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This standard is the revised edition of GB/T 12243-1989 "Spring loaded safety valves".
This standard is modified on the basis of JIS B 8210 "Steam and gas spring safety valve" (Japanese Edition, 1994).
There are some significant differences between this standard and JIS B 8210:1994 as follows:
——The original code is modified from editing according to the requirements of GB/T 1.1.
——The normative references are added in this standard according to the requirements of GB/T 1.1-2002.
——Article 4.5 of JIS B 8210:1994 is deleted in this standard with reference to the requirements of API Std 527:1991 "Valve seat tightness of pressure release valve".
——Article 6.2 (flange measurement chart) of JIS B 8210: 1994 is deleted in this standard.
There are some significant changes in this standard over GB/T 12243-1989 as follows:
——Major technical contents are modified correspondingly; the requirements of liquid safety valve are added; the tightness requirements and test procedures are modified according to API Std 527: 1991.
——Pressure scope of application is modified from "nominal pressure PN 0.1~ 32 MPa" to "set pressure 0.1 MPa~ 42.0 MPa".
——Malleable iron castings, spheroidal graphite iron castings and copper alloy castings are added in valve material parts, so the scope of application of this standard in material aspect is enlarged.
——"Design, material and structure" is stated in one chapter separately (chapter 4) including chapter 3 "technical requirements" of the original standard, and "performance requirements" therein are excluded which form a new chapter - chapter 5.
——Deviation table of building ring distance is deleted; see the provisions of GB/T 12241 "General requirements of safety valve" for the requirements of spring ring pitch.
——In the chapter 5 "performance", the start-stop pressure difference of steam boiler safety valve is increased by "≤4% set pressure" as the adopted requirements negotiated by the seller and buyer.
——In the chapter 5 "performance" and the chapter 6 "test and inspection", the tightness requirements and test procedures are modified for air, other gas, water or other liquid safety valves.
This standard replaces GB/T 12243-1989.
This standard is put forward by the Machinery Industry Association.
This standard is under jurisdiction of China valve TCST (SAC/TC 188).
Drafting organization of this standard: Shanghai Anderson·Greenwood·Crosby valve Co., Ltd; Hefei General Machinery Research Institute.
Chief drafting staff of this standard: Huang Guanyu, Wang Deping and Wang Xiaojun.
This standard replaces the previous version:
——GB/T 12243-1989.
Spring loaded safety valves
1 Scope
Design, material, structure, performance, test & inspection, marking & lead sealing and delivery of spring loaded safety valves are specified in this standard.
This standard is applicable to steam boiler, pressure vessel and pipe safety valves whose set pressures are 0.1MPa~42.0MPa and flow diameters are greater than or equal to 8mm.
2 Normative references
Clauses of the following documents are quoted into this standard. As for all dated references, all subsequent modification sheets (excluding correcting contents) or revised editions are not applicable to this standard. However, each side of this standard is encouraged to research if the latest editions of these references can be applied. As for all undated references, their latest editions are applicable to this standard.
GB/T 1239.2 Cold coiled helical compressions springs - Technical specifications
GB/T 1239.4 Hot coiled helical springs - Technical specifications
GB/T 1239.6 Design of helical springs
GB/T 9440 Malleable iron castings
GB/T 12220 General purpose industrial valves-Marking (GB/T 12220-1989, idt IS0 5209: 1977)
GB/T 12224 General requirements for industrial steel valves
GB/T 12225 General purpose industrial valves - Specification of copper alloy castings
GB/T 12227 General purpose industrial valves - Specification of spheroidal graphite iron castings
GB/T 12228 General purpose industrial valves - Specifications of carbon steel forgings
GB/T 12229 General purpose industrial valves - Specification of carbon steel castings
GB/T 12230 General purpose industrial valves - Specifications of austenitic steel castings
GB/T 122 41 Safety valve - General requirements (GB/T 12241-2005, IS0 4126-1:1991, MOD)
GB/T 12242 Performance test code - Pressure relief devices
JB/T 7928 General purpose industrial valves - Delivery specification
3 Terms and definition
Terms and definition in GB/T 12241 are applicable to this standard.
4 Design, material and structure
Design, material and structure of safety valves shall be in accordance with the general requirements of GB/T 12241.
4.1 General provisions
4.1.1 Steam safety valve whose set pressure is larger than 3.0 MPa, or air or other gas safety valve whose medium temperature is larger than 235℃ shall prevent exhausted medium from directly eroding springs.
4.1.2 In design, safety valve shall be guaranteed to reach specified discharge even damaged partly. When spring is damaged, spare parts shall as valve clack shall not fly off the valve body.
4.1.3 Looseness proof devices must be installed in order to prevent looseness of structures for adjusting spring compression amount.
