Hi All,
I have a system where a new centrifugal pump (taking suction from an existing Tank) has a FIC with control valve at the downstream and which discharges finally in an existing crude oil line. The new pump shutoff pressure is higher (Class #300) than the downstream system design pressure (Class #150). Hence a relief valve needs needs to be installed (for blocked outlet case) at the discharge with a set pressure same as the downstream system design pressure to protect the downstream pipework.
The problem is the normal pump discharge pressure is close to the relief valve set pressure, therefore during alternate cases like turndown operation, as the pump head rises along the performance curve, the relief valve if it is installed at the immediate pump discharge is expected to pop-up frequently. Hence my understanding is that the PZV at the pump discharge should be shifted at the downstream of flow control valve while the pump discharge line including the control valve shall be designed for the pump shutoff pressure (#300).
Moreover Aramco standard SAES-J-601 mentions that for such system where a PZV is installed for downstream protection, a high pressure trip should also be configured at a set point slightly less than the relief valve set pressure. Typically I have seen pressure transmitters installed at the immediate pump discharge for high pressure trip. But in this specific case, I believe the PT having a set point slightly less than the relief valve set pressure should also be installed at the downstream of the control valve.
This is because the normal operating pressure at the pump downstream upto the control valve is near to the relief valve set pressure. If the pressure transmitter with relief valve is installed at the immediate pump discharge, any upset or a turndown operation would lead to head rise with frequent pump trip and occasionally triggering the PZV also to pop-up. Therefore I want to verify with the senior members in the group that if my location of pressure sensing element and relief valve at the downstream of control valve seems correct and to give their valuable inputs (if any).