Various valve pressure test methods
Under normal circumstances, industrial valves in use do not do strength test, but after repair or corrosion damage of the valve body and cover of the valve body and cover should do strength test. For safety valves, the setting pressure, return pressure and other tests should comply with their specifications and related regulations. Valve installation should be strength and tightness test. Low-pressure valve spot check 20%, such as unqualified should be 100% inspection; Medium and high pressure valves should be 100% inspected. Valve pressure test commonly used media are water, oil, air, steam, nitrogen, etc., all kinds of industrial valves with pneumatic valve pressure test methods are as follows:
Pressure test method of ball valve
The strength test of pneumatic ball valve should be carried out in half open state.Floating ball valve sealing test: the valve is in a half-open state, one end into the test medium, the other end closed; Turn the ball several times, open the closed end to check when the valve is in the closed state, and check the sealing performance of the packing and gasket at the same time, no leakage phenomenon. Then introduce the test medium from the other end and repeat the above test.
Fixed ball valve sealing test: in the test before the ball unloaded rotation several times, fixed ball valve is in a closed state, from one end of the test medium to the specified value; Check the sealing performance of the inlet end with a pressure gauge. The accuracy of the pressure gauge is 0.5 ~ 1, and the range is 1.5 times of the test pressure. In the specified time, no step-down phenomenon is qualified; Then introduce the test medium from the other end and repeat the above test. Then, the valve is in a half-open state, both ends are closed, the inner cavity is filled with medium, and the packing and gasket are checked under test pressure, and there shall be no leakage.
Three-way ball valves should be tested for tightness at all positions.
Pressure test method for check valves
Check valve test state: lifting check valve disc axis in horizontal vertical position; Swing check valve aisle axis and disc axis are approximately parallel to the horizontal line.Strength test, from the inlet end of the test medium to the specified value, the other end closed, see the valve body and valve cover no leakage for qualified.
The sealing test introduces the test medium from the outlet end, and checks the sealing surface at the inlet end. No leakage at the packing and gasket is qualified.
Pressure test method of pressure reducing valve
The strength test of pressure reducing valve is generally assembled after a single test, or after assembly test. Strength test duration: DN150mm > 3min. After the bellows are welded to the assembly, the strength test shall be performed with air at 1.5 times the highest pressure after applying the reducing valve.The sealing test is carried out according to the actual working medium. When using air or water test, 1.1 times of the nominal pressure to carry out the test; The steam test shall be carried out at the highest allowable working pressure at the operating temperature. The difference between inlet pressure and outlet pressure must be no less than 0.2mpa. The test method is: after the inlet pressure is set, gradually adjust the regulating screw of the valve, so that the outlet pressure can be sensitively and continuously changed in the range of maximum and minimum values, without stagnation and blockage. For the steam pressure reducing valve, when the inlet pressure is adjusted away, the valve is closed and then the valve is cut off. The outlet pressure is the highest and lowest value. Within 2 minutes, the appreciation of the outlet pressure should meet the provisions in Table 4.176-22, and the pipeline volume behind the valve should meet the provisions in Table 4.18 as qualified. For water and air pressure reducing valve, when the inlet pressure is set and the outlet pressure is zero, close the pressure reducing valve for sealing test, and no leakage within 2min is qualified.
Pressure test method of butterfly valve
The strength test of pneumatic butterfly valve is the same as that of globe valve. Butterfly valve sealing performance test should be introduced from the medium flow end of the test medium, butterfly plate should be opened, the other end closed, injection pressure to the specified value; After checking the packing and other sealing places without leakage, close the butterfly plate, open the other end, check the butterfly plate sealing places without leakage is qualified. Do not do sealing performance test for butterfly valves used to regulate flow.
Pressure test method of plug valve
When the strength test of the plug valve is carried out, the medium is introduced from one end, the rest of the path is closed, and the plug is rotated to the fully open working position in turn for the test. No leakage is found in the valve body.Sealing test, straight-through cock should keep the pressure equal to the cavity and the path, the plug is rotated to the closed position, check from the other end, and then rotate the plug 180° to repeat the test; Three-way or four-way plug valve should be kept in the chamber and one end of the channel pressure is equal, the plug in turn to the closed position, pressure from the right Angle end, from the other end at the same time to check.
Before the plug valve test, a layer of non-acid dilute lubricating oil is allowed on the sealing surface, and no leakage and expanded water droplets are found within the specified time. Plug valve test time can be shorter, generally according to the nominal diameter of L ~ 3min.
Gas plug valves shall be air sealed at 1.25 times working pressure.
