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Installation method and maintenance of buried fully welded ball valve

1.1 Pressure test before installation of buried fully welded ball valve

Pipeline valves should be pressure tested before installation to ensure the tightness and safety of the valve itself.

(1) Strength test. Water is used as the medium for the strength test; high pressure caps are welded on the sleeves on both sides of the valve. After opening the valve to the position of 45 degrees Celsius, inject water into the ball valve through the pressure test valve on the sleeve. Boost the pressure to 1.5 times the nominal pressure of the ball valve, and keep the pressure for 15 minutes; no leakage is qualified.

(2) tightness test. Nitrogen is used as the medium in the rigorous test; the ball valve is closed. Inject nitrogen into the ball valve from the pressure test valve on the sleeve. When the pressure rises to 1.1 times of the nominal pressure of the ball valve, the middle cavity pressure relief valve connects the hose to the water container for detection. The insertion depth is 1cm; it is qualified if no air bubbles are generated within 5min.

1.2 Installation

(1) Hoisting. The valve should be hoisted in the correct way. In order to protect the valve stem, do not tie the hoisting chain to the handwheel, gearbox or actuator. Do not remove the protective caps at both ends of the valve sleeve before welding.

(2) Welding. The connection between the directly buried fully welded ball valve and the main pipeline is welded. The quality of the weld seam must comply with the "Radiography of Disc Fusion Welded Joints" (GB3323-2005) Class II film standard. Usually, one-time welding cannot fully guarantee that all are qualified. Therefore, when ordering valves, the manufacturer should be required to add 1.0m to both ends of the valve. Sleeve, once the weld is unqualified, there is still enough length to cut off the unqualified weld and re-weld it on the ball valve. The temperature of the internal seal of the valve does not exceed 140 degrees Celsius, and appropriate cooling measures can be taken if necessary.

(3) Valve well masonry. Directly buried fully welded ball valve adopts special

Structural design, with the feature of maintenance-free, Pu special anti-corrosion coating is coated on the outside of the valve before burial, and three injection pipes for emergency grease injection of the valve seat and valve stem, the middle chamber vent pipe and the valve stem according to the The depth of the Huangdi is appropriately extended so that the staff can complete various operations on the ground. After the direct burial is realized, a small valve manual well can be built by masonry, as shown in Figure 4. However, conventional non-fully welded ball valves cannot be buried directly, and large valve wells need to be built. As a result, a dangerous confined space is formed, which is not conducive to safe operation. At the same time, the valve body itself and the bolt connection parts between the valve body and the pipeline will be corroded, which will affect the service life of the valve.

2Daily operation and maintenance

In order to prolong the life of the valve, the valve should be operated and maintained in accordance with the following procedures.

2.1 Buried fully welded ball valve operation

Frequent operation of the valve can not only prevent impurities from accumulating on the surface of the valve seat or ball, but also avoid local excessive wear of the inlay of the valve seat.

(1) Opening and closing time requirements. Switching the valve too fast will cause the valve to twist and load too much. And damage the valve stem; too slow switching will cause the surface of the valve seat to be washed and worn by the medium for a long time. Therefore, the operating time should be kept within an appropriate range. According to experience, the lower limit of valve switching time (seconds) can be controlled by half of the valve's nominal size (inches), and the upper limit can be estimated by five times the valve's nominal size (inches).

(2) When the valve is in operation, the valve ball should be fully open or fully closed, and should not be in a half-open or half-close position to avoid damage to the valve seat.

2.2 Routine maintenance

The seat cavity is the most easily polluted area of the pipeline valve. In order to ensure the free movement of the valve seat, it should be cleaned once a year, and the tightness of the valve should be checked regularly through the sewage nozzle. The valves of the auxiliary gas main line are often seldom adjusted. They should be switched on and off at least once a year and an appropriate amount of grease should be injected to prevent the ball and the valve seat from gluing and sub-grinding between the valve ball and the valve seat.

The good technical characteristics of the buried fully welded ball valve make the whole gas pipeline integrated (all welded), which enhances the overall stress resistance and geological disaster (such as geological subsidence) ability of the pipeline (including valves). Reduced the possibility of air leakage. The reliability of the valve is improved, the service life is extended, and the installation and maintenance are also very convenient.

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