BEST MANAGEMENT PRACTICE
Mitigation of External Corrosion on Buried Pipeline Systems June 2009
2009-0011
The Canadian Association of Petroleum Producers (CAPP) represents 130 companies that explore for, develop and produce more than 90 per cent of Canada’s natural gas and crude oil. CAPP also has 150 associate member companies that provide a wide range of services that support the upstream oil and natural gas industry. Together, these members and associate members are an important part of a $120-billion-a-year national industry that affects the livelihoods of more than half a million Canadians.
Review by July 2013
Disclaimer This publication was prepared for the Canadian Association of Petroleum Producers (CAPP). While it is believed that the information contained herein is reliable under the conditions and subject to the limitations set out, CAPP does not guarantee its accuracy. The use of this report or any information contained will be at the user’s sole risk, regardless of any fault or negligence of CAPP or its co-funders. .
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www.capp.ca Ÿ
[email protected]
Contents Overview ...................................................................................................................................1 1
Failure Statistics (Alberta) ...........................................................................................2
2
Corrosion Mechanisms and Mitigation.......................................................................3 2.1 2.2 2.3
2.4
Localized and General Corrosion ...................................................................3 Soil Types.........................................................................................................4 Plant Applied Protective Coatings..................................................................4 2.3.1 Thermally Insulated Pipelines ............................................................6 2.3.2 Field Applied Protective Coatings .....................................................6 2.3.3 Installation Quality for Field Applied Coatings ................................7 2.3.4 Coating Degradation – Heat Damage, Disbondment & Blistering ..8 2.3.5 Coating Degradation - UV Damage...................................................9 2.3.6 Shielding of Cathodic Protection Current..........................................9 Contributing Factors........................................................................................9
3
Recommended Practices ............................................................................................13
4
Corrosion Mitigation Techniques..............................................................................18
5
Corrosion Monitoring Techniques ............................................................................19
6
Inspection Techniques ...............................................................................................20
7
Leak Detection Techniques .......................................................................................21
8
Repair and Rehabilitation Techniques......................................................................22
9
Additional Resources .................................................................................................24
Figures Figure 2-1: Operating Pipeline Failures Caused by External Corrosion...........................................2
Tables Table 2-1: Soil Resistivity Effect on Corrosion Rates4 ......................................................................4 Table 2-2: Contributing Factors and Mitigation of External Corrosion.................................... 10-12 Table 4-1: Recommended Practices - Design and Construction ............................................... 13-15 Table 4-2: Recommended Practices - Operating ........................................................................ 15-17 Table 5-1: Corrosion Mitigation Techniques....................................................................................18 Table 6-1: Corrosion Monitoring Techniques ..................................................................................19 Table 7-1: Inspection Techniques......................................................................................................20 Table 8-1: Leak Detection Techniques ....................................................................................... 21-22 Table 9-1: Repair and Rehabilitation Techniques ...................................................................... 23-24 Page i
June 2009 Recommended Practice for the Mitigation of External Corrosion on Buried Pipeline Systems
Overview Corrosion is a dominant contributing factor to failures and leaks in pipelines. To deal with this issue, the CAPP Pipeline Technical Committee has developed industry recommended practices to improve and maintain the mechanical integrity of upstream pipelines. They are intended to assist upstream oil and gas producers in recognizing the conditions that contribute to pipeline corrosion incidents, and identify effective measures that can be taken to reduce the likelihood of corrosion incidents. This document addresses the design, maintenance and operating considerations for the mitigation of external corrosion on buried pipelines constructed with carbon steel materials. This document does not address failures due to environmental cracking such as stress corrosion cracking (SCC) and hydrogen induced cracking (HIC). This document is complementary to CSA Z662 and supports the development of corrosion control practices within Pipeline Integrity Management Programs, as required by CSA Z662 and the applicable regulatory agency. In the case of any inconsistencies between the guidance provided in this document and either Z662 or regulatory requirements, the latter should be adhered to. This document is intended for use by corrosion specialists involved with the development and execution of corrosion mitigation programs, engineering teams involved in the design of gathering systems, and operations personnel involved with the implementation of corrosion mitigation programs and operation of wells and pipelines in a safe and efficient manner. It contains a consolidation of key industry experience and knowledge used to reduce external corrosion; however, it is not intended to be a comprehensive overview of all practices. Additional corrosion mitigation recommended practices available are: • • • •
Best Management Practice for Mitigation of Internal Corrosion in Sour Gas Pipeline Systems Best Management Practice for Mitigation of Internal Corrosion in Sour Gas Pipeline Systems Best Management Practice for Mitigation of Internal Corrosion in Oil Effluent Pipeline Systems Best Management Practice for Mitigation of Internal Corrosion in Oilfield Water Pipeline Systems
These documents are available free of charge on the CAPP website at www.capp.ca.
