In order to ensure that cryogenic valves can operate safely and reliably at low temperatures, there are some special considerations and requirements in the design and manufacture of cryogenic valves. Similarly, the test of cryogenic valve and ordinary valve is also different. The following JB / T7749-1995 "cryogenic valve technical conditions" and the British BS6364: R1998 "cryogenic valve" test methods, test requirements and test device for a brief introduction. 1. Low-temperature valve test (JB / T7749-1995) (1) Test conditions Low-temperature test of the valve at room temperature after passing the test. Before the test should eliminate the valve moisture and grease, tighten the bolt to a predetermined torque or tension, record the value. With the test requirements of the thermocouple and the valve connected to test the body during the test, the valve cover temperature. Low-temperature test cooling medium is a mixture of liquid nitrogen and alcohol or liquid nitrogen, the test medium is helium. (2) Test Procedure 1) The low-temperature valve test device is shown in Figure 2-46. As shown in the figure, install the valve in the test vessel and connect all fittings to ensure that the valve packing is in the upper part of the vessel and the temperature is maintained at 0 ° C. 2) At room temperature and the maximum test pressure of the valve, nitrogen as early as the test, to ensure that the valve under the appropriate conditions for testing. 3) The valve is immersed in a mixture of liquid nitrogen and alcohol or liquid nitrogen cooled to the valve operating temperature conditions, the level of cover valve body and bonnet. 4) At low temperature conditions, according to the following steps: ①at low temperature conditions, soaking the valve until the temperature stabilized everywhere, with thermocouple measurements to ensure that the temperature uniformity throughout the valve; ② at the test temperature , Repeat the initial test 2.11.1 (2) -2); ③ in the test temperature and the nominal valve pressure, switch the valve 5 times to do low-temperature performance test, with the valve drive device according to the above requirements for action test ; ④ In the maximum valve test pressure, according to the normal valve to do the valve seal test, the two-way seal valve should be tested separately, with a flow meter to measure leakage, the leakage rate should be in accordance with Table 2-23; ⑤ valve In the open position, close the needle valve outlet valve (see Figure 2-46, and the valve body pressure to the seal test pressure for 15min, check the valve packing, the valve body and bonnet junction seal; ⑥ bonnet seal inspection, there is a seal on the valve should be sealed test, the test valve is fully open, closed at both ends, to the valve through the helium to seal the test pressure, release the packing gland Checking the tightness of the seal. 5) low temperature performance test results shall be as specified in Table 2-23. 6) Return the valve to ambient temperature and repeat the 2.11.1 (2) -2) helium test to measure and record the valve leakage, switch the torque and compare the result with the reading obtained in 2.11.1 (2) -2) Compare 7) After the test, remove the valve in a clean and dust-free environment, check the ease of disassembly and inspect the wear and tear of the parts. 8) on behalf of the temperature test valve should be clean, dry, the valve is closed. 2.BS6364 "cryogenic valve technical conditions" standard Low-temperature valve test content Cryogenic valve should not only comply with the provisions of BS6364, but also to comply with the corresponding product standards. BS6364 standard scope is: ①DN ≥ 15mm, the maximum nominal size determined by the corresponding product standards; ② temperature range is -50 degrees to -196 degrees. Test items include: ①shell test; ② shell seal test; ③ seat seal test; ④ low temperature test. (1) Shell test Cryogenic valve body test methods and requirements of the same general valve. But pay attention to two points: ①For austenitic stainless steel valves, the chloride content of the water used in the hydrostatic test should not exceed 30 × 10-6 (ppm); ② After the hydrostatic test, each part of the valve should be thoroughly washed Net and remove grease. (2) Shell seal test After the test of water pressure or pressure shell, the joint of valve body and valve cover should be rubbed with soap or immersed in the water at the packing of the valve, and the shell seal test should be conducted with dry oil-free air or nitrogen . The rest is the same as ordinary valve. (3) seat seal test dry oil-free air or inert gas test, and the rest of the same with the ordinary valve. (4) Marine valves should be low temperature test. Valves for all other uses are to be tested only at the user's request. Low temperature test temperature of -196 degrees. The test methods, test procedures and test requirements are as follows: 1) Preparation before test ①Remove the grease of valve parts, dry them and install the valve in a clean, dust-free and grease-free environment. (2) Tighten the bolt to a predetermined torque value or tension value, and record the value. ③ with the appropriate thermocouple and valve connection, which can be monitored throughout the test valve body, valve cover temperature. 2) Test ①Figure 2-47 is a low temperature test device. Install the valve in the test vessel and connect it, making sure the packing is free of vaporizing gas at the top of the window. ② Perform an initial system verification test at room temperature with helium gas at the maximum valve seat test pressure to ensure that the valve is in the proper condition and begin the test. ③ The valve immersed in liquid nitrogen for cooling, the liquid level at least cover the valve body and the valve cover connection parts. The valve is supplied with helium throughout the cooling process. During cooling, the temperature of the valve body and bonnet is monitored using a thermocouple mounted in place. ④ When the body and bonnet temperature reaches -196 degrees, perform the following procedures a) to e): a) Allow the valve to soak for at least 1 h at the test temperature until all temperatures have stabilized. Measure the temperature with a thermocouple to make sure the valve temperature is uniform. b) Repeat the initial verification test at the test temperature. c) open and close the valve 20 times, at least the first and last operation should be determined when the opening force and closing force d) valve seat pressure on the inlet side of the pressure test. Two-way valve can be sealed, the two seats were tested. Gradually increase pressure from the increments given in Table 2-24 until the nominal seat pressure is raised. Where the valve seat rating has been given by the manufacturer, the value set by the manufacturer is used as the rated valve seat test pressure. Measure and record the leak rate at each pressure level. The leak rate measured by the flowmeter must not exceed 200mm3 / s × DN for check valves and 100mm3 / s × DN for all other valves. e) With the valve in the open position, close the side-view needle valve on the valve outlet (see Figure 2-47) and raise the pressure in the valve chamber to the seat test pressure. The pressure is maintained 15min, check the valve material and the valve body and the valve cover is connected at the leak. There should be no visible leakage. ⑤ The valve was returned to room temperature, and then the following steps a) and b), and the results and ④ results. a) Repeat the helium verification test described in ②. Measure and record leakage through the valve. b) Measure and record the valve opening torque and closing torque. ⑥ After the test is completed, the valve is disassembled in a clean, dust-free environment in order to check the wear and tear of all the parts. Search Keyword: More Valve Technical Articles
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