Must the rating of the centrifugal pump inlet isolation valve be the same as that of the outlet isolation valve?
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I would like to ask fellow sailors: For this centrifugal pump, the inlet pressure is 0.03 MPaG and the outlet pressure is 5.4 MPaG. Based solely on the operating pressures at the inlet and outlet, PN16 and PN63 could be used respectively. However, HAZOP analysis requires that the pressure rating from the pump inlet up to the manual shut-off valve be increased to match that of the outlet. What could be the reason for this? Are there any mandatory regulations? I have encountered this requirement more than once during HAZOP reviews, but I still don’t quite understand it. I hope everyone can share their insights; thank you.
The reason for raising the rating of the centrifugal pump inlet shut-off valve to match that of the outlet shut-off valve is primarily to ensure the safety of the entire system. Although the inlet pressure is relatively low, if backflow occurs or the pressure inside the pump increases, the pressure on the inlet side may rise temporarily, thereby posing a safety hazard. Furthermore, valves of a unified grade can facilitate the safe shutdown and maintenance of pumping stations in emergency situations. These potential risks are usually taken into account in HAZOP analyses. Although there are no specific regulations requiring it, raising the rating of the inlet valve is a prudent approach for safety reasons. .
Thank you for your explanation. I still want to know under what circumstances the internal pressure will increase. I remember that the grade of the inlet flange on our pumps was not very high earlier on. If such conditions do arise, shouldn’t it be the pump manufacturer who first raises the grade of the pump’s inlet flange?
Situations in which internal pressure increases are usually related to abnormal pump operation. For example, when the outlet valve closes accidentally or remains only partially open, although the pump continues to operate, there is no sufficient outlet for the fluid, resulting in pressure building up inside the pump. Furthermore, the backflow phenomenon can also cause an increase in pressure on the inlet side, especially when there are high-pressure areas in the system. As for the grade of the pump inlet flange, pump manufacturers typically select an appropriate grade based on standard design requirements and typical operating conditions, which ensures safety and cost-effectiveness under normal operating conditions. However, safety assessment methods such as HAZOP are designed to identify and address potential abnormal situations (such as sudden accidents or equipment failures), and therefore may recommend higher safety precautions, including upgrading the grade of inlet valves. This doesn’t necessarily mean that the components provided by pump manufacturers are inadequate; rather, under certain project or safety requirements, system design must be carried out more carefully to ensure safety under extreme conditions. .