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June 2009 Recommended Practice for the Mitigation of External Corrosion on Buried Pipeline Systems
1
Failure Statistics (Alberta) •
In 2008, 13% of the total incidents in Alberta were due to external corrosion. Unknown (17), 2% Operator Error (21), 2%
Earth Mo vement (13), 1% Overpressure (21), 2%
Weld Failure (Girth or Seam Rupture) (24), 2% Mechanical or Valve/Fitting Failure (82), 8% Internal Corrosion (384), 39% Construction Damage/ Installation (93), 10%
Miscellaneous/ Pipe Failure (90), 9% Damage by Others (98), 10%
External Corrosion (131), 13%
Figure 1-1: Operating Pipeline Failures Caused by All Causes
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2
Corrosion Mechanisms and Mitigation Corrosion of underground structures such as pipelines is controlled by the use of protective coatings and by maintaining adequate levels of cathodic protection (CP). The role of the coating is to act as a physical and dielectric (low or nonconductive) barrier. The protective coating acts as the primary or first line of defense against corrosion; however no coating systems are perfect. To protect the pipe against corrosion at coating voids, or breaks referred to as holidays, cathodic protection current is applied. Effective cathodic protection will reduce the soil side corrosion rate to a negligible level. CSA Z662, Oil and Gas Pipeline Systems, specifies requirements for external coatings and cathodic protection of pipelines.
2.1
Localized and General Corrosion External corrosion of pipelines typically occurs where coating defects allow contact of the steel with the wet soil. The common features of this mechanism are: •
• •
Coating defects such as holidays1, wrinkling or disbanding2 Moisture from the soil is in contact with the metal surface Cathodic protection is shielded3 or is not sufficient
External corrosion of underground structures manifests itself as either general wall loss or localized corrosion. Industry experience has shown that underground corrosion rates on bare unprotected pipe (i.e. no coating or CP) vary depending on a number of factors including soil resistivity. Although the corrosion rates may vary it is generally accepted that all soils are corrosive. External corrosion damage which may start as localized pitting can interact to an extent that the load bearing capability of the pipeline is decreased and a failure may result. When doing predictions and engineering assessments of external corrosion on carbon steel underground structures, the failure mode should be considered in the consequence analysis. (1) A holiday is a break in the coating system that exposes the bare metal to the environment (2) Disbondment is a failure of the bond between the coating and the steel pipe. Disbondments allow water to migrate under the coating. (3) Shielding is the prevention or diversion of cathodic protection current from its intended path. There must be a continuous electrolytic path between the protected pipe and the anodes. Disbonded coating may create a holiday as well as shield the cathodic protection current.
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2.2
Soil Types Soil pH, salinity, moisture content, resistivity, and microbes all affect corrosivity where bare steel is exposed. The soil resistivity at different areas on a pipeline will vary based on moisture content and mineral composition. Table 2-1 summarizes the effect of different soil types/resistivity on typical external corrosion rates. The corrosion rates identified in Table 2-1 are for bare steel and no cathodic protection. Table 2-1: Soil Resistivity Effect on Corrosion Rates
SOIL RESISTIVITY (ohm-cm)
SOIL TYPE
MOISTURE
CORROSION (mm/yr)
1.0
500 - 2000
Loams/clays
Mainly wet
Corrosive to moderately corrosive 0.5 – 1.0
2000 - 10000
Gravels, sandy
Mainly dry
Mildly corrosive 0.2 - 0.5
>10000
Arid, sandy
Always dry
Non-corrosive < 0.2
Source: Modified from Corrosion Basics—An Introduction, NACE Press
2.3
Plant Applied Protective Coatings Coatings perform two distinct functions. They provide a physical corrosion barrier between the steel structure and the surrounding environment. Coatings also reduce the amount of cathodic protection current required by lowering the amount of metal which directly contacts the soil. Coating technology has changed over time, which has resulted in the use of many different types of coating systems, including but not limited to the following: 1) Fusion Bond Epoxy (FBE) • Epoxy coating consisting of resins, curing agents, catalysts, accelerators, etc.
