15-50 15-20 30-60 2-5 5-10
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2.7
October 1999
TEMPORARY PROTECTION PROTECTION Essential features of any temporary preventive include the following: It must be easy to apply and even more important, easy to remove. While it is on the metal, it must resist the corrosive effects of humidity, fumes, fingerprints, weathering and water. These coatings prevent mechanical damage, such as nicks and burs, and preserve the metal's original appearance. The major preventives include (1) grease types, (2) oil types, (3) solvent types, and (4) strippable plastic types. Each has special advantages or limitations.
2.7.1
Grease Preventives Grease preventives are thick coat compounds that won't melt or flow at ordinary room temperature. Materials range from soft petrolatums to hard waxlike compounds. Softer coatings are for moderate shipping and storage temperatures. Harder coatings stand up under higher temperatures. Dipping in heated tanks is the usual method of applying the greases and, except for some hard solvent/drying types, they require the most time and effort to remove.
2.7.2
Oil Preventives Oil preventives include the non-drying, non-setting oils of various viscosities. Even with the heaviest of these oils, protective films won't be thicker than .0002 in. They attain final thickness by draining only, without setting or drying.
2.7.3
Solvent Cut Back Preventives Solvent Cut Back Preventives can be subdivided according to the solvent and material dissolved in them. Dry Type Films
These are asphaltic, resin and waxy films which are thin, fairly hard films that look like varnish. They are on par with protection achieved with heavy greases and withstand abrasion and handling.
Water Displacing
These usually contain substantial amounts of soaplike materials that actually remove droplets of water from metal surfaces by 'preferential wetting.' Preservatives attraction toward the metal surface is greater than that of water, displacing the water. The major reason for their use includes the reduction of time and labor required by permitting the easy preservation of wet parts in one simple dip.
Fingerprint Removers
These contain water, an organic solvent and preserving additives. After fingerprint residues (acidic organic materials, salt, etc.) are dissolved, the additives form a protecting film. For long-term storage, remove this film and replace it with a more lasting preservative.
Combination Solvent Preservatives
This solvent is combined with either an oil, grease or wax-type preservative. If solvent content is low and it is sprayed or brushed on, the final film will be relatively thick, comparable to greases. However, more often, these films are thin.
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Water Soluble Compound
October 1999
A water soluble compound is a low-cost coating from which the water evaporates, leaving an oily film.
2.7.4
Strippable Plastics Strippable plastics are a combination of special oils, plasticizers, inhibitors, synthetic resins and plastics. Coatings are thick, from .050 to .100 in, and have several unique features. They provide top corrosion as well as mechanical protection, and they can easily be removed by slitting and peeling. These coatings are applied from hot tanks.
2.8
GALVANIZING Protective coating systems fall into two major groups. The first group includes paints and plastics which provide a barrier coating but give no protection around the edges or a points of mechanical damage. The second group includes barrier systems such as zinc coatings which protect by sacrificial action even when they are moderately damaged. Hot dip galvanizing is used very extensively for corrosion protection of structurals and exposed carbon steel in many refineries, particularly those on the coast. A thick zinc multilayer coating is metallurgically bonded to the steel substrate. The coating corrodes at a rate of about 3-10% of the underlying steel. Typical coating weight minimum is about 610 g/m2 (2 oz/ft2). In most environments the life of the coating is proportional to the weight of the coating. An even thickness of the galvanized coating is applied to edges and flat surfaces. The zinc covers corners, edges seams and rivets to give complete protection to what may be potential failure points in other protective systems. Hot dip galvanizing applied after fabrication is tough and will tolerate handling which would damage most other coatings. The galvanizing process may vary from plant to plant but basically is as follows: 1. Cleaning - In most plants, this is a two step operation. The material is first immersed in a hot caustic bath or some other similar solution to remove oil, grease and other organic contaminants. The workpiece is then rinsed and taken into a mineral acid bath to remove rust, mill scale and other inorganic contaminants. The material is then rinsed and is ready for the next step in the process. 