MAWP and Safety Valve Set Pressure
MAWP and Safety Valve Set Pressure
(OP)
Hi all,
I have a strange question about pressure vessel designing in ASME code.
Is it possible to have a design pressure of 2.5 bar and a safety valve set to 1 bar ?
After the calculation of the components, I will have the MAWP of the completed vessel that must be equal or higher than the design pressure.
Looking at the definition of MAWP i read the following:
"...It is the basis for the pressure setting of the pressure setting of the pressure relieving devices protecting the vessel. The design pressure may be used in all cases in which calculations are not made to determine the value of the MAWP..."
What does it mean exactly? Does it force me to use a safety valve equal or over the design pressure?
Thank you in advance
I have a strange question about pressure vessel designing in ASME code.
Is it possible to have a design pressure of 2.5 bar and a safety valve set to 1 bar ?
After the calculation of the components, I will have the MAWP of the completed vessel that must be equal or higher than the design pressure.
Looking at the definition of MAWP i read the following:
"...It is the basis for the pressure setting of the pressure setting of the pressure relieving devices protecting the vessel. The design pressure may be used in all cases in which calculations are not made to determine the value of the MAWP..."
What does it mean exactly? Does it force me to use a safety valve equal or over the design pressure?
Thank you in advance





RE: MAWP and Safety Valve Set Pressure
In any case the first relief valve must lift at or below MAWP.
"Whom the gods would destroy, they first make mad "
RE: MAWP and Safety Valve Set Pressure
I'll try to explain better.
I need to have design pressure at 2.5 bar and so the MOWP will be at least 2.5 bar.
Then I need to set the pressure of the safety valve at not more than 1 bar to restrict the maximum operating pressure.
Is it possible?
My concerning is that the safty valve to 1 bar may force me to reduce the "official" MOWP or design pressure under 1 bar.
RE: MAWP and Safety Valve Set Pressure
However setting any operational limit is up to you - it should not affect any ratings of the vessel and you could have any pressure you like equal to or less than the MAOP which itself can be set anywhere equal to or less than the design pressure.
As said above, the purpose of the MAOP and pressure setting of the "safety valve" is to protect the vessel itself and any directly connected components, not act as any sort of operational control hence the wording in the code.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: MAWP and Safety Valve Set Pressure
RE: MAWP and Safety Valve Set Pressure
Please note that MAWP of the vessel shall not be less than Design pressure,you can consider MAWP same as design pressure code allows it.
Regarding pressure relief valve , i think you can set a pressure Of relief valve between MAWP of vessel and Operating pressure. In no case set pressure shall be more than MAWP of the vesseL.
Bmechz
RE: MAWP and Safety Valve Set Pressure
RE: MAWP and Safety Valve Set Pressure
A pressure relief valve should not be used for process control purposes: it's a safety valve, which needs to be actuated infrequently so that its availability in the case of an emergency is high- you don't want it to be worn out or damaged when the emergency happens. And if your desired operating pressure is 1 bar, don't forget that the relief valve will start to "simmer" (prematurely open) at a pressure somewhat lower than 1 bar.