1. General requirements for materials
The materials of the valve body, bonnet, and flange should be selected according to the conditions of use and manufacturing requirements, and should meet the requirements of GB 12228, GB 12229, GB 12230 and GB 3077.
The materials of nuts, bolts and studs can be A5, 25, 35, 30CrMoA and 40MnVB, etc., which should be selected according to the working pressure and temperature, and should meet the requirements of GB 700, GB 699 and GB 3077.
Precision castings shall not be used for valves with a nominal pressure PN> 10.0MPa.
It should be noted that the material may graphitize in the following situations:
When carbon steel is higher than 425℃;
Carbon-molybdenum steel is about higher than 470℃;
Chrome-molybdenum steel (containing less than 0.6% chromium) is approximately above 525°C.
In the following situations, attention should be paid to the possible peroxygen reaction (scaling):
1Cr-0.5Mo steel, 1.25Cr-0.5Mo steel, 2Cr-1Mo steel and 3Cr-1Mo steel above 565℃
5Cr-0.5Mo steel above 595℃
2. Regulations on the selection of materials for main parts
The material of the main parts of the carbon steel valve with the medium temperature of -20~425℃ shall meet the requirements of "Table 1".
The material of the main parts of the alloy steel valve whose temperature is lower than or equal to 540℃ shall meet the requirements of "Table 2".
The main materials of alloy steel valves whose temperature of the conveying medium is lower than or equal to 550℃ shall meet the requirements of "Table 3".
The material of the main parts of the stainless, acid-resistant steel valve whose temperature is lower than or equal to 200℃ shall meet the requirements of "Table 4".
The sealing surface material of the wedge gate valve that is used for A and B grade pipelines and frequently opens and closes should be made of cemented carbide.
If there are special requirements for the main parts and materials of the pipeline valves for transporting corrosive media, they should be put forward when ordering.
The alloy steel and stainless steel valve bracket material separated from the bonnet should be carbon steel or determined according to order requirements.
Manufacturers of valve packing and gaskets must conduct performance tests on their products by the relevant seal inspection unit, and the technical performance should meet the following requirements:
The surface of the gasket body should not have defects such as scars, unevenness and rust spots;
The non-metallic belt should protrude evenly from the metal belt, and should be smooth and flat;
The gasket shall not be pre-pressed or processed, and the solder joints shall not have defects such as false welding and over-burning.