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June 2009 Recommended Practice for the Mitigation of External Corrosion on Buried Pipeline Systems
• Excellent adhesion and resistance to soil stress, gouging and abrasion. Does not shield cathodic protection current (i.e. fails safe) 2) Abrasion Resistant Fusion Bond Epoxy (Dual Power – DPS) • Several layers of FBE, or FBE overcoated with a liquid epoxy, to provide improved abrasion resistance • Often used for horizontal directional drill (HDD) sections 3) Three (3) Layer Extruded Polyethylene • Product consists of three layers; an FBE primer, a co-polymeric adhesive, and a extruded polyethylene outer sheath 4) Two (2) Layer Extruded Polyethylene (i.e. YJ-1, Yellow Jacket) • Rubber modified asphalt adhesive covered by an extrudes polyethylene outer sheath 5) Thermally insulated Pipeline coatings such as: • Polyurethane foam applied direct to pipe, polyethylene tape or extruded polyethylene outer jacket – outdated • Primer, polyethylene tape anti corrosion barrier, polyurethane foam, extruded polyethylene outer jacket • Primer, polyethylene tape anti corrosion barrier, polyurethane foam, polyethylene tape outer jacket - outdated • Two layer extruded polyethylene anti-corrosion barrier, polyurethane foam, extruded polyethylene outer jacket - outdated • Fusion bond epoxy anti-corrosion barrier, polyurethane foam, extruded polyethylene outer jacket • Three layer extruded polyethylene anti-corrosion barrier, polyurethane foam, extruded polyethylene outer jacket 6) Polyethylene Tape (solid film backing) • Primer, butyl rubber or similar adhesive, and polyethylene solid film backing applied in a spiral wrap • Poor adhesion, soil stress resistance. Low operating temperature. 7) Coal-tar enamel and asphalt mastics • 1950-60’s technology no longer in use. Coal tar pipe coatings can contain kraft paper layers, asbestos, or fiberglass layers to improve their performance • Care must be taken when working with coal tar coatings to avoid asbestos hazards
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June 2009 Recommended Practice for the Mitigation of External Corrosion on Buried Pipeline Systems
2.3.1 Thermally Insulated Pipelines Coating systems, which provide thermal insulation, are widely used on upstream pipelines that transport wet gas. The thermal insulation helps prevent hydrates from forming. Typically a thermally insulated pipe system will include an anti corrosion barrier on the pipe (ie. Polyethylene tape or FBE applied directly to the steel surface), a layer of polyurethane foam (typically 2” thick), and a polyethylene outer jacket coating. The outer jacket coating is meant to prevent water ingress into the insulation as well as to provide mechanical protection to the insulation. The outer jacket can, for a number of reasons, be damaged and not completely effective. The polyurethane foam material used for the insulation is not water resistant. Therefore, it cannot be relied upon to protect uncoated steel. If water does reach the pipe surface the anti-corrosion barrier is meant to prevent corrosion. In the past, some thermally insulated pipelines were installed without an anti corrosion barrier. Due to serious problems with external corrosion the current recommended industry practice is to always apply an anti-corrosion barrier coating. At the field joints, the insulation system is commonly provided by the use of half shells. Gaps along the edges of the half-shells can allow the easy ingress of water. An alternative approach involves the use of field-molding the girth weld insulation, using a portable mould. The molded insulation fills the girth-weld insulation cavity better than half-shells and adds an additional moisture seal. The field molding process is highly recommended and leads to a much lower risk of external corrosion. For insulated pipelines, cathodic protection is believed to have very limited benefit. This is due to the multiple layers of dielectric material that tend to shield the protective current. Insulated pipelines rely solely on the integrity of the external outer jacket coating, and the anti-corrosion barrier, to prevent external corrosion. 2.3.2 Field Applied Protective Coatings It is important to ensure that the joint coating material used is compatible with the plant applied pipe coating material. An industry recommended practice is to select joint coating that closely matches the performance characteristics of the plant applied protective coating.
