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The testing of safety valves includes shell testing, performance testing, and displacement testing. To ensure the scientificity and accuracy of valve testing, the measuring instruments used for testing must meet the following requirements. 1. Atmospheric pressure measurement: An barometer with an error of no more than ±50 Pa is used to measure atmospheric pressure. When the discharge pressure of the safety valve is greater than or equal to 0.15 MPa, the average atmospheric pressure at the location of the test can be used. 2. Pressure measurement: Liquid pressure gauges can be used to measure pressures below 0.1 MPa, while Bourdon tube pressure gauges or other pressure measuring instruments can be used for pressures equal to or greater than 0.1 MPa. The error should be less than or equal to 0.5% of the instrument’s range, and the pressure being measured should fall within the range of 1/3 to 2/3 of the instrument’s range. The location of the pressure measurement point should ensure that the static pressure of the medium is measured. When there is a water column or another liquid column between the pressure measurement point and the pressure gauge, the pressure reading must be corrected. 3. Temperature measurement: The minimum resolution of the temperature measuring instrument should be less than or equal to 0.5°C. Except that glass liquid thermometers must be inserted into a sleeve before being installed in the pipeline, other temperature sensing elements can either be placed inside a sleeve or directly installed in the pipeline ； When the temperature being measured does not exceed 150°C, it is best not to use a sleeve. The thermometer bulb should be clean and free of rust, and it should be filled with an appropriate liquid whose boiling point is higher than the highest temperature to be measured. Apart from the medium being measured, heat transfer between the temperature sensing element and the outside environment due to radiation or conduction should be kept to a minimum. The area around the thermometer insertion point and its exposed parts should be insulated. When measuring the temperature of the medium in a pipe, the sensing part of the temperature sensor should be inserted near the center line of the pipe. When the pipe diameter is greater than 300 mm, the insertion depth should not be less than 150 mm. When measuring the temperature of a flowing medium, the sensing part of the temperature sensor should not be placed in areas where the flow of the medium has come to a standstill. 4. Flow measurement: Flow measurement is carried out using calibrated standard throttling devices or other flow meters; it can also be done through direct measurement by collecting and weighing the discharged medium or its condensate. The throttling device shall comply with the following requirements: 1). The throttling device shall be installed on the upstream side of the inlet to the valve under test ； 2). The ratio of the orifice diameter to the inner diameter of the pipe should satisfy 0.2 ≤ m ≤ 0.7 ； 3). The pressure difference before and after the throttling device should be no less than 980 Pa and no more than 24525 Pa for compressible fluids ； For incompressible fluids, it should be no less than 980 Pa ； 4). To ensure uniform flow near the throttling device and reliable pressure measurement ； Sufficiently long straight pipe sections should be provided before and after the throttling device. During flow measurement, the flow must remain stable, and the differential pressure fluctuation (double amplitude) should not exceed 2%. When conducting tests with saturated steam, the humidity of the steam should be determined. 5. Enable height measurement. In principle, a dial indicator is used for height measurement; other calibrated measuring instruments can also be employed. The zero point of the measuring instrument should be adjusted before the valve discharge test. When the safety valve is discharging and the valve disc or valve stem vibrates, the opening height should be measured at the center of the vibration amplitude. 6. Steam humidity measurement: Throttling calorimeters are used to measure steam humidity. The superheat of the superheated steam at the outlet of the throttling calorimeter should be greater than or equal to 4.5°C. The measurement error of the emission temperature under steady state should be less than or equal to 0.5°C. The orifice diameter of the throttling calorimeter should be as large as possible. It must be installed on a container or pipe near the steam source. The calorimeter and connecting pipes should be properly insulated. Calibration should be performed using steam with a known enthalpy value. Section 1: Shell testing of safety valves 1. Testing method: Seal the valve seat surface, and apply a test pressure to the chamber on the inlet side; this pressure should be 1.5 times the nominal pressure of the safety valve. For safety valves that discharge to atmosphere or those that generate back pressure only during discharge, it is not necessary to test the discharge side chamber. When the safety valve is subjected to additional back pressure or is installed in a closed discharge system, the discharge side chamber shall be tested at a pressure equal to 1.5 times the maximum back pressure. 2. Test duration: During the test, the test pressure should be maintained for a sufficient length of time to allow for visual inspection of all surfaces and connections of the valve. The test duration must not be shorter than the specified time; for safety valves with a nominal diameter greater than 600 mm, the minimum test duration increases proportionally. The test duration for the discharge side cavity is determined by its test pressure and outlet diameter. 