2. Fluxing - The steel is immersed in a tank containing an aqueous preflux solution to remove any oxides which may have formed on the material during the handling process. A molten flux blanket on the surface of the molten zinc in the kettle is also often used to clean the steel surface before the part is immersed or dipped into the bath. 3. Coating - The workpiece is then submerged in the molten zinc bath where it remains until the alloying reaction is complete. Depending upon the chemical composition of the steel, configuration, and mass of the material being coated, this process can take from 30 seconds to 8 hours. When the alloying reaction is complete, the steel is removed from the kettle. After the material is removed, it is either allowed to air cool or is immersed in a water quench tank. The quench tank operation freezes any further reaction between the base steel and the coating. The quench water may be treated with other chemicals to give the coating certain post treatments such as wash primers or zinc dust primers for eventual top coatings. Galvanizing usually does not cause a loss of ductility problem unless the material has been severely cold worked. Therefore, any shapes to be galvanized should be stress relieved before galvanizing. The acid bath pickling will generate hydrogen which will accumulate in the cold
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worked areas and embrittle the workpiece if it is not allowed enough time to diffuse out. Bessemer steels or other steels that may strain age embrittle should not be galvanized due to potential embrittlement problems There are ASTM specifications that cover safeguards to prevent embrittlement, warping and distortion during hot dip galvanizing as well as a specification covering the actual hot dip galvanizing procedure. As with any coating system, hot dip galvanizing needs proper specifications and inspection so that a quality product is furnished.
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3.0
October 1999
PLASTICS Plastics are increasingly replacing metal parts because of their light weight and good corrosion resistance to a wide range of chemicals. However, most plastics cannot be used above 250oF (121oC), and have lower strength than metals. The mechanical properties of the plastics may be increased by the addition of glass fibers to the plastic resin. The chemical properties can be altered by adding modifiers to protect it against specific environments. However, in most petrochemical operations, safety concerns limit the use of plastics in vessels and piping because of the potential for fires and unfamiliarity with the material. The primary uses for plastics in the petrochemical industry include wrapping for electrical components, housing for electrical components, hoses and protective coatings for tanks and piping. A plastic can be defined as a material consisting of long chained, organic molecules which are formed by combining short chained, organic molecules together in a viscous state. Plastics can be divided into two types, based on the final structure of the chains in the molecules: 1) thermoplastics and 2) thermosetters. Thermoplastics can be repeatedly heated with only a minimum reduction in their properties because the side chains of the molecules are not connected. Generally, thermoplastics are fabricated by injection molding or casting. Thermosetters have their side chains cross-linked. When heated above their maximum use temperature, the side chains are permanently broken, thus causing the plastic to degrade. The thermosetting plastics are usually made by combining a liquid resin with a catalyst. An exothermic reaction is produced, causing the material to set into a hard plastic. With the rapid advances in technology, plastics are being produced which are both thermosetters and thermoplastic. The selection of a particular plastic for an application is similar to choosing a metal. Design properties for the selection of a plastic include tensile strength, heat deflection point, toughness, creep modulus, specific gravity, shrinkage, expansion coefficient, resistance to the operating environment, and cost. The dielectric strength is important when a plastic will be used for an electrical application. Plastics can undergo mechanical failure from stress corrosion cracking, fatigue, rupture, embrittlement and overload. Corrosion is usually caused by chemicals, water, heat, and ultraviolet light interacting with the polymer chains, causing their degradation. Physical signs of corrosion include bloating, hardening, softening, discoloration and elongation. Unlike metals, dissolution of material from the plastic is uncommon. A wide range of plastics exists with each one having unique properties. Because of the complexity of plastics, coupons of the material should be tested in the operating environment before the selection is made. The following list gives the overall properties of some groups of plastics, but individual plastics within the group can behave differently. Many of the materials can be reinforced with fibers in the resin to give increased physical properties.
