Relief Valve Size Calculation

This article is about How to do calculation of Relief valve size as per International Code ASME Technical Requirements. We mentioned here Example of Relief Valve Size Chart, Inlet and outlet sizes, thermal relief valve sizing calculation and Relieving capacity Calculation.

Relief Valve Size Calculation | Size Chart | ASME Requirements

We take example here and read thoroughly understand this and apply on your application where you want to testing.

1) Pneumatic Test Pressure

– Design Pressure: 40.9 barg (= 593.2 psig)
– Test Pressure: 45 barg (= 652.7 psig)

2) Source of pressurization

a) Compressor
– Rated Operation Pressure: 10.3 barg (= 150.0 psig)
b) N2 Cylinder with regulator
– N2 cylinder Pressure: 140 barg (1,900- 2,000 psig)
– Regulator specification: see below chart

3) Relief valve size and capacity

– Size : ¾” x1″
– Set pressure: 49.50 bar g (= 717.9 psi g)
– Capacity at set pressure:871 SCFM

4) Pressurization process

1° step – Pressurized by compressor up to maximum 10.0 bar g.
2″ step – Pressurized by N2 cylinder up to test pressure 45 bar g = 652.7 psi g

5) Justification of relief valve sizing

a) Line is pressurized by compressor as 1 step. Maximum compressor pressure is 10.3 barg and it is enough lower than design pressure for piping line 40.9 bar g (593.2 psi g).

b) As 2″ step, line is boosted up to test pressure by N2 cylinder. Pressurization by N2 cylinder is controlled by regulator which is equipped on the cylinder. So, relief valve sizing should be considered regulator’s capacity.

c) According to regulator specification as per below chart, regulator capacity is 3,000 SCFH (= 50 SCFM) at set pressure of relief valve (see blue dotted line). This is enough lower than relief valve capacity (871 SCFM). In addition, even though regulator is accidentally fully opened during pressurize operation, flow rate is 11,000 SCFH (= 183 SCFM) and it is also still lower than relief valve capacity.