NACE ISO15156 1

[tired]

I have a pressure vessel which is in sour service and needs to comply with NACE and the plate needs to be HIC tested.
Is it acceptable for the external welded attachments not in contact with the process fluid i.e support saddles etc to be non NACE compliant.
Does NACE only apply to wetted pressure parts?

 

[gr2vessels]

Obviously, the sour service applies only to the 'wetted' parts.
Cheers,
gr2vessels

 

[tired]

I wasn't sure if welded attachments were also required to meet the requirements. I will request the same material specification as the shell for the welded attachments like clips re-pads etc but without the NACE requirement.
Thanks for the reply.

 

[valvesarefun]

There are some instances where MR0175 applies to Non wetted parts. For example if the metallic components are located outside the process fluid, but will be covered in insulation, plastic wrap, wax tape, soil, etc then those metallic components should also be in compliance with NACE. Flange bolts are a classic example of this. Although they are not going to be exposed to the process fluid, it is still reccomended that NACE bolting be used. I can't say for sure that the same principle applies to welds, but I would assume that it does.

If you are welding those directly to the outer wall of the vessel. then it is definately reccomended that you qualify your weld procedure. It is my understanding that welding will create residual stresses in the wall of the vessel, that may lead to increased suceptibility to cracking, even if the weld iteself is not exposed to the process fluid.

-Vrf

 

[gr2vessels]

Clips and reo pads are not normally full pen welds, rather fillet or partial pen, hence they do not affect the internal structure of the shell or other pressure bearing components. The external attachments are only subject to environmental influence (which is different from the process fluid affect).
Cheers,
gr2vessels

 

[SJones]

Flange bolts are a classic example of this. Although they are not going to be exposed to the process fluid, it is still reccomended that NACE bolting be used.

Precisely because if the flange leaks, they will be exposed. As to whether any other part of the system requires compliant material under insulation, that would be a matter of exposure risk assessment. The attachment weld zone will need to comply with ISO 15156 requirements; therefore, if the attachment material starts out too hard, it is unlikely that the weld will comply. Remember, the cracking mechanism is hydrogen driven and hydrogen does not just sit at the internal wetted surface. That's why hardness criteria apply at the external cap too.

Steve Jones
Materials & Corrosion Engineer

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

 

[valvesarefun]

Sorry for the late reply. I realize that its probably well after the fact here, but my main point was that even if the weld is not a full penetration weld it may still create changes in the microstructure of the vessel wall if a suitable weld technique is not used. This is why MR0175 covers fillet welds in addition to other types of welds. Bottom line is that there will still be a HAZ that will need to be considered. It may or may not be an issue, but you can't know for sure until you check it out as directed by MR0175.

Best regards,
VRF