Pressure test method for industrial valves
In general, the strength test is not required for industrial valves in use, but the strength test shall be conducted for the repaired valve body and bonnet or the valve body and bonnet with corrosion damage. For the safety valve, its constant pressure, reseating pressure and other tests shall comply with its instructions and relevant regulations. Before valve installation, valve strength test and valve sealing test shall be conducted on the valve hydraulic test bench. Spot check 20% of low-pressure valves, and 100% of them shall be inspected if they are unqualified; Medium and high pressure valves shall be 100% inspected. The commonly used media for valve pressure test are water, oil, air, steam, nitrogen, etc. the pressure test methods of various industrial valves (including pneumatic valves) are as follows:
Pressure test method of stop valve and throttle valve
For the strength test of stop valve and throttle valve, the assembled valve is usually placed in the pressure test rack, the valve disc is opened, the medium is injected to the specified value, and the valve body and bonnet are checked for sweating and leakage. The strength test can also be conducted on a single piece. The sealing test is only for stop valves. During the test, the valve stem of the stop valve is vertical, the valve disc is opened, the medium is introduced from the lower end of the valve disc to the specified value, and the packing and gasket are inspected; After passing the test, close the valve disc and open the other end to check whether there is leakage. If the strength and sealing test of the valve are required, the strength test can be conducted first, then the pressure can be reduced to the specified value of the sealing test, and the packing and gasket can be inspected; Then close the valve disc and open the outlet end to check whether the sealing surface leaks.
Pressure test method of gate valve
The strength test of gate valve is the same as that of stop valve. There are two methods for sealing test of gate valve.
- ① The ram is opened to raise the pressure in the valve to the specified value; Then close the gate valve, take out the gate valve immediately, check whether there is leakage at the seals on both sides of the gate, or directly inject the test medium into the plug on the valve cover to the specified value, and check the seals on both sides of the gate. The above method is called intermediate pressure test. This method is not suitable for sealing test of gate valves with nominal diameter less than dn32mm.
- ② The other method is to open the ram to increase the test pressure of the valve to the specified value; Then close the ram, open the blind plate at one end, and check whether the sealing surface leaks. Repeat the above test until it is qualified.
The sealing test at the packing and gasket of the pneumatic gate valve shall be conducted before the sealing test of the ram.
Pressure test method of ball valve
The strength test of pneumatic ball valve shall be carried out in the half open state of the ball.
- ① Sealing test of floating ball valve: put the valve in half open state, introduce the test medium at one end and close the other end; Rotate the ball several times, open the closed end for inspection when the valve is closed, and check the sealing performance of the packing and gasket at the same time, and there shall be no leakage. Then, the test medium is introduced from the other end and the above test is repeated.
- ② Sealing test of fixed ball valve: before the test, rotate the ball several times without load, keep the fixed ball valve closed, and introduce the test medium from one end 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 1.6 times of the test pressure. It is qualified if there is no pressure reduction within the specified time; Then introduce the test medium from the other end and repeat the above test. Then, put the valve in the half open state, close both ends, and fill the cavity with medium. Check the packing and gasket under the test pressure to ensure there is no leakage.
- ③ The three-way ball valve shall be subject to sealing test at each position.
Pressure test method of plug valve
- ① During the strength test of the plug valve, the medium is introduced from one end, and the rest of the passages are closed. The plug is rotated to the fully open working positions for the test. If no leakage is found in the valve body, it is qualified.
- ② During the sealing test, the straight through cock shall keep the pressure in the cavity equal to the passage pressure, rotate the plug to the closed position, check from the other end, and then rotate the plug 180 ° to repeat the above test; The three-way or four-way plug valve shall keep the pressure in the cavity equal to that at one end of the passage, rotate the plug to the closed position in turn, and the pressure shall be introduced from the right angle end and inspected from other ends at the same time.
It is allowed to apply a layer of non acidic thin lubricating oil on the sealing surface before the plug valve test bench. It is qualified if no leakage or enlarged water drop is found within the specified time. The test time of the plug valve can be shorter, generally it is 1-3min according to the nominal diameter.
The plug valve for gas shall be tested for air tightness at 1.25 times the working pressure.
