allowable overpressure for low pressure vessel

[jcrein]

We are doing relief valve sizing for a client who has numerous vessels, which have an MAWP of 0.6 psig. We realize these do not fall under ASME, but if we were to install an RV, RD or tank vent at a Pset of 0.6 psig, what would be an acceptable overpressure?

Utilzing 10% or 21% for fire would only yield 0.726 psig relieving pressure. If you refer to pressure vessels between 15-30 psig, you can utilize 3 psig overpressre, but seems quite excessive. I have also heard of a proposed ASME code which would allow 2 psig overpress for MAWP < 15 psig??

I am wondering if anyone has guidance on how ASME specifies the allowable overpressure and what ASME code would be for the MAWP of <15 psig?

Thanks

 

[zdas04]

Have you looked at the welded tank codes like API 12F? It seems like you are in that pressure range instead of the BPVC.

David

 

[Latexman]

Does it have a bottom head, or is it flat bottom?

Good luck,
Latexman

 

[jcrein]

These look and are constructed like a pressure vessel - elliptical heads. There are even some calculations which look like they compared the design to ASME Section VIII calcs. But the ultimate MAWP listed on the name plate is 0.6 psig.

 

[BenThayer]

i would be looking to see if you could them re-rated. many tanks are built to a higher criteria but are only stamped with what the customer requests.

if it has elliptical heads, it might be good for several psig. we have taken several vessels that were stamped for 35 psig and FV and had them rerated for +50 psig.

basically you need to find someone with a pressure vessel design program, have an inspection and do a hydro-test.

 

[zdas04]

It sounds like the client is satisfied with the performance of the vessels with the fractional psi MAWP. Re-rating so that you can do a PSV calc that makes sense seems to be a bit counter-indicated. The question seems to be "psv sizing for a vessel with a very low (but acceptable) MAWP" not "how can I twist the vessels to match the code".

If you can't do it with an Anardo Valve (tank specs) then I'm out of ideas.

David

 

[Duwe6]

Use a Protectoseal #53300. At 0.6 psig, a "Code" relief valve is not mandatory, nor is it available. 53300's are available at 1-1/4 oz and up. And they are big enough to handle 'Fire Case' without any overpressure.

Little pressures require huge relief devices during 'Fire Case'.

 

[MJCronin]

Gentlemen,

In my opinion, this discussion points toward a "minimum recommended design pressure" that should be part of ASME VIII, API-650 and similar codes. Some older in-house design standards by PENZOIL, EXXON and others used to have these

ASME and API are silent about this.

I suggest for example:

- Any metallic vessel with eliiptical heads and a diameter of less than 10 ft should have a MRDP of 5 psig and be tested to 7.5 psig

- Any flat bottomed tank of API-650/620 construction should have a MRDP of +10 IWG and -5 IWG

- FRP, plastic and vessels of any other construction should be bound by the limitations agreed upon by the purchaser and the fabricator.

 

[psafety]

I regularly calc with the ASME calculations. Sounds as if a PVVV (Pressure Vacuum Vent Valve) is in order. Be aware some flow printed capacity at 100% over pressure.