Chemical production, as long as there is fluid through, will use the valve, the importance of the valve in the chemical industry is self-evident. Well, today, Yi Guanjun discusses pressure testing methods and precautions for commonly used valves with everyone.
Valve pressure test commonly used media are water, oil, air, steam, nitrogen, etc., all kinds of industrial valves with pneumatic valve pressure test method is as follows:
1 Globe valve and throttle valve
For the strength test of the shutoff valve and the throttle valve, the assembled valve is usually placed in the pressure test stand, the valve flap is opened, the medium is injected to the specified value, and the valve body and the valve cover are checked for sweating and leakage. It is also possible to carry out strength tests in one piece. Sealing test only as a stop valve. During the test, the valve stem of the stop valve is in a vertical state, the valve flap is opened, the medium is introduced from the bottom end of the valve flap to the specified value, and the filler and the gasket are inspected; after the passage, the valve disc is closed, and the other end is opened to check for leakage. If the valve strength and sealability tests are to be done, strength tests may be done first, then depressurized to the sealability test value, check the packing and gaskets; then close the valve flap, open the outlet end and check the sealing surface for leakage.
2 gate valve
The strength test of the gate valve is the same as the shut-off valve. There are two methods for sealing the valve.
1 The gate is opened, so that the pressure in the valve rises to the specified value; then, the gate is closed, the gate valve is immediately taken out, the leakage at the seals on both sides of the gate is checked, or the test medium is directly injected into the plug on the valve cap to the specified value. Check the seals on both sides of the gate. The above method is called intermediate pressure test. This method is not suitable for sealing tests on gate valves with a nominal diameter of DN32mm or less.
2 Another method is to open the gate, so that the valve test pressure rises to the specified value; then close the gate, open the end of the blind, check the sealing surface leakage. And then down, make the above repeated test until qualified.
Pneumatic gate valve packing and gasket seal test shall be conducted before the gate seal test.
3 ball valve
The strength test of the pneumatic ball valve shall be performed with the ball half open.
1Floating ball valve sealing test: The valve is in a half-open state, one end is introduced into the test medium, the other end is closed; the ball is rotated several times, the closed state is opened when the valve is closed, and the sealing performance at the packing and the gasket is checked at the same time. There must be no leakage. The test medium is then introduced from the other end and the above test is repeated.
2 Fixed ball valve sealing test: Before the test, the ball is rotated several times without load, the fixed ball valve is in the closed state, and the test medium is introduced from one end to the specified value; the sealing performance of the introduction end is checked with a pressure gauge, and the precision of the pressure gauge is used 0.5 ~ 1st, the range is 1.6 times the test pressure. Within the prescribed time, no depressurization is acceptable; the test medium is then introduced from the other end and the above test is repeated. Then, the valve is in a half-open state, both ends are closed, the inner cavity is filled with the medium, and the filler and the gasket are checked under the test pressure without leakage.
3 The three-way ball valve shall be tested for hermeticity at various locations.
4 Plug valves
When a plug valve was used for the strength test, the medium was introduced from one end, and the rest of the passage was closed. The plug was rotated to the fully open working positions in order to perform the test. The valve body was found to have no leakage.
2 In the sealing test, the through-flow cocks should keep the pressure in the chamber equal to the passage, rotate the stopper to the closed position, check from the other end, and repeat the above test by rotating the stopper 180°; three- or four-style plug valves The pressure in the chamber and the end of the passage should be kept equal, and the stoppers are rotated to the closed position in turn, the pressure is introduced from the right angle end, and the inspection is performed from the other end at the same time.
A non-acidic, dilute lubricating oil was allowed to be applied to the sealing surface before the plug valve test rig. No leakage and enlarged water droplets were found to be acceptable within the specified time. The plug valve test time can be shorter, generally regulated by the nominal diameter of 1 ~ 3min.
Gas plug valves shall be tested for air tightness at 1.25 times the working pressure.
5 butterfly valve
The strength test of the pneumatic butterfly valve is the same as the shut-off valve. The sealing performance test of the butterfly valve shall be introduced from the medium end to the test medium. The butterfly plate shall be opened and the other end closed. Fill the pressure to the specified value. After checking the packing and other seals for no leakage, close the butterfly plate and open the other end to check the butterfly. No leakage at the seal of the board is acceptable. As a butterfly valve for adjusting the flow rate, sealing performance test may not be performed.
6 Diaphragm valve
Diaphragm valve strength test from the introduction of media at either end, open the valve flap, the other end closed, the test pressure rose to the specified value, see the valve body and valve cover no leakage is qualified. Then step down to the leak test pressure, close the disc, open the other end of the inspection, no leakage is acceptable.
7 check valve
Check valve test state: The lift check valve spool axis is in a horizontal and vertical position; the swing check valve passage axis and the valve flap axis are in a position approximately parallel to the horizontal line.
In the strength test, the test medium is introduced from the inlet end to the specified value, and the other end is closed to see if the valve body and the valve cover have no leakage.
Sealing test The test medium was introduced from the outlet end and the sealing surface was inspected at the inlet end. No leakage at the packing and gaskets was acceptable.
