I have an ASME Div. 1 Sec. VIII SA240-316L SST pressure vessel that has internal coils at -238F. The vessel itself is normally operated at atmospheric pressure or under vacuum at -103F, but is also periodically steam sterilized at 30 psig and 275F. I usually rate these at 30 psig/FV at 275F with an MDMT of -103F at 30/FV. Not actually true conditions since the vessel could never see pressure and the MDMT at the same time.
My customer wants to change the MDMT rating on these to -238F, but this brings in the requirements for impact testing of production welds and qualifying the filler metal. Our weld procedures and welders are qualified down to -320F so this isn't a problem other than the extra testing.
My question is, since the low temperature MDMT is not concurrent with a pressure condition, can the vessel be rated in such a way as to avoid the UHA-51 requirements (Basically consider the vessel as not be code rated during it's cold cycle)?
My customer wants to change the MDMT rating on these to -238F, but this brings in the requirements for impact testing of production welds and qualifying the filler metal. Our weld procedures and welders are qualified down to -320F so this isn't a problem other than the extra testing.
My question is, since the low temperature MDMT is not concurrent with a pressure condition, can the vessel be rated in such a way as to avoid the UHA-51 requirements (Basically consider the vessel as not be code rated during it's cold cycle)?