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The most common field joint coating systems used for upstream gathering system pipelines are: • • •
Heat shrink sleeves Polyehylene tape wrap Hand applied liquid epoxy
Heat shrink sleeves applied in the field to pipeline girth welds are either two-layer or three-layer systems depending on what type of plant applied coating is used. If the pipe is coated with a two-layer extruded polyethylene system the sleeve will typically be a two-layer sleeve to match. Wrap-around style sleeves are superior in performance. The use of older tube style sleeves is not recommended as they tend to get contaminated before they can be shrunk down. Polyethylene tapes can be applied by hand wrapping, or by using portable hand wrapping equipment. The key to successful application relies on tape selection, surface preparation and proper application. Soil stresses tend to damage tapes especially on large diameter pipelines. Woven Geotextile tapes are also available. Similar to polyethylene tape but with superior soil stress resistance. These generally require the use of a hand wrapping machines. Hand applied two part liquid epoxies are typically used for fusion bond epoxy pipelines as their performance characteristics closely match the FBE material. Irregular shapes are often encountered on pipelines. These include shop bends, 45 deg elbows, 90 deg elbows, tees, weld-o-lets, repair sleeves, etc. Shrink sleeves or tape coatings are not designed to coat such irregular shapes, and have lead to corrosion problems in service. Irregular shapes should be coated with Petrolatum tapes or other conformable coatings specifically meant for the task. Liquid epoxy may also be used for the same purpose. 2.3.3 Installation Quality for Field Applied Coatings Field applied coatings used for coating weld joints, fittings, risers, or for making repairs to damaged coatings, are an important part of any coating system. The field application of pipeline coatings is always challenging. These coatings are applied outside in non-ideal weather conditions and in difficult terrain. However, if the quality of the work is not comparable to the plant applied coating corrosion problems, often referred to as joint corrosion, will result. CSA Z662 requires that field applied coatings be applied in accordance with documented procedures and an appropriate quality program. Coatings must also be inspected prior to backfill. The sole use of coating manufacturer’s installation guides does not adequately cover the above requirement. It is important that owner companies develop specific coating application standards, specifications,
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June 2009 Recommended Practice for the Mitigation of External Corrosion on Buried Pipeline Systems
or procedures to make clear the minimum requirements for field applied coatings. Such standards should consist of the following elements. •
List of Approved Coatings – suitable coatings selected to be compatible with the plant applied coating are described by manufacturer and product name
•
Contractor Supervision and Crew Size - a coating crew foreman responsible for quality is important. The number of workers in a coating crew must be sufficient to ensure quality and the required productivity.
•
Application Crew Training – The workers must be trained on how to proper apply protective coatings
•
Minimum List of Tools and Equipment – specialized tools and equipment are needed to do the work properly
•
Storage and Handling Requirements – most coating materials should not be frozen, or otherwise contaminated prior to use
•
Surface Preparation – the level of surface preparation is crucial for achieving a bond to the pipe. Grit blasting helps improve adhesion for all coatings and is mandatory for some types of coatings.
•
Pre-Heating – pre-heating is crucial form most types of pipeline coatings
•
Application Requirements – application procedures should meet or exceed the coating manufacturers minimum requirements
•
Inspection – CSA Z662 requires that coating work be inspected. Inspection may include item such as grit blast profile, hardness (cure), peel tests for shrink sleeves, etc. Poor inspection, or a lack of inspection, is a common aspect of joint corrosion.
Common barriers to obtaining good quality field applied coatings are lack of worker supervision, poor training of the workers that are applying the coatings, and a lack of proper coating inspection. Addressing these issues will improve the long term performance of any coating system and help avoid disbonded and shielding joint coatings. 2.3.4 Coating Degradation – Heat Damage, Disbondment & Blistering Excessive heat can cause pipe coatings to soften, flow, or become cracked and brittle. The result will be a disbonded and ineffective coating. Soil stresses from due to backfill weight, soil-induced shear stress applied to the coating due to thermal expansion, pipe settlement or soil settlement, can cause disbondment or wrinkling of the coating.
