GB T12241-2005 safety valve general conditions

1 Scope This standard specifies the terminology, design and performance requirements, testing, displacement determination, equivalent displacement calculation, marking and lead sealing, quality assurance system and general requirements for installation, adjustment, maintenance and repair of safety valves. This standard applies to all types of safety valves with a flow channel diameter greater than or equal to 8 mm and a set pressure greater than or equal to 0.1 MPa. This standard does not limit the applicable temperature of the safety valve. 2 Normative references The clauses in the following documents have become clauses of this standard after being quoted in this standard. For dated reference documents, all subsequent amendments (excluding errata content) or revisions do not apply to this standard. However, all parties that have reached an agreement based on this standard are encouraged to study whether the latest versions of these documents can be used . For undated reference documents, the latest version is applicable to this standard. GB/T 1047 Nominal diameter of pipeline components (GB/T 1047—2005, ISO 6708: 1995, MOD) GB/T 1048 Nominal pressure of pipeline components (GB/T 1048—2005, ISO 7268: 1996, MOD) GB/T 1048—2005, ISO 7268: 1996, MOD T 1239.6 Cylindrical spiral spring design calculation GB/T 7306.1 55° sealed pipe thread Part 1: Cylindrical internal thread and cylindrical external thread (GB/T 7306.1-2000, eqvISO 7-1: 1994) GB/T 7306.2 55° sealed pipe Thread Part 2: Conical internal thread and conical external thread (GB/T 7306.2-2000, eqvISO 7-1: 1994) GB/T 9113 (all parts) Overall steel pipe flange GB/T 9124 Steel pipe flange Technical conditions GB/T 12224 Steel valves General requirements GB/T 17241.6 Monolithic cast iron pipe flanges JB/T 79 (all parts) Monolithic cast steel pipe flanges JB/T 1752 Valve structure elements External thread connection end dimensions JB/T 2769 PN16.0～32.0 MPa threaded flange 3 Terms and definitions The following terms and definitions apply to this standard. 3.1 Safety valve A safety valve is an automatic valve that uses the force of the medium itself to discharge a rated amount of fluid without any external force.

To prevent the pressure from exceeding the rated safety value. When the pressure returns to normal, the valve closes again and prevents the medium from continuing to flow out. 3. 1. 1 Direct-loaded safety valve A direct-loaded safety valve is a safety valve that only relies on direct mechanical loading devices such as heavy hammers, lever-increased hammers or springs to overcome the force generated by the medium pressure under the disc. 3.1.2 Assisted safety valve with power assisted safety valve This safety valve can be opened when the pressure is lower than the normal set pressure with the help of a power assisted device. Even if the device fails, the valve can still meet all the requirements of this standard for safety valves. 3.1.3 Safety valve with supplementary loaded safety valve This kind of safety valve always maintains an additional force to enhance the seal before its inlet pressure reaches the set pressure. This additional force (supplementary load) can be provided by an external energy source, and should be reliably released when the inlet pressure of the safety valve reaches the set pressure. The size of the supplementary load should be set such that when the load is not released, the safety valve can still reach the rated displacement under the premise that its inlet pressure does not exceed the percentage of the set pressure specified by national regulations. 3.1.4 Pilot-operated safety valve A safety valve that relies on the discharge of medium from the pilot valve to drive or control the safety valve. The pilot valve itself should be a direct load safety valve that meets the requirements of this standard. 3.2 Pressure 3.2.1 set pressure The predetermined pressure at which the safety valve starts to open under operating conditions is the gauge pressure measured at the valve inlet. Under this pressure, the force generated by the medium pressure to open the valve and the force to keep the valve seat on the valve seat balance each other under the specified operating conditions. 3.2.2 Overpressure The pressure increase that exceeds the set pressure of the safety valve,

It is usually expressed as a percentage of the set pressure. 3.2.3 Re-seating pressure After the safety valve is discharged, its valve disc contacts the valve seat again, that is, the static pressure at the valve inlet when the opening height becomes zero. 3.2.4 Cold differential test pressure The safety valve is adjusted on the test bench to the inlet static pressure when it starts to open. This pressure includes corrections to operating conditions such as back pressure and temperature. 3.2.5 Discharge pressure relieving pressure Set pressure plus over pressure. 3.2.6 Built-up back pressure The pressure formed at the outlet of the valve due to the medium flowing through the safety valve and the exhaust system. 3.2.7 Additional back pressure superimposed back pressure The static pressure existing at the outlet of the safety valve immediately before it operates is caused by other pressure sources in the exhaust system. 3.2.8 Blowdown pressure difference The difference between the blowdown set pressure and the return pressure. It is usually expressed as a percentage of the set pressure; when the set pressure is less than 0.3 MPa, it is expressed in MPa. 3.3 Opening height lift The actual stroke of the valve disc from the closed position. 3.4 Flow area flow area The minimum cross-sectional area of ​​the flow path from the inlet end of the valve to the sealing surface of the closing member, which is used to calculate the theoretical flow rate without the influence of any resistance. 3.5 Flow diameter flow diameter Corresponding to the diameter of the flow path area. 3.6 Displacement discharge capacity 3.6.1 Theoretical discharge capacity The calculated displacement of an ideal nozzle with the cross-sectional area of ​​the flow channel equal to the flow channel area of ​​the safety valve, expressed in mass flow or volume flow. 3.6.2 Rated displacement certified (discharge) capacity The part of the actual measured displacement that is allowed to be used as a safety valve application benchmark. The rated displacement can be taken as one of the following three: a) The measured displacement is multiplied by the reduction coefficient (take 0.9); b) The theoretical displacement is multiplied by the displacement coefficient, and then multiplied by the reduction coefficient (take 0.9); c) Theoretical The displacement is multiplied by the rated (ie reduced) displacement coefficient. 3.6.3 Equivalent calculated displacement The calculated displacement of the safety valve when the use conditions such as pressure, temperature or medium conditions are different from the applicable conditions of the rated displacement. 3.7 mechanical characteristics 3.7.1 frequency jump chatter safety valve disc moves back and forth quickly and abnormally, and the valve discriminates against the valve seat during movement. 3.7.2 Flutter The flap of the flutter safety valve moves back and forth quickly and abnormally, and the flap does not touch the seat during the movement. 3.8 Independent authority An organization that is responsible for supervising tests and reviewing safety valve displacement calculations and certificates. 3.9 Inspection authority inspection authority The competent authority responsible for reviewing compliance with this standard. It may or may not be the same agency as the independent supervisory agency.