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3.1 THERMOPLASTICS ABS (Acrylonitrilebutadiene-styrene copolymerization)
Acetals
Fluorocarbon
Nylon
Polypropylene
Polycarbonates
Polyester
Polyethylene Polyvinyl Chlorides
3.2
Resistant to weathering; good all around properties; should not be used above 190oF ( 88oC); used for pipes and pump impellers
Clear; excellent fatigue life; toughness and strength; high abrasion resistance; excellent against solvents; poor with acid and bases; may be used from -40 to 220oF ( -40 to 104oC); uses include pipes, impellers, gears Maximum continuous use temperature of 490oF (254oC); inert to most chemicals; low coefficient of friction; low mechanical properties, but can be reinforced with fibers; uses include nonlubricated bearings, pipes, gaskets, and seals Good toughness, impact resistance, and strength; abrasion resistant; resistant to solvents and bases, but not acids; absorbs moisture, which leads to swelling; temperature limit of 250oF (121oC); used for gears, bearings, and machinery Temperature limit restricted to below 200oF (93oC); good resistance to acid and bases, but poor to solvents; moderate physical properties; inexpensive; uses include pipes, ropes, and ducts High toughness and dimensional stability, low creep; temperature use up to 270oF (132oC); transparent; resistant to acids and some solvents; uses include electrical housings. Excellent dimensional properties; high strength, toughness, and low creep; good chemical resistance; maximum continuous operating temperatures of 320oF (160oC); used for tanks, sinks, and pump housings Stress cracks when exposed to solvents; low temperature limit (130oF) (54oC) Maximum temperature limit of 150oF (66oC); high strength; resistant to acids and bases, but poor against solvents; used for pipes, tanks, valves, and gaskets.
THERMOSETTERS Epoxies
High strength, impact resistance, and toughness; maximum continuous temperature limit is 250oF (121oC); resistant to most chemicals, except for oxidizing agents; used for linings, protective coatings, adhesives and castings
Silicones
Maximum temperature up to 500oF (260oC); resistant to moisture; chemical resistance is poor; used for gaskets, coatings, electrical and components
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Ureas
October 1999
Corrosion resistance poor; good toughness and wear resistance; maximum temperature at continuous use is 150oF (66oC); used for pulleys, pump impellers, and conveyor belts
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4.0
October 1999
REFRACTORIES A refractory is a non-metallic substance that is resistant to prolonged exposure at high temperatures without undergoing a reduction in its physical properties. Refractories are widely used within various process equipment in the refining and petrochemical industry to protect the vessel metallurgy from excessive heat, erosion and/or corrosion. The type of refractory selected for installation will depend on several parameters including: 1. 2. 3. 4.
the design shell temperature the corrosiveness/erosiveness of the process the expected service life of the lining minimizing heat loss from the process
Consideration must also be given to the economics and ease of installation. 4.1
MATERIAL CLASSIFICATION Refractory materials can be classified several ways. In this section, the classification will be based on the manufacturing method used to make the material and subdivided by their common physical properties and/or chemical properties.
4.1.1
Castable and Gunning Mixes Castable and gunning mixes are very similar types of materials and exhibit most of the properties of standard concrete. Installation of castables requires the addition of water to a dry mix within a mixer. After approximately 5 minutes of mixing, the material is removed from the mixer and poured into place between forms. Gunned refractory mixes are applied by shooting a dry or slightly dampened mix through a high pressure air hose and adding water to the material at the hose's nozzle. The major differences between gunning and casting grade mixes are the types of additives used in the product to adjust the setup time for the cement and to facilitate the application of the gunned material. Therefore, castable and gunning mixes should not be interchanged unless the manufacturer specifies it as both gunning and casting grade material. Most of the gunning and casting mixes consist of calcium aluminate cement phases and fired alumina-silica rich aggregates. The types of cements and aggregates are changed to obtain the desired properties. The calcium aluminate cement enables a refractory to be used at higher temperatures than portland cement based concrete which is composed of calcium silicate phases and impurities. When mixed with water, the calcium/alumina cement becomes hydrated and forms a gel which bonds the aggregates together. Before the material can be used at high temperatures, the water in the concrete must be removed by a controlled curing and dryout schedule. Improper removal of the water will cause damage to the lining and vessel along with possible endangerment to human life. This is due to the high steam pressure generated within the refractory by evaporating the water at high temperatures. Lightweight refractory mixes are used within fired heaters where erosion is low and maximum heat retention is required. Gunned, medium weight mixes are the most commonly used refractory (based on tonnage) in refinery operations. They are used in FCCU reactors, regenerators, transfer lines, cokers and other various large volume vessels with low erosion. A new product line of extra high-strength, medium-weight material has been developed to meet