3. Test medium: Purified water is usually used as the test medium. Generally, gases should be avoided as the testing medium, but with the consent of all relevant parties, air or other suitable gases can be used as the testing medium in the following situations: 1) Valves that are not suitable for being filled with liquid due to their design and structure. 2) Valves used in operating conditions where even the slightest traces of water are not permitted. 4. Test requirements: No leakage or structural damage is allowed during the shell test. If the test medium is water, there should be no visible water droplets, and the surface should not be wet. 5. Safety requirements (1) Safety requirements during liquid testing 1) The valve body should have an exhaust outlet to remove any residual air. 2) If the part of the valve that is subjected to testing contains materials prone to fracturing, the valve, or that part of it, as well as the testing medium, must be maintained at a sufficiently high temperature during testing to prevent fragmentation. 3) During testing, the valve or its components shall not be subjected to any form of impact load. (2) Safety requirements during gas testing 1) Personnel are not allowed to approach during the pressure increase process. One can approach the testing apparatus only after the voltage boost is complete. 2) For valves that are to undergo pressure testing, the design should take into account the fact that the materials of their various components will not suffer from brittle fracture during the test; in other words, there should be an appropriate difference between the material’s brittle failure temperature and the test temperature. 3) It should be noted that the temperature will drop when the high-pressure gas in the storage tank is depressurized to the test pressure of the valve. 4) The valve shall not be subjected to any form of impact load during testing. 5) Prevent the pressure from exceeding the test pressure. Section 2: Performance Tests of Safety Valves 1. Sealing Performance Test (1) Test Method and Procedure: Increase the pressure at the valve inlet; once the pressure reaches 90% of the set pressure, the rate of pressure increase should not exceed 0.01 MPa/s. Observe and record the set pressure of the valve. Then reduce the pressure at the valve inlet to bring the valve back into a sealed state. Adjust the inlet pressure of the valve and maintain it at the sealing test pressure to check the valve’s sealing performance. (2) Test pressure: The sealing test pressure for safety valves is specified as per regulations. (3) Test medium: The sealing test medium for safety valves is specified according to regulations. (4) Sealing requirements: 1) Sealing requirements for safety valves used with steam: During the sealing test, the outlet end of the valve is inspected visually or by listening; if no leakage is detected, the sealing is considered satisfactory. 2) Sealing requirements for safety valves in air or other gases: Leak testing is conducted using a testing system. Except for the air leakage outlet pipe, all other parts of the safety valve in this system should be completely sealed from the outside environment. The inner diameter of the air leakage outlet pipe is 6 mm, and its outlet end should be parallel to the water surface and 13 mm below it. If the number of bubbles leaked per minute by the safety valve is less than the value listed in the table, its sealing performance is considered satisfactory. The measurement of the number of leakage bubbles starts timing from the appearance of the first bubble, and the average value over 2 minutes is taken. If no bubbles appear from the start of the test or within 5 minutes (for valves with a nominal diameter DN ≤ 80 mm) or within 10 minutes (for valves with a nominal diameter DN > 80 mm), the leakage rate is considered to be zero. 3) Sealing requirement for safety valves used with water or other liquids: The sealing surface is considered to have satisfactory sealing performance if no water droplets flow on it during the specified test duration of 2 minutes. 2. Performance testing under operation (1) Selection of the test valve: The safety valve used for testing should be able to represent the design performance, as well as the pressure and diameter ranges, of those valves for which testing is required. Both the ratio of the valve inlet area to the flow channel area and the ratio of the flow channel area to the outlet area should be taken into consideration. For a series of valves with different pipe diameters, valves of 6 different diameters should be used for testing. If the series contains no more than 6 specifications, it can be reduced to 2 types. When the range of path lengths in the series expands to the point where the original tests can no longer represent the entire series, further testing should be conducted. The test valves for each path should be tested at three pressures that differ significantly from one another, and these three pressures should represent the pressure range in which the valve is used. The test can be conducted on a single valve using springs with 3 different pressures, or it can be carried out on 3 valves with the same diameter but equipped with different springs. To confirm the repeatability of its performance, each test should be conducted at least 3 times. For newly designed or specially designed valves with only one bore and no more than 3 pressure classes, with the approval of the supervising authority, it is permissible to conduct only one pressure test per pressure class. For valves that have only one port but more than 3 pressure levels, testing should be conducted using 3 different springs that can represent the pressure range in which the valve is used. (2) Test medium: The medium used for testing the operating performance of safety valves is determined according to Table 10-4-5 below. Table 10-4-5 Test medium for safety valve operation performance; Applicable media for safety valves; Test medium for safety valves: Steam, air, or other gases; Steam, air, or other gases whose properties are known; Liquids: Water or other liquids with known properties. (3) Requirements for operation performance: General requirements for the operation performance of safety valves. The operating performance of spring-loaded direct-load safety valves shall meet the requirements. (4) Test system: The recommended layout for the steam test system. Recommended arrangement of the test system for testing with air, other gases, or liquids. When the valve is subjected to additional back pressure, the test valve is arranged on the discharge side of the system. When the back pressure is merely the discharge back pressure, the test valve is arranged in the discharge side system. (5) Test procedure 1) Establish and adjust the additional back pressure on the valve to reach the required value (only when the valve is under additional back pressure). 