Pressure test method of butterfly valve
The strength test of pneumatic butterfly valve is the same as that of stop valve. For the sealing performance test of butterfly valve, the test medium shall be introduced from the medium flowing end, the butterfly plate shall be opened and the other end shall be closed, and the injection pressure shall reach the specified value; After checking that there is no leakage at the packing and other sealing parts, close the butterfly plate, open the other end, and check that there is no leakage at the sealing part of the butterfly plate. The butterfly valve used for regulating flow may not be subject to sealing performance test.
Pressure test method of diaphragm valve
In the strength test of diaphragm valve, introduce medium from either end, open the valve disc, and close the other end. After the test pressure rises to the specified value, the valve body and bonnet are qualified if there is no leakage. Then depressurize to the sealing test pressure, close the valve disc and open the other end for inspection. If there is no leakage, it is qualified.
Pressure test method of check valve
Check valve test status: the valve disc axis of the lifting check valve is at a position perpendicular to the horizontal; The passage axis and the disc axis of the swing check valve are approximately parallel to the horizontal line.
During the strength test, the test medium shall be introduced from the inlet end to the specified value, and the other end shall be closed. The valve body and bonnet shall be qualified if there is no leakage.
The test medium shall be introduced from the outlet end for the tightness test, and the sealing surface shall be inspected at the inlet end. It is qualified if there is no leakage at the packing and gasket.
Pressure test method of safety valve
- ① Like other valves, the strength test of safety valves is conducted 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 the upper part of the valve body and the bonnet, the pressure is introduced from the outlet El end, and the other ends are closed. The valve body and bonnet are qualified if there is no leakage within the specified time.
- ② For sealing test and constant pressure test, the commonly used medium is: saturated steam is used as the test medium for steam safety valve; The valve for ammonia or other gases uses air as the test medium; Valves for water and other non corrosive liquids use water as the test medium. Nitrogen is often used as the test medium for safety valves at some important positions.
The sealing test shall be conducted with the nominal pressure value as the test pressure, and the number of times shall not be less than two. It is qualified if there is no leakage within the specified time. There are two leak detection methods: first, seal the joints of the safety valve, and paste the tissue paper on the outlet flange with butter. If the tissue paper bulges, it is a leak, and if it does not bulge, it is qualified; Second, use butter to seal the thin plastic plate or other plates on the lower part of the outlet flange, fill water to seal the valve disc, and it is qualified if the water does not bubble. The number of constant pressure and reseating pressure tests of safety valve shall not be less than 3, and it is qualified if it meets the requirements.
See GB/T 12242-1989 performance test methods for safety valves for various performance tests of safety valves.
Pressure test method of pressure reducing valve
① The strength test of the pressure reducing valve is generally assembled after the single piece test, and can also be tested after the assembly. Duration of strength test: 1min when DN < 50mm; More than 2min for dn65-150mm; More than 3min for DN > 150mm.
After the bellows and components are welded, the strength test shall be conducted with air at 1.5 times of the maximum pressure after the pressure reducing valve.
② The sealing test shall be conducted according to the actual working medium. When tested with air or water, the test shall be conducted at 1.1 times of the nominal pressure; The steam test shall be carried out at the maximum allowable working pressure under the working temperature. The difference between inlet pressure and outlet pressure shall not be less than 0.2MPa. The test method is: after the inlet pressure is set, gradually adjust the adjusting screw of the valve to make the outlet pressure change sensitively and continuously within the range of maximum and minimum values without stagnation and jamming. For the steam pressure reducing valve, after the inlet pressure is adjusted, close the block valve behind the valve, and the outlet pressure is the highest and lowest. Within 2min, the appreciation of the outlet pressure shall comply with the provisions in table 4.176-22. Meanwhile, the pipe volume behind the valve shall comply with the provisions in table 4.18; For water and air pressure reducing valves, when the inlet pressure is set and the outlet pressure is zero, close the pressure reducing valve for sealing test. It is qualified if there is no leakage within 2min.
Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.sfutube.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Stainless Steel Valves, Stainless Steel Flanges, Stainless Steel Pipe Fittings, and Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels, and other industries.)
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