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more severe process conditions in these large volume vessels. Standard-weight materials are usually installed in secondary lines that have problems with erosion, but not coking. Heavyweight materials are used in the FCCU riser lines because of their abrasion resistance and resistance to spalling by coke impregnation but they are usually vibrocast into place. The high alumina castables are mainly used in sulfur recovery units (SRU) and gasification vessels. 4.1.2
Vibration Castable Vibration castables are similar to castables in chemistry. However, by installing the wet mix with vibrators attached to the vessel shell, the air bubbles trapped in the wet castable mix are driven out of the material. A vibrocast mix will be more dense, less porous and stronger than its cast counterpart. The vibration energy also allows the material to be placed with a much lower water content than a castable. Because less water is used to set up the concrete, the type and the amount of cement will vary between a castable and vibration castable mix. Special additives are often used to obtain better flow properties for a vibrocast material versus a regular castable mix. Therefore, castable and vibrocast mixes are not interchangeable and the proper mix needs to be specified prior to installation. Also vibrocast material is not suited for gunning applications. Advantages of using vibrocast refractory over gunning and castables mixes are: 1. less porosity is present, which inhibits coke penetration 2. less water is used during installation, which reduces shrinkage and increases the strength and abrasion resistance of the material; both improving refractory life Disadvantages of vibrocast material versus gunning and casting include: 1. 2. 3. 4.
increased difficulty to install higher installation cost higher shell temperature and vessel weight increased difficulty in tearing out the material for replacement or repairs
Vibration casting may be done in place or the line can be vibrocast in a shop and assembled in the field. Shop casting usually offers better quality control of material but increases the number of field joints which are considered weak links in the line. Also, shop vibrocasting can be done in advance of a Turnaround, thus reducing the amount of time necessary for installation and easing scheduling problems. In-place vibration casting reduces the number of field joints but improperly placed vibrators may cause damage to welds in the line. Most vibrocasting has been done in FCCU riser lines. Hand held vibrators are often used in casting material into gasifiers and other large diameter vessels. 4.1.3
Plastics A plastic refractory is made at the manufacturers' plant and has a stiff consistency similar to modeling clay. No water is added to the plastic. Usually, the plastic is installed with pneumatic ramming guns onto hexmetal anchors or S-bar anchors. Plastics are mainly used in erosive environments because of their abrasion resistance. Their insulating value is poor. The most commonly used plastics are usually 85% or 90% alumina phos-bonded material. The 85% alumina plastics are preferred over the 90% alumina plastic because they are cheaper and no difference in abrasion resistance has been noted when installed side-by-side in cyclones. Installation time with plastics can be 200% quicker than the material it often replaces (Resco AA22) and less material is thrown away when using plastic over AA-22. Plastics have been used extensively in cyclones, air rings and parts of transfer lines.
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The limitation for plastics is that they must be cured to 750oF (399oC) without being exposed to steam. If the material does not reach this temperature, it will become soft. Also, care must be taken during curing and dryout, especially with linings over 1 inch, to prevent laminations from developing that will lead to spalling. Laboratory data also indicates that the higher the temperature the plastic achieves during dryout, the better the abrasive resistance. 4.1.4
Ramming Mixes Ramming mixes are prepared similarly to castables but have the consistency of a plastic after mixing. The extra stiffness of the mix allows it to be worked into place with ramming guns or hammers. Ramming mixes usually have higher cement content than castables and are often difficult to work with. These mixes are not widely used in the refining or petrochemical industry.
