Selection of Build-up Welding Materials for Valves' Sealing Surfaces

The sealing surface of steel valves is generally manufactured by build-up welding. The materials used for build-up welding of valves are divided into four categories according to alloy types, namely cobalt based alloys, nickel based alloys, iron based alloys and copper based alloys. These alloy materials are used to manufacture welding rods, welding wire, welding flux (including transition alloy flux) and alloy powder. Build-up welding methods such as manual arc welding, oxyacetylene flame welding, tungsten argon arc welding, automatic submerged arc welding and plasma arc welding are adopted.
 
The selection of build-up welding materials for the valve's sealing surfaces is generally based on use temperature, working pressure, corrosiveness of media, types of valves, structure of sealing surfaces, sealing specific pressure, allowable specific pressure, or production and manufacturing conditions of the company, processing capacity of the equipment, build-up welding technology and users' requirements. Optimal design should also be adopted. Sealing surface materials with low prices, simple production processes and high production efficiency should be selected on condition that the performance of the valve is met.
 

Materials used for the build-up welding of the valve's sealing surfaces have only one form, that is,  electric welding rods or welding wire or alloy powder. Therefore, only one build-up welding method can be used. Some materials can have many forms such as electric welding rods, welding wire and alloy powder. For example, stellite 6 alloy can be used to produce electric welding rods (D802), welding wire (HS111) and alloy powder (PT2102), and build-up welding methods such as manual arc welding, oxygen Acetylene flame welding, argon tungsten arc welding, wire feeding plasma arc welding and powder plasma arc welding can be selected. When choosing the build-up welding material for the sealing surface of the valve, we should choose the build-up welding method with mature technology, simple process and high production efficiency so as to ensure the performance of the build-up welding on the sealing surface.
 
The sealing surface is a key part of the valve, and its quality directly affects the service life of the valve. Reasonable selection of materials of the valve's sealing surfaces is one of the important ways to improve the service life of the valve. The following misunderstanding should be avoided when the sealing surface material of the valve is selected:
 
Misunderstanding 1: When the hardness of the valve's sealing surface material is good, its wear resistance is good.
Experiments show that the wear resistance of the valve's sealing surface material is determined by the structure of the metal material. A small amount of metal with hard phase structure is added for some metal whose matrix is austenite; although the hardness is not very good, the wear resistance is very good. The valve requires certain good hardness for its sealing surfaces to avoid being scratched by hard debris in the medium. The hardness value of the valve should be between HRC35 and 45 after overall consideration.
 
Misunderstanding 2: The material of the valve's sealing surface has high price, and the valve has good performance.
The price of a material is its own commodity characteristics, while the use performance of a material is its physical characteristics. There is no necessary connection between the two. Cobalt in the cobalt based alloy is imported and its price is high, resulting in the price of cobalt based alloys being high. Cobalt based alloys are characterized by good wear resistance in high temperature, but when they are used in normal and medium temperature conditions, their price or performance is relatively high. When the valve's sealing surface materials are chosen, materials with relatively low price or performance should be selected.
 
Misunderstanding 3: If the valve's sealing surface material has good corrosion resistance in a  much corrosive medium, it must be suitable for other corrosive media.
The corrosion resistance of metal materials has a complex mechanism. A material has good corrosion resistance in a much corrosive medium, but if the conditions change slightly, such as changes in temperature or medium concentration, the corrosion resistance will change. For another corrosive medium, its corrosion resistance changes more. The corrosion resistance of metal can only be known through experiments. You must know the relevant conditions before using the related information for reference, and don't blindly choose anything.