Applying UG-140 - Liquid Service

[Cotton21]

We have a filter housing (that is liquid full) has had a PSV installed for a fire case situation and are SCFM and not GPM. I'm a Mechanical Engineer and API Inspector (510, 570, 653) and have been for almost 15 years now. It is my understanding that you still need a PSV to protect the vessel from over pressure.

My question is do you need to have a Fire case PSV and an over pressure PSV installed concurrently?

What my thoughts are.
1. It is a pressure vessel it is required to have a PSV.
2. It is liquid so the over-pressure PSV's should be GPM and not SCFM.
3. It is being said that since the system can not over pressure this vessel that an "Over Pressure" PSV is not required. This however is not noted on the U1a. Therefore, it is required to have an over pressure PSV installed per "ASME Section VIII UG-125 and UG-140"
4. Fire case PSV's do not protect from system over-pressure.
5. PSV's that are for liquid are not interchangeable for a gas service.

Thoughts? Concerns?

 

[The Obturator]

Hi Cotton21

My comments to your thoughts;-

1. It is a pressure vessel it is required to have a PSV.
In the USA, and as per ASME VIII for unfired vessels, anything above 15 PSIG requires a PRV.

2. It is liquid so the over-pressure PSV's should be GPM and not SCFM.
You also mention fire case. If so, it may well be the application of the PRV is for the overpressure relief of vessel from external fire causing the liquid to be vapourised and generating a vapour flow rate. It is critical to establish the application(s). Do you have a specification sheet available?

3. It is being said that since the system can not over pressure this vessel that an "Over Pressure" PSV is not required. This however is not noted on the U1a. Therefore, it is required to have an over pressure PSV installed per "ASME Section VIII UG-125 and UG-140"
? Not too sure what is being stated, but if above 15 PSIG PRV is required.

4. Fire case PSV's do not protect from system over-pressure.
PRV's protect against all types overpressures.

5. PSV's that are for liquid are not interchangeable for a gas service.
Some manufacturers designs can have trims to handle both. Though testing is likely to be different.

See also API-520 for sizing and API-521 for general installation.

Hope that helps.


Per ISO, only the term Safety Valve is used regardless of application or design.

 

[The Obturator]

Just to add to my earlier comments...
3. I did not take into account UG-125 and UG-140 and cannot comment further as I do not have these. Although I will add that, a Pressure Relief DEVICE (PRD) is likely to be required (can be a Rupture disc, fusible plug etc., not just a PR Valve) or at the very least, overpressure precautions can be proven. I am sure there is a Code Case on this.

Per ISO, only the term Safety Valve is used regardless of application or design.

 

[chicopee]

To add to the rating of the PRV, you will note that hot water heaters will have their PRV rated in BTU/HR at a certain rated temperature.