2) Increase the pressure at the valve inlet; once the pressure reaches 90% of the set pressure, the rate of pressure increase shall not exceed 0.01 MPa/s. Monitor and record the valve’s set pressure as well as the back pressure (for valves with a back pressure higher than atmospheric pressure). For steam safety valves, once the pressure rises to the sealing test pressure, check the valve’s sealing integrity by visual inspection or listening for any noises. 3) Continuously increase the pressure at the valve inlet until the valve reaches and remains in its fully open position; meanwhile, observe the valve’s operation, and record the valve’s discharge pressure, opening height, and back pressure (for valves with a back pressure higher than atmospheric pressure). Then gradually reduce the pressure at the valve inlet until the valve closes, while observing the valve’s operation and recording the valve’s return pressure as well as the back pressure (for valves with a back pressure higher than atmospheric pressure). 4) Repeat 1), 2), and 3) until the set pressure, discharge pressure, return pressure, and backpressure all reach stable values (but at least twice should be repeated). During the experiment, it is prohibited to make any adjustments to the valves. However, after each test, based on the measured data, the performance of the valve can be adjusted by changing the position of the adjustment screw and the adjustment ring, until the optimal performance is achieved. Once the optimal performance is achieved, keep the positions of the adjustment screw and the adjustment ring unchanged, and repeat the test at least 2 times. (6) Test data processing and test report: The actual test data can be plotted as needed to show: ① the relationship curve between the valve opening height and the pressure before the valve ； ②Curves showing the changes over time in the pressure before the valve, the back pressure (if any), and the valve opening height. Format parameters for the safety valve test report. Section 3: Discharge Test of Safety Valves 1. Determination and requirements for the test The valves used for testing should be able to represent the design characteristics, as well as the pressure and diameter ranges, of those valves for which testing is required. The condition of the valve should be the same as that of the valve used for the performance test; that is, the opening degree of the valve. For valves equipped with a regulating ring, the position of this regulating ring should be the same as that determined during the performance test. The opening height is taken as the average value. When using a displacement test to determine the displacement coefficient, for a given valve design, measurements should be taken at 3 different pipe diameters, with 3 different pressures for each diameter; if the valve series includes no more than 6 pipe diameters, the number of diameters for testing can be reduced to 2. For new or specially designed valves that have only one bore but multiple pressure classes, testing should be conducted at 4 different opening pressures. These test pressures should be able to represent the actual pressure range of the valve in use, or be determined by the testing equipment. In all cases, within the limitations of the test equipment, the bore size and pressure range of the test valve should be able to represent the series of that design. If the valve diameter is large enough to exceed the flow capacity of the testing equipment, the regulatory authority will decide, based on its judgment, whether a flow verification test at the installation site is necessary. When testing to determine the displacement coefficient using three prototypes with different diameters but similar geometries, if the diameters used are not identical to those used in the performance tests, the performance of at least one of the valves must be verified through testing. 2. Test medium – The medium used for displacement testing. 3. Test system and requirements – For testing with steam, a recommended test system layout that uses a flow meter to measure displacement ； Recommended layout of the emission side for the test system using the weighed condensate method to measure displacement. Recommended test system layout for measuring displacement using a flow meter when testing with air, other gases, or liquids. For liquid tests, the recommended test system layout for measuring displacement using the weighing method is employed. The design and operation of the testing equipment should ensure that the error in the actual displacement measured during testing remains within ±2%. During the displacement test, the pressure at the inlet of the safety valve should be equal to the rated discharge pressure. However, due to limitations such as the pressure and capacity of the test medium, it is permissible to conduct displacement tests at a pressure lower than the rated discharge value in order to determine the valve displacement coefficient. When conducting displacement tests under these conditions, the valve disc should be mechanically held at