Due to the sealing element’s function of interrupting and connecting,regulating and distributing, separating and mixing media in the valvpassage, the sealing surface is often subject to corrosion, erosion, and wear by the media, which makes it highly susceptible to damage.
Key Words：the sealing surface；corrosion；erosion；wear
There are two reasons for the damage to the sealing surface: human damage and natural damage. Human damage is caused by factors such as poor design, manufacturing, material selection, improper installation, poor use, and maintenance. Natural damage is the wear and tear of the valve’s normal working conditions and is caused by the inevitable corrosion and erosion of the sealing surface by the media.
The reasons for the damage to the sealing surface can be summarized as follows:
Poor machining quality of the sealing surface: This is mainly manifested in defects such as cracks, pores, and inclusions on the sealing surface. This is caused by improper selection of welding and heat treatment standards, as well as poor operation during welding and heat treatment. The sealing surface’s hardness is too high or too low due to improper material selection or improper heat treatment. The sealing surface’s uneven hardness and poor corrosion resistance are mainly due to blowing the underlying metal onto the surface during the welding process, which dilutes the sealing surface’s alloy composition. Of course, design issues also exist in this regard.
Damage caused by improper selection and operation: This is mainly manifested in the failure to select valves according to working conditions, using a shut-off valve as a throttling valve, resulting in excessive pressure during closure, rapid closure, or incomplete closure, causing erosion and wear on the sealing surface. Incorrect installation and poor maintenance lead to abnormal operation of the sealing surface, causing the valve to operate with illness and prematurely damaging the sealing surface.
Chemical corrosion of the medium: The medium surrounding the sealing surface chemically reacts with the sealing surface without producing a current, corroding the sealing surface. Electrochemical corrosion, contact between the sealing surfaces, contact between the sealing surface and the closing body and valve body, as well as differences in the concentration and oxygen content of the medium, all produce potential differences, causing electrochemical corrosion and corroding the anode-side sealing surface.
Erosion of the medium: This is the result of wear, erosion, and cavitation of the sealing surface when the medium flows. At a certain velocity, floating fine particles in the medium collide with the sealing surface, causing local damage. High-speed flowing medium directly erodes the sealing surface, causing local damage. When the medium mixes and partially vaporizes, bubbles burst and impact the sealing surface, causing local damage. The combination of erosion and chemical corrosion of the medium strongly erodes the sealing surface.
Mechanical damage: The sealing surface will be scratched, bumped, and squeezed during the opening and closing process. Atoms between the two sealing surfaces permeate each other under high temperature and pressure, producing an adhesion phenomenon. When the two sealing surfaces move relative to each other, the adhesion point is easily torn apart. The higher the roughness of the sealing surface, the more likely this phenomenon is to occur. When the valve is closed, the valve disc will bump and squeeze the sealing surface, causing local wear or indentation on the sealing surface.
Fatigue damage: The sealing surface is subjected to alternating loads during long-term use, causing fatigue and resulting in cracks and delamination. Rubber and plastic are prone to aging after long-term use, which leads to decreased performance. From the analysis of the above causes of sealing surface damage, it can be seen that in order to improve the quality and service life of valve sealing surfaces, appropriate sealing surface materials, reasonable sealing structures, and processing methods must be selected.
TWS valve mainly dealing with rubber seated butterfly valve, Gate valve, Y-strainer, balancing valve, Wafe check valve, etc.
Post time: May-13-2023
