1、NACE International This Technical Committee Report has been prepared by NACE International Task Group 169* on Control of External Corrosion of Steel Pipelines in Natural Waters: Report Electrical Isolation/Continuity and Coating Issues for Offshore Pipeline Cathodic Protection Systems 2005, NACE Int
2、ernational This NACE International technical committee report represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone from manufacturing, marketing, purchasing, or using products, processes,
3、 or procedures not included in this report. Nothing contained in this NACE International report is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as indemnifying or pr
4、otecting anyone against liability for infringement of Letters Patent. This report should in no way be interpreted as a restriction on the use of better procedures or materials not discussed herein. Neither is this report intended to apply in all cases relating to the subject. Unpredictable circumsta
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10、oreword This state-of-the-art report provides owners, engineers, contractors, and operators with information on electrical isolation/continuity issues and coating issues to consider when designing and operating offshore pipeline cathodic protection (CP) systems. The detailed specifications for appli
11、cation of pipeline coatings are beyond the scope of this report, though it gives references to some specifications that are used. This report is a support document for the pipeline CP design standards. This technical committee report was prepared by Task Group (TG) 169 on Control of External Corrosi
12、on of Steel Pipelines in Natural Waters. TG 169 is administered by Specific Technology Group (STG) 30 on Oil and Gas ProductionCathodic Protection, and sponsored by STG 05 on Cathodic/Anodic Protection and STG 35 on Pipelines, Tanks, and Well Casings. This report is issued by NACE International unde
13、r the auspices of STG 30. _ * Chair Ian Rippon, Shell Global Solutions Intl. BV, Rijswijk, The Netherlands. Item No. 24228 NACE International Publication 30105 NACE technical committee reports are intended to convey technical information or state-of-the-art knowledge regarding corrosion. In many cas
14、es, they discuss specific applications of corrosion mitigation technology, whether considered successful or not. Statements used to convey this information are factual and are provided to the reader as input and guidance for consideration when applying this technology in the future. However, these s
15、tatements are not intended to be recommendations for general application of this technology, and must not be construed as such. NACE International 2 Definitions For the purposes of this report, the terms and definitions given in NACE International 2002 Glossary of Corrosion-Related Terms and the fol
16、lowing apply: Bracelet Anodes: Galvanic anodes with geometry suitable for direct attachment around the circumference of a pipeline. These may be half-shell bracelets consisting of two semi-circular sections or segmented bracelets consisting of a large number of individual anodes. Cathodic Protection
17、 (CP): A technique to reduce the corrosion of a metal surface by making that surface the cathode of an electrochemical cell. Coating: A liquid, liquefiable, or mastic composition that, after application to a surface, is converted into a solid protective, decorative, or functional adherent film. Coat
18、ing Disbondment: The loss of adhesion between a coating and the pipe surface. Corrosion: The deterioration of a material, usually a metal, that results from a reaction with its environment. Disbondment: The loss of adhesion between a coating and the substrate. Holiday: A discontinuity in a protectiv
19、e coating that exposes unprotected surface to the environment. Insulated: The subject (for example, a pipeline) is dielectrically insulated (or electrically isolated) from a related object. This does not refer to thermal insulation. J Tube: Piece of pipe attached to an offshore platform through whic
20、h a riser is run. The top of the J tube is above the splash zone, and the bottom ends somewhere between the bottom of the splash zone and the seabed. When the riser is installed it is pulled up through the J tube. The J tube provides protection to the riser from lateral forces and speeds up riser in
21、stallation. Riser: (1) That section of pipeline extending from the ocean floor up to an offshore platform. (2) The vertical tube in a steam generator convection bank that circulates water and steam upward. For the purposes of this report, the first definition applies. Shielding: (1) Protecting; prot
22、ective cover against mechanical damage. (2) Preventing or diverting cathodic protection current from its natural path. For the purposes of this report, the second definition applies. Splash Zone/Spray Zone: The area immediately above and below the waterline that, because of local conditions, remains
23、 wet or submerged the vast majority of the time. CP is not effective in the splash zone; protection by coatings, wear plates, etc., is typically used. Electrical Isolation/Continuity General Electrical isolation design and equipment are discussed in detail in NACE Standard RP0286.1Electrical isolati
24、on/continuity is generally considered when offshore CP system control is designed or assessed. Electrical isolation in a pipeline is normally accomplished by use of a dielectric insulation flange assembly, using an electrical isolation joint in the line, or other means whereby the pipeline is contin
25、uous but electrical continuity is not. There are a number of situations in which the corrosion control designer has considered the use of such devices. Examples are as follows: At Changes of OwnershipA change of ownership often occurs at a riser attached to a host structure of different ownership. W
26、hen there is a change of ownership, isolation between structures is normal practice. A riser attached to a host structure of different ownership is normally electrically isolated from the riser clamps and a dielectric insulation flange or an electrical isolation joint is installed in the above-water
27、 section of the riser. At LandfallsWhen an offshore pipeline makes landfall, it is often accompanied by a change in the CP system; there is often a switch between an offshore sacrificial and an onshore impressed current system. The systems are normally separated at this point to facilitate more accu
28、rate monitoring and control of each system and to prevent potentially detrimental system interactions. At Change of CP System TypeGalvanic anode systems are electrically isolated from impressed current systems when offshore pipelines connect with structures or other pipelines protected with impresse
