Are rated capacity of all PSVs always certified at 10% overpressure, regardless of their application for fire case or non-fire case?
Regards

Yor prompt reply/recommendation will be highly appreciated,because i am in force for clarifying the mentioned issue.

Actually i want to know if relief valves are always certified (rated) at 10% overpressure for section VIII valves (3% for section I) for all cases including fire case.

Thanks a lot

The rated capacity is normally stamped on the PSV tag but in terms of the test medium, i.e. air or steam. You will need to convert it to your specific relief load demand.

Thanks for your reply, but i didn't get my answer.I really want to know:
if relief valves are always stamed/certified (rated) at 10% overpressure for section VIII valves (3% for section I) for all cases including fire case.
Thanks again

Fallah,
There is a posting "Relate PSV Relieving Flow to Stamped Capacity (click here)".

A PSV is have stamped capacity with a test medium, i.e. air or steam at test pressure.

When you have a specific relief load demand which based on particular relieving condition i.e 100% of Pset for non-fire case or 121% of Pset for fire case, you convert it to equivalent steam flow (or air depend test medium) and check if a PSV if sufficient for you.

In return, based on the stamped capacity, you back calculate the rated flow for relieving fluid at relieving condition. You will used the rated flow (subject to PSV type) for your inlet pipe and tail pipe sizing

Thanks again for your valuable comments,but:
1-I think you mean 110% instead 100%
2-My main concern is to obtain actual relief load (for flare load estimation) of a PSV using SCALE-UP (Ratioing) of effective orifice area up to the stamped orifice (the next largest size) without having stamped capacity.Is the obtained data reliable? If so, is the SCALE-UP method applicable/credible for both 10% and 21% overpressure?
Regards

Yeap. It is a mistake. Should be 110%. .


Which state you are in now ? Still in design ? If design, is the vendor selected ?

Anything prior to PSV selection is still estimate and shall be confirmed once the PSV is selected.



If the method in API is used, it should within reasonable accuracy. Nevertheless, it shall always check and confirm once the PSV is selected.