The valve is the control part in the pipeline fluid transportation system, it is used to change the path section and the medium flow direction, has the diversion, the cut-off, the throttle, the check, the shunt or the overflow relief pressure and so on function. The damage of sealing surface is caused by damage and natural damage. Artificial damage is caused by such factors as poor design, manufacturing, improper material selection, improper installation, poor use and poor maintenance. Natural damage, is the valve under normal working conditions of wear, is the media on the sealing surface of the inevitable corrosion and erosion caused by damage.
  Specifically, the main causes of valve sealing surface damage are as follows:
  Improper installation and maintenance lead to abnormal sealing surface work, and premature damage to the sealing surface of the valve.
  Damage caused by improper selection and poor handling. The main performance is that the valve is not selected according to the working conditions, and the cut-off valve is used as the throttle valve, which leads to too much sealing pressure, too fast sealing or lax sealing, making the sealing surface subject to erosion and wear.
  Sealing surface machining quality is bad, mainly displays in the sealing surface defects such as cracks, porosity and clamp design, because of the overlaying welding and heat treatment specification improper selection and overlaying welding and heat treatment process control, caused by the bad sealing face hard through the high or low, because of the differences caused by error or improper heat treatment, select material sealing surface hardness uneven, no corrosion, mainly because of the underlying metal in welding process blow to the above, to dilute the sealing surface of alloy composition. Of course, there are design issues.
  Mechanical damage, sealing surface in the process of opening and closing will produce abrasions, bruises, squeezes and other damage. Between the two sealing surfaces, under the action of high temperature and pressure, atoms permeate and exude each other, resulting in adhesion. When two sealing surfaces move each other, adhesion is easily pulled off. The thicker the surface of the sealing surface, the easier this phenomenon happens. Valve in the process of sealing, disc in the process of back seat will be bruise and squeeze the sealing surface, make the sealing surface local wear or indentation.
  Erosion of medium is the result of wear, washing and cavitation of sealing surface when medium is active. Medium at a certain speed, the floating fine particles in the medium impact on the sealing surface, causing local damage, high-speed activity of the medium directly wash the sealing surface, causing local damage, medium mixed flow and local vaporization, produced gas bubble blasting impact on the surface of the sealing surface, causing local damage. The erosion of medium combined with chemical erosion alternations will strongly erode the sealing surface
  Electrochemical erosion, mutual contact of sealing surface, contact between sealing surface and sealing body and valve body, difference of concentration of medium, difference of oxygen concentration and other reasons, will produce potential difference, electrochemical erosion, resulting in the anode side of the sealing surface is eroded.
  Chemical erosion of the media, the media near the sealing surface without generating electric current, the media directly and the sealing surface of chemical action, erosion of the sealing surface.

2019-08-02

Seven tips to avoid damage to valve sealing surface

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