Difference between Weld Neck Flange and Slip On Flange

Slip On Flange is a flange that extend steel pipes, fittings, etc. into flanges and connect to equipment or pipes through fillet welds. Inserting steel pipes or fittings into flanges connected to equipment or pipes by fillet welds. It can be used in pipes with higher pressures because short necks increase the strength of the flanges and improve the bearing capacity of the flanges. Slip On Flange is a part of connect pipes to pipes. There are holes in the flange. Bolts connect the two flanges  tightly. Flange connection refers to the removable connection composed of flanges, gaskets and bolts, which are connected together as a group of combined sealing structures. Pipe flange refers to the flange for distribution piping in the piping device. For equipment, it refers to the inlet and outlet flanges of equipment, and the flanges are sealed with gaskets.

Weld Neck Flange is a flange with a neck and transition from a round pipe to a butt-welded tube. The weld neck flange is not easy to deform and seal well. It has corresponding rigidity and elasticity requirements and reasonable butt-weld thinning transition. The distance between the weld joint and the joint surface is large and the joint surface is free from welding temperature deformation. The weld neck flange is butt-welded to the pipe in a manner similar to that of the pipe and pipe. It is suitable for pipelines with high pressure or temperature fluctuations or for pipelines with high temperature, high pressure and low temperature, as well as for pipelines conveying petroleum, chemicals, flammable and explosive media.

Difference between Weld Neck Flange and Slip On Flange

• Structural differences: Slip On Flange is a recess machined in the inner hole slightly larger than the outer diameter of the pipe. Weld Neck Flange is the same diameter and wall thickness of the joint end as the pipe to be welded.

• The welding seams are different: The fillet weld is used for the Slip On Flange, while the circumferential weld is used for the Weld Neck Flange. Flat welding and butt welding refer to the welding method when connecting flanges and pipes. Flat welding flanges need only one side welding without welding the inner opening of pipes and flange connections. Flange double side welding is required for welding and installing butt welding flanges.

• Material difference: The material of Slip On Flange is made of ordinary steel plate with required thickness, the material of Weld Neck Flange is made of forged steel parts.

• Nominal pressure is different: For Slip On Flange, the nominal pressure is 0.6 - 4.0MPa,  for Weld Neck Flange, the nominal pressure is 1 - 25MPa. Slip On Flange is suitable for medium and low pressure, Weld Neck Flange is suitable for high pressure

• The NDT is different: The welds between Weld Neck Flange and joint with neck belong to Class B. The welds between Slip On Flange with neck and joint with neck belong to Class C. The NDT after welding is different.

• Product testing is different: Slip On Flange and Weld Neck Flange can not be replaced casually. In terms of manufacturing angle, large inside diameter of Slip On Flange means small weight and low cost. In addition, Weld Neck Flange whose nominal diameter is more than 250mm need to be tested, but Slip On Flange does not need to be tested.

Connecting Surface

The connecting surface of Weld Neck Flange and Slip On Flange:

• Raised Face 

• Male Face 

• Female Face 

• Tongue Face

• Groove Face

• Ring Joint Face

• Flat Face

Pressure Rating

The pressure rating of Weld Neck Flange and Slip On Flange:

• Class 150lb

• Class 300lb

• Class 400lb

• Class 600lb

• Class 900lb

• Class 1500lb

• Class 2500lb