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This code is a revision of GB/T 12242-1989 Performance test methods for safety valves.
This code is modified based on ASME PTC 25:1994 Pressure relief devices - Performance test code (English version).
The following main changes have been made with respect to ASME PTC 25:
——Editorial changes has been made to this code with respect to the original code in terms of structure and drafting rules in accordance with the requirements of GB/T 1.1;
——US standards for measurements and instruments cited in the original code are not cited in this code;
——The US units and calculation formulas adopted in the original code are converted into metric units and calculation formulas in this code.
The following main changes have been made with respect to GB/T 12242-1989:
——The scope of application has expanded from safety valves to including non-reclosing pressure relief devices, and the code name has been changed accordingly;
——“Terms and definitions” is added;
——The content of test on rupture disk drag coefficient is added;
——The contents of in-service testing and bench testing are added;
——Annex A "Test report form", Annex B "Test summary report form" and Annex C "Examples of flow error determination" are added.
Annexes A, B and C of this code are informative.
This code replaces GB/T 12242-1989.
This code was proposed by the China Machinery Industry Federation.
This code is under the jurisdiction of SAC/TC 188 National Technical Committee on Valve of Standardization Administration of China.
The previous edition of the code replaced by this code is as follows:
——GB/T 12242-1989.
Performance test code - Pressure relief devices
1 Scope
This code provides guidance and rules (including the preparation of test reports) for the operational characteristics (including mechanical properties) and relieving capacity testing of pressure relief devices. Those tests are used to determine the operational characteristics and relieving capacity of pressure relief device which is used to prevent overpressure in boilers, pressure vessels, and associated piping equipment.
There are inlet and outlet conditions for the test procedures of this code, and steam, gas (air) or liquid (water) whose physical properties are known is used as the test medium. This code is applicable to the following types of reclosing and non-reclosing pressure relief devices:
a) safety valve;
b) rupture disk device;
c) breaking/shear pin device;
d) fusible plug device.
Other pressure relief devices may be tested provided all parties to the test agree to accept the provisions of this code.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this standard. For dated references, subsequent amendments (excluding corrections), or revisions, of any of these publications do not apply to this code. However parties to agreements based on this code are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition applies.
GB/T 12241 Safety valves - General requirements (GB/T 12241-2005, ISO 4126-1: 1991, MOD)
GB/T 12243 Spring loaded safety valves (GB/T 12243-2005, JIS B 8210: 1994, MOD)
3 Terms
For the purposes of this code, the terms and definitions given in GB/T 12241 apply.
3.1 General
3.1.1
pressure relief device
device designed to prevent internal medium pressure from rising above a predetermined maximum pressure in a pressure vessel exposed to emergency or abnormal conditions
3.1.2
operational characteristics and flow capacity testing
testing of a pressure relief device to determine its operating characteristics including measured relieving capacity
3.1.3
in-service testing
testing of a pressure relief device while protecting the system on which it is installed to determine some or all of its operating characteristics using system pressure solely or in conjunction with an auxiliary lift device or other pressure source
3.1.4
bench testing
testing of a pressure relief device on a pressurized system to determine set pressure and seat tightness
3.2 Types of pressure relief devices
3.2.1
reclosing pressure relief device
pressure relief device that is closed after action
a)
safety valve
automatic valve which discharges rated amount of fluid by virtue of the force of the medium itself but not any other external force to prevent the pressure from exceeding a rated safe value and, after the pressure returns to normal, closes to prevent the medium from continuing to flow out
b)
direct-loaded safety valve
safety valve that overcomes the acting force generated by the pressure of the medium under the valve disk relying only on direct mechanical loading device such as counter weight, a lever plus counter weight or spring.
