Optimization of TIG surfacing process parameters for inner wall of small diameter steel pipe and microstructure and properties of surfacing layer

Objective The aim is to improve the corrosion resistance of the pipeline by optimizing the process parameters of tungsten inert gas welding (TIG) surfacing on the inner surface of small diameter steel pipes. Methods The TIG surfacing process for the inner wall of low-carbon steel pipe with a inner diameter of 76 mm is optimized through orthogonal experiments, and the microstructure and corrosion resistance of the surfacing layer are studied. Results The optimal parameters are obtained, such as 160 A welding current, 150 mm/min welding speed and 1.8 m/min wire feeding speed. Research results on microstructure and corrosion resistance shows that a sensitized zone is formed within each weld pass of the surfacing layer due to the thermal influence of the subsequent weld pass. In the sensitized zone, the precipitation of σ phase and secondary austenite phase take place, the content of ferrite phase significantly decreases. The pitting corrosion during electrochemical corrosion testing mainly occurs in the sensitized zone. The Cr content, ferrite phase content and corrosion resistance on the surface of the surfacing layer are significantly higher than those inside the surfacing layer. Conclusion No noticeable corrosion weight loss is observed on the surface of surfacing layer deposited with the optimized process parameters after immersion corrosion test.