Code exemption for vessel containing water?
Code exemption for vessel containing water?
(OP)
A vendor for a water softener package that includes a 300 Gal. vessel containing water (not heated) with a design pressure of 125 psig claims that a relief valve is not required per the ASME code. It appears from the ASME Code Section VIII, U-1 (c)(2)(f), that this is correct since this is "a vessel for containing water under pressure" that has a design pressure under 300 psig and a design temperature under 210 °F. I can't believe this is permitted. Am I missing something? There have been many process "water" vessels in the past that did not exceed these requirements that I did not hesitate for a minute to include a relief valve. I would appreciate any input on this. Thanks.





RE: Code exemption for vessel containing water?
prex
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RE: Code exemption for vessel containing water?
"U–1(c)(2) Based on the Committee’s consideration, the following classes of vessels are not included in the scope of this Division; however, any pressure vessel which meets all the applicable requirements of this Division may be stamped with the Code U Symbol:"
"(f) a vessel for containing water under pressure, including
those containing air the compression of which serves only as a cushion, when none of the following limitations are exceeded:
(1) a design pressure of 300 psi;
(2) a design temperature of 210F."
This may be somewhat "picky" about the text but I would say the vendor's vessel "could" fall outside the scope of ASME Sec VIII and therefore would not need to follow the overpressure protection requirements per the code rather than say "a relief valve is not required per the ASME code".
However, the plant I'm working at now requires that any vessel purchased with a design pressure > 15 psig must be built to ASME code. I would ask if the vendor sells his vessel with an ASME stamp, then it seems you would need to follow the code requirements per the last statement in U–1(c)(2).
RE: Code exemption for vessel containing water?
ASME: Always-Sometimes-Maybe-Except
PED: Pain Every Day
RE: Code exemption for vessel containing water?
relief devices are not that expensive.
That said, most water softener units do not have relief devices. the rational is that the pressure is limited by the mains, and there is no source of heat (as in a hot water heater).