Valve manufacturer: Discuss the reasons for valve sealing surface damage

Valves are pipe accessories used to open and close pipes, control flow, regulate and control the parameters of the conveying medium (temperature, pressure and flow). From simple globe valves to the various valves used in extremely complex automatic control systems, there are many varieties and specifications. Nominal diameters of valves range from very small instrument valves to industrial pipe valves with a diameter of 10m. It can be used to control the flow of various types of fluids such as water, steam, oil, natural gas, mud, various corrosive media, liquid metals and radioactive fluids. The working pressure of the valve can be under the ultra-high pressure of 0.0013MPa to 1000MPa, and the working temperature can be under the ultra-low temperature of c-270℃ to the high temperature of 1430℃. The sealing surface of the valve is often damaged during the use of the valve, and it will lead to internal leakage. Why is this? There are many aspects to understand, let the valve manufacturer take us to have a look.

Mechanical damage, in the opening and closing process, the sealing surface will be scratched, bruised, crushed and other damage. Between the two sealed surfaces, under the action of high temperature and pressure, atoms penetrate and seep out of each other, resulting in adhesion. When the two sealing surfaces move against each other, the adhesive force is easily torn. The higher the roughness of the sealing surface, the more likely this phenomenon is to occur. The sealing surface of the valve can be scraped and crushed during the closing process of the valve, and the disc can be damaged during the reinstallation process, resulting in partial wear or depression of the sealing surface.

When the medium is active, the corrosion of the medium is the result of the wear of the sealing surface, cleaning and cavitation. When the medium moves at a certain speed, the floating particles in the medium will collide with the sealing surface, resulting in local damage. The high-speed moving medium cleans the sealing surface directly, causing local damage. When the medium is mixed and partially vaporized, bubbles and explosions impact the sealing surface, causing local damage. The alternating action of medium corrosion and chemical corrosion will strongly corrode the sealing surface.

Electrochemical corrosion, the contact between the sealing surface, the contact between the sealing surface and the sealing body and the valve body, the concentration difference of the medium, the concentration of oxygen, etc., will produce a potential difference, and electrochemical erosion will occur, resulting in the corrosion of the sealing surface on the anode side.

Chemical corrosion of the medium, the medium near the sealing surface does not produce current, and the medium directly interacts with the sealing surface chemically to corrode the sealing surface. Improper installation and poor maintenance result in the sealing surface not working properly, the valve is not functioning properly, and the sealing surface is damaged prematurely.

Improper selection and operation can cause damage. The main performance is that the valve is not selected according to the working conditions, and the globe valve is used as a throttle valve, which will lead to too large specific closing pressure and close too fast or too tight, resulting in corrosion and wear of the sealing surface. The processing quality of the sealing surface is not good, which is mainly manifested in the defects of cracks, pores and ballast on the sealing surface. This is due to improper selection of surfacing and heat treatment specifications and improper operation during surfacing and heat treatment. The sealing surface is too hard or too low due to incorrect material selection or improper heat treatment. The sealing surface has uneven hardness and corrosion resistance, mainly because the underlying metal is blown onto it during the surfacing welding process, thus diluting the alloy composition of the sealing surface.