The reasons for the damage of the sealing surface can be summarized as follows:
1. The processing quality of the sealing surface is not good
Mainly manifested in defects such as cracks, pores and slag inclusions on the sealing surface, which are caused by improper selection of surfacing and heat treatment specifications and poor operation during surfacing and heat treatment. The hardness of the sealing surface is too high or too low, which is caused by incorrect material selection or improper heat treatment. The hardness of the sealing surface is uneven and not corrosion-resistant, which is mainly caused by blowing the bottom metal to the top during the surfacing process, diluting the alloy composition of the sealing surface. Of course, there are also design problems here.
2. Damage caused by improper selection and poor operation
It is mainly manifested in the failure to select valves according to working conditions, using the shut-off valve as a throttle valve, resulting in excessive closing pressure, too fast closing or lax closing, erosion and wear of the sealing surface, improper installation and poor maintenance leading to abnormal operation of the sealing surface, valve operation with disease, premature damage to the sealing surface:
3. Chemical corrosion of the medium
The medium around the sealing surface directly reacts chemically with the sealing surface without generating current, corroding the sealing surface, electrochemical corrosion, contact between the sealing surfaces, contact between the sealing surface and the closing body and valve body, and the concentration difference of the medium, concentration difference, etc., will generate potential difference, electrochemical corrosion occurs, and the sealing surface on the anode side is corroded.
4. Erosion of the medium
It is the result of wear, scouring, and steam on the sealing surface when the medium flows. At a certain speed, the floating fine particles in the medium collide with the sealing surface, causing local damage. The high-speed flowing medium directly washes the sealing surface, causing local damage. When the medium is mixed and partially vaporized, bubbles burst and impact the sealing surface, causing local damage. The impact of the medium and the alternating chemical corrosion will strongly erode the sealing surface.
5. Mechanical damage
The sealing surface will be scratched, bruised, squeezed and other damages during the opening and closing process. Between the two sealing surfaces, atoms penetrate each other under the action of high temperature and high pressure, resulting in adhesion. When the two sealing surfaces move relative to each other, the adhesion is easy to tear. The higher the surface roughness of the sealing surface, the more likely this phenomenon will occur. The valve will bruise and squeeze the sealing surface during the closing process and the valve will return to the seat during the reseating process, causing local wear or indentation on the sealing surface.
6. Fatigue damage
The sealing surface will be fatigued under the action of alternating loads during long-term use, resulting in cracks and delamination. Rubber and plastic are prone to aging after long-term use, resulting in poor performance. From the above analysis of the causes of sealing surface damage, it can be seen that in order to improve the quality and service life of the valve sealing surface, it is necessary to select appropriate sealing surface materials, reasonable sealing structures and processing methods.
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