How should the size of a safety valve be chosen?

I think it should be calculated based on the maximum discharge capacity of the pipe or container

HG/T20570.2 explains it very clearly

Principles for selecting and determining the type of safety valve: a) Select the safety valve based on the calculated minimum discharge area, in accordance with the manufacturer’s product specifications. The principle is that the actual discharge area of the selected safety valve must not be less than the minimum discharge area. b) The American Petroleum Institute standard API-526 specifies the throat diameter area and its code for safety valves, as shown in Table 16.4. Based on the calculated minimum discharge area (throat diameter cross-sectional area), select the throat diameter code by rounding up according to the table; then, use the manufacturer’s product data to choose the safety valve corresponding to that throat diameter code. Selection of safety valve type 1: For discharging gases or steam, a full-open safety valve should be used. 2 When discharging liquids, use a fully open or slightly open safety valve. 3 When releasing water vapor or air, a safety valve equipped with a wrench can be used. 4 For safety valves used with gases having a set pressure greater than 3 MPa and a temperature exceeding 235°C, safety valves equipped with radiators should be selected to prevent the discharged medium from directly eroding the spring. 5 When the emission medium is allowed to leak into the atmosphere, an open-type valve cap safety valve should be used ； For applications where leakage to the atmosphere is not allowed, a safety valve with a closed valve cap should be used. 6 For the discharge of highly toxic, highly corrosive, and extremely dangerous media, a bellows-type safety valve should be used. 7 In cases of high back pressure, use a back pressure balanced safety valve or a pilot-operated safety valve. 8 On some important occasions, it is sometimes necessary to install two safety valves that serve as backups for each other. Mechanical interlock devices should be used for the inlet and outlet isolation valves of the two safety valves, to ensure that the required discharge area for the vessel is met at all times, including during maintenance and repair.

I’ve learned it, thanks for sharing above!

Go and ask the people in the engineering department :victory:

One can refer to the first part, \"Design and Calculation\", of the \"Manual for the Installation Design of Process Piping in Petrochemical Plants\"; Section 1 of Chapter 9 provides detailed guidance on the classification, structure, design principles, process calculations, selection, and installation design of safety valves – it is excellent material.

HG/T20570.2 already states that the specific details will be considered later; calculations are required

Reference: Process Installation Piping Design Manual, 3rd edition, Part 1, P315. Over the past three years, 12 spherical tanks have been built, and I checked this manual every time a calculation needed to be done. I recommend that you take a look at it

It seems there are calculation formulas after the tolerance specifications

If only size is considered, the required channel diameter still needs to be calculated according to the corresponding standards and specifications； Based on the flow channel diameter, the nominal inlet and outlet diameters of the corresponding safety valve are selected, thereby determining the size of the safety valve.

It is calculated based on the maximum discharge capacity of the pipeline or container; after selecting the throat diameter, the type is chosen according to the properties of the medium, and careful consideration must be given to this

Calculated based on the maximum operating pressure of the pressure vessel, the setting pressure of a safety valve is generally higher than the maximum operating pressure but lower than the design pressure of the pressure vessel

View Appendix B of GB150-89 – Overpressure Relief Devices for Steel Pressure Vessels