Regarding the selection of safety valves!
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What are the differences in the backpressure and set pressure calculations for safety valves on equipment versus those on pipelines?
In practical applications, safety valves are sometimes installed on the equipment itself, and sometimes on the pipelines. In fact, the back pressure and set pressure of both are basically calculated based on the design pressure of the equipment. This is because the design pressure of pipes is often much higher than that of the equipment, and the safety valves in a system should be set according to the lower design pressure.
Explanation of terms: 1. Back pressure: It is the pressure at the outlet of the pressure relief device or at the discharge point, and it is generated by the pressure from the equipment in the discharge system. If it is emptied directly, this pressure may be only atmospheric pressure. It may also have some positive pressure, which is due to the flow of steam, gases (or possibly liquids) in the gas collection system, or it may be caused by connection to a venting or flare system that has a specified backpressure during flow. 2. Fixed pressure: The set pressure system, expressed in MPa (gauge), refers to the inlet pressure at which the safety or relief valves are adjusted to open. Its set pressure is independent of the back pressure at the valve outlet, and it should not be confused with the spring setting provided by the manufacturer.
Essentially, the principles and procedures for designing safety valves on pipelines are the same as those for safety valves on equipment. ‘
The following two standards can be referred to: GBT 12241-2005 on the installation and selection of safety valves, and HG/T 20570.2-95.