Set presure tolerance for PSVs- ASME Section 8, UG-134 D 1

[Nasim12345]

Dears

While testing the PSVs, we are following the set pressure tolerance based on below ((ASME Section 8, UG-134 D (1))

The set pressure tolerance for pressure relief valves shall not exceed ±2 psi (15 kPa) for pressures up to and including 70 psi (500 kPa) and ±3% for pressures above 70 psi (500 kPa), except as covered in (2) below.

What is the meaning of 2nd statement from ASME Section 8, UG-134 D.10% Tolerance is mentioned in below statement. (ASME Section 8, UG-134 D (2))

"The set pressure tolerance of pressure relief valves which comply with UG-125(c)(3) shall be within −0%, +10%.".

Find attached snapshot from ASME. My query is about 10% tolerance.

Thanks
Nasim

 

[The Obturator]

You should now be using ASME XIII for Pressure-relief Devices.

You are referencing a section in ASME VIII which has since 2021 been taken out and replaced by ASME XIII.

Refer to table 3.6.3.1-2 in ASME XIII for the current legislated set pressure tolerances.

(The 2nd statement you referenced in the old ASME VIII, referred to section UG-125(c)(3) which clearly explains when those different tolerances where to be used - it's in the same ASME VIII document you have).

*** Per ISO-4126, the generic term
'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the ASME/API used term ***

 

[JAlton]

Its is for Fire Sizing, This is for use in addition to the PRV set for typical overpressure protection.

JAC