c)
assisted safety valve
such safety valve can be opened with the help of a power assist device when the pressure is lower than the normal set pressure
d)
supplementary loaded safety valve
such safety valve always maintains an additional force for enhancing the seal before its inlet pressure reaches the set pressure, with the additional force, i.e., the supplementary load, able to be provided by an external source of energy, reliably released when the safety valve inlet pressure reaches the set pressure and so designed that, assuming such load is not released, the safety valve can still reach the rated relieving capacity with its inlet pressure not exceeding the percentage of the set pressure specified by national regulations
e)
pilot-operated safety valve
safety valve which is actuated or controlled by the medium discharged from a pilot valve which is a direct-loaded safety valve
f)
vacuum relief valve
safety valve designed to admit fluid to prevent an excessive internal vacuum; it is designed to reclose and prevent further flow of fluid after normal conditions have been restored
3.2.2
non-reclosing pressure relief device
pressure relief device designed to remain open after operation
a)
rupture disk device
non-reclosing pressure relief device actuated by the static differential pressure between the inlet and outlet of the device and designed to function by the bursting of a pressure containing disk
b)
breaking pin device
non-reclosing pressure relief device actuated by inlet static pressure and designed to function by the breakage of a load-carrying section of a pin which supports a pressure containing member
c)
buckling pin device
non-reclosing pressure relief device actuated by inlet static pressure and designed to function by the buckling of a load-carrying section of a pin which supports a pressure containing member
d)
shear pin device
non-reclosing pressure relief device actuated by inlet static pressure and designed to function by the shearing of a load-carrying section of a pin which supports a pressure containing member
e)
fusible plug device
non-reclosing pressure relief device designed to function by the yielding or melting of a plug of suitable melting temperature material
3.3 Safety valve dimensional characteristics
3.3.1
discharge area
minimum sectional area of fluid flow path during valve discharge
3.3.2
flow area
minimum cross-sectional area of flow between valve inlet end and closure member sealing surface
3.3.3
flow diameter
diameter corresponding to the flow area
3.3.4
curtain area
area of the cylindrical or conical discharge opening between the seating surfaces created by the lift of the disk above the seat, see Figure 1
3.3.5
lift
actual travel of the disk away from closed position
3.3.6
rated lift
design lift at which a valve attains its rated relieving capacity
3.3.7
seat angle
angle between the axis of a valve and the seating surface. A flat-seated valve has a seat angle of 90°
3.3.8
seat area
area determined by the seat mean diameter
3.3.9
seat mean diameter
mean diameter of contact between the valve disk and the seat
3.4 Non-reclosing pressure relief device dimensional characteristics
3.4.1
net flow area
area which determines the flow after a non-reclosing pressure relief device has operated. The (minimum) net flow area of a rupture disk is the calculated net area after a complete burst of the disk, with appropriate allowance for any structural members which may reduce the net flow area through the rupture disk device
3.5 Operational and flow capacity characteristics of pressure relief device
3.5.1
set pressure
preset pressure under which the safety valve in operating conditions starts to open and the force opening the valve generated by medium pressure in specified operating conditions is balanced with that keeping the valve disk on the valve seat
3.5.2
overpressure
pressure increase over the set pressure of a safety valve, usually expressed as a percentage of set pressure
3.5.3
re-seating pressure
pressure at which the valve disk reestablishes contact with the seat or at which lift becomes zero
3.5.4
blowdown
difference between set pressure and re-seating pressure expressed as a percentage of set pressure or in pressure units
3.5.5
relieving pressure
set pressure plus overpressure
3.5.6
flow-rating pressure
upper limit of relieving pressure specified by the standard or specification, which is the inlet static pressure at which the relieving capacity of a pressure relief device is measured
3.5.7
back pressure
static pressure existing at the outlet of a pressure relief device due to pressure in the discharge system
3.5.8
built-up back pressure
pressure existing at the outlet of a pressure relief device caused by the flow through that particular device into a discharge system
3.5.9
superimposed back pressure
pressure existing at the outlet of a pressure relief device at the time the device is required to operate. It is the result of pressure in the discharge system from other sources
3.5.10
cold differential test pressure
inlet static pressure at which a pressure relief valve is adjusted to open on the test stand. This test pressure includes corrections for service conditions of back pressure and/or temperature
3.5.11
tight test pressure
inlet static pressure under which tightness test is conducted and under which the leak rate for flowing through the closure member seat
3.5.12
burst pressure
value of inlet static pressure at which a rupture disk device functions
3.5.13
specified burst pressure of a rupture disk device
value of increasing inlet static pressure, at a specified temperature, at which a rupture disk is designed to function
3.5.14
breaking pressure
value of inlet static pressure at which a breaking pin, buckling pin or shear pin device functions
3.5.15
primary pressure
pressure at the inlet in a pressure relief device
3.5.16
secondary pressure
pressure existing in the passage between the actual discharge area and the valve outlet in a safety valve
