Main points of stainless steel submerged arc welding operation
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Please tell me, teachers, when our factory uses submerged arc welding to make stainless steel pressure vessels, the qualification rate of flaw detection is very low, only about 70%. I would like to ask teachers how to improve the quality of welds. Thanks
Please give me some advice, I also have a similar problem.
The defect of stainless steel that fails the flaw detection should be explained, whether it is a pore or something else. According to the form and characteristics of the defect, it should be analyzed whether it is a problem with the welding material or inappropriate welding parameters. Different defects have different causes and different treatment methods, and the specific situation must be analyzed in detail.
Some personal opinions on improving the qualification rate of non-destructive testing of stainless steel submerged arc welding: 1. The main reason is that the flux was not dried according to regulations, or was not kept well during use, especially in the rainy weather and when the air humidity is high. 2. The thermal conductivity of stainless steel is larger than that of carbon steel. The plate thickness is different and the requirements for line energy are different. The line energy must be appropriately adjusted according to the welding process evaluation. 3. The groove and weld bead must be cleaned.
When submerged arc welding of stainless steel, pores are mainly prone to occur, and cracks are less likely to occur. 1. The welding process selected must be appropriate, and the oxides, oil stains, and water in the groove must be cleaned. The flux must be baked and used according to regulations, and the surface of the welding wire should be cleaned. 2. The selection of process parameters is very important. On the one hand, it can be determined by consulting the data, and on the other hand, it can be tested through trial welding to check the shape of the weld. Generally, the ratio of penetration width to penetration depth is suitable between 1-2. Of course, after roughly determining the parameters, the welding process evaluation of the joint must be carried out. 3. The groove form and size of the joint also have an impact on the generation of pores. Since the viscosity of the stainless steel bath metal is relatively high and the fluidity is poor, which is not conducive to gas escape, the general groove angle should not be small, especially for thick plates. 4. If cracks occur, basically judging the process parameters is incorrect. 5. The submerged arc welding method of stainless steel is commonly used and is easy to master. However, when used in situations where corrosion resistance is required, the corrosion resistance of the joint needs to be evaluated. It uses a relatively larger linear energy than manual welding, lengthens the residence time in the sensitization zone, and the tendency of intergranular corrosion will be greater.
The thermal conductivity of austenitic stainless steel is much smaller than that of ordinary carbon steel, but the expansion coefficient is much larger, so thermal cracks must be prevented.