4.1.4 Fall lift and medium lift safety valves shall be equipped with structure controlling lift altitude.
4.1.5 Steam safety valve shall be equipped with spanners. When the medium pressure is over 75% of the set pressure, spanner can be used to lift valve clacks. Spanners shall not block valve actions.
4.1.6 Safety valves for poisonous or combustible media shall be closed type.
4.1.7 As for safety valves with superimposed back pressure, back pressure balance mechanism shall be installed with regard to the back pressure size and fluctuation situation.
4.2 End connection
End connection of safety valves shall be in accordance with the provisions of GB/T 12241.
4.3 Limit deviation of structure length and verticality
Limit deviation of safety valve structure length and inlet & outlet flange end verticality shall be in accordance with the provisions of figure 1 and table 1.
Figure 1
Table 1 Limit deviation of safety valve structure length and inlet & outlet flange end verticality
Nominal diameter DN/mm Limit deviation of structure length/mm Limit deviation of verticality
△L △L1 a
≤100 ±1.5 ±1.5 ±30′
>100-250 ±3.0 ±3.0 ±20′
>250 ±3.0 ±3.0 ±15′
4.4 Valve body
4.4.1 Valve body design shall ensure safety valves free from any injurious deformation in strength test and working conditions and shall be convenient for fabrication and maintenance.
4.4.2 As for liquid and steam safety valves, drain screw holes must be installed on positions lower than the tight surface of valve seat.
4.4.3 Flange shall be casted or forged with integral valve body, or welding or threaded connection may be adopted. Welded flange shall be butt welding type in accordance with the welding requirements of GB/T12224.
4.5 Valve seat and valve clack
4.5.1 The tight surface of valve seat and valve clack shall generally be plane or conical. When conical tight surface is adopted, the oblique angle of tight surface to valve stem axis should be 45o. Tight surface material may adopt the valve body material, a welded material or inlaid nonmetal elastic material.
4.5.2 The hardened layer thickness of welded valve seat or valve clack tight surface shall be greater than or equal to 2 mm.
4.6 Spring
Spring of safety valve shall be in accordance with GB/T 1239.2 or GB/T 1239.4 and the following provisions. When inconsistency exists, it shall subject to the following provisions.
4.6.1 Spring slenderness ratio (ratio of free height and pitch diameter) shall be less than 3.7.
4.6.2 The supporting plane greater than or equal to 3/4 ring shall be equipped at both ends of the spring. The end of the support ring shall tightly close to the building ring. Verticality deviation value of spring axis to both-end supporting plane shall be no larger than 1.7mm per 100mm.
4.6.3 The spring index (ratio of pitch diameter and steel wire diameter) may be adopted at the range of 4~8.
4.6.4 Limit deviation of the spring free height shall be in accordance with the provisions in table 2.
Table 2 Limit deviation of the spring free height Unit: mm
Free height H0 ≤20 >20~60 >60~120 >120~200 >200~300 >300~450 >450~600 >600
Limit deviation ±1.2 ±1.6 ±2.5 ±3.5 ±4.5 ±7.0 ±9.0 ±1.5%H0
Note: according to the design requirements, asymmetrically distributed limit deviation may be specified for the free height, but the tolerance value shall be in accordance with the provisions of this table.
4.6.5 Limit deviation of the spring inside diameter shall be in accordance with the provisions in table 3.
Table 3 Limit deviation of the spring inside diameter Unit: mm
Inside diameter D1 ≤40 >40~60 >60~80 >80~100 >100~150 >150
Limit deviation +0.6
0 +0.8
0 +1.0
0 +1.2
0 +1.5
0 +1%D1
0
Note: in particular cases, especially for large-scale spring, single adapted spring seat with spring may be specified in the design, but as for its adapted tolerance value, see the provisions of this table.
4.6.6 The spring ring pitch shall be uniform. When the spring is compressed to 80% deformation amount of testing load (namely, the maximum load of allowable spring load bearing), building rings shall not contact with each other.
4.6.7 Strong pressure treatment or warming strong pressure treatment shall be carried out for the spring as design requirements; permanent deformation tests shall be carried out for all springs. Namely, the original free height of the spring is measured after it is compressed for at least 3 times with testing load, and then its final free height is measured after it is compressed for other 3 times with testing load. The D-value of measured free heights is permanent deformation value which shall not exceed 0.5% of the original free height.
4.6.8 The limit deviation of spring rigidity shall be ±10% (asymmetrically distributed limit deviation value may be specified in the design as required). 10% of the springs of the same specification (no less than 2)shall be taken from the identical heat treating furnace, and their rigidity shall be measured at the range of the specified working load (or amount of deformation) in design.
4.6.9 Anti-rust treatment shall be carried out on the surface of the spring.
4.6.10 The calculation and testing loads of the spring shall be in accordance with the provisions of GB/T 1239.6.
4.6.11 Spring deformation amount under the minimum working load shall be calculated according to the following equation:
