Some doubts regarding the safety valve condition table
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Some doubts regarding the safety valve specifications: 1. The operating pressure of the equipment is 10 MPa, while the maximum operating pressure is 11 MPa. Therefore, the design pressure should be 1.1 times the maximum operating pressure, which equals 12.1 MPa. But what should be the setting pressure, or the pressure at which the safety valve activates, for this equipment? Is it 10*1.1=11 MPa? Does the setting pressure for the safety valve also need to be rounded?
The set pressure shall be the design pressure, with no need for rounding.
Is there any evidence for this? {:2_32:} Thank you
This is stated in the specifications for basically all safety valves; take a look at the commonly used 20570.2
I think you might have misunderstood. It refers to the pressure set at the same level, not the design pressure of the device – they are two completely different concepts
What is stated in 20570 refers to the set pressure; set pressure and design pressure are two different concepts, right?
The setting pressure of the safety valve shall not be greater than the design pressure of the equipment being protected. The claim of 20570. This is also the usual approach in design; when a single safety valve is used to protect only one device, the design pressure is generally sufficient – it can be equal to that value, as long as it is not lower. If a safety valve protects a system (consisting of multiple devices) in which there are piping connections but no shut-off valves, then the setting pressure of the safety valve is determined based on the lowest design pressure among them, calculated back using the pressure drop in the pipelines. Due to the pressure drop in the same system, the design pressures also vary (this is especially true for high-pressure systems; otherwise, the investment would be high). Of course, the setting pressure of the safety valve can also be lower than the design pressure, but it should not be too close to the operating pressure; otherwise, it will activate due to pressure fluctuations, which is detrimental to production.
I was also involved in the certification process for safety valves, and in my opinion； The safety accessories of a device must not exceed the maximum pressure specified in its design; that is, the set pressure should be below the design pressure. It should be determined by multiplying the maximum operating pressure specified in the device’s design by a certain coefficient. The maximum operating pressure is usually provided by the design institute. For example, in the case of a gas boiler, if the maximum operating pressure is 4.0 MPa, then the maximum set pressure would be 4.4 MPa. However, the design pressure might be 4.85 MPa. I’m not sure if this understanding is correct; I hope experts can give me some guidance
The safety valve lies between the design pressure and the operating pressure of the equipment. It seems that there are no specific numerical guidelines for selecting this set pressure, and this is what’s most troublesome
The set pressure of the safety valve should be less than or equal to the design pressure of the equipment, but higher than the operating pressure; refer to SH3136 for details
Generally, equipment is specified with a maximum operating pressure determined by a design institute; the operating pressure multiplied by a certain coefficient gives the setting pressure for the safety valve. This is exactly what we do nowadays