4 Design and performance requirements 4.1 Design, material and structure 4.1.1 General 4.1.1.1 A guiding mechanism shall be designed to ensure the stability of movement and sealing. 4.1.1.2 Unless the valve seat is integrated with the valve body, the valve seat should be securely fixed on the valve body to prevent loosening during operation. 4.1.1.3 All external adjustment mechanisms shall be locked or sealed to prevent or facilitate the discovery of unauthorized adjustment of the safety valve. 4.1.1.4 The safety valve used for toxic or combustible media should be closed to prevent the media from leaking to the outside world. 4.1.1.5 Unless other drainage measures are taken, a drainage interface should be provided at the lowest part of the valve body of the safety valve where liquid may accumulate. 4.1.1.6 The design stress of the stressed parts should not exceed the requirements of the corresponding national standards. 4.1.2 Nominal diameter and nominal pressure 4.1.2.1 The nominal diameter of the valve shall meet the requirements of GB/T 1047. 4.1.2.2 The nominal pressure level of the valve should meet the requirements of GB/T 1048. 4.1.2.3 The pressure-temperature rating shall be in accordance with GB/T 9124. 4.1.3 End connection 4.1.3.1 End connection type a) Flange connection shall be in accordance with GB/T 9113, GB/T 17241.6, JB/T 79 or JB/T 2769. b) The threaded connection shall be in accordance with the provisions of GB/T 7306.1～7306.2 or JB/T 1752. c) The welding end shall comply with the regulations of GB/T 12224. d) According to the user’s requirements, the end connection can also be in accordance with other standards. 4.1.3.2 End connection design The design of the end connection of the safety valve, regardless of its type, should make the passage area of ​​the connecting pipe or branch pipe at least equal to the cross-sectional area of ​​the safety valve inlet (see Figure 1). 4.1.4 Minimum requirements for safety valve springs 4.1.4.1 Spring materials The materials used to make safety valve springs should meet the requirements of the corresponding material standards and be compatible with their working conditions. 4.1.4.2 Spring markings Spring markings, including stamping or etching, should be limited to the ineffective ring. When the diameter of the spring wire is less than 6 mm, it can be marked by hanging metal signs or other suitable methods. 4.1.4.3 Spring Quality Assurance Certificate The spring manufacturer shall provide the relevant spring quality assurance certificate, indicating that the spring has been processed and tested in accordance with the technical requirements of the safety valve manufacturer. 4.1.4.4 Allowable stress The allowable stress shall be determined with reference to GB/T 1239.6 and based on past satisfactory experience. The service temperature of the spring and its working environment should be considered. 4.1.4.5 Spring coil spacing The spring coil pitch should be uniform. When the safety valve disc reaches the opening height corresponding to its rated displacement, there should be no contact between the spring working rings. At this time, the deformation of the spring should be less than or equal to 80% of the deformation when the coil is tightened. 4.1.4.6 Inspection, test and tolerance The manufacturing quality, test and tolerance of the spring shall be guaranteed to satisfy its use function. All springs should undergo permanent deformation tests. That is, after the test load specified by the spring safety valve manufacturer is compressed at least 3 times, the original free height is measured; then the spring is compressed 3 times with the test load, and the final free height is measured again. The difference between the two measured free heights, that is, the permanent deformation of the spring, should not exceed 0.5% of its original free height. 4.1.5 Safety valve material 4.1.5.1 The safety valve material should be suitable for the process medium, adjacent parts and the environment in which it is used. 4.1.5.2 The material of the guide surface should be corrosion resistant and should be selected to minimize the possibility of biting or jamming. 4.1.5.3 The materials used for pressure-bearing parts should be controlled by the safety valve manufacturer in accordance with the technical specifications. This technical specification shall ensure that the quality, chemical composition and mechanical properties of the controlled materials are at least equivalent to the provisions of the corresponding standards. 4.2 Action performance and displacement 4.2.1 Action performance 4.2.1.1 Set pressure deviation The set pressure deviation should not exceed ±3% of the set pressure or ±0.015MPa, whichever is greater. 4.2.1.2 Discharge pressure The upper limit of discharge pressure shall comply with relevant standards or regulations. 4.2.1.3