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Excessive CP current can also cause blisters in FBE coating, especially in hot and wet soil environments. The locally increased pH and/or hydrogen molecules being liberated at a holiday in the coating may cause the coating to disbond around a holiday. 2.3.5 Coating Degradation - UV Damage Cracking or embrittlement of coatings can occur due to prolonged ultraviolet exposure prior to burial. This can happen if coated pipe is stored outside for prolonged periods. Ultraviolet exposure of fusion bond epoxy coatings may result in chalking and should be evaluated with the manufacturer prior to use. This can also occur at locations where the pipe coating comes above ground but it not protected from the elements. 2.3.6 Shielding of Cathodic Protection Current The shielding of cathodic protection current is a common problem that can lead to external corrosion damage and pipeline failures. Coatings with high dielectric strength such as extruded polyethylene, shrink sleeves, and polyethylene tape may lead to the shielding of cathodic protection current if damaged or disbonded. Improving the quality of the application work can reduce the affects of disbonded and shielding pipe coatings. Alternatively non-shielding (i.e. fail safe) coatings such as FBE can be used, especially at high consequence areas such as waterways, populated areas, environmentally sensitive areas, etc. Most over the line survey techniques will not reliably detect the presence of shielding coatings. In-line inspection and repair is the best way reduce corrosion failures if disbonded coatings and CP shielding are present. 2.4
Contributing Factors Table 2-2 describes the most common contributors, causes and effects of external corrosion of pipelines. The table also contains corresponding industry accepted mitigation methods used to reduce external corrosion.
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Table 2-2: Contributing Factors and Mitigation of External Corrosion Contributor
Cause/Source
Effect
Mitigation
Excess operating temperature
• Coating failure
• Water ingress
• Coating disbondment
• cathodic shielding
• Reduce operating temperature below limit of coating and mastic • Select coating system with temperature greater than operating temperature
Pipe movement/soil stress
• Excess operating temperature • Operating temperature variation
• Coating damage • Water ingress • cathodic shielding
• Improper support Ground movement/soil stress
Improper handling and backfill
• Coating selection that meets the design requirements
• Unstable soils
• Coating damage
• Route selection
• Freeze thaw cycles
• Water ingress
• Soil stabilization
• cathodic shielding
• Coating selection
• Coating damage
• Proper construction practices
• Rock damage
• Water ingress • cathodic shielding
Poor joint coating
• Proper pipeline design
• Poor joint coating selection / Incompatible pipe and joint coating • Improper application of joint coating
• disbonded coating • water ingress • cathodic shielding
• Inadequate personnel training • Limited supervision or inspection of work
• Coating selection • proper design and engineering • application standards or specifcations • trained personnel • construction QC • coatings inspection
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June 2009 Recommended Practice for the Mitigation of External Corrosion on Buried Pipeline Systems
Contributor
Cause/Source
Effect
Mitigation
See NACE RP0303 Field Applied Heat Shrinkable Sleeves For Pipelines; Application, Performance, Quality Control Insulation
• pipelines without a corrosion barrier between pipe and insulation • Poor joint coating quality that allows water ingress
• water can enter at holidays and follow the pipe wall • water can enter joint area • outer coating and insulation will shield cathodic protection
• ensure coating system includes anti-corrosion barrier • Follow written coating standards or specification to ensure quality work done on joint coatings • Injection mould foam at joint rather than half shells • Employ qualified coating inspectors to ensure quality of work
Concrete weights and anchor blocks
• pipelines with out adequate coating with in the concrete portion • damaged coating
• water ingress • Cathodic shielding by the concrete
• Coating must be designed with consideration for anchor • coat pipe prior to pouring concrete • inspect coating prior to installing anchor
Externally weight-coated pipe, and rock shielding
• these are not corrosion barriers
• water ingress • cathodic shielding
• install 100% holiday free corrosion barrier applied directly to pipe
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June 2009 Recommended Practice for the Mitigation of External Corrosion on Buried Pipeline Systems
Contributor
Cause/Source
Effect
Mitigation
Cased Crossings
• casing in contact with carrier pipe
• Cathodic shielding by casing
• install non metallic centralizers
• damaged coating
• Insufficient cathodic protection
• ensure coating is 100% holiday free • keep water out of casing
Bored Crossings – no casing
Soil to Air Interface (Risers)
• coating damaged during installation
• water ingress • cathodic shielding by protective coatings used as rock shields