Pressure test method of diaphragm valve
Diaphragm valve strength test from either end of the introduction of medium, open the valve disc, the other end of the closed, test pressure to the specified value, see the valve body and valve cover no leakage for qualified. Then step down to sealing test pressure, close the disc, open the other end for inspection, no leakage is qualified.
Pressure test method for globe valve and throttle valve
Strength test of globe valve and throttle valve, usually put the assembled valve in the pressure test frame, open the disc, inject medium to the specified value, check whether the body and bonnet sweat and leakage. Strength test can also be carried out individually. Sealing test only for globe valves. The stem of the globe valve into a vertical state when the test, the disc is opened, the medium is introduced from the bottom end of the disc to the specified value, check the packing and gasket; When qualified, close the disc and open the other end to check for leakage. If the valve strength and sealing test to do, can first do the strength test, and then buck to the sealing test specified value, check the packing and gasket; Then close the disc and open the outlet end to check whether the sealing surface is leaking.
Pressure test method for gate valves
The strength test of gate valves is the same as that of globe valves. There are two methods for sealing test of gate valves.Gate open, so that the valve pressure up to the specified value; Then close the gate, immediately remove the gate valve, check the seal on both sides of the gate for leakage or directly into the plug on the valve cover to the specified value, check the seal on both sides of the gate. The above method is called intermediate pressure test. This method should not be used for sealing test of gate valves with nominal size less than DN32mm.
Another method is to open the gate, so that the valve test pressure to the specified value; Then close the gate, open one end blind plate, check sealing surface for leakage. Then turn the head, repeat the above test until qualified.
Pneumatic gate valve packing and gasket sealing test should be carried out before the gate sealing test.
Pressure test method for safety valve
The strength test of the relief valve, like any other valve, is done with water. When testing the lower part of the valve body, the pressure is introduced from the inlet I=I end, and the sealing surface is closed; When testing upper body and bonnet, pressure is introduced from exit El end and other ends are closed. No leakage of valve body and bonnet within specified time is qualified.Sealing test and constant pressure test, the general use of medium is: steam safety valve with saturated steam as the test medium; Ammonia or other gas valve with air as the test medium; Water and other non - corrosive liquid valves with water as the test medium. Nitrogen is commonly used as the test medium for some important safety valves.
Sealing test with nominal pressure value as the test pressure for the test, the number of not less than two times, no leakage in the specified time for qualified. There are two methods of leak inspection: one is to seal the joint of the safety valve, and paste the thin paper on the El flange with butter. The thin paper is leaky and not qualified. Two is to use butter to thin plastic plate or other plate seal affixed to the lower part of the export flange, filling water seal valve disc, check the water does not bubble for qualified. Safety valve constant pressure and return pressure test times are not less than 3 times, meet the requirements for qualified. See GB/T 12242 "Safety valve performance Test Method" for all performance tests of safety valves.
Valve pressure test management regulations
1, all valves should be inspected after opening the box, including the nameplate on the valve body is complete, product quality documents, the valve is in the closed state, no flange surface and other damage, no dirt, both ends of the protective cover, etc..2, the operator should be familiar with the pressure test table operation.
3, valve pressure test JHA perfect, the operator of valve pressure test, reverse transport and other processes of safety risks should be familiar with and have the corresponding preventive measures.
4, valve pressure test process is: valve shell strength test, sealing test, sealing test.
(1) the valve shell strength test medium is water, the pressure is 1.5 times the nominal pressure of the valve, the pressure holding time is 5min, no dripping or moisture is qualified.
(2) The sealing test medium on the valve is water, the pressure is 1.5 times of the nominal pressure, the pressure holding time DN≤50 is 15s, 65≤DN≤300 is 60s, DN≧350 is 120s, no leakage is qualified.
(3) Valve sealing test low-pressure sealing test, the test medium is air (gate valve), the pressure is 0.6mpa, the pressure holding time DN≤50 is 15s, 65≤DN≤150 is 60s, DN ≥ 200 is 120s, and the permeability meets the requirements is qualified.
(4) After the pressure test is qualified, the water in the valve cavity should be blown dry with compressed air in time.
(5) The qualified valve shall be marked √ on the valve body and the unqualified valve shall be marked ×.
(6) After pressure test, the valves should be stacked separately according to the device and model specifications, and the unqualified products should be stacked separately; Visible signs shall be erected in each stacking area. After pressure test, the valve should be covered back and protected with colored strip cloth in the stacking area.
(7) After the valve pressure test, the valve/Pipe Fitting Test Record should be filled in according to the device in time, and the number of the purchase contract on the valve body should be filled in the model column.
(8) The release of qualified valves shall be filled in valve Release Record and signed by both parties.
(9) Unqualified valves shall be separately established unqualified valve Information Ledger.