29、d current. Bare Structures Tied to Coated PipelinesExcept as covered in previous paragraphs, electrical pipeline isolation between galvanic anode CP systems installed on platforms and pipelines is often omitted. With good CP design, both platform and pipeline are typically adequately protected witho
30、ut impairing the lives of their individual CP systems. However, offshore pipelines are typically isolated from other unprotected or less-protected structures, which can drain current from the pipeline CP system. Flexible SectionsFlexible sections have been installed in offshore pipelines as jumpers
31、or to handle excessive seabed movements. The flexible section is usually electrically continuous to avoid an electrical NACE International 3 discontinuity in the pipeline. If the flexible section is not electrically continuous, continuity bonding provisions are often made, or both sides of the flexi
32、ble section are protected independently. At Changes in Material Being ProtectedWhere different cathodic protection potentials are typically used for different materials being protected. For example, the protection potential of stainless steel pipelines is typically held above -800 mV in order to avo
33、id hydrogen induced stress cracking; electrical isolation would be used if this was connected to a carbon steel pipeline or a carbon steel structure. When possible, the insulator is installed at a point with easy access to improve system maintainability. At a platform, the insulator is normally inst
34、alled in the riser above the splash zone. If the flange is installed at an inaccessible location, CP monitoring is often difficult unless test leads are installed. The most common electrical bypasses (electrical shorts) on offshore systems are uninsulated riser clamps, damaged insulation flange asse
35、mbly, stainless steel control tubing bypasses, topside pipe supports, and piping bypasses. Riser clamps that are electrically insulated from the pipeline are typically cathodically protected either by bonding to the structure or by the provision of dedicated sacrificial anodes. Bolting does not alwa
36、ys guarantee electrical continuity, especially with coated bolts. The design is typically checked at all flanges where electrical continuity commonly occurs. Continuity bonding straps or exothermically welded continuity bond wires are commonly employed in order to ensure electrical continuity. The p
37、otential sparking hazards of insulating devices are typically considered in the design and location of such devices. Precautions to prevent arcing are typically considered when these devices are installed where combustible environments may exist. Coatings Introduction This section addresses common p
38、ractices used for selecting, testing, evaluating, applying, handling, storing, and inspecting external coating systems for external corrosion control on offshore pipelines used in conjunction with a CP system. External coatings are also selected to provide resistance to marine biological growth (bio
39、fouling). Internal coatings for corrosion control or operating performance are not within the scope of this report. Tables 1, 2, and 3 are general listings of external coating references used for coating materials and application, coating evaluation, testing and inspection, and storage, handling, an
40、d transportation. (NOTE: Many other references are available; thus the tables are not comprehensive.) Coating evaluation, testing and inspection, and storage and handling for each type of coating are also typically contained in the specific application specifications in Table 1. The latest revisions
41、 of each specification are used. Table 1: External Coating Materials and Application “External Fusion Bonded Epoxy Coating for Steel Pipe” CSA(A)-Z245.202“Application, Performance, and Quality Control of Plant-Applied, Fusion-Bonded Epoxy External Pipe Coating” NACE Standard RP03943“Fusion-Bonded Ep
42、oxy Coatings for the Interior and Exterior of Steel Water Pipelines” ANSI(B)/AWWA(C)C 2134“External Polyethylene Coating for Pipe” CSA-Z245.215“Polyethylene Coatings for Steel Pipes and FittingsRequirements and Testing “ DIN(D)306706“Extruded Polyolefin Coatings for the Exterior of Steel Water Pipel
43、ines” ANSI/AWWA C 2157“Extruded Polyolefin Resin Coating Systems with Soft Adhesives for Underground or Submerged Pipes” NACE Standard RP01858“Coal-Tar Protective Coatings and Linings for Steel Water PipelinesEnamel and TapeHot Applied” ANSI/AWWA C 2039“Tape Coating for the Exterior of Steel Water P
44、ipelines” ANSI/AWWA C 21410“Specification for the Application of Thermal Spray Coatings (Metallizing) of Aluminum, Zinc, and Their Alloys and Composites for the Corrosion Protection of Steel” NACE No. 12/AWS(E)C2.23M/SSPC(F)-CS 23.0011“Plant-Applied, External Coal Tar Enamel Pipe Coating Systems: Ap
45、plication, Performance, and Quality Control” NACE Standard RP039912“Field-Applied Fusion-Bonded Epoxy (FBE) Pipe Coating Systems for Girth Weld Joints: Application, Performance, and Quality Control” NACE Standard RP040213“Field-Applied Coal Tar Enamel Pipe Coating Systems: Application, Performance,
46、and Quality Control” NACE Standard RP060214“Exterior Protective Coatings for Seawater Immersion Service” NACE Standard TM020415NACE International 4 “Offshore Platform Atmospheric and Splash Zone Maintenance Coating System Evaluation” NACE Standard TM030416“Offshore Platform Atmospheric and Splash Zo
47、ne New Construction Coating System Evaluation” NACE Standard TM040417“Technical Specification for the External Protection of Steel Line Pipe and Fittings Using Fusion Bonded Powder and Associated Coating Systems” BGE(G)CW618“External Fusion-Bonded Epoxy Coating for Steel Pipes” AS/NZS(H)3862:200219(
48、A)CSA International (CSA), 175 Rexdale Blvd., Etobicoke, Ontario M9W 1R3. (B) American National Standards Institute (ANSI), 11 West 42nd St., New York, NY 10036. (C)American Water Works Association (AWWA), 6666 West Quincy Ave., Denver, CO 80235. (D)Deutsches Institut fer Normung (DIN), Burggrafenst
49、rasse 6, D-10787 Berlin. (E)American Welding Society (AWS), 550 NW LeJeune Road, Miami, FL 33126. (F)Society for Protective Coatings (SSPC), 40 24th St., 6th Floor, Pittsburgh, PA 15222-4656. (G)British Gas plc, 326 High Holborn, London, WC1V 7PT. (H)Standards Australia International Ltd, 286 Sussex St, Sydney, NSW, 2000. Note: There are a number of locations around the world where the installation of a coal tar coating is no longer allowed because of potential hazards to personnel during construction. There are, however, many pipelines in service tha
