Research on Root Pass Welding Process of Flat Welding Position for Hydrogen Pipeline Narrow Bevel TIG Automatic Welding

The use of TIG automatic welding for root pass welding is one of the effective technical means to improve the efficiency of hydrogen pipeline laying. In response to the special process requirements for hydrogen pipelines, an automatic welding test platform was established. Using TIG automatic welding for the root pass welding, narrow bevel welding tests were conducted on X52 pipeline steel in flat welding position. Based on the single-factor method and the response surface method, the influence law of wire feeding speed, welding speed and welding current on the weld seam forming was investigated. The results show that, under conditions that meet the matching accuracy requirements, when the wire feeding speed is 6.5 m/min, the welding speed is 13 cm/min, and the welding current is 145 A, the root pass weld bead is aesthetically pleasing, consistent, and free of obvious defects such as incomplete fusion or lack of penetration. The specific effects of these parameters on the weld formation are as follows: increasing the wire feed rate increases the thickness of the root pass and the penetration depth; increasing the welding speed reduces the heat input, which can lead to uneven fusion on the side walls and lack of penetration, thereby affecting the formation of the back-side weld; increasing the welding current promotes single-sided welding with double-sided formation to a certain extent, but excessive high current can cause defects such as droplet sagging or even burn-through.