Derating subsea pipeline (pipelines on offshore structures) using B31G

[NATIVES]

Can anyone please state your experience to derate MAOP of a corroded pipeline using ASME 31G? Is the result obtained by using B31G reliable? Any good or bad experience? What is the difference bwteen B31G, B31G modified, and RSTRNG method? Any advantage o using one method over the other one? How prevalent is it offshore pipeline system, specially Gulf of Mexico Area? Can anyone point me towards right direction to get more info. Thanks.

 

[DSB123]

If you know the extent of the defect you could use ASME/API 579 or there is a program called RSTRENG which is more accurate than B31G which is conservative.

 

[LittleInch]

You're possibly better asking this question in the corrosion engineering section tbh.

B31G is quite conservative and RSTENG better, but really you can't call it - you need someone who is used to using these calculations to define it and then take responsibility for the pressure rating as it stands.

The usual problem is that the actual corrosion doesn't match the nice neat diagrams and hence quite a lot of "interpretation" needs to go on. Also I don't know how well it is at looking at other stresses other than hoop stress. On a platform you will have a lot of other stresses which make one pipe more vulnerable than another.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[NATIVES]

Thanks both for your response! I will post this question in Corrosion engineering also.