Thermal Expansion Relief in Piping 3

[RJB32482]

Hello,
I am looking at sizing a relief system looking at thermal expansion in piping. I have the correlation from Crowl and Louvar:

Q=(beta/density*Cp)*(UA(deltaT))

My questions are as follows:

1. Is there any correlation or charts that have the U values for all sizes of stainless steel pipes?

2. One of the cases in question is solar radiation heating the pipe up. Any correlations on heat input due to solar radiation?

Thanks.

 

[Latexman]

RJB32482,

Within a plant's boundaries, this excludes long pipelines that are measured in miles or kilometers, it is acceptable to provide a small PSV with no calculations for ambient heating thermal relief. I have seen "small" interpreted as 1/2" to 1", with 3/4" being the most common.

Good luck,
Latexman

 

[RJB32482]

Thanks for the reply:

The pipe is 6" Sch. 40 that holds around 45 gallons of liquid. Problems are occuring since when this part of the line is blocked in, the valve to our reactors leak through. We want thermal relief to prevent the valve from "leaking through" and causing process upsets.

Thanks.

 

[TangoCleveland]

I've heard these devices called "Sun Valves." For heat input to piping, take a look at

http://www.naima.org

for free software called "3E Plus". It's based on ASTM C-680 and intended for insulated piping, but does an excellent job of calculating natural convection and emissivity considerations.

Larry

 

[Montemayor]

RJB32482:

I can only add to Latexman's excellent, terse reply by saying that from an OSHA PSM viewpoint, no calculations for thermal relief valves are ever required. I personally consider them a waste of good engineering time. There is a good, sound, and practical engineering reason for this.

Any serious attempt to calculate the accurate amount of liquid volume that you have to evacuate through the valve will reveal that the total volume amounts to a cubic centimeter - at most. I realize I'm being general, but this is one of Nature's rare, free "gimmees" and you should enjoy it because engineers don't get many "gimmees".

In over 46 years of applying these things, I've found the 3/4" size to be a generous, cheap overkill for this relief application. This should make a lot of young engineers very happy.

 

[Ashereng]

Just to clarify: is this for both a gas and liquid systems?

 

[TangoCleveland]

No, the rationale for small liquid relief valves won't apply to a gas system. It also doesn't apply where you have a liquid cryogen that might be blocked in an area. For gas and cryogenic applications you need to evaluate failure scenarios and the amount of gas to be relieved.

Larry

 

[Ashereng]

Thanks. Didn't think of the cryogenic situation.

 

[Montemayor]

Tango:

That's good engineering detail - the rest of us failed to be specific in pointing out the obvious expansions related with cryogens and gases.

 

[TangoCleveland]

Art,
I keep seeing your posts in the forums I frequent, and I'm impressed with your technical talent and communication ability. A compliment from you is a real honor. Thanks!

Larry