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    Home > Active Ingredient News > Drugs Articles > Manufacturing and inspection technology of three precision all welded ball valve

    Manufacturing and inspection technology of three precision all welded ball valve

    • Last Update: 2014-02-12
    • Source: Internet
    • Author: User
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    With the adjustment of energy structure and regional focus of energy, China's oil and gas pipelines have made rapid development In the pipeline engineering construction represented by the first and second lines of the west east gas transmission project, many of its on-off regulating valves are fully welded ball valves, which are widely used in the world In recent years, the demand for all welded ball valve is very large in China, which greatly promotes the progress of all welded ball valve technology in China At the same time, because the pipeline system in China has higher requirements for pressure, material and environment, it also puts forward higher requirements for all welded ball valve At present, the requirements of long-distance pipeline for ball valve are: uniform stress, reliable sealing, compact structure, light weight, high strength, etc This paper introduces the manufacturing process and welding process of all welded ball valve in order to provide reference for the development of the industry 1 Structure and application of all welded ball valve The ball valve introduced in this paper adopts single ball weld and automatic welding process The ball valve is characterized by uniform stress, reliable sealing, compact structure, light weight and high strength It is a pipeline ball valve with both technology and economy It is widely used at home and abroad, and breaks the pattern of domestic pipeline valves mainly made of barrel 1.1 structural design of ball valve The big difference between this ball valve and the traditional three-stage ball valve Zui is that the way of sealing the ball is welding Therefore, the internal and external linings are very important in the welding process In addition, the ball valve is also installed on the pipeline by welding The structure of valve seat seal is generally double seal, i.e upstream and downstream double seal Seat insert ring has excellent corrosion resistance, wear resistance, good elasticity and high sealing performance The structure of the valve seat is shown in Figure 2 The principle of double seal structure of valve seat is as follows (1) sealing principle of upstream valve seat: due to upstream pressure, the valve seat is squeezed by the ball to form a seal, as shown in Figure 3 The pressure f on the valve seat is: where p is the pressure in the pipe; FS is the spring force (2) sealing principle of downstream valve seat: the valve seat is compressed by the ball due to the pressure in the valve body, as shown in Figure 4 Under the pressure F: where p is the pressure in the pipe; FS is the spring force G-T (fluorinated rubber and polytetrafluoroethylene) sealing ring with strong rotation resistance is used for the sealing of the valve rod, and the upper and lower double sealing is carried out Emergency sealing grease can be injected between the double sealing rings for emergency repair The sealing structure of the valve rod is shown in Figure 5 1.2 use and maintenance of ball valve once the valve seat needs emergency repair, it can be repaired in the way shown in Figure 6, without damaging the welding structure The static electricity generated by the parts (ball, seat ring, etc.) inside the valve body is discharged to the valve body through the spring and washer From the operational point of view, due to the trunnion support, it can be operated with a smaller force The trunnion adopts polytetrafluoroethylene bearing with small friction resistance The valve seat is a floating valve seat, and the force of the valve seat squeezed by the ball is relatively small compared with the fluid pressure In terms of maintenance management, ball valves generally do not need to be maintained In case of leakage of sealing parts, sealing grease can be injected for emergency repair For emergency repair of valve seat and stem seal, ikss-3l sealing grease shall be used 2 Manufacturing of all welded ball valve 2.1 materials of main components of ball valve (1) forgings are mainly used for valve body; (2) forgings after surface treatment are mainly used for ball valve; (3) 18Cr-8Ni stainless steel forgings are used for valve seat ring; (4) surface treatment is required for valve rod; (5) sealing materials are mainly used (harmonious) Nitrile rubber and epichlorohydrin rubber 2.2 welding materials and welding process the ball valve welding process is fully automatic welding (1) valve body welding GTAW (gas tungsten arc welding) + saw (submerged arc welding) (2) valve stem welding GTAW (gas tungsten arc welding) + GMAW (gas fusion arc welding) (3) nozzle welding GTAW (gas tungsten arc welding) + saw (submerged arc welding) 3 Inspection of all welded ball valve Because the installation of all welded ball valve is directly welded on the pipeline, the inspection items it needs to carry out are also very different from the ordinary ball valve The special testing requirements