Thermal Relief Load

[Berenger]

Hi all,

My question is straight forward. Can you size a thermal relief valve FOR GAS ONLY SYSTEM? If yes, how do you calculate the load requirement?

I have gone through API 520 and 521, and nowhere do they discuss or explain thermal relief for a gas only system. I know 521 section 5.14 talks about liquid systems and liquid/gas systems, but nowhere in the standards do they talk about gas only systems.

If anybody has any reference material or equations with references, can you share.

Berenger...

 

[Compositepro]

In a gas only system it would simply be called pressure relief. The pressure rise in gasses with increasing temperature is relatively low and linear. In liquid systems the term thermal relief is used to indicate that it is sized to relieve only very small flows associated with liquid thermal expansion. It is actually a pressure relief but will not protect against high-flow sources of pressure.

 

[Mikey M]

I think the question is about gas only system and how to size for a gas only system. I’ve have similar issues in the past. I used all the PVT relationships and equations but the gas volume never increases by much (say 0.5%).

I’m interested in this discussion. We all know about gas expansion being small and gas temperature - pressure relationships being linear and small...but can you size a thermal relief for a gas only system? Does the volume change much? What load do you use in calculating the area.

Curious.

 

[Compositepro]

Describe what you think this "thermal relief system" is supposed to do in a gas only system. Keep the pressure from rising 0.5%? That would require a pressure control system, not thermal relief.

 

[georgeverghese]

This topic was discussed recently:

https://www.eng-tips.com/viewthread.cfm?qid=437998