8 Safety valve
1 The strength test of a safety valve is the same as other valves and it is tested with water. When the lower part of the valve body is tested, the pressure is introduced from the inlet I=I end and the sealing surface is closed. When the upper part of the valve body and the valve cover are tested, the pressure is introduced from the outlet end El and the other end is closed. No leakage of valve body and bonnet in the specified time is qualified.
2 Sealing test and constant pressure test, the general medium is: steam safety valve with saturated steam as test medium; ammonia or other gas valve with air as test medium; water and other non-corrosive liquid valves with water as test medium. Nitrogen is commonly used as a test medium for safety valves in some important locations.
The sealing test shall be conducted with the nominal pressure value as the test pressure for not less than twice and no leakage shall be qualified within the specified time. There are two methods for leak detection: one is to seal the connection points of the safety valve, and the thin paper seal is attached to the El flange with grease; the thin paper is bulging as a leak, and the bulge is not qualified; and the second is thinning with butter. The plastic plate or other plate is attached to the lower part of the outlet flange, and the valve is sealed with irrigation water to check that no bubbling occurs in the water. The number of safety valve constant pressure and seat back pressure tests shall not be less than 3 times and meet the regulations as qualified.
9 Pressure reducing valve
1 The strength test of the pressure reducing valve is usually assembled after a single test, or it can be assembled after the test.
Duration of strength test: 1 min for DN <50 mm; greater than 2 min for DN65 ~ 150 mm; greater than 3 min for DN> 150 mm.
After the bellows and the components were welded, the maximum pressure was 1.5 times after the application of the pressure reducing valve and the air was used for the strength test.
2 According to the actual working medium for sealing test. When tested with air or water, the test is performed at 1.1 times the nominal pressure; with the steam test, it is performed at the highest working pressure allowed at the operating temperature. The difference between the inlet pressure and the outlet pressure is not less than 0.2 MPa.
The test method is: After the inlet pressure is set, the adjustment screw of the valve is gradually adjusted so that the outlet pressure can be sensitively and continuously changed within the range of the maximum and minimum values, without stagnation or jamming.
Valve pressure check
(1) Under normal circumstances, the valve shall not be subjected to strength tests. However, after the repair, the valve body and valve cover or corrosion damage of the valve body and valve cover shall be tested for strength. For safety valves, their constant pressure and seatback pressure and other tests shall comply with the specifications of their instructions and related procedures.
(2) The valve installation should be tested for strength and tightness. 20% for low-pressure valve checks, and 100% for failures; 100% for medium- and high-pressure valves.
(3) During the test, the valve installation position should be in the direction of easy inspection.
(4) Welded valves can be tested by taper seals or O-ring seals when the pressure test is not possible with a sampan plate.
(5) The valve air should be excluded as much as possible during the hydraulic test.
(6) The pressure during the test should be gradually increased and it is not allowed to pressurize suddenly and abruptly.
(7) The duration of strength test and seal test is generally 2~3min, and the important and special valves should last 5min. Small-diameter valve test time can be correspondingly shorter, large-diameter valve test time can be longer. During the test, the test time can be extended if in doubt. In the strength test, the valve body and valve cover are not allowed to sweat or leak. Sealing test, the general valve only once, safety valve, high pressure valve and other raw materials need to be carried out twice. During the test, trace leakage is allowed for low pressure, large-diameter, non-essential valves and valves that are permitted to leak. For common valves, power station valves, marine valves, and other valve requirements, leakage requirements are required. Should be implemented in accordance with relevant regulations.
(8) Throttle valves are not to be tested for sealability of the closure, but strength tests and sealing tests at the packing and gaskets are to be made.
(9) In the pressure test, the closing force of the valve allows only one person's normal physical strength to close; it must not be forced by tools such as a lever (except torque wrenches). When the diameter of the handwheel is greater than 320 mm, the two are allowed to work together. shut down.
(10) Valves with upper seals shall be removed and tested for leaktightness. After the seals are sealed, check for leaks. When using the gas as a test, check the water in the stuffing box. For the packing tightness test, the upper seal is not allowed to be in the dense position.
(11) Where a valve is provided with a drive device, the use of a drive device to close the valve is used to test the leak tightness of the valve. For manual drive devices, sealing tests should also be performed to close the valve.
(12) The bypass valve mounted on the main valve after the strength test and sealability test shall be tested for strength and tightness at the main valve; the main valve closing member shall also be opened when it is opened.
(13) In the cast iron valve strength test, use a copper hammer to tap the valve body and valve cover to check for leakage.
(14) When the valve is tested, except for the provisions of the plug valve that allow the sealing surface to be oiled, other valves are not allowed to be oiled on the sealing surface.
(15) When the valve is pressure tested, the pressure of the blind plate on the valve should not be too large, so as to avoid deformation of the valve and affect the test results (If the cast iron valve is too tight, it will be damaged).
(16) After the pressure test of the valve is completed, the water in the valve shall be promptly removed and wiped clean. A test record shall also be made.