4.1.5
Chemical Setting Mixes Chemical setting mixes, such as AA-22, are materials that will harden due to the reaction of acids or other chemicals with the cement in the refractory mix. The materials are similar to castables except that water and a chemical must be mixed at the same time. The reaction is more sensitive to air temperature than a hydraulic mix, making this type of material difficult to work with in the field. AA-22 is the standard erosion resistant material for high wear areas in slide valves and regenerator cyclones. Acid resistant concrete is another type of chemical setting mix usually consisting of silica grains with a potassium silicate binder phase. Acid is added to the mix forming a gel between the aggregates. As with castables, proper curing and dryouts are necessary before the material develops optimal strength. During application and cure out, acid fumes may be given off and care must be taken during installation. The material can be applied by casting or gunning, but gunning is sometimes difficult and laminations may form in the lining. An organic membrane is recommended to be used behind the material to further protect the shell. Acid resistant linings usually begin to deteriorate above a pH 9, thus the lining should not be exposed to caustic wash or when the process has a high pH. The most common areas for acid resistant material are within incinerators, sulfur recovery vessels which are acidic, and knockout drums. In vessels that have varying pH between 5 and 9, a haydite/lumnite castable should be used. The lining is not as acid resistant as the potassium silicate bonded material but is more forgiving and easier to apply.
4.1.6
Fiber Linings Fiber linings are most often used in process heaters. Two types of lining used are: 1) wallpaper construction consisting of layers of 1 inch thick blanket, and 2) modules consisting of blocks of folded 1 inch blankets. The blanket consists of interwoven alumina/silica glass fibers. The fiber blankets are very good for insulation purposes but can be easily abraded. As with other refractory linings, anchors must be used to hold the blankets onto the vessel shell. Fiber modules are often installed in units that need thick insulation, operate at high temperatures, or in units burning dirty fuels because their fabrication makes them more resistant to the process, faster to install, and more economical than wallpaper construction. The modules consist of folded blankets with metal rods through their base to hold them together and assist in installing the modules to the shell. During fabrication, the folded blankets are compressed which enables better wear than the wallpaper design. Fiber boards are denser compressed fibers in a matrix. The boards are often used in front of the blankets for abrasion protection. These types of linings are generally less robust than conventional refractory linings and do not give good long-term performance in firebox conditions. There are also health and safety concerns with fiber lined applications.
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Fiber ropes, gaskets and seals have been used in various applications for expansion gaps and as replacements for asbestos material. The gaskets and ropes are made with similar fibers, as the blankets, but are woven together for additional strength. 4.1.7
Bricks/Formed Shapes Bricks and formed shapes are made at the manufacturers' plant and sent to the site for installation. The bricks are fired at high temperatures, giving them a ceramic bond instead of a cement bond typically found in castables. Therefore, bricks tend to be more resistant to acids and other chemicals than castables of similar chemistry. Brick installation usually takes more time than castables and relies on mortar between the bricks to maintain the integrity of the lining. High alumina bricks are often used in sulfur recovery units and hydrogen generation units, whereas super-duty insulating bricks are more readily used in stacks coming off incinerators and heaters. In most applications, low iron content in the brick is required to prevent chemical attack of the brick by CO, CO2, and H2S04· Formed shapes are used in burner outlets of heaters and in areas of high abrasion such as air ring nozzles. During installation, mortar is used between the bricks and formed shapes to keep gas from moving to the shell. If the wrong mortar is used, the bricks may become loose or be chemically attacked by the mortar.
4.2
MATERIAL SPECIFICATIONS SPECIFICATIONS When refractories are used, the type of material needs to be stated along with the method of installation. Once the type of refractory is chosen, the material requested should meet minimal specifications.
4.2.1 Chemical Composition The chemical composition of a refractory is important for determining: 1. the maximum operating temperature 2. the corrosion resistance of the refractory to the operating environment 3. the resistance to thermal cycling The composition of the refractory will be a function of the type of aggregates and cement binders. The aggregates are typically alumina silicates and the binder is normally calcium aluminates. Therefore, an increase in calcium content of the product generally corresponds to an increase in the cement content or to the use of a lower melting, calcium aluminate cement. Besides melting at lower temperatures, calcium rich cements do not offer good protection against acid attack. High alkali contents in a cement reduce the quality of the refractory and limit the temperature at which the refractory should be used. Also, a high alkali content may indicate that additives have been mixed with the cement to adjust the setting time which should not be done. In C02/CO rich environments, low iron refractories are specified to prevent the material from crumbling because of the chemical reaction between iron and CO2/CO. High alumina refractories are specified for units operating above 2200oF (1204oC) and in units with a H2 rich atmosphere (the H2 will cause silica to vaporize). 4.2.2
Bulk Density The bulk density of the material is needed for design purposes to assure proper loading of the vessel or line. Generally, an increase in the density of the product will increase the strength, thermal conductivity and abrasion resistance of the material.
