Abstract: When oil and gas pipelines were welded in all-positions,on which subsection was usually carried out mechanically at a fixed angle.During this process,the molten pool was prone to instability and flow,resulting in poor formation of weld.The force of the molten pool during the all-position welding process was analyzed in this paper,and a new subsection process based on the change of the radial force of the molten pool was established to solve the problem of poor formation in the inner and outer walls of the pipeline during all-position welding.Through the STT bottom welding test for 220 mm×10 mm×400 mm X70 pipeline steel,it was found that this subsection process had a good effect on suppressing the instability and flow of the molten pool during all-position welding,and the inner wall formed more smoothly and beautifully,which was suitable for automatic pipe welding.The subsection problem in the process had a certain reference value.Highlights:According to the change of radial force in molten pool,a new section process was proposed,formation in the inner and outer walls of the pipeline was more stable and instability tendency decreased in the section process.