Like the API steel pipe, the high frequency welding of seamless steel pipes uses the skin effect of alternating current and adjacent effect. After rolling forming, the steel gets the formation of a cross section of broken circular tube billet. There is a set of rotating impedance in the middle of the tube billet inside near the induction coil. And the electromagnetic induction loop is around impedance and tube billet. Under the action of skin effect and the adjacent effect of tube, the powerful and concentrated heat effect is produced at the edge. This can make the welding edge rapidly heated to the temperature required by roller extrusion. Welding metal of the API steel pipes of the molten state will realize the joint between the crystals. After cooling it can form a firm butt weld.

There are two main types of weld physical seamless processing methods: weld local processing method and the overall heat treatment method. Weld local processing method is more suitable for large diameter steel pipe for two reasons: weld local heating can significantly save energy; when welded steel pipe diameter is larger, the weld tracking is easier. Because there are hardening phenomena in the weld heat affected zone and low mechanical properties, the first thing we should consider for is the weld local processing method. This kind of method is to use medium frequency induction heating equipment to weld heat affected zone to 927 degrees Celsius, and then air cooling below 538 degrees Celsius. Finally add water if necessary.

For small diameter API steel pipes, we can adopt the method of medium frequency induction or flame heating tube billet heated to 900 degrees Celsius, then make the air cooling or cooling in the cooling chamber with a controlled atmosphere. The welded steel pipe and black steel pipe are also available. Through the weld heat treatment, the welded pipe is physical seamlessly to eliminate stress, homogenization and refine the organization, improving comprehensive mechanical properties of welding heat affected zone. Seamless pipe welding technology needs good control during welding and it should ensure the welding quality of steel pipe quality and function of the subject. It can exert the important role and value in use.