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4.2.3
Cold Crushing The cold crushing strength becomes important in coking environments, in areas exposed to heavy vibrations and for general mechanical stability of the lining. Higher strength material usually lasts longer but may be more difficult to remove, have high thermal conductivity and may undergo thermal shock compared to standard strength material.
4.2.4
Permanent Liner Change During curing and dryout, the refractory will undergo changes due to dehydration. Normally, the material shrinks causing cracking in the concrete. Excessive shrinkage can cause large cracks, pull the material away from the shell, and leave gaps between different layers of refractories. Any of these problems could lead to hot spots or poor lining performance.
4.2.5
Thermal Conductivity The amount of heat loss from a process should be kept minimal. Therefore, materials should be chosen with the lowest thermal conductivity to reduce heat loss. Thermal conductivity is important in most areas except for internally lined systems such as cyclones. Different refractory suppliers measure thermal conductivity in various ways which can produce very dissimilar results. When comparing one refractory with another, care should be taken to ensure an accurate comparison.
4.2.6
Abrasion Resistant Erosion loss is important in vessels that have impingement of particles, such as catalyst, against the side of the unit. For high wear areas, the abrasion resistance of the material is usually the most critical parameter.
4.2.7
Temperature Temperature limits are normally not a concern for many applications in refineries because of the low operating temperatures. However, in sulfur recovery units, where heaters and gasifiers can operate over 2000oF (1093oC), temperature limits are important. Most materials have a maximum use temperature several hundred degrees lower than the melting point of the material. However, at this temperature and under loads, the material may shrink and densify or undergo creep, causing the lining to fail.
4.2.8
Porosity Porosity is a concern in environments that will attack refractories such as coke, sulfur or slag. With low porosity materials, the penetration of the attack is reduced and refractory life is increased. However, low porosity materials are more sensitive to thermal shock, steam spalling at cure-out and have higher thermal conductivities.
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Table 1-7
October 1999
GENERAL TYPES OF REFRACTORY MATERIAL FOR CHEMICAL PROCESS INDUSTRY (CPI) USE NOMINAL DENSITY
COMP. STRENGTH psi
COMMENTS
CASTABLES Erosion Resistant
120-180
5000-15000
For cyclones and catalyst lines, need erosions resistance (ASTM C-704) of 10 cc or less.
Dense High Strength
120-130
3000-6000
For high strength vessel and duct lining
Semi Insulating (one-shot)
75-95
1000-3000
For general vessel, stack and duct lining
Insulating
50-80
500-2000
For furnace and boiler linings and as back-up lining
Chemical Bond Mortars
120-180
1000-4000
Both alumino-phosphate and silicate bonded materials are used for patching and rebuilding
120-180
1000-6000
Frequently have good erosion resistance used for patching and rebuilding. Heat sets usually not used because of low temperature in refining and chemical process industry
Insulating Fire (IFB)
30-80
100-1000
Used in furnaces and as back-up lining
Dense Firebrick
130-200
4000-12000
Available as working lining in high abrasion areas.
CERAMIC FIBER
4-24
--
Available in blanket, module and spray-on form.
PLASTICS Chemical Bond
BRICK
Table 1-8 SELECTION OF REFRACTORIES FOR REFINERY USAGE UNIT
CONDITIONS
REFRACTORY TYPE
FCCU vessels
1000-1400oF (538-760oC), mild erosion oxidizing or reducing atmospheres
One-shot lining in independent anchors.
Cyclones, catalyst transfer lines and slide valves
1000-1400oF (538-760oC), extreme erosion
Special erosion-resistant castables (consult refractory manufacturer.)
Naphtha Reformers
1000oF (538oC), low to moderate erosion, high-hydrogen atmospheres
Insulating concrete (low iron) protected by stainless steel shroud or layer of dense low-iron concrete.
