The Elephant in the Pipeline Room

This is a big, corrosive elephant. The corrosion control world acknowledges its existence, but a whole lot of people are acting like it doesn’t exist.

Several weeks ago, at the Banff/2009 Pipeline Workshop, one of our Polyguard employees was asked by a corrosion engineer; “Why doesn’t your company change its ad?” Actually, we have changed the ad...three times to be exact. But we haven't changed the THEME of the ad for several years.

The theme of our ads, which are addressed to management of companies who operate oil and natural gas transmission pipelines, goes something like this:

• There is a really big problem here
• At least half of the oil and gas pipeline world is ignoring this problem
• Please - take a look at all the red flags, and do something about it.

The really big problem is unnecessary corrosion eating away pipelines worldwide. Corrosion and potential leaks are an ongoing concern to the pipeline industry. Corrosion surveys confirm there is a continuing problem with external corrosion, especially around girth weld areas, where field application can compromise corrosion coating performance.   

This situation should not exist. Advances have been made in corrosion coatings to protect pipelines, as well as in the field of cathodic protection (CP). And especially impressive advances are being made in the area of inspection tools and surveys to spot external corrosion. Pipeline operators almost universally agree that a good corrosion coating system is required, plus a CP system which will provide backup corrosion protection in any areas where the corrosion coating system begins to fail.

The problem is that, in perhaps half or more of the corrosion protection decisions made worldwide today, little or no consideration is given to the whether the corrosion coating or coatings being used are compatible with the CP system. Thus, there are an increasing number of instances where the corrosion coating develops areas of failure - and the CP system, designed to provide backup protection when this happens, is unable to furnish protective electrical current because it is blocked by the failed area of the corrosion coating system. The corrosion coating system, designed to protect the steel, is now actually protecting the corrosion process going on underneath the coating. This is because the high dielectric strength property of the failed coating system is blocking the path of the protective electrical current from the CP system...

You can see a more thorough definition of this problem, which the industry terms cathodic shielding, on Wikipedia. http://en.wikipedia.org/wiki/Cathodic_protection.

We don't mean to imply that nothing is being done about this problem. Importantly NACE began offering several years ago a course entitled Coatings in Conjunction with Cathodic Protection (http://web.nace.org/departments/education/Program.aspx?id=2ce9ffdb-8816-db11-953d-001438c08dca) which is concerned with familiarizing the industry with the cathodic shielding problem. Additionally, NACE SP0169 (Control of External Corrosion on Underground or Submerged Metallic Piping)⁽¹⁾ cautions against the use of materials that create electrical shielding and mentions the shielding problem in four sections of the standard.  Moreover, US Federal regulations for both natural gas pipelines and petroleum/products⁽²⁾ call for corrosion coatings to have properties compatible with cathodic protection.

The above list certainly sounds like it is a lot more than "nothing"! But the impact of all of this is far less than you would think. Obviously some knowledgeable technical people have managed to get the cathodic shielding problem added to training, recognized in standards, and added to regulations. But in practice - when people design corrosion control systems - the problem is not addressed by many, if not most operators.

Thus the title of this article: cathodic shielding is the 'elephant' in the pipeline room. It's really big, most people have heard about it, but few seem to want to talk about it. Why is this? One theory is that many people are uncomfortable talking about cathodic shielding; it's a technical subject, and one which seems to contradict much of what has been taught about corrosion control in the past. For pipeline corrosion coatings, a high dielectric strength property has always been considered a firm requirement - highly desirable. Now we find that the same dielectric property which made coatings effective can turn against you when the coating develops failed areas and the CP system tries to function. 

Some experts have referred to the cathodic shielding problem as "insidious". Certainly when you were taught that corrosion coatings must have high dielectric strength, and now you find that this property only helped you to the point where there began to be a problem, and then began to work against you, the word "insidious" applies. No wonder some people are hesitant to face the cathodic shielding problem - they are confused, and embarrassed to admit it.

We at Polyguard set out to put the cathodic shielding problem on the industry table. Three years ago we began an advertising campaign aimed at getting operators to recognize and address the cathodic shielding issue.

Our early ads (2007) carried a polite headline "Pipeline corrosion coatings and shielding - a problem you need to know about".

This ad attempted to point out that, over the last 25 years, much has been published in the technical and trade press concerning the problem and dangers of cathodic shielding.

In 2008, our ad switched to a graphic illustration of the concept of cathodic shielding, adding an attention grabbing headline "Is CP Worthless?". (We recognize of course that a well designed CP system should be at the base of any pipeline corrosion protection program. Our aim was simply to get readers to realize that shielding coatings can destroy the effectiveness of CP systems.)

And now, in 2009, our headline simply says; "Follow the Instructions". This is to focus the reader's attention on the NACE SP0169 standard, which provides pretty specific instructions to avoid the use of shielding coatings.

In addition to advertising, which is only one piece of our efforts, we have published papers, made presentations, educated people on our website⁽³⁾, and most importantly done a lot of talking with people about the shielding problem.  Is the problem going away? Hardly. But we do see a slowly growing awareness of the shielding problem among the people we talk to.  And sales of our 21 year old non-shielding pipeline coating, RD-6™, are now growing at a gratifying faster rate.

Will we continue to advertise this theme? Probably. We know operators who now use our products - and they didn't start until they had discovered shielding problems on their own lines (mostly around girth welds). If that is what it takes, we will do well to keep our name in front of operators when they start, however belatedly, to be concerned about cathodic shielding problems.   

References:

1. SP0169: Control of External Corrosion on Underground or Submerged Metallic Piping; NACE - National Association of Corrosion Engineers http://www.nace.org/content.cfm?currentID=1018&parentID=1018

2. US Federal regulations calling for corrosion coatings to have properties compatible with cathodic protection §49 CFR 192.461(Natural gas pipelines) http://www.setonresourcecenter.com/49CFR/Docs/wcd0000d/wcd00d52.asp, §49 CFR 195.559 (Petroleum and products pipelines) http://www.setonresourcecenter.com/49CFR/Docs/wcd0000e/wcd00e75.asp     

3. Graphic explanation of the concept of cathodic shielding http://www.polyguardproducts.com/flash.htm