Assessment of corrosion defects in buried pipe lines

[09091960]

Resent ILI data shows that 75% Wt loss for 10mm x 15mm area for a API 5L X52 (7.9 mm thick)
Gas pipe line. As per the effected area method calculation this defect can be attended by blasting the surface and by applying epoxy coating to the surface. Apart from coating for an in service pipe line, is there any other method to rectify this wall loss defect? Can we go step further and have a type A sleeve repair by using clock spring?

 

[SJones]

Wall loss from the inside or the outside?

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[09091960]

Wall lost from outside.

 

[SJones]

If you have established that you still have fitness for service with the reported defect AND it is verified that you aren't losing any material from the inside of the pipe, you then will have to check how your company and the regulatory authority views the 'permanence' of the repair method. Some companies and authorities would regard a composite wrap as a very temporary repair. If welding close to the pipe is an issue for you, an epoxy grouted sleeve would look the best bet as it may involve less 'messing about' than a tight fit sleeve.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[brimmer]

Absolutely, you can use a clockspring or type A sleeve for additional piece of mind (assuming no internal corrosion). To state what has already been said above, depending on your regulatory body, they may consider this only a temporary repair, however given that you state no repair is necessary it would not matter in the short term. If there is a class location upgrade or you want to hydrotest the line in the future it might be an issue, but then the defect would be an issue by itself.
You did not mention if you will field verify the area, only the ILI tool has given these measurements. You should always field verify the ILI data and run your own effective area calculations based on what you find, as ILI data is often innacurrate despite what ILI vendors would have us believe.

 

[09091960]

Hi All,

Many thanks for both of you guys (S.Jones & Brimmer)for your
excellent outputs