Relief valve inlet line sizing

The inlet line to the relief valve is designed for a maximum pressure drop of 3% of the relief valve set pressure. The pressure drop should be in between the equipment being protected and the inlet to the relief valve. However, the line size should not be smaller than the inlet flange size of the relief valve. 

Process engineering and design using Visual Basic 

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The inlet line size shall not be less than the inlet nozzle size of the PRV. When two or more relief valves are placed on one connection, the inlet internal cross-sechonal area of this connection must either be sized to avoid restricting flow to the PRVs or made at least equal to the combined inlet areas of fhe relief valves connected to it. 

The relief valve was sized to take the full inlet flow with all exit lines closed. 

Safety features for the tank include a pressure relief-valve system on the tank roof, to be opened when draining or adding to the tank contents. A bursting disc system also allows for pressure release in the event of pressure build-up. Amanhole providesaccessto the tank for internal maintenance. The product inlet line is standard nominal pipe size 1.5, schedule number 40S. This inlet is sized for the maximum production flowrates. The product outlet line is of standard nominal pipe size 6, schedule number 120. This line is sized such that a standard-size road tanker may be filled in 15 minutes. 

Inlet line Nominal pipe size 1.5. schedule number 40S Outlet line Nominal pipe size 6, schedule number 120 Manhole, bursting disc, pressure relief valve on roof No insulation... 

The pressure drop allowed through the inlet and discharge lines is unlimited as long as the capacity of the line is adequate for the relief requirements. That is, at the required flow rate the vessel pressure must not exceed the maximum allowable accumulated pressure. In sizing a safety disc, it is usually assumed that the entrance loss at the nozzle is the governing restriction insofar as capacity is concerned. Thus the effective orifice area is considerably larger than the effective orifice area of a safety valve of the same pipe size. Consequently,... 

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