Corrosion in HAZ

[millimeters]

Hi, I appreciate any input on this.

Two corroded area reported on NPS 36 9.5mm wall. Pipe is X65-448 gr. Corrosions do not meet our criteria to repair (RPR is > 1) based on general corrosion. I wanted to get your thoughts on the close proximity of these features to the welds. They do not directly interact with the Girth weld but they are in the HAZ. NDT contractor performed radiography and advised they would pass these welds based on the present day Z662-11 criteria. They performed ultrasonics and shear wave+MPI and found no internal corrosion or linear indications on the interior/exterior. External mapping was completed with pit gauge and UT.


Do you see any issue as corroded area is on HAZ and very close to weld. Is there any risk of stress corrosion cracking?

 

[SJones]

Whether there is an 'issue' has to be ascertained via a fitness for service assessment, e.g. API 579-1, BS 7910. The risk of stress corrosion cracking will be driven by the exposure environment which can be roughly assessed by reference to API RP 571 and NACE SP0472.

Steve Jones
Corrosion Management Consultant

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

All answers are personal opinions only and are in no way connected with any employer.

 

[millimeters]

Thank you sir.

 

[millimeters]

SJones,
Does API 579-1 covers gas transmision pipelines?

 

[brimmer]

I don't see any issue unless the corrosion is very sharp edged. They did MPI and found no SCC, so once you recoat there is not a further risk of SCC, as you need the environment in contact with the pipe (at least until your coating breaks down again, if ever).

 

[stanweld]

External corrosion under the field wrap coating is common due to the annular space often created between the coating and HAZ area. Water solution will in time migrate into the annular space. You have indicated that the corrosion is not severe enough to warrant repair; in which case, remove the present coating, clean/prepare the area of concern and re-wrap/recoat. To mitigate the influence of weld geometry on producing the annular space, blend grind the butt weld.