Valves are control components in pipeline fluid delivery systems. It is used to change the passage section and the flow direction of the medium, and has the functions of diversion, cut-off, throttling, non-return, shunt or overflow pressure relief. There are two reasons for the damage of the sealing surface: man-made damage and natural damage. Man-made damage is caused by factors such as poor design, poor manufacturing, improper material selection, improper installation, poor use and poor maintenance. Natural damage is the wear and tear of valve products under normal working conditions, and it is the damage caused by the inevitable corrosion and erosion of the sealing surface by the medium.
Improper installation and improper maintenance can cause the seal faces to malfunction, malfunctioning valves, and premature damage to the seal faces. The damage caused by improper selection and poor operation is mainly manifested in that the valve is not selected according to the working conditions, and the shut-off valve is used as a throttle valve, resulting in excessive closing pressure and fast closing or poor closing, which makes the sealing surface subject to erosion and wear.
It is mainly manifested in defects such as cracks, pores and ballast on the sealing surface, which are caused by improper selection of surfacing and heat treatment specifications and poor operation during surfacing and heat treatment. The hardness of the sealing surface is too high or too low, which is caused by the wrong material selection or improper heat treatment. In addition, the uneven hardness and corrosion resistance of the sealing surface are mainly caused by blowing the underlying metal to the top during the surfacing process, which dilutes the alloy composition of the sealing surface. Of course, there may also be design flaws here.
During the opening and closing process, the sealing surface will be damaged such as scratches, bumps, squeezing and so on. Between the two sealing surfaces, under the action of high temperature and high pressure, the mutual penetration and exudation of atoms occurs, resulting in the phenomenon of adhesion. When the two sealing surfaces move to each other, the adhesion is easily pulled and torn. The higher the roughness of the sealing surface, the easier this phenomenon occurs. Therefore, during the closing process of the industrial valve, the valve flap will bump and squeeze the sealing surface during the process of returning to the seat, so that the sealing surface is partially worn or indented.
It is the result of wear, flushing and cavitation on the sealing surface when the medium is active. When the medium is at a certain speed, the floating fine particles in the medium touch the sealing surface, causing local damage. The high-speed moving medium directly flushes the sealing surface, causing local damage. In addition, when the medium is mixed and partially vaporized, the resulting bubbles will explode and impact the sealing surface, which will also cause local damage. The erosion of the valve product medium and the alternating action of chemical erosion will strongly erode the sealing surface.
The contact of the sealing surfaces with each other, the contact between the sealing surface and the sealing body and valve products, and the concentration difference of the medium, the oxygen concentration difference, etc., will generate a potential difference, which will cause electrochemical erosion, resulting in the erosion of the sealing surface on the anode side.