Butt welded flange

Butt welding flange is a type of pipe fitting, which refers to a flange with a neck and a circular pipe transition, and is connected to the pipe by butt welding

Welding flanges are not easy to deform, have good sealing, and are widely used. They have corresponding rigidity and elasticity requirements, and reasonable welding thinning transitions. The distance between the welding junction and the joint surface is large, and the joint surface is not affected by welding temperature deformation. It adopts a relatively complex horn shaped structure, suitable for pipelines with large pressure or temperature fluctuations or pipelines with high temperature, high pressure, and low temperature. It is generally used for connecting pipelines and valves with PN greater than 2.5MPa; It is also used on pipelines for transporting expensive, flammable, and explosive media

1. The level and technical requirements of welding flanges should comply with the corresponding requirements of JB4726-4728. 1. Carbon steel and austenitic stainless steel forgings with a nominal pressure PN of 0.25MP-1.0MPa are allowed to use Grade I forgings. 2. Except for the following provisions, forgings with a nominal pressure PN of 1.6MPa-6.3MPa shall meet the requirements of forging grade II or above. 3. If one of the following conditions is met, it should meet the requirements of III and forgings: (1) flange forgings with a nominal pressure of PN ≥ 10.0MPa; (2) Chromium molybdenum steel forgings with a nominal pressure PN greater than 4.0 MPa; (3) Ferritic steel forgings with a nominal pressure PN greater than 1.6 MPa and a working temperature of ≤ -20 degrees Celsius

Secondly, butt welded flanges are generally made using forging or forging and rolling processes. When using steel plates or profiles for manufacturing, the following requirements need to be met: 1. Welding flanges should undergo ultrasonic testing and have no delamination defects; 2. It should be cut into strips along the direction of steel rolling, bent and welded into circular rings, and the surface of the steel should form cylindrical rings. Steel plates shall not be directly machined into neck welded flanges; 3. The butt weld of the circular ring should be a full penetration weld; 4. The butt weld of the circular ring should undergo post weld heat treatment and undergo 90% radiographic or ultrasonic testing, and the radiographic testing should meet the level II requirements of JB4730, while the ultrasonic testing should meet the level I requirements of JB4730

3. The outer slope of the neck of the welding flange should not exceed 70 °. Strict control of technical parameters during production and welding of butt welded flanges ensures that protection can fully play its role and value in production and use