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Trim material of high pressure ball valve
High-pressure ball valve internals mainly refer to the sealing surface and upper sealing seat of the valve rod, gate (disc) and valve seat sealing pair. In foreign countries, trim is often used to refer to high-pressure ball valve internals. The selection principle of high-pressure ball valve internals materials is based on the condition of main materials, medium characteristics, structural characteristics, and the role and stress of parts. For conventional general high-pressure valves, the standard has specified the materials of high-pressure ball valve internals or specified several materials to be selected by the designer according to the specific conditions. For some high pressure valves with special requirements, such as high temperature, high pressure, medium corrosion and other working conditions, it is necessary to select and release the material of the high-pressure ball valve internals, the material of the sealing surface of the opening and closing parts, that is, the general name of the parts that cut off or regulate the flow of medium, such as the gate (valve disc), ball, etc. according to the working conditions. The sealing surface of the hoist and valve seat is one of the main working surfaces of the high-pressure valve. Whether the material selection is reasonable and its quality directly affects the function and service life of the high-pressure valve.
1. Operating conditions of the sealing surface of the hoist and valve seat
Because the high-pressure valve is widely used, the working conditions of the sealing surface of the high-pressure valve vary greatly. The pressure can range from vacuum to ultra-high temperature and high pressure, and the temperature can range from - 269 ℃ to 816 ℃. Some working temperatures can reach 1200 ℃. The working media range from non-corrosive media to various acid and alkali and other highly corrosive media. From the stress condition of the sealing surface, it is squeezed and sheared. From the perspective of tribology, there are abrasive wear, corrosion wear, surface fatigue wear, erosion and so on. Therefore, appropriate sealing surface materials should be selected according to different working conditions.
(1) Abrasive wear
Abrasive wear refers to the wear that occurs when a rough hard surface slides on a soft surface. When the hard material is pressed into the soft material surface, a tiny groove will be drawn on the contact surface, and the material falling off the groove will be pushed away from the surface of the object in the form of debris or loose particles.
(2) Corrosive wear
When the metal surface is corroded, a layer of oxide is produced. This layer of oxide is usually covered on the corroded part, which can slow down the further corrosion of the metal. However, if sliding occurs, the oxide on the surface will be removed and the exposed metal surface will be further corroded.
(3) Surface fatigue wear
Repeated cyclic loading and unloading will lead to fatigue cracks on the surface or the lower layer of the surface, forming debris and pits on the surface, and eventually leading to surface damage.
(4) The wear ring of erosive material is caused by sharp particles impacting objects. It is similar to abrasive wear, but its surface is very rough.
(5) Scratch refers to the damage of the material caused by friction during the relative movement of the sealing surface.