the same opening height achieved during the performance test. When conducting displacement tests using a test system, it is necessary to stabilize the pressure in the test container with high accuracy at the rated discharge pressure, to ensure that the flow rate measured by the flow meter is equal to the actual discharge volume of the safety valve. If constrained by the capacity of the test system, it is not possible to ensure stability of the pressure in the test container during testing. This test system omits the test container between the test valve and the flow meter, connecting the test valve directly to the flow measurement tube. With this testing system, the test pressure has little effect on the discharge coefficient of the safety valve. At present, China also uses the pressure reduction method to test the discharge coefficient of safety valves. Pressure reduction displacement test system. Using this testing method, before the test, open cut-off valve 1 to raise the pressure in the system to a certain value, and then close the cut-off valve. Then, open electric valve 11; at this point, the medium in the system is discharged outward through the safety valve. After a period of discharge, the pressure in the system decreases steadily, and then the temperature, pressure, and flow rate values are measured at the same instant. During the pressure reduction test, the discharge volume measured at the flow meter is not equal to that of the safety valve; the measured discharge volume should be corrected using the following formula: 4. Test procedure (1) Increase the pressure at the inlet of the valve until it reaches and remains at the rated discharge pressure. At this point, the valve is in a stable discharge state [the flow meter and back pressure gauge (for tests with back pressure higher than atmospheric pressure) indicate stability]. (2) Close the discharge valve of the test vessel, and observe and record the initial level of condensate indicated by the liquid level gauge (for steam tests). (3) Record within the shortest possible time: 1) Valve inlet pressure ； 2) Valve inlet temperature (not required to be measured when using saturated steam for testing) ； 3) Heat meter discharge temperature at the valve inlet (for steam tests) ； 4) Valve disc opening height ； 5) Inlet pressure of flow meter ； 6) Inlet temperature of the flow meter (not required to be measured when using saturated steam for testing) ； 7) Flowmeter reading ； 8) Discharge temperature of the calorimeter at the flow meter (for steam tests) ； 9) Back pressure at the valve outlet (for tests with back pressure higher than atmospheric pressure). (4) Maintain a stable emission state, and read and record data according to the pre-agreed emission time intervals using the same procedure. (5) Use a stopwatch, a synchronous timing device, or other appropriate methods to measure and record the duration of the emission in seconds, as well as the time at which the data are recorded. (6) Read and record the new level of condensate indicated by the level gauge at the end of the emission time interval. Use mass or volume measurement methods to determine and record the amount of condensate generated in the inner container over time intervals of emission (for steam tests). Accurately measure the amount of liquid added to the weighing container over the emission time interval (for liquid tests, when the weighing method is used). (7) Record atmospheric pressure. (8) If the additional back pressure varies within a given range (for tests where the valve is subjected to additional back pressure), or if it is necessary to conduct valve tests within a specific back pressure range (for tests where the valve is only subjected to discharge back pressure), then the lowest or highest value of that back pressure range can be chosen as the back pressure. Then, a certain increment or decrement in the back pressure value is applied step by step, and the aforementioned test procedure is repeated each time the back pressure value is changed. 5. Test data processing and test report The purpose of the safety valve discharge test is to determine the rated discharge of the safety valve or its rated discharge coefficient. (1) Calculation of actual displacement 1) When a throttle device is used to measure displacement, the measured flow rate at the inlet of the throttle device. 2) The actual discharge capacity of the safety valve should be the total flow rate of the medium that passes through it. ① When using a flow meter to measure the discharge at the inlet side of the test valve, the mass of fluid that condenses in the pipes and containers between the flow meter and the test valve, as well as the mass of fluid discharged through the calorimeter, should be deducted from the flow rate measured by the flow meter. ② When measuring the displacement using the method of weighing the condensate, the amount of circulating cooling water that leaks into the condenser (determined by a condenser leakage test) should be deducted from the total amount of condensate collected, and the amount of medium that leaks through the safety valve cover and discharge pipes should be added. ③ When the medium is steam, the actual discharge capacity of the safety valve is corrected to the dry saturated condition at the valve inlet. (2) Calculation of theoretical displacement 1) The medium is an ideal gas. 2) The medium is dry saturated steam (steam with a minimum dryness of 98% or a maximum superheat of 10°C), when the absolute pressure at the valve inlet p ≤ 11 MPa. 3) The medium is superheated steam (steam with a superheat greater than 10°C), when the absolute pressure at the valve inlet p ≤ 11 MPa. 4) The medium is air or other real gases. 5) The medium is a liquid. (3) Calculation of rated displacement coefficient 1) Calculation of displacement coefficient. 2) Calculation of rated displacement coefficient. (4) Calculation of rated displacement