Air Receivers built right on the line

[crosby84]

I think this has been addressed previously, sort of, but I couldn't find my answer.

We evaluate pre-existing vessels (mechanical integrity, as they say) and frequently come across air receivers (ASME code stamped, NB#, etc.) that when we run thickness calculations, they are often at or below minimum required thickness. Even if the U-1 states a nominal shell thickness of 0.25", the min required thickness is 0.255" (exclusive of corrosion allowance), for example, and we have to tell the client that their vessel isn't good for the pressure on the nameplate, even if it hasn't corroded.

Why would manufacturers so frequently build these things right on the line with no CA, often even below the required thickness? Does anybody else run into this regularly?

Just curious to get others' experiences with this. Thanks!

 

[keyen]

croby84, does this happen to various vessels from various manufactures at various plants? If that's the case, is it possible that your evaluation is flawed somehow? It seems unlikely that you'd come across different designers all cutting things so close.

 

[JStephen]

See Table A1.1 in A20, which shows 2 decimal places in all cases.

I think that interpretation needs an interpretation. The way I read that, it relates to the undertolerance on plate, but doesn't address rounding in the design requirements.

 

[metengr]

We evaluate pre-existing vessels (mechanical integrity, as they say) and frequently come across air receivers (ASME code stamped, NB#, etc.) that when we run thickness calculations, they are often at or below minimum required thickness. Even if the U-1 states a nominal shell thickness of 0.25", the min required thickness is 0.255" (exclusive of corrosion allowance), for example, and we have to tell the client that their vessel isn't good for the pressure on the nameplate, even if it hasn't corroded.

So, you are evaluating in-service vessels rather than new construction. I would bet you are using the 2017 Edition of the Code to evaluate in-service vessels. If this is the case, you should be using the edition of the Code most applicable to what is being FFS. In other words, the applicable edition of the construction Code.

 

[marty007]

Just throwing out an idea from left field...

Is there any chance these air receivers are mass produced, with geometry that can't be easily calculated with code rules?

If so, could the MAWP have been established by proof test? Is there any reference to para. UG-101?

Cheers,
Marty