Checking PSV size against flow rate 2

[kevinwaltun]

I was wondering if anybody knew how to double check the sizing of a psv on a vessel against the flow rate of a well. Take for example if a 2" PSV was rated for 8078 SCFM (AIR) could you determine if it was able to properly relieve a vessel seeing 5000 MCFD of natural gas flow.

 

[TD2K]

https://www.google.com/url?sa=t&rct...cd=1&cad=rja&uact=8&ved=0CB0QFjAA&url=http://

http://www.candksouth.com/_literatu...NwGmkk76ZXkxDwo6Q&sig2=ChEkPqwwpKXRh1XflbsY2w

I am concerned sending you off on your own to check a PSV size because of the potential consequences if you make a mistake. My apologies if you are familiar with sizing PSVs.

Basically, if I was doing this, I would take the air capacity of the PSV and first verify that the above equation equals the provided orifice. That's a little redundant I realize but it gives you a check that you are doing the calculations properly. Then I would take the conditions I needed to relieve the natural gas at (flow rate: 5000 Mscfd, relieving pressure, relieving temperature, compressibility, MW, etc) and calculate the new area. If it's less than the area of the existing PSV, it has enough capacity. If not, get a new one. Also check the materials of construction and the flange ratings that they are suitable for your conditions.

I'm assuming that this is strictly gas, if the relief is two phase then the calculations are quite different. Look at API 520 and 521, those are good references in any event to review if you are going to be doing PSV calculations.

Your last step should be to get someone familiar with PSV sizing to double check your work.

 

[bljnv]

Please check the PSV is not oversized. Oversized PSV Can cause valve chatter

 

[kevinwaltun]

TD2K,

That's exactly the process I was going to use. I have read API 520 and several other API codebooks along with ASME code. I wanted to see if my logic aligned with someone else's that was a little more experienced than me. I just went through using API 2000 to evaluate some low pressure storage tanks for venting. I have both the original manufacture drawings for the gpu and the valve data sheet. I am also in contact with both of those companies so if any questions would arise I could ask them to give me proof that the psv was sized properly. And yes oversizing is also a concern.