Monday, March 24, 2008


I want thank everyone who participated in the TG 360 (SP0169) meetings last week at NACE CORROSION 2008. Hopefully we have helped the committee with making a better decision about what revisions are made to the SP0169 document.

For those that were not there or want a copy of my presentation to the committee, we will be posting that on the web very soon. It hit me Monday night (March 17) that we have in over 40 years thousands of miles of FBE coated pipelines over the world that have been in service. For the first 30 to 35 years the only criteria that was used to protect these pipelines was an "ON" -850 mV or more negative without much consideration (if any) for IR drop. Some still use this criteria today for these lines.

We have now run many ILI (smart pigs) thorough these pipe lines over last 20 years, yet find very little, if any, external corrosion on these pipelines. When external corrosion is located it is usually because of shielding from a foreign object (rocks, plastics, other metal in close proximity, high resistant soils, etc.), from other coatings (usually on girth welds or repairs) that have disbonded and shield the CP (such as solid film backed tapes, shrink sleeves, etc.) or from AC or DC interference. There are cases where inadequate CP (if any) was applied for a period of time and corrosion may have developed.

For those of you who have FBE coated pipelines, please look at this data and see what I am talking about. If we can prove this fact, this disproves the theory that we must always consider IR drop or use a Polarized -850 mV to protect our pipelines.
If these things are true would we not have extensive external corrosion on FBE coated pipelines? Especially where FBE coating failure and disbondments have occurred! From my experiences and discussions with many companies external corrosion is a very rare occurrence on FBE coated pipelines. This also proves the validity of using pipelines coatings when possible that have proven non-shielding (to CP) properties if disbondments occur(such as FBE or Polyguard RD-6).

There is nothing in this industry that is 100%. I am sure there are some rare instances where external corrosion has occurred that cannot be explained. In those cases none of the criteria would have likely worked.

Pipelines coated with coatings other than FBE still have external corrosion occurring, but again these are in areas of disbonded coating that is still shielding the CP. In these cases, increasing cathodic protection will have minimal affect in most cases.

The point here is that increasing the amount of CP or changing to a more stringent criteria will not give the end user much BANG for their BUCK. The scales are weighted in this argument on the side of leaving the criteria as it stands and using better tools (ILI and ECDA) and training for those responsible to actually be able to control the external corrosion problems without tying their hands to more stringent criteria. Using these tools to find areas of shielding (whether coatings or other) and correcting those areas by recoating with coatings that have proven non-shielding properties will help eliminate many of the ongoing external corrosion problems.

I will ask anyone who has data, reports and papers that can be posted on this site to please send those, but more importantly send this data to the committee. By the way this site accepts comments from all sides of this issue, not just opposition to these changes. We all learn from those who study this issue and who have written papers and made presentations in support of the proposed changes. There are times when considering IR drop and using a polarized -850mV criterion are needed and valid, but I do feel these are rare occurrences.

Richard Norsworthy