2 replies to this topic

[RRahman]

Dear all respected fellow engineers,

 

I am really new to this forum and this is my first time posting a question here. Here it goes.

 

 

I am currently doing a mitigation study for relief valves (RV) in a crude oil terminal. One of  the RV is related to overpressure caused by thermal expansion (or hydraulic expansion as in API 521). I understand for thermal relief valves (TRV), it is a common practice not to size them since the generic 3/4" x 1" D orifice size would normally be adequate. Now, my question is as follows:

 

(1) Will the criteria for inlet piping pressure losses which is max 3% of set P (as per API) apply to this TRV catering for liquid thermal expansion?. Do we need to consider the static head also?

 

(2) Is there a difference between thermal relief and thermal expansion relief? From my reading it differs in terms of the vapour pressure and design pressure but I would like to know whether this understanding is correct.

 

 

I have talked to my fellow senior engineers, from their experiences, normally the inlet line loss for TRV is not considered for study or mitigation since the function of TRV is just to release small amount of liquid or (mix. liquid + vapour) to reduce the overpressure from expanding volume (due to temperature). This is also not a continuous mechanism.

 

Appreciate the response from you guys. Have a good day.

 

Warm regards,

 

YoungChemEng89

[ankur2061]

The size 3/4" X 1" is applicable to short piping or pipeline sections or cold side of heat exchangers. Typically the TERVs  or TRVs are mounted close to the piping / pipeline section for a blocked in piping  / pipeline or directly on a tapping in the cooling medium return piping from the heat exchanger. This negates the need for doing any inlet line losses calculation for the TERV (TRV).

 

For long pipeline sections running through above-ground open terrain and exposed to solar radiation with isolation valves spaced kilometers apart, a 3/4" X 1" TERV or TRV won't suffice. You may need to provide a bigger TERV (TRV), say 1.5" X 2" or 2" X 3". Relief rate calculations may also be required to be done based on the procedure given in API STD 521 for hydraulic expansion relief rate. 

 

For some more information on where and when TERVs (TRVs) are required refer the link below:

 

http://www.cheresour...e-relief-valve/

 

Hope this helps.

 

Regards,

Ankur.

[RRahman]

Dear Mr. Ankur,

 

Thank you so much for the reply ! Will surely look into that.

 

 

Regards.