SOHIC and PWHT

[CoCoE]

Do SOHIC prone piping (sour gas), require PWHT to get rid of/reduce the impact of it? There are restrictions provided for welded pipes to use in sour service without PWHT by some companies, but I don't know why there is no PWHT for girth welds if they need to reduce the impact of it. Can anybody suggest on this?

 

[SJones]

NACE Corrosion 2007, Paper 07115

SOHIC at pipe seams tends to be driven by hoop stress in the pipe. This hoop stress doesn't act in quite the same way at girth welds.

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.

 

[ParickT]

SOHIC can be considered an augmented form of SSC due to crack-jumping, linked to HIC cracking susceptibility ahead of the SSC crack, due to stress and hydrogen local concentration.
Hence, mitigation measures against SSC like proper PWHT helps.
Also, a HIC resistant steelmaking practice is mandatory to mitigate the HIC cracking.
However, HIC susceptibility being considerably augmented due to the localization of the problem, the 2 precautions above can be considered necessary, but not sufficient: the third precautions is to change the starting microstructure to minimize banding effect in the steel. A very efficient and commercialized way is to apply NACT heat treatment on a high-quality HIC resistant materials. You can refer e.g. to NACE Corrosion papers 04480 and C2014-4017.