H2 producing units
2000-3000oF (1093-1649oC), high-hydrogen atmospheres
Super-duty brick or castable of low silica content (consult refractory manufacturer.)
Process furnaces, stills and boilers
1800-2400oF (982-1316oC), oxidizing atmospheres, some mechanical or thermal spalling
Side walls and roof may be of insulating or oneshot concrete or of insulating firebrick; burner and flame-impingement walls may be of super-duty plastic, brick or high-strength refractory concrete; floors may be of dense castable or fire-clay brick.
Stacks and breechings
600-1500oF (316-816oC), mild erosion, some mechanical or thermal spalling
One-shot linings; areas subject to erosion or thermal spalling can be faced with an aluminophosphate-based refractory.
Incinerators
2000-2800oF (1093-1538oC), ash attack, mechanical or thermal spalling
Super-duty brick, plastic
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4.3
October 1999
MATERIAL TESTING To assure that the proper material is being used for a given application, material testing needs to be done to prequalify the material. Manufacturers generally forego extensive testing of their material after manufacturing. Therefore, many refining companies have specified testing the refractory before accepting the material. Material which fails these tests is often sent to a buyer who does not have specifications or who does not test the material. The material testing is performed by removing a sample of refractory from each pallet or at a set interval and preparing the material similar to field installation. The samples are made according to standard ASTM methods and are tested for cold crushing, density and permanent linear change as a minimum. Abrasion testing is specified for erosive resistant material. Materials not passing any one of the tests are retested. If the average of the two tests is still below specification, the material should be rejected. Most refractory mixes have a recommended shelf life of approximately six months. After this time, the cement in the mix will begin to deteriorate, especially in humid conditions. Therefore, any material stored more than 2 months after manufacturing or not kept in a protective enclosure should be retested prior to use. For large turnarounds, the ordering of the material should be planned in advance so that the manufacturer can deliver the material on-site at a given date to minimize storage time. Testing is also required during application of the material to: 1. assure the material was installed correctly 2. to assist in developing the root cause should the lining fail If any of the field test samples fail during installation testing, core drilling and testing of the core may be required to assure the line is in good condition. Hammer testing and visual inspection of the liner should also be done if the unit is not immediately placed into service after dry-out or when a prefabricated line/vessel is received at the plant.
4.4
DESIGN The design of a refractory lining is dependent on the process conditions (temperature, atmosphere, velocity, particulates in the gas, etc.), vessel support structures, desirable shell temperature and length of downtime. For most applications, monolithic linings are easier to install and maintain than a two component lining. The main criteria for a design is to keep as much heat in the process as possible without destroying the refractory lining through erosion/corrosion or by exerting high stresses within the lining. High stresses can be caused by improper anchor placement, thermal cycling and improper expansion joints. Usually the lowest temperature for design is approximately 50oF (10oC) above dew point at the shell refractory interface to prevent corrosion of the shell. Temperature profiles for the lowest temperature with maximum wind and highest temperature with no wind should be calculated to assure the lining will meet design criteria for the process or the metallurgy. Typically, materials with higher strengths and abrasion resistance are the poorest in insulating value. Denser materials are more thermal shock sensitive but tend to last better in heavy coking environments. Before FCC riser cracking was developed, most of the riser lines had either a medium weight material or two component lining. Heavy coking during riser cracking forced refineries to heavy weight material, adding an extra 10 tons to the support springs and calling for support calculations.
