Lower MDMT for 304 Stainless

[jgibbs22]

Good evening everyone:

I have a extremely large liquid oxygen sphere that was originally designed for liquid nitrogen at -320 deg. F, built back in the mid 60's. I have a need to sub-cool my liquid nitrogen to around -340 deg F. If I were to perform a Code alteration per NBIC, I assume I would need to perform Code required impact testing. My question though, is how many of my welds would I need to prepare samples from? All? Certain percentage?

How about impact testing of the B16.5 flanges?

I know it would be much less headache to buy new, but if I were to stay this course, could use some guidance on just how much destructive testing and re-welding I would need to do.

Thanks

jgibbs22

 

[metengr]

First, you need to locate the ASME data report (contact the National Board to obtain a copy), second, contact the Jurisdiction and Insurance company and let them know of your re-rate plans. They will inform you of what the minimum testing requirements would be for lowering the MDMT. Since you are requesting only a -20 deg F reduction, the Jurisdiction may waive any additional testing, impact versus volumetric examination of seam and girth welds.

Are the flanges austenitic stainless steel? If so, you might receive a waiver.