are as follows 3.1 bending test the bending test of ball valve simulates that the pipeline flexes in different settlement areas, and the test process is shown in Figure 7 Test method: (1) connect the valve, apply 4200kn · m bending moment, and measure the stress of the valve and pipeline (2) Test the sealing performance of the valve under the nominal working pressure of air medium (3) Measure the opening and closing torque of the valve Test qualification criteria: (1) the stress of each part of the valve is below the yield strength (2) no external leakage or seat leakage (3) The operating torque is normal 3.2 valve tensile and compression test the process of valve tensile and compression test is shown in Figure 8 Test methods: (1) the pipe connecting the valve is loaded with a tensile force and a compressive force of 19900kn (2) Apply air pressure of 0.4-0.7mpa to conduct external leakage, valve seat leakage and torque measurement test (3) Measure the stress of valve and sleeve Test qualification criteria: (1) the stress of each part of the valve is below the yield strength (2) no external leakage or seat leakage (3) The operating torque is normal 3.3 scour test scour test is a test to simulate the process of oil and gas transportation The test process is shown in Figure 9 Test method: (1) inject nitrogen with nominal working pressure into the piping of scour test device (2) Open the valve and allow fluid to flow through the seat (3) check whether the valve seat is abnormal Judgment basis for test qualification: (1) no abnormality found on valve seat (2) The sealing performance of the valve seat is normal 3.4 repeated pressure operation test: the repeated pressure operation test mainly simulates the operation condition and durability of the valve in the actual operation process Test method: (1) first close the valve, apply the air pressure of nominal working pressure to the valve seat, and then fully open the valve Repeat this operation for 200 times (2) Check the valve seat for leakage under the air pressure of 0.4-0.7mpa and nominal working pressure Judgment basis for test qualification: (1) no leakage found on valve seat (2) The valve seat is normal 3.5 low temperature repeated operation test the low temperature repeated operation test simulates the operation of valves in Northwest and Northeast China under extremely cold conditions in winter Test method: (1) cool the ball valve to - 45 ℃, and repeat the opening and closing 200 times (2) after repeated switching, check the valve seat for leakage under the pressure of 0.4-0.7mpa and nominal working pressure Judgment basis for test qualification: (1) no leakage found on valve seat (2) The valve seat is normal 3.6 foreign matter occlusion test foreign matter occlusion test simulates the situation of foreign matters in the process of oil and gas transportation It is required that the ball valve can still operate normally when the foreign matters enter the ball valve Test methods: (1) put 100ml of sand, rust and oxide skin of different mesh on the contact of valve seat and ball (2) Make 250 switches (3) Check the valve seat for leakage under 0.6MPa and 7MPa air pressure for 50 times of opening and closing (4) inject sealing grease into the valve seat for emergency repair test Test qualification criteria: (1) 150 times of opening and closing, no leakage of valve seat (2) switch for 200 times, with leakage less than 180ml / min (3) switch 250 times, less than 625ml / min leakage (4) The valve seat shall be free of leakage after the sealing grease is injected into the valve seat (5) There is no change in operating torque and the operation is in good condition 3.7 scale blowing test: Test Method: (1) close the valve, place 1L of foreign matter in front of the valve seat, apply 7MPa of air pressure on the side where the foreign matter is placed, open the valve for 16%, and blow the foreign matter into the valve seat (2) The valve seat leakage test shall be conducted under the air pressure of 0.6MPa and 7MPa Test qualification criteria: no leakage of valve seat and no abnormal operating torque 3.8 aseismic test: simulate the earthquake On the vibration test-bed, use different loads, amplitudes and vibration frequencies to carry out the aseismic test on the ball valve The test methods are as follows: (1) when the extension bar is loaded, it is equivalent to the earth pressure bending load produced by the foundation landslide (2) Measure the stress of valve and extension rod (3) Conduct sealing test under the pressure of 11.3mpa (4) Conduct operation torque test The basis of test qualification: (1) the stress of each part is below the yield strength (2) The valve shall be free of leakage and abnormality (3) The operating torque is normal 4 Conclusion the ball valve with spherical structure has the advantages of uniform force, compact structure, light weight and high strength The valve seat structure with double piston effect and special sealing rubber material can effectively enhance the reliability of sealing and ensure the service life of the ball valve up to 30 years Through a series of tests of the valve, the use requirements of the valve under special working conditions can be guaranteed.
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