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Non-Shielding Coating

If you have come to this page, you probably have questions about non-shielding pipeline coatings. Shielding is hardly a new problem. Concerns were published about shielding starting in the early 1980’s. Click here to go to the Technical Reference page, where Polyguard is accumulating a collection of published references to this serious problem.

Definition


First some definitions of “shielding”. Shielding of cathodic protection currents is a major problem today in pipeline coatings. During October, 2006, no less than five articles mentioning the shielding problem appeared in the pipeline trade press.

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  • The five articles are:

  • S.Papavinasam, M. Attard, and R. W. Revie, External Polymeric Pipeline Coating Failure Modes, Materials Performance, October 2006, published by NACE International, Houston, TX 77084, p.27.

  • M. Roche, D. Melot, and G. Paugam, Recent Experiences with Pipeline Coating Failures, Journal of Protective Coatings and Linings, October 2006, published by Technology Publishing Company, 2100 Wharton St, Suite 310, Pittsburgh, PA 15203-1951.

  • RD-6T. Fore, and K. Varughese, FBE Found Effective After 30 Years of Service, published by Pipeline and Gas Journal, October 2006, Houston, TX 77079, p.64.

  • R. Norsworthy, Is Your Pipeline Coating ‘Fail/Safe’?, Pipeline and Gas Journal, October 2006, Houston, TX 77079, p.62.

  • RD-6T. Fore, and K. Varughese, FBE Found Effective After 30 Years of Service, published by Pipeline and Gas Journal, October 2006, Houston, TX 77079, p.64.

 
 
 
 

NACE defines shielding as:

“Preventing or diverting the cathodic protection current from its intended path”

NACE Standard RP0169-2002, Control of External Corrosion on Underground or Submerged Metallic Piping Systems, NACE International, Houston Texas 77084-4906, p3.,
http://www.techstreet.com/cgi-bin/detail?doc_no=nace%7Crp0169_2002;product_id=1031003

 NACE defines Shileding Diagram
 
 

Background of the Shielding Problem


In spite of the growing body of evidence concerning the seriousness of the shielding problem, a large percentage – we estimate as much as 70% - of pipelines worldwide still use corrosion coatings with shielding potential.

How can this be? We at Polyguard believe that there are many reasons for the continued wide usage of shielding coatings, but the largest reason may be the fact that shielding is a difficult and highly technical subject.

Here on our website, Polyguard is attempting to give concerned engineers a simplified explanation of the shielding problem. We apologize for the fact that we risk oversimplifying this issue. NACE has a full six day course concerning this area entitled the CP Protection Program. Polyguard’s purpose here is to sound the alarm, to get people talking to those who are working with this problem, and to point to some sources of information and solutions.

When underground pipelines are constructed today for transmission of oil, products, or natural gas, and even water or sewage, the pipeline design almost always includes corrosion coating with a cathodic protection system. The cathodic protection system is intended to act as backup corrosion protection in the event that the corrosion coating system were to fail.

The surprising thing is the frequency that coating systems are used which can partially or completely block the effectiveness of the cathodic protection system.

In recent years, knowledgeable engineers and scientists have begun to try to highlight this incompatibility. Beavers and Thompson summarized the shielding incompatibility in the newly released Volume 13 of the ASM Handbook:

“Ultimately, the effectiveness of a coating system in preventing corrosion is related to two primary factors: (a) the resistance of a coating to degradation over time and (b) the ability of the coating to conduct CP current should the coating fail (minimize shielding). For SCC resistance, these factors as well as the type of surface preparation used with the coating are important.”

Beavers, J.A. and Thompson, N.G., External Corrosion of Oil and Natural Gas Pipelines, ASM Handbook, Volume 13C, Corrosion: Environments and Industries (#05145), ASM International, Materials Park Ohio 44073-0002, p1021. http://www.asminternational.org/content/ASM/StoreFiles/ACFAB96.pdf


The Solution: RD-6 Coating System


We hope that if you begin looking for answers to the shielding problem, you will evaluate Polyguard’s RD-6 coating system as one of the available solutions. Polyguard’s RD-6 product has been in wide use for over 25 years now. RD-6 is a proven solution. .


  • RD-6 has a 25 year field history, with thousands of installations worldwide, including this one shown on the January 1992 cover of Pipeline and Utilities Construction magazine.

  • View a discussion of this history.

 
 
 
 
 
 
 

Frequently Asked Questions


What are some other things NACE says about shielding?

 

What is the shielding behavior of various pipeline coatings in use throughout the world?

 
 
 
 
 
 

Tapes are widely condemned above. Isn’t Polyguard RD-6 a tape?

 

What are some other things NACE says about shielding?

 

If users knew 20 years ago that solid film backed corrosion coatings created shielding problems, how come there are so many specifications in place today for them?