Several possible causes of valve sealing surface damage

Several possible causes of valve sealing surface damage

Valve is a control component in pipeline fluid transmission system. It is used to change the channel section and medium flow direction. It has the functions of diversion, cut-off, throttling, check, diversion or overflow pressure relief. There are two reasons for the damage of the sealing surface: man-made damage and natural damage. Man made damage is caused by poor design, poor manufacturing, improper material selection, improper installation, poor use and poor maintenance. Natural damage refers to the wear of the valve under normal working conditions and the damage caused by the inevitable corrosion and erosion of the medium on the sealing surface.

Specifically, the main reasons for the damage of the valve sealing surface are as follows:

1.     Improper installation and poor maintenance led to abnormal operation of the sealing surface, faulty operation of the valve and premature damage to the sealing surface.

2.     Damage caused by improper selection and poor operation. The main performance is that the valve is not selected according to the working conditions, and the block valve is used as a throttle valve, resulting in excessive sealing specific pressure, too fast sealing or lax sealing, so that the sealing surface is eroded and worn.

3.     The poor processing quality of the sealing surface is mainly reflected in the defects such as cracks, pores and slag inclusion on the sealing surface, which are caused by improper selection of surfacing and heat treatment specifications and poor manipulation in the process of surfacing and heat treatment. The hard transition of the sealing surface is too high or too low, which is caused by different and wrong material selection or improper heat treatment. The hardness of the sealing surface is uneven and non erosion resistant, mainly because the bottom metal is blown onto it during surfacing, It dilutes the caused by the alloy composition of the sealing surface. Of course, there are also design problems.

4.     Mechanical damage: the sealing surface will be scratched, bumped and squeezed during opening and closing. Between the two sealing surfaces, atoms permeate and exude each other under the action of high temperature and high pressure, resulting in adhesion. When the two sealing surfaces move with each other, the adhesive part can be easily pulled and torn. The higher the coarseness of the sealing surface, the easier this phenomenon occurs. During the sealing process of the valve and the reseating process of the valve disc, the sealing surface will be bumped and squeezed, causing local wear or indentation on the sealing surface.

5.     The erosion of medium is the result of wear, flushing and cavitation of the sealing surface when the medium is active. When the medium is at a certain speed, the floating fine particles in the medium collide with the sealing surface and cause local damage. The high-speed moving medium directly washes the sealing surface to cause local damage. When the medium is mixed and partially vaporized, it produces gas bubble blasting to impact the sealing surface and cause local damage. The alternating action of medium erosion and chemical erosion will strongly etch the sealing surface.

6.     Electrochemical erosion, the contact between sealing surfaces, the contact between sealing surface and sealing body and valve body, as well as the concentration difference of medium and oxygen concentration difference, will produce potential difference and electrochemical erosion, resulting in the erosion of the sealing surface on the anode side.

7.     Chemical erosion of medium: under the condition that the medium near the sealing surface does not generate current, the medium directly plays a chemical role with the sealing surface and erodes the sealing surface.