In an air system, normal operating pressure is 14.5 psig, however surge conditions may go to 17.5 psig (relief valve setting). We assume MAWP is 17.5 psig and verify adequacy of vessel design to that pressure. Does vessel require code stamp even though normal operation is below 15 psig?

Does your vessel discontinue being in service while experiencing surges? Shouldn't you asses cyclic load detrimental effect?

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Konrad Anikiel

jman6147,

Very strange that the design pressure is less than the maximum operating pressure.

Unsder steady state conditions the design pressure will always be greater than the maximum operating pressure anticipated to be experienced by the vessel.

There are guidelines to fix the design pressure. One, being that design pressure is max operating pressure divided by 0.9. Another says that design pressure is 1.10 times the maximum operating pressure. As a pressure vessel enginner, typically the design pressure and temperature is typically NOT set by you but by the process enginner.

hope this helps.

-jehan

At first you should decide which MAWP you like to stamp on your nameplate . This would be a basis for the next step.

Michael

The question whether or not Code stamping is required, depends on the laws at the location of installation.

Section VIII does not allow operation (even temorary regular operation) above MAWP. Relief valve shall be set no higher than MAWP.

In my opinion the vessel is in the scope of Section VIII.

DK

Jman,

Since vessel can see 17.5 psig during surge condition, it will be better to select Design Pressure and/ or MAWP slightly higher than 17.5 psig. A suitable marging can be considered for the same and for relief valve setting otherwise relief valve will pop-off every time during surge condition and may require re-setting after each pop-off which may cause inconvenience for operation group.

This again depends how frequent this surge condition occur. If it is a rear occurance, you may consider DP/ MAWP (as stamped on name plate) as 17.5 psig but in no case less than 17.5 psig.

Regards