Thread Content
Overview of the reasons for 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 valve sealing surface include both human-induced damage and natural damage. Human-induced damage is caused by factors such as inadequate design, poor manufacturing quality, 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. Analysis of the reasons for damage to the valve sealing surface: 1. Improper installation of the valve 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; for example, using a shut-off valve as a throttle valve, which results in an excessive sealing pressure, too rapid sealing, or inadequate sealing, thereby causing erosion and wear of the sealing surfaces. 2. The poor quality of the valve sealing surface is manifested by defects such as cracks, pores, and inclusions on the surface; this is caused by improper selection of welding and heat treatment procedures, 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 reasons behind this. 3. Mechanical damage to the valve sealing surface, which can result in scratches, dents, 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 torn 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. 4. Erosion by the medium: it is the result of wear, scouring, and cavitation on the sealing surface caused by the movement of the medium. At certain speeds, the fine particles present in the medium come into contact with the sealing surface, causing localized damage. The high-speed flow of the medium directly washes against the sealing surface, leading to localized damage as well. When the medium mixes and vaporizes locally, gas bubbles are formed which burst and impact the surface of the sealing surface, resulting in localized damage. The alternating action of erosion by the medium and chemical attack severely wears down the sealing surface. 5. Factors such as the mutual contact of the valve sealing surfaces, the contact between the sealing surfaces and the housing as well as the valve body, along with differences in medium concentration and oxygen concentration, can all generate 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 absence of an electric current, the medium in the vicinity of the sealing surface reacts chemically with the sealing surface itself, thereby eroding it.