GB/T 12243-2021Spring loaded safety valves (English PDF)

4.1 General

4.1.1 The design of the safety valve shall comply with the provisions of GB/T 12241.

4.1.2 The applicable temperature range of the safety valve shall be determined according to its structure (such as spring heat insulation and cold insulation), material, medium working characteristics, and temperature change limit value during discharge. The safety valve shall work normally within the marked temperature range.

4.1.3 When the safety valve used for compressible gas medium is in the discharge state, due to the phenomenon of condensation and frost due to temperature drop, the suitability of its structure and materials shall be fully considered. Prevent jamming and other phenomena during the action of the disc.

4.2 End connection The end connection of the safety valve shall be in accordance with the provisions of GB/T 12241.Safety valves with threaded end connections shall be provided with wrench flats for easy installation.

4.3 Structural length and verticality limit deviation The structural length of the safety valve is in accordance with the provisions of JB/T 2203 or the requirements of the order contract. The structural length and the limit deviation of the verticality of the end face of the inlet and outlet flanges shall be in accordance with the regulations in Figure 1 and Table 1.

4.4 Valve body

4.4.1 The design of the valve body shall ensure that the safety valve does not undergo any harmful deformation under the strength test and working conditions and is easy to manufacture and maintain.

4.4.2 The reaction force when the safety valve discharges shall be considered. Reinforcement measures need to be taken on the inlet or outlet flange of the valve, such as. adopting the thickness of the flange adjacent to the higher pressure grade or the flange adjacent to the nominal size of the larger grade.

4.5 Valve seat and disc

4.5.1 The material of the valve seat and disc shall be shock-resistant and medium- resistant. Cast iron materials shall not be used.

4.5.2 The sealing secondary material can be the material of the valve seat and the disc body. It can also be welded with another alloy material, or inlaid with non-metallic elastic sealing material.

4.5.3 The sealing surface of the valve seat and disc shall be in the form of a plane. When the tapered sealing surface is used, the angle between the sealing surface and the valve axis is preferably 45°.

4.6 Spring

4.6.1 The requirements for springs shall not be lower than those specified in GB/T 12241.When 4.6.2~

4.6.15 is inconsistent with the requirements stipulated in GB/T 12241, the regulations in 4.6.2~

4.6.15 shall be followed.

4.6.2 The slenderness ratio (ratio of free height to middle diameter) of the spring shall be less than 3.7.

4.7.2 Valve seat and disc

4.7.2.1 The corrosion resistance of the valve seat and disc body material shall not be lower than that of the valve body material. Iron materials are not allowed. It shall be suitable for the discharge condition of the safety valve.

4.7.2.2 Safety valve seats for steam and saturated water with nominal pressure greater than or equal to 10MPa and operating temperature greater than 370°C shall be forged or rolled materials.

4.7.3 Guide sleeve The material of the guide sleeve shall have good wear resistance and corrosion resistance. It shall be suitable for the discharge condition of the safety valve.

4.7.4 Spring The material of the spring shall be selected according to GB/T 23935 and meet the requirements of the corresponding standards.

4.8 Non-destructive testing The non-destructive testing of safety valves shall be in accordance with the provisions in Annex A.

5.3 Opening-closing pressure difference

5.3.1 The opening-closing pressure difference of safety valve for steam shall be in accordance with the provisions in Table

7.The opening-closing pressure difference of the safety valve for the steam power boiler with the set pressure greater than 0.4MPa can be determined separately according to the requirements of the order contract.

5.3.2 The opening-closing pressure difference of safety valve for gas shall be in accordance with the provisions in Table 8.

5.3.3 The opening-closing pressure difference of safety valve for liquid shall be in accordance with the provisions in Table 9.

5.4 Opening height The opening height of the full-lift safety valve is greater than or equal to 1/4 of the diameter of the flow channel. The opening height of the low-lift safety valve is greater than or equal to 1/40 of the diameter of the flow channel and less than 1/4 of the diameter of the flow channel.

5.5 Mechanical properties During the opening and reseating process of the safety valve, there shall be no frequency jump and no jamming. When the discharge pressure is reached, it shall be stable without flutter.

5.6 Sealing

5.6.1 The sealing test pressure shall be in accordance with the provisions in Table 10.

5.6.2 The sealing test medium shall comply with the provisions in Table 11.

5.6.3 Sealing requirements

5.6.3.1 When carrying out the sealing test of the safety valve for steam, check the outlet port of the valve visually or by listening to the sound. If no leakage is found, the sealing is considered qualified.

5.7 Displacement The displacement and size of the safety valve shall be determined according to the provisions of GB/T 12241.For safety valves for steam and gas whose displacement coefficients have not been measured, calculations can be made with reference to the provisions in Annex B.

6.1 Test and inspection items

6.1.1 The inspection items of the safety valve are divided into exit-factory inspection and type test. Test items according to the provisions of Table 14.

6.1.2 Safety valves shall be inspected one by one before leaving the factory. The products can leave the factory after passing the inspection. The exit-factory inspection shall comply with the provisions in Table 14.

6.1.3 Newly designed products or design changes (design modifications that affect fluid passages, opening heights, and safety valve action characteristics) shall be subject to the type test.

6.2 General requirements

6.2.1 The exit-factory test shall be carried out before painting.

6.2.2 Test equipment, instruments and test procedures shall comply with the provisions of GB/T 12241 and GB/T 12242.The accuracy of the pressure gauge during the shell strength test shall not be lower than level 1.6.

6.2.3 The safety requirements during the test shall comply with the provisions of GB/T 12241.

6.2.4 The set pressure test before leaving the factory shall be carried out according to

6.3 Test medium During the type test, for the safety valve that is used for steam, the test medium is steam. For safety valves for gas, the test medium is air or nitrogen. For safety valves for liquid, the test medium is water. The set pressure of the safety valve for steam and the safety valve for liquid before leaving the factory and the medium used for the sealing test are allowed to be replaced by air or nitrogen.

6.4 Test methods

6.4.1 Shell body strength The shell body strength test complies with the provisions of GB/T 12241.There shall be no leakage and structural damage during the test.