Material: Weld neck flanges are made from thick ordinary steel plates, while slip on flanges are primarily made from forged steel parts.

Weld Type: Welds in weld neck flanges cannot be inspected by radiographic testing, while slip on flanges can. The welding method between the pipe and flange in a weld neck flange is a fillet weld, while the welding method between the weld-on-neck flange and pipe is a circumferential weld. Slip-on flanges use two fillet circumferential welds, while weld-on-neck flanges use a butt circumferential weld.

The difference between weld-on-neck flanges and slip on flanges lies in the weld joint. Weld-on-neck flanges have one more weld joint than slip on flanges. Slip on flanges use fillet welds, and the flange boss also uses a fillet weld. The weld between a weld-on-neck flange and a pipe is a Class B weld, while the weld between a weld-on-neck flange and a pipe is a Class C weld.

The connection methods differ: The structural difference between slip-on flanges and weld neck flanges lies in the connection method between the pipe and the flange. Slip-on flanges are generally connected via flange angles, while weld neck flanges are connected to the pipe by a butt joint.

The nominal pressures differ: Slip-on flanges have a nominal pressure range of 0.6~4.0 MPa, while weld neck flanges have a nominal pressure range of 1~25 MPa.

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