Six major causes of valve sealing surface damage

　　Since seals play a role in shutting off and opening, regulating and distributing, separating and mixing media in valve passages, the sealing surfaces are frequently subjected to corrosion, erosion, and wear from the media, making them easily damaged.

　　There are two types of sealing surface damage: man-made damage and natural damage. Man-made damage is caused by factors such as poor design, imprecise manufacturing, improper material selection, incorrect installation, improper use, and poor maintenance. Natural damage is wear and tear during normal valve operation, resulting from the inevitable corrosion and erosion of the sealing surface by the media.

　　The causes of sealing surface damage can be summarized as follows:

　　1. Poor quality of sealing surface machining

　　This is mainly manifested in defects such as cracks, pores, and inclusions on the sealing surface, which are caused by improper selection of welding and heat treatment specifications and poor operation during welding and heat treatment. Excessive or insufficient hardness of the sealing surface is caused by improper material selection or heat treatment. Uneven hardness and poor corrosion resistance of the sealing surface are mainly caused by the base metal being blown to the top during welding, diluting the alloy composition of the sealing surface. Of course, there are also design issues involved.

　　2. Damage caused by improper selection and operation

　　This is mainly manifested in the failure to select valves according to operating conditions, using shut-off valves as throttling valves, resulting in excessive closing pressure and closing too quickly or not tightly, causing erosion and wear of the sealing surface.

　　Incorrect installation and poor maintenance lead to abnormal operation of the sealing surface, causing the valve to operate with defects and prematurely damaging the sealing surface.

　　3. Chemical corrosion of the medium

　　In the absence of current generation, the medium around the sealing surface directly reacts chemically with the sealing surface, corroding it. Electrochemical corrosion occurs due to contact between sealing surfaces, contact between the sealing surface and the closing member and valve body, and differences in medium concentration and oxygen concentration, resulting in a potential difference and electrochemical corrosion, causing corrosion of the sealing surface on the anode side.

　　4. Erosion of the medium

　　This is the result of wear, scouring, and cavitation erosion of the sealing surface by the flowing medium. At a certain speed, the suspended fine particles in the medium collide with the sealing surface, causing local damage. The high-speed flowing medium directly scours the sealing surface, causing local damage. When the medium is mixed and partially vaporized, bubble bursting impacts the sealing surface, causing local damage. The combined action of medium erosion and chemical corrosion will strongly corrode the sealing surface.

　　5. Mechanical damage

　　The sealing surface may be scratched, bumped, or squeezed during opening and closing. Under high temperature and high pressure, atomic interpenetration occurs between the two sealing surfaces, resulting in adhesion. When the two sealing surfaces move relative to each other, the adhered areas are easily torn. The higher the surface roughness of the sealing surface, the more likely this phenomenon is to occur. During the closing process of the valve and the seating process of the valve disc, the sealing surface may be bumped and squeezed, causing local wear or indentation on the sealing surface.

　　6. Fatigue damage

　　During use, the sealing surface experiences fatigue under alternating loads, resulting in cracks and delamination. Rubber and plastic materials are prone to aging during use, leading to deterioration of performance.

　　From the above analysis of the causes of sealing surface damage, it can be seen that to improve the quality and service life of valve sealing surfaces, it is necessary to select appropriate sealing surface materials, reasonable sealing structures, and processing methods.