Are all tapes bad?

By Nate Muncaster, Director Global Business Development, Polyguard Products, Inc.

In some world regions, tapes have a very deep rooted reputation for failures. Mere usage of the word “tape” can produce a negative impression. This article examines some reasons tapes historically did have issues, and how some manufacturers designed around these issues.

In the energy industry, product failures have severe consequences. If the failure occurs on a pipeline coating, this can result in asset and product losses, service interruptions, and even catastrophic failures like a rupture or explosion. Everyone knows the primordial importance of protecting your metal and the contents it contains. Thus, extreme care is taken in the design, specific and selection of all materials involved in a pipeline.

If, for some reason, a component of this system fails, this logically and justifiably produces an emotional reaction that stays with the user - in many cases permanently. In my personal experience I have found the oil & gas industry to be highly risk averse. I couldn’t agree more with that posture. But often after a failure occurs, and the subsequent investigation is finished, what the majority of the people, especially those not directly involved, will remember is a paraphrased reason. This becomes the definition of the problem, and these people tell this to others, who pass along to other colleagues, etc.

A coating with a reputation for failures is tapes. But tapes is a very broad term. If you hear that “tapes fail” – does this mean you shouldn’t use them at all? What if the reasons behind the failure was repeatedly found to be disbondment due to poor adhesion to the metal surface, or wrinkling due the deleterious effects of soil stress? And, having failed, that the nature of the materials used in the vast majority of tapes, i.e. polyethylene, cause cathodic shielding due to the higher dielectric strength of polyethylene?

What if a tape had been designed of materials that didn’t shield cathodic currents, didn’t elongate or wrinkle remotely as easily, and had stronger inherent adhesion properties? And it was as simple and logical a system as the original tape systems manufacturers had in mind when designing pipe wrapping materials?  Polyguard Products, Inc. of Ennis, Texas manufactures such a tape, the RD-6 coating system, that has been designed to be non-shielding, have superior adhesion, and resist soil stress to a much greater extent. The effectiveness of the RD-6 has been proven for over 2 decades in the North American market and is specified by a number of the North American oil & gas majors, and a growing number of users outside of North America.

Would this be cause to reconsider?

If we attempt to understand the issue better, many would state that one root cause is the simple matter of polyethylene as the backing material for the tapes. Initially selected for its dielectric resistance and stretchiness, these very strengths have been found to be weaknesses in the long term. Regrettably, when one buries a pipeline, a great deal can occur underground in the long term. In North America, many companies had arrived at the end of the “long term” in the late eighties, having widely applied polyethylene tapes since the 1960s. The polyethylene tapes acquired a very negative reputation, and in many instances it was merited. But mere usage of the term “tape” created a mental association with failures, and the understanding of the reasons behind the failures did not spread as widely as the negativity.

In 1988, Polyguard Products saw this market trend, and designed a coating system (the RD-6) that addressed the root causes of tape failures (disbondments/soil stress) and did not impede the cathodic protection current. Simultaneously, the system retained all the classic strengths of a tape; simplicity and speed of application being foremost.

Part of this solution was as simple as switching the material for the backing. By using polypropylene in a woven mesh form (the mesh has no dielectric strength) the material has comparatively much less elongation and is non-shielding to cathodic currents.

Thus, while the stretchiness of polyethylene, classically lauded as an application advantage, appears good at first glance, it becomes a severe liability once the backfill begins to settle. The larger the pipe, the more surface area to absorb the weight of the soil, which in turn pulls on the polyethylene, provoking wrinkles towards the bottom area (the most typical failure mode).

And the same mechanical resistance of polyethylene, an advantage against rocks in the backfill or other damage risks, once again converts to a liability due to its higher resistivity. Cathodic currents are unable to pass through the higher resistivity polyethylene, thus leading to the phenomenon known as cathodic shielding. Cathodic shielding, while known about for decades, has become an increasingly studied topic, and NACE has issued SP1069-2007 and launched a course titled “Coatings in Conjunction with Cathodic Protection”. This is as a result of the growing number of reported instances of shielding, especially high at girth welds under high dielectric strength coating materials. Industry study groups and experts have begun to respond.

One begins to appreciate the importance of proper comprehension of coating systems and the materials that they are composed of.  For something that represents such a tiny part of the cost of laying, operating, maintaining and repairing a pipeline, it plays a disproportionate role!
So, if a coating system that has been proven for over a generation (or as we say – “life cycle”) on thousands of miles of buried pipelines, offered a solution to the classic problems associated with “tapes”, would it entice you to think twice? Considering the number of coating technologies that have been found to cause problems in the long run, shouldn’t one prioritize demonstrated results in an industry with such importance and impacts associated with performance failures of coatings? In our professional opinion, not all tapes are bad. There are just some bad designs.