• Damaged coating • Lack of coating
• install 100% holiday free corrosion barrier • apply cathodic protection
• Coating UV degradation
• proper coating selection
• Coating mechanical damage
• install coating above interface
• water ingress
• inspection and maintenance
• unreliable CP due to intermittent electrolyte
• mechanical shielding
Cathodic protection insufficient
• cathodic protection system operating below NACE RP0169 criteria
• external corrosion at coating defects
• perform CP system survey and adjust
Cathodic interference
• foreign cathodic protection systems
• Improper cathodic protection
• Properly design cathodic protection system
• AC power lines
Excess CP
• Improperly operated system
• Proper survey and maintenance • Possible coating damage
• Perform CP system survey and adjust
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3
Recommended Practices Table 3-1 describes the recommended practices for mitigation of external corrosion during the design and construction phase of a piepline’s lifecycle. Table 3-2 describes the recommended practices for the mitigation of external corrosion during the operating phase of a pipeline lifecyle. Table 3-1: Recommended Practices – Design and Construction
Element
Recommended Practice
Benefit
Comments
Coating – Plant Applied
• Select coating system with design temperature exceeding operating temperature
• Prevent disbondment and cathodic shielding
• monitor operating conditions to prevent exceeding design specifications
• Coating selection should consider type of soil (water, sand, clay, rock) Coating – Plant Applied Thermally Insulated Pipe
• Select coating system that includes an anticorrosion barrier between pipe and insulation
• Minimize cathodic protection current needed to prevent external corrosion
• Prevents water ingress to pipe surface
• Protect install outer jacket coating system in rocky soils
• cathodic shielding may occur due to the insulation • cannot holiday check outer coating, therefore corrosion barrier must be 100% holiday free.
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June 2009 Recommended Practice for the Mitigation of External Corrosion on Buried Pipeline Systems
Element
Recommended Practice
Benefit
Comments
Coating – Field Applied at Joints
• select a joint coating system that considers the current and future operating conditions
• prevents water ingress
• quality control is essential
• ensures coating system integrity
• applicators must be trained
• select a joint coating system that is compatible with the pipe coating system
• applicator must be using the correct equipment and written procedures
• select a joint coating system appropriate for the field construction environment
• Coating inspection to ensure quality and prevent joint corrosion
• use proper surface preparation as recommended by the coating manufacturer • Develop coating application standards or specifications Joint type
• if joints other than butt welds (i.e. zap-lok) are used consider the effects on cathodic protection
• ensures electrical continuity necessary for CP system to function along the full length of the pipeline
• Verify by periodic system surveys
Cathodic Protection
• Install cathodic protection system
• Protects pipe against corrosion at coating holidays or damage
• Design in accordance with NACE RP0169 • Use proper electrical isolation to avoid current drainage to surface facilities and well casings
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June 2009 Recommended Practice for the Mitigation of External Corrosion on Buried Pipeline Systems
Element
Recommended Practice
Benefit
Inspection Capability
• Install or provide capability for inspection tool launching and receiving
• Internal inspection • Consideration using intelligent pigs is should be given to the most effective the design of bends, method for confirming tees, and risers to overall pipeline allow for passage of integrity inspection tools
• Use consistent line diameter and wall thickness. • Use piggable valves, flanges, and fittings
Comments
• Proper design allows for pipeline inspection without costly modifications or downtime
Table 3-2: Recommended Practices – Operating Element
Recommended Practice
Benefit
Comments
Corrosion Assessment
• Understand what type of coatings exist in a gathering system
• Understand and document design and operating parameters
• Refer to CSA Z662 Clause 9 – Corrosion Control
• Ensures reliability of CP system
• regulatory requirement
• Enables proof of regulatory compliance
• need to include deactivated, discontinued, or suspended lines
• Evaluate operating temperature against coating system design • Assess potential for cathodic shielding • Re-assess CP system operation subsequent to a line failure or system addition CP system maintenance
• Perform annual survey to verify sufficient CP current • Check all insulating kits/joints • Check for interference • Check rectifiers periodically and record outputs
• only abandoned lines should have cathodic protection disconnected
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Element
Recommended Benefit Comments Practice Note: ensure all personnel are trained and hold the required certification for the work being performed.
