PIPELINE
TECHNICAL REFERENCE
Documenting the Problem of Cathodic Shielding
Documenting the Problem of Cathodic Shielding
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PIPELINE
TECHNICAL REFERENCE Documenting the Problem of Cathodic Shielding |
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| THIS SECTION INCLUDES: | ||
During the first decade of the 21st century, the industry and regulators, recognizing the problem of cathodic shielding, began to implement requirements for preventive measures: |
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| In 2002, NACE issued RP0169-2002, which includes instructions not to use shielding materials on the pipeline. | ||
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NACE
Standard RP0169-2002, "Control of External Corrosion on Underground
or Submerged Metallic Piping Systems" NACEInternational, Houston,
TX 77084-4906, pg.4
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| 2002 also saw the issuance of new federal regulations which called for coatings which support cathodic protection. As of 2007, both CFR §192.461 (natural gas) and CFR §195.559 contain the requirement that coatings must support CP. | ||
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| 2009 - U.S. DOT CFR § 192.112 | |
| In late 2009, the
U. S. DOT published explicit requirements for non-shielding pipeline
coatings.
(1) The pipe must
be protected against external corrosion by a non- shielding coating. |
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PUBLISHED
PAPERS AND ARTICLES CONCERNING THE PROBLEM OF CATHODIC SHIELDING - 1988 TO PRESENT |
| 1988 - Pipeline Safety Research Committee |
| An early summary of
this problem was the 1988 Pipeline Research Council, which identified
the CP shielding problem as a prime cause of both corrosion and SCC.
Additionally, this study was the first to indicate that shielding coatings
might help to defeat defect survey systems.
Along with similar Canadian research, this study was probably responsible for the beginning of the decline of use of solid film backed corrosion coatings in North America. |
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Excerpt
Page 3 "A Review of Gas Industry Pipeline Coating Practices" |
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Excerpt
Page 4 "A
Review of Gas Industry Pipeline Coating Practices" |
Pipeline
Research Committee,1988 "A
Review of Gas Industry Pipeline Coating Practices", Pipeline
Research Council International©, p.3 and 4 |
| 1989 - S. Nunez |
| An early consensus definition of cathodic shielding was given in this informally circulated document. |
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Excerpt
Page 1 "Cathodic Protection Shielding Definition" |
Nunez,
S., Eastman, A.D. et al, 1989, "Cathodic
Protection Shielding Definition", page 1, AGA Corrosion Supervisory
Committee |
| 1993 - Office of Pipeline Safety DOT Report 910001 |
| This failure report does not qualify as research, but since we showed it in one of our advertisements, we should show its source. It is indicative of a growing awareness in the field of a growing concern with the CP shielding problem. |
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Excerpt "OPS
DOT Report ID 910001" |
"OPS
DOT Report ID 910001", 1993, pg.498 |
| 1995 - Transportation Safety Board of Canada |
| This report, concerning ruptures and fires on a Manitoba natural gas line, includes a definition of how CP shielding by polyethylene backed coatings encourages SCC. |
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Excerpt page 10 "TSB Canada Report P95H0036,1995" |
Transportation
Safety Board of Canada, 1995, Report Number P95H0036, pg. 10 Click here for information |
| 1996 - National Energy Board |
| This extensive report concluded that polythylene tapes had coated 76% of SCC pipeline failures in Canada between 1977 and 1996 (table 6.1, pgs. 102-103). Another conclusion was (p.29) as highlighted above. |
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Excerpt page 29 "SCC Report" 1996 |
National
Energy Board, 1996, "Report of the Inquiry Stress
Corrosion Cracking on Canadian Oil and Gas Pipelines" pg.29 |
| 1998 - National Transportation Safety Board |
| This recommendation, resulting from a Texas failure which caused two fatalities, concluded with a recommendation that included; "Revise 49 Code of Federal Regulations Part 195 to include performance measures for the adequate cathodic protection of liquid pipelines. (P-98-36)." |
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NTSB
Safety Recommendations, November 18, 1998, Ref P-98- pg's. 34 through
38 |
| 1999 - Transportation Safety Board of Canada |
| This report, concerning a 20,600 bbl.spill from a Saskatchewan crude oil line, includes a conclusion that CP shielding by polyethylene backed tape coatings (p.6); 'has also resulted in a much higher susceptibility to producing general surface corrosion and NAEC-type defect conditions.' |
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Transportation
Safety Board of Canada, Report Number P99H0021,1999, pg. 6 Click to view report |
| 2000 - D. Neal |
| This paper discusses the shielding problem, and summarizes the research to date concerning the proof that FBE does not shield cathodic protection currents. |
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Neal,
D., Spring 2000, "Pipeline Coating Failure-Not
