Brief Introduction To Repair And Maintenance Of Valves in Power Plants

Thermal power plant valve pressure plugging technology. Power plant valves are mainly used to control the operation of various equipment and fluid media on their pipelines. Valve leakage often occurs in packing, flange seals and valve bodies. Long-term valve leakage can cause The erosion of the valve stem and flange sealing surface will eventually cause the valve to be scrapped. In addition, the valve plugging technology under pressure for the medium fluid thermal power plant. Power plant valves are mainly used to control the operation of fluid media on various equipment and pipelines. Valve leakage often occurs on packing, flange seals and valve bodies. Long-term valve leakage can cause the valve stem and flange sealing surface to be flushed. Corrosion will eventually cause the valve to be scrapped, and the loss of the medium fluid will increase the consumption of the power plant, increase the cost, and decrease the economic benefits. If the medium fluid is toxic, flammable, explosive, corrosive, etc., it is prone to accidents such as poisoning, fire, explosion and other casualties, and accelerates the corrosion rate of plant equipment, shortens its service life, pollutes the surrounding environment, and destroys electricity Production harms people’s health. The existence of leakage seriously threatens production safety and increases unplanned shutdown accidents of power plants. The following introduces some of the reasons for valve leakage, plugging methods, and valve repair and maintenance methods for reference.

1: Forms and factors of valve leakage

Leakage and causes of valve packing

  During the operation and use of the valve, there is relative movement between the valve stem and the packing, which includes rotation and axial movement. As the number of switches increases, the number of relative movements also increases, as well as the temperature, pressure, and characteristics of the fluid medium. The valve packing is the most prone to leakage. It is caused by the gradual weakening of the contact pressure of the filler, the aging of the filler itself, and the loss of elasticity. At this time, the pressure medium will leak outward along the contact gap between the packing and the valve stem, which will blow away part of the packing and flush the valve stem out of the groove for a long time, thereby expanding the leakage.

2: Leakage of flange

 The flange sealing of the valve mainly relies on the pre-tightening force of the connecting bolts, and the gasket achieves sufficient sealing specific pressure to prevent the leakage of the sealed pressure fluid medium. There are many reasons for its leakage. The pressure of the gasket is insufficient, the roughness of the joint surface does not meet the requirements, the deformation of the gasket and mechanical vibration, etc. will cause the sealing gasket and the flange joint surface to leak tightly. . In addition, the deformation or elongation of the bolts, the aging of the gasket, the decrease of resilience, and the cracks will also cause the flange surface to be leaky due to the lack of sealing. There are also human factors that cannot be ignored in the flange leakage, such as the offset of the sealing gasket, the partial sealing pressure is insufficient, the tightening force is excessive, the design limit of the sealing gasket is exceeded, and the uneven force or two methods in the flange tightening process Leakage is prone to occur due to the deviation of the center line of the orchid, causing false tightening.

3: Leakage of the valve body and its cause

  The main leakage of the valve body is caused by casting or forging defects in the production process of the valve, such as sand holes, pores, cracks, etc., and the erosion and cavitation of the fluid medium are also common factors that cause the valve body to leak.

3.1 Principle of leak plugging under pressure

  The principle of plugging under pressure is based on the sealing mechanism of the solid sealing material under the dynamic conditions of the liquid medium. The method is to install special equipment at the leaking part, use the cavity formed between the sealing part and the special equipment, and use a special high-pressure glue injection tool to inject the sealant into the chamber, and fill the entire chamber space to make the sealant squeeze The force is balanced with the pressure of the leaking medium, and a new sealing structure is established to block the channels of the leaking pores and block the leakage of the medium.

3.2 Advantages of leak plugging under pressure