The causes of sealing surface damage can be summarized into the following six types:

1. The processing quality of the sealing surface is poor

The main manifestations are 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 the surfacing and heat treatment processes. 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. The main cause is that during the surfacing process, the base metal was blown onto the surface, 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

The main manifestations are that valves are not selected according to the working conditions, and the shut-off valve is used as a throttle valve, resulting in excessive closing specific pressure, rapid closing or incomplete closing, which causes erosion and wear on the sealing surface.

Incorrect installation and inadequate maintenance led to abnormal operation of the sealing surface, causing the valve to run while faulty and prematurely damaging the sealing surface.

3. Chemical corrosion of the medium

The medium around the sealing surface directly undergoes a chemical reaction with the sealing surface without generating current, corroding it. Electrochemical corrosion, due to the mutual contact of sealing surfaces, the contact between sealing surfaces and the closing body and valve body, as well as the concentration difference of the medium and the oxygen concentration difference, etc., will all generate potential differences, causing electrochemical corrosion and resulting in the corrosion of the sealing surface on the anode side.

4. Erosion by the medium

It is the result of wear, erosion and cavitation 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 erodes the sealing surface, also causing local damage. When the medium mixes and partially vaporizes, bubbles burst and impact the surface of the sealing surface, causing local damage. The alternating effect of medium erosion and chemical corrosion will strongly erode the sealing surface.

5. Mechanical damage

The sealing surface may suffer from scratches, bumps, squeezes and other damages during the opening and closing process. Between the two sealing surfaces, under the effect of high temperature and high pressure, atoms penetrate each other, resulting in adhesion. When the two sealing surfaces move towards each other, the adhered areas are prone to tearing. The higher the surface roughness of the sealing surface is, the more likely this phenomenon will occur. During the closing process of the valve and the repositioning process of the valve disc, the sealing surface may be scratched or squeezed, causing local wear or indentation on the sealing surface.

6. Fatigue damage

During long-term use, the sealing surface, under the action of alternating loads, causes fatigue on the sealing surface, resulting in cracks and peeling layers. Rubber and plastic are prone to aging after long-term use, leading to a decline in performance.

From the above analysis of the causes of sealing surface damage, it can be seen that 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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