Christine74,
This all stems from rerating a vessel according to NBIC.
First try to get the original calculations from the manufacturer if not you have to have a PE acceptable to the inspector recalculate the original.
Without typing it all out, you have to establish the reratings according to the code used when the vessel was built or you have start from scratch and recalculate according to the latest code if all essential details are known. If all details are known they usually require recalculation according to the latest code.
Check the inspection records to if see if the vessel is fit for service and the pressure test according to code that was used to rerate the vessel.
In others if every thing is in order you can rerate the vessel under the code that it was built.
All the time the AI is looking over your shoulder.
Somebody get on me if they have changed this as I'm several years out of service.
You got it, it sounds like you have done this in the past.
The only thing I would like to add is that as of the more recent ASME Sec VIII Div 1, which permits the use of higher allowable stress values. These higher values can not be used for in rerating a pressure retaining item constructed before the 1968 Edition of ASME Sec VIII Div 1.
NBIC Interpretion 98-14 will also have other minimum criteria for rerating to a later edition/addenda which permits higher allowable stress values.
Basically the numbers crunch to the tank being designed with an allowable stress of somewhere around 22,000 psi in order to get to the fabricated thickness. I have a U1 form, the drawings, no calcs, and now have to figure out what was done 34 years ago. Of course the manufacture is out of business.
Fzob,
I run into this type of problem frequently, but not to the extent that you are suggesting. Often, my problems tend to be centering around the confusion of joint efficency for seamless heads.
