3 replies to this topic

[AlanInTexas]

Per guideline, "if the blocked in pipe section is of small diameter of leses than 100 ft in length, the required thermal expansion relieving capacity is less than the leakage of the blocked valve, so a thermal relief valve is not required."
 
Can anyone advise: What it the definition of a "small diameter?"
 
I have a 4 in pipe of 10 ft length that can be potentially liquid full upon isolation.  I would love to write off as not requiring a thermal PSV, if it is allowed.

[Art Montemayor]

Who is the guideline from?  What are the circumstances?  What is the fluid in question?  What are the probabilities of the blocked-in liquid achieving rupture pressure in the pipe?

 

If the "guideline" comes from the company you work for, you may have to follow that advice - unless you have the initiative, justification, or guts to challenge it.

 

If it comes from someone who is not a stakeholder in your work results, then I would seriously challenge his/her recommendation.

 

If the liquid in question that is unidentified by you turns out to be cooling water or something similar in properties, I'd just forget about this "expert" advice and install a $50 1/2" thermal relief valve.

[Bobby Strain]

If you are working with a world scale LNG plant, small diameter can be 10 inches. So, be wary. In all my years, I have never seen a thermal relief valve provided for a 4 inch pipe 10 feet long.

 

Bobby

[sgkim]

Refer to the following:  

 

http://www.chemwork....l_expansion.pdf

 

I'd like to quote the last term - but I am not sure where this criteria come from: 

 

(Quote/)

10. Pipes with diameter more than 1 ½” and longer than 30 m are generally considered large pipes. The rupture cost of smaller

pipe is expected to be lower than the TRV cost, so no TRV is required in this case. This advice should be considered

carefully and approved by project owner. Equipment operating full of liquid should be provided with a thermal relief valve if

the quantity of blocked in liquid is higher than 0.5 m3

(/Unquote) 

 

~Stefano

Edited by sgkim, 18 November 2016 - 05:53 AM.