In order to ensure the cryogenic valve 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 and valves of the cryogenic valve is also different. Here JB/T7749-1995 "the cryogenic valve technical conditions" and the British BS6364: R1998 cryogenic valves test methods, test requirements and degree of inspection device for a brief introduction.
Cryogenic valves test (JB/T7749-1995)
(1) Test conditions
Cryogenic valves, low temperature test at room temperature after passing the test.
The valve should be removed before the test water and grease, tighten the bolts to a predetermined torque or tension, record its value. Meet the test requirements of the thermocouple and valve connection, clinical testing during the test the temperature of the body, bonnet. The low-temperature test cooling medium is a mixture of liquid nitrogen and alcohol or liquid nitrogen test medium for helium.
(2) Test procedure
1) low temperature valve test apparatus is shown in Figure 2-46. As shown, the valve is installed in the test vessel and connected all joints the valve packing at the top of the container, and the temperature is kept above 0 degrees.
2) at room temperature and the maximum valve test under pressure, using nitrogen do such as early detection tests, to ensure that the valve to be tested under appropriate conditions.
3) valves immersed in the liquid nitrogen and alcohol mixture or liquid nitrogen to cool to the temperature of the valve Cryogenic its horizontal plane to cover the body and the valve cover.
4) the temperature of the low-temperature conditions, to operate according to the following steps: weaving dreams, good weaver of dreams
① The temperature of the low-temperature conditions, soaking the uniformity of temperature of the valve until the temperature throughout the stable, measured with a thermocouple to ensure that the valve throughout;
(2) at the test temperature, 2.11.1 (2) -2) of the initial testing is repeated;
Test temperature and valve nominal pressure, the switch valve 5 times to do the low-temperature operating performance test with the valve drive device according to the above requirements, the action test;
Do the valve seal test (4) maximum valve test pressure, according to the normal flow of the valve should be tested separately for bi-directional sealing valves, with flowmeter leakage, the leakage rate shall comply with Table 2-23;
⑤ valve is in the open position, close to the outlet end of the valve needle valve (see Figure 2-46, to the valve body pressure to seal test pressure, 15 minutes, check valve packing body and bonnet connection at the seal sex;
⑥ bonnet seal checks on sealing valve should cook seal test trials when the valve is fully open, closed at both ends until the seal test pressure to pass into helium valve, loosen the packing gland, check sealing tightness.
5) low temperature performance test results should meet the requirements of Table 2-23.
6) the valve to return to ambient temperature, 2.11.1 (2) -2) helium test and inspection is repeated, the measurement and recording of the amount of leakage of the valve, the switching torque and the resultant reading of the results with 2.11.1 (2) -2) comparison.
7) After the test, in a clean, dust-free environment split valve, check the ease of disassembly and inspection of the various components wear and damage.
8) on behalf of the thermal test, qualified valve should be clean, dry, the valve is closed.
2.BS6364 "the cryogenic valve technology conditions" standard cryogenic valve test content
The cryogenic valve should not only meet the requirements of BS6364, but also in line with the provisions of the appropriate product standard. The scope of the BS6364 standard is:
① DN ≥ 15mm, its maximum nominal size is determined by the appropriate product standards;
② temperature range is -50 degrees to -196 degrees.
Pilot project include: ① shell test; ② casing seal test; ③ seat, seal test; ④ low temperature test.
(1) Shell test
Test methods and requirements of the the cryogenic valves Code of body is the same as the ordinary valves. But to pay attention to two points: ① For austenitic stainless steel valves, hydrostatic testing water chloride content should not exceed 30 × 10-6 (ppm); ② hydrostatic test, each component of the valve should be thoroughly washed after net and degreasing.
(2) the housing seal test
Hydraulic or pneumatic shell test, at the junction of the body and bonnet, the valve at the filler rub on soap or immersed in water, the casing seal test with a dry, oil-free air or nitrogen. The others are the same as the ordinary valves.
(3) The seat seal test
With a dry, oil-free air or an inert gas, the test, the others are the same as the ordinary valves.
(4) marine valves should be done at low temperature. For all other uses of the valve, but only when the user requests a low-temperature test. Cryogenic test temperature of -196 degrees. Test methods, test procedures and test requirements are as follows:
1) before the test preparation
① remove grease valve parts, they are dry and clean, no dust and grease valve installed.
② bolts tightened to a predetermined torque value or pull value and record the value.
③ suitable thermocouple and valve connection, so that it can monitor the temperature of the body, bonnet during the entire experiment.
2) Test
① Figure 2-47 is a low-temperature testing apparatus. Valve will be installed in the test container and connected to ensure that at the top of the window is not the position of the vaporized gas valve packing.
(2) at room temperature using helium maximum seat test pressure for initial system validation tests, in order to ensure that the valve is in the appropriate state, and then start the test.
③ the valve is immersed in liquid nitrogen for cooling, the level of the liquid is obscured at least the connecting portion of the valve body and bonnet. Helium has been provided to the valve in the cooling process. During the cooling process, with a thermocouple mounted in the appropriate position on the temperature of the valve body and the valve cover to be monitored.
(4) when the valve body and the lid temperature reaches -196 degrees, the following a) to e) of the procedure:
a) valve at the test temperature for at least dip 1h, stable until all the temperatures have been reached. To make sure that the temperature of the valve to achieve uniform temperature measured with a thermocouple.
b) is repeated at the test temperature ② said initial validation test.
c) open, close valve 20, the opening force when the first and the last operation and the closing force should be measured at least
d) in the inlet side of the valve seat pressure test. Capable of bi-directional sealing valves, the two seat tested respectively. From Table 2-24 are given in delta value gradually boost, until the valve seat rises rated test pressure.
In the case of seat ratings given by the manufacturer to a predetermined value, then the manufacturer as a rated seat test pressure. Measured and recorded in each of the pressure level of the leak rate.
Flowmeter measured leakage rate shall not exceed 200mm3 / s × DN (check valve) and 100mm3 / s × DN (for all other valves).
e) the valve is in the open position, close the valve outlet startling and visually needle (see Figure 2-47), the pressure in the valve chamber rose to the seat test pressure.
To maintain the pressure 15min, check valve material at the body and bonnet connection for leaks. There should be no visible leakage.
(5) so that the valve was restored to room temperature, and then the following a) and b) of step, and the results with the results of comparison of ④.
a) Repeat ② said helium verification test. Measured and recorded through the valve leakage.
b) measuring and recording the opening torque of the valve and closing moments.
⑥ After the test is completed, in a clean, dust-free environment in the valve apart, in order to test all parts for wear and damage.
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