3.5.17
simmer pressure
audible or visible escape of fluid between the seat and disk at an inlet static pressure below the set pressure of safety valve and at no measurable capacity. It applies to safety valve on compressible-fluid service
3.5.18
theoretical relieving (discharge) capacity
computed capacity expressed in gravimetric or volumetric units of a theoretically perfect nozzle having a minimum cross-sectional flow area equal to the flow area of a safety valve or net flow area of a non-reclosing pressure relief device
3.5.19
measured relieving (discharge) capacity
relieving capacity of a pressure relief device measured at the flow-rating pressure, expressed in gravimetric or volumetric units
3.5.20
rated relieving capacity (certified discharge capacity)
that portion of the measured relieving capacity permitted by the applicable code or regulation to be used as a basis for the application of a pressure relief device
3.5.21
equivalent calculated capacity
calculated capacity of a pressure relief device when the service conditions for pressure, temperature or medium are different from the applicable conditions of rated relieving capacity
3.5.22
coefficient of discharge
ratio of measured relieving (discharge)capacity to theoretical relieving (discharge) capacity
3.5.23
rated coefficient of discharge
ratio of rated relieving capacity (certified discharge capacity) to theoretical relieving (discharge) capacity
3.5.24
chatter
abnormal rapid reciprocating motion of the valve disk of a safety valve in which the disk contacts the seat
3.5.25
flutter
abnormal, rapid reciprocating motion of the valve disk of a safety valve in which the disk does not contact the seat
3.5.26
reference conditions
those conditions of a test medium which are specified by either an applicable standard or an agreement between the parties to the test, which may be used for uniform reporting of flow capacity testing results
Flat-seated valve
Curtain area = πDL
Bevel-seated valve
Curtain area = πB(D+DB)/2
Bevel-seated valve
Curtain area = πB(D+DB)/2
Bevel-seated valve
Curtain area = πB(D+DB)/2
Radial-seated valve
Curtain area = πB(D+DB)/2
Radial-seated valve
Curtain area = πB(D+DB)/2
L = lift
D = smallest diameter at which seat touches disk
DB = other diameter of frustrum of cone
B = slant height of frustrum of cone
θ = seat angle
R = radius
Note: Curtain area is the discharge area unless the disk attains sufficient lift for the flow area to become the smallest sectional area of the passage.
Figure 1 Typical curtain areas of safety valves
4 General
4.1 The measurement deviation of this standard test is as follows: for the flow capacity testing, the deviation of the final flow capacity measurement shall not exceed ±2.0% of the measured value; for the operational characteristics testing, the deviation of the pressure measurement shall not exceed ±0.5% of the measured value; for the in-service testing and bench testing, the deviation of the pressure measurement shall not exceed ±1.0% of the measured value.
4.2 It is assumed that the testing facility has adequate capacity and sufficient pressure to conduct the tests specified in this code. The diameter of the test vessel for operational characteristics and flow capacity testing shall be at least ten times the device nominal inlet diameter when testing with steam or gas, and four times the pressure relief device nominal inlet diameter when testing with liquids. Operating conditions shall be maintained in accordance with the requirements of the procedure used (see 5.4). The duration of the test shall be that required to obtain the necessary performance and capacity data under stable conditions.
4.3 Field installation and/or abnormal operating conditions may adversely affect the function of the pressure relief device. It is not the intent of this code to attempt to assess the suitability or reliability of the pressure relief device under such conditions.
Foreword i
1 Scope
2 Normative references
3 Terms
3.1 General
3.2 Types of pressure relief devices
3.3 Safety valve dimensional characteristics
3.4 Non-reclosing pressure relief device dimensional characteristics
3.5 Operational and flow capacity characteristics of pressure relief device
4 General
5 Operational characteristics and flow capacity testing of pressure release devices
5.1 Testing facility and instrument
5.2 Measurement methods
5.3 Test requirements
5.4 Test procedure
5.5 Computation of results
5.6 Test summary report
6 In-service and bench testing
6.1 Instruments and methods of measurements
6.2 In-service testing procedures
6.3 Bench testing procedures
6.4 Seat tightness test
6.5 Computation of results
6.6 Test summary report
Annex A (Informative) Test report form
A.1 Symbolic description of test record
A.2 Test report form
Table A.1 Test report form for pressure relief device tested with steam and water - Weighed-water method
Table A.2 Test report form for pressure relief device tested with steam - Flow-meter method
Table A.3 Test report form for pressure relief device tested with liquid - Flow-meter method
Table A.4 Test report form for pressure relief device tested with air or other gases - Flow-meter method
Table A.5 Test report form for pressure relief device tested with air or other gases - Sonic-flow method
Table A.6 Test report form for pressure relief device tested with fuel gas - Flow-meter method
Table A.7 Test report form for rupture disk device tested with air - Resistance coefficient method
Annex B (Informative) Test summary report form
Table B.1 Test summary report form of pressure relief valve - Steam medium
Table B.2 Test summary report form of pressure relief valve - Water or liquid medium
Table B.3 Test summary report form of pressure relief valve - Air, gas or fuel gas medium
Table B.4 Test summary report form of rupture disk device - Air, gas or fuel gas medium
Annex C (Informative) Examples of flow error determination
