Six major causes of damaged valve sealing surfaces

Thread Content

Since seals play roles such as shutting off and opening, regulating and distributing, as well as separating and mixing media in valve channels, their sealing surfaces are frequently subjected to corrosion, erosion, and wear by the media, making them highly prone to damage. 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, improper 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. The reasons for damage to the sealing surface can be summarized as follows: 1. Poor quality of sealing surface processing – this is manifested by defects such as cracks, pores, and inclusions on the sealing surface; it is caused by improper selection of welding and heat treatment procedures, as well as poor operation 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 corrosion resistance of the sealing surface are mainly due to the upper layer of metal being blown onto the surface during welding, thereby diluting the alloy composition of the sealing surface. Of course, there are also design issues involved here. 2. Damage caused by improper selection and poor operation is mainly manifested in the failure to choose valves according to the operating conditions; shut-off valves are used as throttle valves, resulting in excessive closing pressure, too rapid closing, or incomplete closure, which causes erosion and wear of the sealing surfaces. Improper installation and inadequate maintenance led to abnormal operation of the sealing surfaces, causing the valve to operate under faulty conditions and resulting in premature damage to those sealing surfaces. 3. Chemical corrosion of the medium: In the absence of an electric current, the medium surrounding the sealing surface reacts chemically with the sealing surface itself, thereby corroding it. Electrochemical corrosion occurs due to factors such as the contact between sealing surfaces, the contact between sealing surfaces and the valve body as well as the closing element, as well as differences in medium concentration and oxygen concentration. These factors create a potential difference that leads to electrochemical corrosion, resulting in the corrosion of the sealing surface on the anode side. 4. Erosion by the medium: It is the result of wear, scouring, and cavitation on the sealing surface caused by the flow of the medium. At a certain velocity, the fine particles present in the medium collide 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, bubbles are formed; the bursting of these bubbles impacts the surface of the sealing surface, resulting in localized damage. The alternating action of erosion by the medium and chemical corrosion severely wears down the sealing surface. 5. Mechanical damage: The sealing surface can suffer damage such as scratches, bruises, and crushes during opening and closing. Between the two sealing surfaces, atomic penetration occurs under high temperature and pressure, resulting in adhesion. When the two sealing surfaces move relative to each other, the stuck areas are prone to tearing. The higher the surface roughness of the sealing surface, the more likely this phenomenon is to occur. During the closing process of the valve, as the valve disc returns to its seat, the sealing surface can be scratched or crushed, resulting in local wear or indentations on that surface. 6. Fatigue damage: Over time, under the action of alternating loads, the sealing surface suffers from fatigue, resulting in cracks and delamination. Rubber and plastics tend to age over time as a result of prolonged use, which leads to a decline in their performance. From the analysis of the above causes of seal surface damage, it can be seen that to improve the quality and service life of valve seal surfaces, it is necessary to select appropriate seal surface materials, as well as reasonable sealing structures and processing methods.