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4.5
October 1999
ANCHORING SYSTEMS SYSTEMS AND STEEL FIBERS Most refractories need to be installed on anchoring systems. The anchors hold the material to the shell after cracks have developed during dryout (hairline cracking is typically found after dryouts of many linings) and normal operations. Even the loss of a few anchors may lead to the development of a hot spot. Steel fibers are also added to the refractory to hold gunned and cast material in place after small cracks develop. Fibers should not be used in CO rich environments. The recommended lengths for fibers are 3/4" for gunning applications and 1" for casting applications. Metallurgy should be Type 304 stainless steel melt extracted fibers. Extruded fibers are not used because they can cause safety problems during inspection since they do not bend downwards. Fibers made from Type 410 oxidize and become embrittled more rapidly than Type 304. The most common problem with the anchors is poor welding. Either incomplete welds are done or poor penetration is obtained. The frequency of the problems are usually increased using automatic stud welding. Every anchor should be visually inspected and hammer tested to make sure the weld is properly done. For most gunned and cast linings, wavy 'v' or 'y' anchors are recommended. Steerhorns should not be used because they have a tendency to cause a shear plane to form at the steerhorn. Several instances have been recorded where large sheets of material have fallen off. To reduce chances of shear planes with the 'v' and 'y' anchors, every other anchor should be rotated 90 degrees. The typical layout for these anchors is a diamond pattern. Hexmetal is used for 1 inch thick liners in cyclones, air rings, dragon heads and other high abrasion areas. Poor welding or improper tie down of the hexmetal end often causes the loss of refractory. In cases of heavy vibration and movement of the metal, the crotch of every biscuit should be welded to the shell. Hexmetal is difficult to install on small diameter areas or in small confined spaces even when flexible hexmetal is used. In these areas, S-bar anchors may be used. S-bar anchors are also recommended for areas that undergo large movements from thermal expansions or for repairing small areas of damaged hexmetal. The S-bars are not recommended for thick lining because they can cause difficulties during installation (the anchors are difficult to gun around because of a shadowing affect). For 2" thick gunned linings, 1:2:4 (Haydite-Lumnite-Vermiculite) crimped anchors and wire mesh may be used. The wire provides additional strength to the lining when using small wavy ‘v’ or ‘y’ anchors. The Plibrico Taco anchor system has been used with services in several FCC locations where hexsteel and S-bars have failed.
4.6
INSTALLATION Even if the best material and design are used for the refractory lining, the lining will give poor service if the installation is performed incorrectly. Testing and inspection during installation can reduce problems in the field, but the refractory lining may have to be torn out resulting in lost money and time. To provide better installation, each individual installer should be pre-qualified for the job. In many instances, the contractor may use inexperienced people to complete the jobs. To help alleviate this problem, the API Task Force for Refractories is developing a certification system so
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individuals will not have to be qualified on every job. During any given job, some of the specifications may be deemed to be unrealistic, time consuming or unnecessary. Before waving the specifications, possible problem areas should be discussed. The main problems to be aware of during installation are: 1. Improper water content of the mix; too little or too much water will reduce the physical properties of the material or cause installation problems in adhering the refractory to the shell 2. Improper mix time which allows poor material to be installed 3. Failure of anchors due to poor welding 4. Laminations in gunned material because of poor installers 5. Poor lining because the installer did not have the proper equipment on site Because most facilities lack qualified inspectors or do not have enough inspectors to cover the job, specialist third party inspection services are sometimes recommended. The inspection services and testing of the material will add approximately 10% to the final cost of the job. However, savings can be quickly realized by prolonging refractory life and the avoidance of unscheduled shutdowns if in-house expertise is not available. Refiners will tend to use third party inspectors with whom they have had good experience. Third party inspectors are similar to installers - some are good; some are not so good. 4.7
CURING AND DRYOUT DRYOUT As mentioned previously, improper curing and dryout will damage the lining. During curing, an exothermic reaction occurs causing heat to be released from the concrete. If the top of the concrete dries out too quickly, thermo-mechanical stresses in the lining could cause excessive cracking of the material. To alleviate this problem, curing compounds are specified for castable and gunning installation. As with portland cement based concrete, the strength of a refractory will develop over time. However, the refractory cannot be used at elevated temperatures until the water in the material is driven off as steam. Controlled dryouts are scheduled to remove the water without causing pressure buildup in the material by the steam. Steam spalling is most likely to occur with dense, low porosity material. Companies specializing in dryout procedures are often contracted to do the work following large turnarounds. The contracted dryout companies will place gas forced air heaters throughout the vessel along with thermocouples to monitor the dryout. The dryout rate of a refractory can be increased by using burnout fibers. The fibers are composed of organic materials which vaporize at low temperatures, leaving small interconnecting channels from which steam can escape. The fibers are not often used because they lower the properties of the refractory and can increase the amount of coking within the refractory.
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