Test Method for Various Valves in Valve Inspection

Test Method for Various Valves in Valve Inspection

In general, industrial valves do not need strength test during use while the repaired valve body and cover or corrosive and damaged valve body and cover shall be conducted for strength test. The set pressure test, reseating pressure test and other tests for safety valve shall meet the requirements in User Manual and relevant procedures. The valve shall be carried out for strength and sealing test before installing. The low pressure valves shall be inspected randomly for 20% but for 100% if unqualified; medium and high pressure valves shall be 100% inspected.

1、Pressure Test Method for Ball Valve

The strength test for pneumatic ball valve shall be conducted at half-open position of the ball.

① Sealing test for floating ball valve: make the valve at half-open position, introduce test medium to one end and seal another end, rotate the ball for several times and open the closed end for inspection when the valve is in close state. At the same time, inspect the sealing performance at packing and gasket, and it shall be no leakage. Introduce the test medium from another end and repeat above test.

②Sealing test for fixed ball valve: rotate the ball under no load for several times before test, the fixed ball valve is in close state this time, and introduce the test medium to specified value from one end. Use the pressure gauge to check the sealing performance of introducing end, and the precision of used pressure gauge is 0.5~1 level with the range of 1.5 times higher than test pressure. It is qualified if there is no pressure releasing within the specified time. Introduce the test medium from another end and repeat above test, and then make the valve at half-open position, close both ends, fill the medium into cavity and check the packing and gasket under test pressure, it shall be no leakage. 

③ Sealing test shall be carried out for each position of three-way ball valve.

2、Pressure Test Method for Check Valve

Test state of check valve: the valve clack axis of lift check valve is in horizontally vertical position, and the channel axis and valve clack axis of swing check valve are approximately parallel to the horizontal line.

During the strength test, introduce the test medium to specified value from inlet end, close another end and check the valve body and cover, it is qualified if no leakage.

For sealing test, introduce the test medium from outlet end, check the sealing surface at inlet end, and it is qualified if no leakage at packing and gasket.

3、Pressure Test Method for Reducing Valve

① For strength test for reducing valve, it is assembled after test for single part generally but it can be tested after assembling as well. The time duration of strength test: lmin for DN<50mm, longer than 2min for DN65~150mm and longer than 3min for DN>150mm. After welding bellows and assembly, the strength test with air and under 1.5 times of highest pressure for reducing valve shall be carried out.

②The actual working medium shall be used for sealing test. If air or water used for test, the pressure 1.1 times of nominal pressure is used for test. When conducting steam test, the highest allowable working pressure under working temperature shall be applied, and the difference between inlet pressure and outlet pressure is required not lower than 0.2MPa. The test method is: after adjusting the inlet pressure, regulate the adjusting screw of the valve gradually to make the outlet pressure can sensitively and continuously change within the range between maximum and minimum value, free from stopping and clamping. Close the block valve behind the steam valve after adjusting inlet pressure. The outlet pressure shall be the highest and lowest value and the rising value within 2 min of outlet pressure shall meet the requirement in Table 4.176-22. Meanwhile the volume of pipe behind the valve is qualified if meets the requirement in Table 4.18. When the outlet pressure is zero after adjusting the inlet pressure for water and air reducing valve, close the reducing valve to conduct sealing test and it is qualified if no leakage within 2 min.

4、Pressure Test Method for Butterfly Valve

The strength test for pneumatic butterfly valve is the same with stop valve. For sealing performance test of butterfly valve, introduce the test medium from the end of medium flowing into, open the butterfly plate, close another end and inject pressure to specified value. After confirming the packing and other sealing sites are free from leakage, close the butterfly plate, open another end and check the sealing of butterfly plate, it is qualified if no leakage. The butterfly valve which is used as regulating the flow can not be used for sealing performance test.

5、Pressure Test Method for Plug Valve

① When carrying out strength test for plug valve, introduce the medium from one end, close other channels, screw the plug to full-open working position in sequence for test, and the valve body is qualified if no leakage found.

