TIG welding for root pass
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When welding pressure pipes, TIG welding is commonly used as the root pass. What impact does TIG welding as the root pass have on the material? Why can’t it be welded directly with a welding machine?
It seems the poster is a beginner; it’s a basic common-sense question. There is a lot of information on TIG welding available online and on forums: http://bbs.hcbbs.com/thread-365426-1-1.html http://baike.baidu.com/view/1196898.htm I hope this helps!
Using TIG welding for the root pass is primarily to prevent the formation of impurities such as slag inside the pipe, which could affect pipeline purging and subsequent production.
I won’t talk about theories here; I’ll instead discuss things based on actual on-site situations. TIG welding is used for the root pass, and manual welding for the finish pass; this welding method yields high quality results. TIG welding produces fewer sparks than manual welding, making it safer. TIG welding can be used to weld very thin pipes, something that is sometimes difficult to achieve with manual welding. TIG welding has high economic costs; it produces a nice appearance, and the radiographs show well-organized images. The main defects that occur are lack of fusion or incomplete penetration, and these defects tend to be long in length. The above are my own summaries from being on site; if there are any shortcomings, I hope everyone can point them out so we can exchange ideas and learn together*