There are 9 kinds of weling process of welded steel pipe:

1.High frequency resistance welding
Using the skin effect of high frequency current and the proximity effect, the edge of the strip of steel billet is quickly heated to reach the molten state, and the molten metal is squeezed and pressed by the squeezing roller to achieve welding. 

2.Submerged arc welding
Arc welding arc welding method in the coverage of the flux. The weld metal pool is solidified into a weld under the protection of the flux coating, and the flux melt layer cools to the slag shell over the outer surface of the weld. 

3.Tungsten inert gas welding (TIG)
The use of pure tungsten or activated tungsten (thorium tungsten, cerium tungsten, etc.) as the electrode of the inert gas welding tungsten inert gas shielded welding, the English referred to as TIG welding. It is under inert gas protection, the use of tungsten arc welding electrodes generated between the hot-melt parent metal and filler wire welding method. 

4.Melting inert gas welding (GMAW)
The use of welding wire for the inert gas welding electrodes. 

5.CO2 gas shielded welding
With a purity of> 99.8% of CO2 as a protective gas welding gas arc welding.

6.Mixed gas welding
By two or more gases, according to a certain percentage of mixed gas as a protective gas gas shielded welding. TIG welding: gas shielded welding using argon as the shielding gas. 

7.Pulse TIG
The use of base current to maintain the main arc of the ionization channel, and periodically add a pulse of the same polarity of high peak pulse current pulse to melt the molten metal and control the transition of argon arc welding.

8.Plasma arc welding
With the help of water-cooling nozzle's restraining action on the arc, a plasma arc with higher energy density can be welded. 

9.Hot brazing
In the welding process, a metal material with a lower melting point than that of the base metal is used as a brazing filler metal, the weldment and the brazing filler metal are heated to a temperature higher than the melting point of the brazing filler metal and lower than the melting point of the base metal, wetting the base metal with the brazing filler metal, gap and mutual diffusion with the parent material to achieve the method of connecting the weldment is called brazing. Commonly used composite brazing method for induction brazing.