Coating issues on a Pipeline

[09091960]

Some of the issues related to tape coated old pipelines (> 40 years) is that vast deterioration of coating which leads to corrosion in the pipeline. To mitigate the issues operating companies have to adequately upgrade the CP systems as per the current requirements and carryout pigging operations to tackle the corrosion issues. My question is between the two pigging runs if the pipe line operator is able to tackle the corrosion issues by having annual dig up and repair program but unable to tackle the coating issues of the pipeline which DCVG results shows the number of coating defects are not manageable due to heavy cost implication of recoating the pipe line. Where do the owner/operator stand on this issue with respect to the integrity of the pipe line? Under the codes and standards can this pipeline operates under the given conditions?

 

[stanweld]

It is not that uncommon to dig up the pipeline and recoat. My former employer (gas utility) certainly did when coating deterioration required such remediative action.

 

[brimmer]

This is a common management strategy in my part of the world, on old tape coated lines. You will never fix the coating problems, there is literally disbonded coating on every joint in some cases. The ILI strategy with excavations is better. ILI will tell you where your corrosion is, and how severe it is. DCVG will show a number of coating defects, but it is exactly that, it does not mean there is a corrosion defect at every coating defect (despite what some people who carry out these surveys would have you believe). With the ILI you can calculate burst pressures, complete various corrosion growth scenarios, come up with a POE, re-inspection intervals, etc. With this data you should be able to go to any regulator and demostrate condition of the line if necessary. DCVG or coating data is exactly that, gives you condition of the coating, does not give an idication of the condition of the steel itself.
If you want to fix the coating, you can do a reconditioning project, but this is usually as expensive as just replacing the pipeline itself. A note on CP, tape coating shields CP, so it does not matter how much current is available, it simply will not provide adequate levels into all disbondments.
If you do have 2 high res pig runs that are adequately spaced apart, this will give you a chance to calculate better corrosion growth rates on the line and focus on your active areas of corrosion.

 

[09091960]

Thanks guys. Its always good to have others opinion.