Always What You Think It Is", NACE Corrosion 2000, Paper 00755, pg.5 ©NACE International 2000 Reproduced with permission from NACE International, Houston, TX USA. All rights reserved. |
| 2001 - Transportation Safety Board of Canada |
| This investigative report on a crude oil pipeline rupture in Alberta points to cathodic shielding as a sause of both corrosion and significant SCC. This line had at least three previous reported failures in which cathodic shielding under disbonded solid film back corrosion coatings was held to be a cause. |
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Transportation
Safety Board of Canada, 2001, Report Number P01H004, pg. 6. |
| 2002 - NACE |
| In 2002, NACE issued RP0169-2002, which includes instructions not to use shielding materials on the pipeline. | ||
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NACE
Standard, 2002, RP0169-2002, "Control of External Corrosion
on Underground or Submerged Metallic Piping Systems" NACEInternational,
Houston, TX 77084-4906, pg.4
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| 2002 also saw the issuance of new federal regulations which called for coatings which support cathodic protection. As of 2007, both CFR §192.461 (natural gas) and CFR §195.559 contain the requirement that coatings must support CP. | ||
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2003
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| An unpublished investigation of field applied girth weld coatings, performed for a large pipeline operator by a major engineering company, noted that shrink sleeves may; "...shield the cathodic protection, rendering it ineffective if they disbond from the pipe surface". |
| 2004 - Richard Norsworthy |
This 2004 article discusses the non-shielding behavior of Polyguard's RD-6® coating system. A link to the complete article is below. |
Norsworthy,
R. June 2004 - "Coatings
used in conjunction with cathodic protection - "Fail/Safe" Pipeline
Coating Systems" pg's. 34-38
©Materials Performance - June 2004 |
| 2005 - Michael Baker |
| This 2005 report identifies "ability to pass CP current" as one of three crucial properties for corrosion coatings in preventing SCC. |
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Michael
Baker Jr., Inc., January 2005, "Stress Corrosion Cracking Study
- Final Report", USDOT OPS Delivery Order DTRS56-02-D-70036 pg's.
38-39, Section 5.7.2
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| 2006 - J.A. Beavers & N.G. Thompson |
| The newly released volume 13C of the ASM Handbook identifies the ability of the coating to conduct CP current should the coating fail as one of "two primary factors" in preventing corrosion. |
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Beavers, J.A. and
Thompson, N.G., 2006 "External Corrosion of Oil and Natural
Gas Pipelines" pg. 1021, ASM Handbook, Volume 13C, |
| 2009 - Malot, Paugram, and Roche | |
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There have been a number of papers by European authors
concerning the cathodic shielding problem. An example:
“The majority of known corrosion cases result from disbonding of coatings, which may prevent access of the cathodic protection current to steel. The cause of failure, known as the “CP current shielding effect, appears to a concern limited to buried pipelines onshore.” |
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Malot,
Paugram, and Roche, September 2009, Disbondments of Pipeline Coatings
and Their Effects on Corrosion Risks, Journal of Protective Coatings
and
Linings,
pg's.
18-31. |
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| 2009 - U.S. DOT CFR § 192.112 | |
| In late 2009, the U. S. DOT published explicit requirements for non-shielding
pipeline coatings.
(1) The pipe must be protected against external corrosion by a non-
shielding coating. |
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U.S.
DOT – December 2009, Pipeline and Hazardous Materials Safety
Administration, CFR § 192.112 |
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PUBLISHED
PAPERS AND ARTICLES ABOUT POLYGUARD RD-6® |
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"Coatings used in conjunction with cathodic protection - "Fail/Safe" Pipeline Coating Systems" - *Materials Performance - June 2004 |
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"Addressing Soil Stress and CP Shielding Used by a Woven Geotextile Fabric-Backed Tape System with Rubber Modified Bituminous Compound." **Presentation at NACE Corrosion 2000. |
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"Rating Underground Pipeline Tape and Shrink Sleeve Coating Systems" ***Materials Performance - Nov. 1999 |
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| * Reproduced with permission from NACE International, Houston, TX. All rights reserved. Published in the June 2004 issue of Materials Performance.© NACE International 2004. | |
| **Reproduced with permission from NACE International, Houston, TX. All rights resered. Paper #00769 presented at Corrosion 2000, Houston, TX. .© NACE International 2000. | |
| **Reproduced with permission from NACE International, Houston, TX. Published in the November 1999 issue of Materials Performance. .© NACE International 1999. | |
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Studies comparing RD-6® to other protective coatings. |
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Concern
about SCC and other corrosion problems created by CP shielding is becomming
more intense.
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