4 replies to this topic

[vikramltv]

Dear all
Can we keep the set pressure of PSV below the design pressure (to lower the relieving pressure) of an ASME vessel ?
Need for the same is arising for the unwetted surface -Fire case where temp. of the vessel content is exceeding the vessel wall temp. at relieving pressure.

[fallah]

Dear all
Can we keep the set pressure of PSV below the design pressure (to lower the relieving pressure) of an ASME vessel ?
Need for the same is arising for the unwetted surface -Fire case where temp. of the vessel content is exceeding the vessel wall temp. at relieving pressure.

vikramltv,

Yes you can provided that you keep the proper margin wiith maximum operating pressure as well.

Your aim for loweing the set pressure in order to decreasing the relieving pressure to prevent vessel failure seems to be proper at first glance but needs to be evaluated in depth if it can really protect the vessel. Be informed with lowering the set pressure the relevant PSV size would be increased.

Fallah

[vikramltv]

Dear Sir
Thanks for your suggesion
so now I understand that API 520 allows the set pressure bellow the design pressure but above max operating pressure with some marging.

[fallah]

Dear Sir
Thanks for your suggesion
so now I understand that API 520 allows the set pressure bellow the design pressure but above max operating pressure with some marging.

vikramltv,

Typically, the maximum operating pressure should be equal or less than 90% of the set pressure (pilot operated PSV is an exception and that of it can be higher) and if you want to decrease the set pressure lower than design pressure, you should keep the difference of 10% or 1 bar (whichever is greater) between maximum operating pressure and design pressure, means you should previously had greater difference than 10%.

Fallah

[vikramltv]

Thank you sir
i understand now..