ASME Section VIII Code Exclusions

[chemicalengr]

I am trying to determine whether a relief valve is required on a vessel due to planned pump upgrades. The pump motor and impeller upgrades in question will generate pressures only 5% greater than the vessel design pressure for the blocked outlet case.

UG-140(b): "If the pressure is not self-limiting, a pressure vessel may be protected from overpressure by system design or by a combination of overpressure by system design and pressure relief devices, if the following conditions are met."

Condition 1 states "The vessel is not exclusively in air, water, or steam service"

Does anyone know why water is excluded? The process fluid I am working with is Seawater - is this excluded as well?

 

[gr2vessels]

I believe that you're missing the point:- refer to the following excerpt of UG-140(b):
"The rules below are not intended to allow for normal operation above the MAWP at the coincident temperature".
Your 'normal operating pressure' should include the shut-off pressure of this new pump. Then you...
1. Try to establish if the vessel MAWP is indeed equal to the old design pressure or is actually higher (check the 'As built" documentation of that vessel). If it is higher, you're in business...
2. Asess per API 579 if required, together with your AI if re-rating of the vessel is required, for higher MAWP. Hopefully, the new MAWP will be at or higher than your 5% overpressure.
cheers,
gr2vessels

 

[GenB]

water and sea water are the same to me.
in lieu of a SV you may consider a bypass on your pump discharge,
genblr