Problems with welding refrigerant stainless steel pipelines
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For DN150 refrigerant stainless steel pipelines, 100% RT non-destructive testing is required. Previously, TIG welding was used for the root pass and shielded metal arc welding for the cover pass, but inspection revealed that many welds did not meet the requirements; later, all TIG welding was employed and the tests were passed successfully. But recently, the supervisor stated that it is not allowed to use argon arc welding throughout; instead, argon arc welding should be used for the base layer while welding with electric welding for the top layer. Do any of you have relevant standards or guidelines that I can refer to? Is the problem with our welders’ skills, or is the supervisor’s opinion incorrect? Thank you.
The selection of pipeline welding methods is usually specified in the design documents. Since the cleanliness requirements and strength requirements for welding joints vary depending on the type of pipeline, general standards do not provide specific details on this matter. For DN150 pipes, argon-electric welding should be used (this is especially required for pressure pipes), as the strength achieved through pure TIG welding is not as high as that obtained with argon-electric welding ； Additionally, the pass rate for X-ray inspections of TIG welding performed by welders is low; if there is no issue with the welder’s skill level, then it must be a problem with the welding materials or the welding parameters. Moreover, the groove gap and the levelness of the pipe ends when they are aligned also affect the welding parameters.
What’s most strange is that it isn’t mentioned in the design specifications; when asked, the design institute replied that it 【depends on the constructor】{:3_54:}
It is carried out in accordance with the welding procedure cards prepared by the welder’s engineer on site; the welder cannot just weld however he wants, nor can welding be prohibited simply because the supervisor says that all welding must be done using TIG welding. Get out the welding procedure card and weld it according to the instructions; the supervisor can’t say anything about it. No such card? Won’t the supervisor take action? It’s just garbage supervision.