② When carrying out sealing test, the straight-through plug shall keep the pressure in cavity equal to pressure in channel. Rotate the plug to close position, check it from another end, and then rotate the plug for 180° and repeat above test. The three-way or four-way plug valve shall keep the pressure in cavity equal to the pressure on one end of channel, rotate the plug to close position in sequence, introduce the pressure from rectangular end and check another end at the same time.

Before test, it is allowable to apply one layer of non-acid thin lubricating oil on sealing surface of plug valve, and it is qualified if no leakage and extended droplet were found in specified time. The test time for plug valve may be shorter and may be 1~3min in general according to nominal diameter. The plug valve for coal gas shall be carried out air sealing test with 1.25-fold working pressure.

6、Pressure Test Method for Diaphragm Valve

For strength test for diaphragm valve, introduce the medium from any of end, open the valve clack and close another end, check the valve body and cover after test pressure rising to specified value, and it is qualified if no leakage. Decrease the pressure to the pressure for sealing test, close the valve clack and open another end for checking, and it is qualified if no leakage.

7、Pressure Test Method for Stop Valve and Throttling Valve

For the strength test for stop valve and throttling valve, usually place the assembled valve onto pressure test frame, open valve clack, inject medium to the specified value, and check whether the valve body and cover are steaming and leaking. Single part can be carried out for strength test as well. The sealing test is only for stop valve here. When testing, the valve rod of stop valve is in vertical state, open valve clack, introduce the medium from one end under the valve clack to specified value and check the packing and gasket. Close the valve clack after it is qualified and open another end to check whether it is leaked. If both strength test and sealing test for valve to be tested, the strength test may be conducted firstly, and then decrease the pressure to specified value by sealing test, check the packing and gasket, close the valve clack, and open outlet end to check whether the sealing surface is leaked.

8、Pressure Test Method for Gate Valve

The strength test for gate valve is the same with stop valve. There are two methods for sealing test of gate valve.

① Open the gate plate to make the pressure in valve rise to specified valve, close the gate plate and immediately take out the gate valve, check whether the sealing parts at both sides of gate plate are leaked, or directly inject test medium into plug position on valve cover to the specified value, and check the sealing at both sides of gate plate. The aforesaid method is called middle pressure testing and not suitable for sealing test of gate valve with nominal diameter lower than DN32mm.

② Another method is to: open the gate plate to make the test pressure of valve rise to specified value, and then close the gate plate, open blind plate at one end to check whether the sealing surface is leaked, and reverse the sequence to repeat the above test until it is qualified.

The sealing test for packing and gasket of pneumatic gate valve shall be conducted before the sealing test for gate plate.

9、Pressure Test Method for Safety Valve

① The strength test for safety valve is the same with other valves and water is taken for test. When testing the lower part of valve body, introduce pressure from inlet I=I end, and close the sealing surface. When testing the upper part of valve body and valve cover, introduce the pressure from outlet El end, and close other ends. It is qualified if valve body and cover are not leaked within the specified time.

② The common medium used for sealing test and constant pressure test is: saturated steam is used as test medium for safety valve for steam; air is used as test medium for valve used in ammonia or other gas; water is used as test medium for valve used in water and other non-corrosive fluids. For the safety valve at some important positions, nitrogen is used as test medium as usual.

The nominal pressure is taken as test pressure in sealing test for at least two times, and it is qualified if no leakage within the specified time. There are two methods for leakage test: the first one is to seal the connection parts of safety valve, paste the thin paper on outlet E1 flange by using grease, and it is leaked if thin paper bulged or qualified if thin paper did not bulge. The second method is to stick the thin plastic plate or other plates onto the lower part of outlet flange by using grease, inject water to seal the valve clack and check it, and it is qualified if no bubbling in water. The set pressure test and reseating pressure test for safety valve shall be conducted for not lower than 3 times, and it is qualified if meeting the requirements. Please see the GB/T 12242-1989 Performance Test Methods for Safety Valves for performance tests for safety valve.