Seven key points to avoid damage to valve sealing surfaces

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Seven key points to avoid damage to valve sealing surfaces Valves are control components in pipeline fluid transportation systems; they are used to change the cross-sectional area of the flow path and the direction of fluid flow, and have functions such as guiding flow, shutting off flow, throttling, checking backflow, diverting flow, or relieving pressure through overflow. The causes of damage to the sealing surface include both human-induced damage and natural damage. Human-induced damage is caused by factors such as poor design, inadequate manufacturing, inappropriate material selection, incorrect installation, improper use, and insufficient maintenance. Natural damage refers to the wear that occurs during the normal operation of a valve, as well as the damage caused by the inevitable corrosion and erosion of the sealing surfaces by the medium. 　　Specifically, the main reasons for damage to the valve sealing surface are as follows: improper installation and inadequate maintenance lead to abnormal operation of the sealing surface, causing the valve to operate under faulty conditions and resulting in premature damage to the sealing surface. 　　Damage caused by improper selection and poor operation. This is mainly manifested by the failure to select valves based on the operating conditions; shut-off valves are used as throttle valves, resulting in an excessive sealing pressure as well as too rapid or inadequate sealing, which causes erosion and wear of the sealing surfaces. 　　The poor quality of the sealing surface is manifested by defects such as cracks, pores, and inclusions on it; this is caused by improper selection of welding and heat treatment parameters as well as inadequate control during these processes. Excessively high or low hardness of the sealing surface results from incorrect material selection or improper heat treatment. Uneven hardness and poor resistance to corrosion of the sealing surface are mainly due to the upward displacement of the underlying metal during welding, which dilutes the alloy composition of the sealing surface. Of course, there are also design issues involved here. 　　Mechanical damage: The sealing surface can suffer scratches, impacts, crushes, and other types of damage during opening and closing. Between the two sealing surfaces, under the effects of high temperature and pressure, atoms penetrate into each other, leading to adhesion. When the two sealing surfaces move relative to each other, the adhered areas can be easily pulled apart. The higher the surface roughness of the sealing surface, the more easily this phenomenon occurs. During the closing process of the valve and as the valve disc returns to its seat, the sealing surface can be scratched or damaged, resulting in local wear or indentations on that surface. 　　Erosion of the medium occurs as a result of the movement of the medium, which causes wear and scouring on the sealing surface as well as cavitation. At certain speeds, the fine particles present in the medium come into contact with the sealing surface, causing localized damage. Medium moving at high speeds washes directly against the sealing surface, leading to localized damage as well. When the medium mixes and vaporizes locally, gas bubbles form and burst, impacting the surface of the sealing surface and causing localized damage. The alternating action of erosion by the medium and chemical attack severely wears down the sealing surface. 　　Electrochemical erosion occurs due to factors such as the contact between sealing surfaces, the contact between sealing surfaces and the enclosure as well as the valve body, as well as differences in medium concentration and oxygen concentration. These factors create a potential difference that leads to electrochemical erosion, resulting in the erosion of the sealing surface on the anode side. 　　Chemical erosion by the medium: In the area near the sealing surface, the medium comes into direct chemical contact with the sealing surface without the generation of an electric current, thereby eroding the sealing surface.