Bolting material in service(e.g. sour, hydrogen..)

[HOYA]

In selection of bolting material for heat exchanger in service environment. We generally use SA193-B7M&SA194-2HM instead of SA193-B7&SA194-2H.

I would like to know why SA193-B7M&SA194-2HM is preferred.

Thank you.

 

[jamesl]

There are many discussions on this issue on this website. Use of B7M in sour service is per NACE RP0175. B7M has control on hardness, which is very important in sour service.