GB/T 12241-2021 English PDF (GBT12241-2021)

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GB/T 12241-2021: Safety valves -- General requirements
GB/T 12241-2021
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 13.240
J 16
Replacing GB/T 12241-2005
Safety valves - General requirements
(ISO 4126-1:2013, Safety devices for protection against excessive pressure - Part 1:
Safety valves, MOD)
ISSUED ON: MARCH 09, 2021
IMPLEMENTED ON: OCTOBER 01, 2021
Issued by: State Administration for Market Regulation;
Standardization Administration of the People's Republic of China.
Table of Contents
Foreword ... 3 
1 Scope ... 6 
2 Normative references ... 6 
3 Terms and definitions... 7 
4 Symbols and units ... 9 
5 Design ... 10 
5.1 General ... 10 
5.2 End connection ... 11 
5.3 Minimum requirements for springs ... 12 
5.4 Pressure-temperature rated values ... 15 
6 Exit-factory tests ... 15 
6.1 Purpose ... 15 
6.2 General ... 16 
6.3 Hydraulic test ... 16 
6.4 Air pressure test ... 17 
6.5 Adjustment of set pressure or cold differential test pressure ... 18 
6.6 Seal test ... 18 
7 Type test ... 18 
7.1 General ... 18 
7.2 Action performance test ... 20 
7.3 Discharge capacity performance test ... 21 
7.4 Determination of coefficient of discharge ... 23 
7.5 Certified coefficient of discharge ... 23 
8 Determination of discharge capacity performance of safety valve ... 24 
9 Determination of safety valve size ... 24 
10 Marks and lead seals ... 24 
10.1 Marks ... 24 
10.2 Lead seal of safety valve ... 25 
Bibliography... 26 
Safety valves - General requirements
1 Scope
This Standard specifies the terms and definitions of safety valve, design, exit-factory
test, type test, determination of safety valve discharge capacity performance,
determination of safety valve size, marks and lead seals.
This Standard is applicable to the safety valves of which the diameter of the flow is not
less than 4mm, and the set pressure is not less than 0.1MPa.
2 Normative references
The following referenced documents are indispensable for the application of this
document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
GB/T 1239.2, Cold coiled helical springs technical specifications - Part 2:
Compressions spring
GB/T 7306 (all parts), Pipe threads with 55-degree thread angle where pressure-
tight joints are made on the threads
GB/T 9124 (all parts), Steel pipe flanges
GB/T 12224, General requirements for industrial steel valves
GB/T 12716, Pipe threads with the thread angle of 60 degrees where pressure-tight
joints are made on threads
GB/T 15530.1, Cast copper alloy integral flanges
GB/T 15530.8, Specifications for copper alloy and composite flanges
GB/T 17241.6, Integral cast iron flanges
GB/T 17241.7, Specifications for cast iron pipe flanges
GB/T 23934, Hot formed helical compression springs - Technical requirement
GB/T 36588, Safety devices for protection against excessive pressure - Common
data (GB/T 36588-2018, ISO 4126-7:2013, MOD)
JB/T 2768, Components of valves - High pressure pipes fittings and end-to-end
dimensions of valves
JB/T 2769, Components of valves - High pressure threaded flanges
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 safety valve
an automatic valve that uses the force of its own medium to discharge a certain amount
of fluid without any external force, so as to prevent the pressure from exceeding a
predetermined safety value
NOTE: When the pressure returns to normal, the valve closes and prevents the medium from
continuing to flow out.
3.2 direct loaded safety valve
safety valves that only rely on direct mechanical loading devices such as weights, lever-
weighted hammers or springs to overcome the force generated by the pressure of the
medium under the disc
3.3 set pressure
the predetermined pressure at which the safety valve begins to open under operating
conditions
NOTE: This pressure is the gauge pressure measured at the valve inlet. At this pressure, the force
resulting from the medium pressure to open the valve under specified operating conditions is
balanced by the force that keeps the disc on the valve seat.
3.4 maximum allowable pressure; pS
the maximum pressure at which the protected equipment is designed
3.5 over pressure
the pressure increments above the set pressure of the safety valve
NOTE: It is usually expressed as a percentage of set pressure.
3.6 reseating pressure
the inlet static pressure when the valve disc is in contact with the valve seat again after
the safety valve is discharged (that is, the lift becomes zero)
3.7 cold differential test pressure
through the valve.
5.2 End connection
5.2.1 End connection type
The end connection type requirements are listed below:
a) Steel flange connection is according to the provisions of GB/T 9124, JB/T 2769.
The surface roughness of the sealing surface is according to the regulations of
GB/T 9124 and JB/T 2768, respectively. Iron flange connection is according to
the provisions of GB/T 17241.6. Surface roughness of the sealing surface is
according to the provisions of GB/T 17241.7. Copper flange connection is
according to the provisions of GB/T15530.1. Surface roughness of the sealing
surface is according to the provisions of GB/T 15530.8.
b) The welding end of the butt-welding connection shall be in accordance with the
provisions of GB/T 12224.
c) The threaded connection is in accordance with the provisions of GB/T 7306 and
GB/T 12716.
d) Other end connections may also be used by agreement between the manufacturer
and the purchaser.
5.2.2 End connection design
No matter what type of safety valve end connection is designed, the internal cross-
sectional area of the external pipe or pipe joint connected to the valve inlet shall be at
least equal to the internal cross-sectional area of the valve inlet connection [see Figure
1a)].
The internal cross-sectional area of the external nozzle at the outlet of the safety valve
shall be at least equal to the internal cross-sectional area of the valve outlet but
excluding the valves that the outlet is internal thread connection [see Figure 1b)].
If the valve outlet is of the structure shown in Figure 1b), a suitable pipe shall be fitted
when carrying out the tests specified in 7.1.4.
tested according to the technical requirements of the safety valve manufacturer.
The allowable stress shall refer to GB/T 23935 and be determined according to
experience. The operating temperature of the spring and its working environment shall
be considered.
5.3.1.2 Materials
The material for the manufacture of safety valve springs shall meet the requirements of
the corresponding material standards and be compatible with its working conditions.
5.3.1.3 Marks
Spring marks, including stamping or etching, shall be limited to their void ring.
For stock springs, labels or other suitable methods may be used to identify when the
above marks are not suitable.
5.3.1.4 Sizes
Size requirements are listed below:
a) Slenderness ratio: that is, the ratio of the free height to the middle diameter, which
shall be less than 5.
b) Winding ratio (spring index): that is, the ratio of the middle diameter to the
diameter of the steel wire, which shall be in the range of 3 to 12.
c) Coil Spacing: the coil pitch shall be uniform. The compression of the spring
(de...