Inspection Program
• Develop an inspection strategy • Utilize root cause analysis results to modify corrosion mitigation and inspection programs
Repair and Rehabilitation
• Inspect to determine extent and severity of damage prior to carrying out repair or rehabilitation
• Provides assurance that the corrosion mitigation program is effective
• Refer to Section 7 for Corrosion Inspection Techniques
• Allows for corrosion mitigation program adjustments in response to inspection results
• Refer to CSA Z662 Clause 9 – Corrosion Control
• Prevents multiple failures on the same pipeline
• Refer to Section 7 for Corrosion Inspection Techniques
• Prevents recurrence of problem
• Based on inspection results, use CSA Clause 10.9.2 to determine extent and type of repair required
Failure Analysis
• Recovery of an undisturbed sample of the damaged pipeline • Conduct a thorough failure analysis
• Refer to Section 9 for Repair and Rehabilitation Techniques • Refer to CSA Z662 Clause 10.10 for repair requirements
• To understand • Adjust corrosion corrosion mechanisms mitigation program detected during based on results of failure analysis inspections or as a result of a failure
• Use the results of failure analysis to reassess CP system • Measure pipe to soil potential at failure site
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June 2009 Recommended Practice for the Mitigation of External Corrosion on Buried Pipeline Systems
Element
Recommended Practice
Benefit
Comments
Leak Detection
• Integrate a leak detection strategy into a Pipeline Operation and Maintenance Manual
• Permits the detection of leaks
• Refer to Section 8 for Leak Detection Techniques
• Integrate an MOC procedure into a Pipeline Operation and Maintenance Manual
• Ensures that change • Unmanaged change does not impact the has resulted in integrity of the pipeline many pipeline system failures
Management of Change
• Maintain records of pipeline operation and maintenance
• Technique utilized depends on access and ground conditions
• Understand and document design and operating parameters
• Refer to Section 10 for Pipeline Integrity Management System
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June 2009 Recommended Practice for the Mitigation of External Corrosion on Buried Pipeline Systems
4
Corrosion Mitigation Techniques Protective coatings have a significant impact on the life cycle costs of a pipeline. The success of preventing external corrosion is highly dependant on the choice of coating and the quality of the field applied coating work. Table 4-1 describes common techniques that should be considered for the mitigation of external corrosion of pipelines once a pipeline is in operation. Table 4-1: Corrosion Mitigation Techniques
Technique
Description
Comments
Cathodic Protection
• Design, install, operate, and maintain CP system in accordance with NACE RP 0169
• Regulatory requirement • CP system require regular maintenance
• Ensure rectifiers are checked routinely to ensure they are operating at the target current output • Reduce unnecessary rectifier down time due to maintenance activities. • Ensure annual CP surveys are conducted • React quickly to insulation deficiencies, continuity bonding issues, and other problems to ensure CP are functioning properly • Replace deplete groundbeds in a timely fashion • Upgrade CP system if more current is need to provide the proper levels of protection
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5
Corrosion Monitoring Techniques Table 5-1 describes the most common techniques for monitoring corrosion and operating conditions associated with external corrosion of pipelines. Table 5-1: Corrosion Monitoring Techniques
Technique
Description
Comments
Production Monitoring
• Ongoing monitoring of fluid temperature
• Excess temperature may damage the coating
Cathodic Protection
• Maintain, check, and operate CP system in accordance with NACE RP 0169
• Regulatory requirement
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6
Inspection Techniques Table 6-1 describes common techniques that should be considered for the detection of external corrosion and coating degradation of pipelines. Table 6-1: Inspection Techniques
Options
Technique
Comments
CP effectiveness survey
• Close interval survey
• Determines adequate protection level
• Annual system survey
• Detects interference • May detect significant coating problem areas
Coating Integrity Survey
• C – Scan Coating Conductance Survey • ACVG (pin to pin) Coating survey
In-Line Inspection
• Magnetic flux leakage (MFL), ultrasonic and eddy current tools are available. MFL is the most commonly used technique
• Detailed coating evaluation techniques intended to identify areas of compromised coating • May employ the NACE PR05202 Pipeline External Corrosion Direct Assessment Methodology • Effective method to accurately determine location and severity of corrosion • In-Line Inspection can find internal and external corrosion defects • The tools are available as self contained or tethered • The pipeline must be designed or modified to accommodate InLine Inspection • May not be effective at risers
Note: Pressure testing alone is not recommended as a method to prove long term pipeline integrity.
