TERV PSV size selection

[Sawsan311]

Dear All,

for moderate pipeline inventory where liquid thermal expansion as a result of solar ambient radiation , API 521 section 4.12.3 is stating a TERV size of 3/4'' x 1''
Do you agree that such size is not certified by API 526 nor further by ASME and hence a minimum of 1 D 2 size shall be considered instead?
is 3/4'' x 1'' purposely mentioned for piping systems and NOT for vessels considering ASME SEC VIII capacity certification requirement is for pressure vessels and not for piping system?

Kindly please appreciate your advice on when to consider 3/4'' x 1'' and whether such Thermal TSV shall follow API 526.

Thanks

Regards,

 

[The Obturator]

ASME VIII Allows a minimum of a 1/2"inlet PRV size.

API-526 Covers flanged PRV's orifice size D to T (1 x D x 2 to 8 x T x 10)

ASME Does not certify. If you require a "UV" Stamped valve it should be certified by The National Board of Boiler % Pressure Vessel Inspections and the maker/PRV listed in the NB-18 publication. ASME is the code/set of rules.

You can have a TRV 3/4 x 1 "UV" stamped. It will not follow API-526 and does not have to.

In future, please post PRV questions in te Safety Relief Valve Forum.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[Sawsan311]

Thank you The Obturator,

Yes, I was referring to certification in accordance with the ASME code rules, however, is there any straight criteria for selecting when to go with 3/4'' x 1'' against API 526 D orifice as a minimum for liquid thermal expansion?

Thanks

Regards,

 

[The Obturator]

None at all. Unless you figure out any actual flow rate which would size for a 1 x D x 2. You can of course select and use a 1 x D x 2 for TR. For thermal relief the flow has always been understood as "nominal" hence a typical 3/4 x 1 is selected. Though you can also have a 3/4 x D x 1 from most manufacturers.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[The Obturator]

FYI There is a small section in API-521 (2020) that makes reference to 3/4 x 1 TRV size. I attach an extract for your info.

I also need to correct my first reply. Minimum PRV size in ASME VIII is 3/4" (not 1/2")

Per ISO-4126, only the term Safety Valve is used regardless of application or design.