Regarding the set pressure of the safety valve
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In the \"Manual for the Installation Design of Process Piping in Petrochemical Plants – Part 1: Design and Calculation\" (5th edition), the settings for safety valves are described as follows. I’m dealing with a tank that has the following configuration; according to the book, the set pressure for my safety valve should be 0.81, which is higher than the design pressure of the equipment. Is this correct? Moreover, in the book it is assumed that the pressure is equal to the design pressure of the equipment or pipelines; if that’s already the case, then what’s there to calculate?
It is necessary to check the relevant information in the drawing data sheet – what are the design standards for this container? GB150, or something else? Check the pressure setting specifications for the safety valve according to the relevant standards. Additionally, it is necessary to look at some other relevant parameters and such; after analysis, then determine the source of the problem.
The setting pressure is determined based on 95% of the design pressure of the protective device. The 10% overpressure tolerance mentioned here refers to the pressure at full opening, that is, the release pressure. From this perspective, the set pressure is set at 0.8*0.95=0.76 MPaG, which means that the safety valve starts to discharge when the gauge pressure reaches 0.76 MPa; however, it does not open completely at this point due to the backseat pressure of the safety valve. The safety valve opens fully and begins to discharge when the pressure reaches 0.8*1.1=0.88 MPaG.