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7
Leak Detection Techniques Table 7-1 describes common techniques that should be considered for the detection of pipeline leaks caused by external corrosion. Proactive leak detection can be an effective method of finding small leaks and mitigating the consequences of a major product release or spill. Table 7-1: Leak Detection Techniques
Technique
Description
Comments
H2S detection
• H2S detection can be portable or permanent tools
• Permanent monitors are used at surface facilities.
Right-of-Way (ROW) Surveillance
• Visual inspection by ground access or aerial surveillance to look for indications of problems
• Indications include soil settlement, gas bubbling, and water, soil, or vegetation discoloration • Can be used in combination with infrared thermography and flame ionization surveys
Production Monitoring
• Volume balancing or pressure monitoring to look for indications of leaks
• Changes in production volumes or pressure can indicate a pipeline failure • This is a more effective tool for finding large leaks and ruptures
Flame Ionization Survey
• Electronic instrumentation used to detect low concentrations of gas
• Equipment is portable and used to find small leaks
Infrared Thermography
• Thermal imaging is used to detect temperature change on Right-ofWay due to escaping gas or produced water
• Need sufficient volume of escaping gas to create an identifiable temperature difference
• Odorant detection using trained animals and patented odorants
• Capable of detecting pinhole leaks that may be otherwise nondetectable
Odor Detection
• Normally completed using aerial techniques
• This can only be used after the system has been purged of fluids and displaced with a special odorant
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Repair and Rehabilitation Techniques Table 8-1 describes common techniques used for repair and rehabilitation of externally damaged pipelines. Prior to the repair or rehabilitation of a pipeline the appropriate codes and guidelines should be consulted, including: •
CSA Z662, Section 10.10 “Permanent and Temporary Repair Methods”
When evaluating localized corrosion, the user is cautioned that in addition to the assessment methods for internal pressure (hoop stress) calculations, consideration must be given to the circumferential extent of corrosion that may affect the load bearing properties where secondary stresses may be critical (e.g. bending loads, thermal stresses, soil stresses). Table 8-1: Repair and Rehabilitation Techniques Technique
Description
Comments
Coating Replacement
• Excavation, stripping or blasting and re-coating
• More suitable for localized areas of damage (e.g. joints) and areas that do not require replacement • May be possible to do without a production outage
Pipe Section Replacements
• Remove damaged section(s) and replace with new externally coated pipe. • Joint areas should be properly coated after the new repair section is installed
• When determining the quantity of pipe to replace consider the extent of corrosion and the condition of the remaining pipeline and joint areas • Impact on pigging capabilities must be considered (use same pipe diameter and similar wall thickness) • For certain services, consideration should be given to the need for coating the inside of the pipe with a corrosion inhibitor prior to commissioning
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June 2009 Recommended Practice for the Mitigation of External Corrosion on Buried Pipeline Systems
Technique
Description
Comments
Repair Sleeves
• Reinforcement and pressurecontaining sleeves may be acceptable for temporary or permanent repairs of external corrosion as per the limitations stated in CSA Z662
• For external corrosion it may be possible in some circumstances for the damaged section to remain in the pipeline as per the requirements in CSA Z662 Section 10 • Different repair sleeves are available including composite, weld-on and bolt-on types. The sleeves must meet the requirements of CSA Z662 Section 10 • Note: See above comments on considerations for secondary stresses when evaluating the use of different types of repair sleeves
Pipeline Replacement
• In situations where it may be difficult or uneconomic to prevent continued external corrosion damage (e.g. insulated pipelines, badly disbonded coatings, damage at joints) replacement of the pipeline may be the best option
• Consider need for pig and inspection tool compatibility • Refer to Section 4 “Recommended Practices ” in this document for details
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Additional Resources For more information on external corrosion of pipelines, pipeline coatings and cathodic protection the reader should refer to the following organizations: • NACE International http://www.nace.org/ • European Federation of Corrosion (EFC): http://www.efcweb.org/ • The American Society of Mechanical Engineers (ASME): http://www.asme.org/catalog/
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