For spherical tanks undergoing airtightness testing, how is the setting pressure of the safety valve determined?
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For spherical tanks undergoing airtightness testing, how is the setting pressure of the safety valve determined? For example: for a certain propylene sphere tank, the design pressure specified in the drawings is 2.16 MPa, while the setting pressure of the safety valve is 2.05 MPa; the safety valve has already undergone type testing. During the airtightness test of the spherical tank, the supervisor stated that all safety accessories must be installed before conducting the test. So here comes the problem: during the airtightness test, the safety valve will activate. 1. Clause 3.12 of the standard GB/T12337-2014 \"Steel Spherical Storage Tanks\" stipulates that for spherical tanks in which the medium is extremely or highly toxic, is a flammable compressed gas or a flammable liquefied gas, and in which even trace leaks are not permitted, a leak test shall be conducted after the pressure resistance test is passed. The airtightness test pressure is equal to the design pressure. 2. Safety valves and rupture discs are considered safety accessories; in accordance with Article 4.1.10.1 of TSG21-2016 \"Safety Technical Inspection Regulations for Fixed Pressure Vessels\", these accessories need to be fully installed when conducting airtightness tests. 3. According to clause 3.1.18 of TSG21-2016 \"Regulations on Safety Technical Inspection of Fixed Pressure Vessels\": For pressure vessels equipped with overpressure relief devices such as safety valves and burst discs, if a gas-tightness leakage test is required in the design, the designer shall specify the maximum allowable operating pressure for such pressure vessel; in this case, the maximum allowable operating pressure shall be used instead of the design pressure to determine the test pressure. 4. The setting pressure of the safety valve or the burst pressure of the rupture disc is generally not greater than the design pressure of the pressure vessel; for those devices for which the maximum allowable operating pressure is specified on the design drawings or nameplate, this maximum allowable operating pressure can be used to determine the setting pressure of the safety valve. Improvement plan: Based on the above considerations, the airtightness test pressure should be greater than the design pressure and less than or equal to the maximum allowable operating pressure. Therefore, the drawing specifies a maximum operating pressure of 2.17 MPa, a design pressure of 2.16 MPa, a airtightness test pressure of 2.16 MPa, a safety valve setting pressure of 2.17 MPa, and the hydraulic test pressure is determined based on the maximum allowable operating pressure of 2.17 MPa. All the problems are solved. Note: The maximum operating pressure specified on the drawing is 2.17 MPa; this value is to be determined based on the minimum wall thickness of the shell, taking into account various loads, a corrosion margin, and the hydrostatic pressure of the liquid column.
The maximum allowable operating pressure is determined based on the actual materials and manufacturing conditions; it is sufficient to ensure that the setting pressure of the safety valve is less than the maximum allowable operating pressure, which in turn should be greater than or equal to 2.16 times the design pressure. That is, airtightness test 2.16, safety valve setting 2.16
The set pressure of a safety valve allows for a certain tolerance: max (±3% of the set pressure or ±0.015 MPa). The pressure for the airtightness test shall be 2.16 MPa; the setting pressure of the safety valve must be no less than 2.23 MPa, and the maximum allowable operating pressure must also be no less than 2.23 MPa.
For pressure vessels that require a gas-tightness test and are equipped with safety valves, the setting pressure of the safety valve is determined based on the vessel’s maximum allowable operating pressure.
Those designed in accordance with technical specifications all have a set pressure for the safety valve; it simply needs to be set according to the drawings, and it must be at least 10.5 times the operating pressure, so that it is impossible for the valve to activate. For such spherical tanks, the maximum allowable operating pressure is ≥ the set pressure of the safety valve > the design pressure > the operating pressure. The pressure for the leakage test is equal to the design pressure (a safety valve must be installed). The pressure for the strength test is equal to the design pressure multiplied by a coefficient (when no safety valve is used). There is absolutely no need to worry about the leakage test pressure exceeding the set pressure of the safety valve. The examples and improvement suggestions you proposed are all incorrect, which is why you keep struggling.