Pipeline welding issues
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Under what circumstances do pipeline welders need to make cuts, and when is TIG welding for root pass required? What are the requirements for making a break and for TIG backing, and what is their significance? I hope to receive guidance from all the teachers! Thank you! (Switching off for maintenance right away; I need to supervise it.)
It is the technical staff who determine the plan; supervision only needs to ensure that they follow the procedures~~~
You can refer to the appendix of the standard GB50236. Grooves are created because the pipes are too thick to be fully welded through; therefore, V-shaped or U-shaped grooves are used, with the type of groove determined by the thickness of the pipe wall. TIG welding is used for root pass welding in order to ensure weld quality and a high standard for the inner surface of the weld; after all, TIG welding is superior to electric welding.
In short, if you want to carry out construction, please provide the welding procedure documents. . . . This includes what welding method to use, what type of groove to prepare, and what welding materials to employ. . Wait
I also read what others have written; failing to create grooves can lead to a decrease in strength parameters, to the point where they don’t meet the required standards. Cracks may appear during bending tests, which in turn means that the performance of the welded joints cannot be guaranteed, posing a potential risk to the safety of the structure. The size of the root edge of the groove should not exceed 6 mm. During docking, when the plate thickness exceeds 6 mm, a groove must be prepared for welding. Furthermore, TIG welding for the root pass produces almost no slag and has a high success rate, which ensures the safe operation of process instrumentation and equipment.
The preparation of grooves involves determining whether flaw detection is required for the pipeline – basically, grooves need to be prepared on all pipelines!
Argon arc backing is used to ensure a smooth inner surface. When welding stainless steel pipes, argon gas is also used as a shielding gas to prevent oxidation of the inner surface during welding, thus maintaining the purity of the pipes!
1. Beveling the edges and leaving a certain alignment gap is done to ensure complete penetration; if the weld does not penetrate completely, it will lead to a decrease in the strength of the welded joint as well as stress concentration. This is considered a welding defect in welding, known as \"incomplete penetration.\" Welding without bevels but with a gap left instead is actually also a type of bevel; in welding terminology, it is called an “I-bevel”. 2. TIG welding for the root pass, followed by MIG welding for the fill and finish passes, is a welding process used in pipelines that require flaw detection; it is known as TIG-MIG hybrid welding. During root welding, the gap at the groove is small; if the welding parameters are not properly controlled, it can lead to slag not being able to float to the surface in time, resulting in defects such as slag inclusions and lack of fusion. Additionally, since there is no protection on the back side of the weld during manual arc welding, pores are likely to form. In TIG welding, argon gas is used for back-side shielding, which ensures adequate protection of the back side of the weld pool. TIG welding does not involve the use of flux, so there is no risk of slag inclusion. Additionally, the high current density facilitates thorough penetration of the material. It fully ensures the welding quality of the root weld.