Stainless steel processing and welding process
In order to ensure the quality of stainless steel processing and welding, it is necessary to formulate scientific and reasonable operating procedures for the entire welding process. Let’s take a look at the stainless steel welding procedures of a certain processing plant. It should be noted in advance that it is suitable for the welding of stainless steel cladding, embedded parts and related structural parts, as well as the welding and installation of all stainless steel pipes and equipment.
The first is welding material selection, which should comply with the design drawings and design specifications.
The second is the choice of welding method. You can choose one with better applicability such as manual arc welding or filler wire tungsten arc welding.
Corresponding preparations must be made before pre-welding processing. Welding operators should have corresponding professional knowledge and skills and have corresponding qualifications. The welded joint type and groove size must also comply with the requirements of the design drawings or relevant national specifications.
The groove to be welded should be inspected and cleaned before welding. Specifically, before welding, clean the welding groove and the surrounding area of no less than 50mm on both sides of the groove to remove oil, water, oxides, dust and other harmful impurities. The method of removal can be based on the specific conditions of harmful impurities. You can use acetone scrubbing, compressed air blowing or stainless steel wire brushing to remove them. The surfaces of the welding groove and the heat-affected zone of the weld must be smooth, flat, free of burrs, slag inclusions, and cracks, and the base metal must be free of delamination and slag inclusions. In addition, corresponding measures must be taken to avoid contamination of the base metal surface by welding spatter, such as spraying anti-spatter agent, covering and blocking, etc.
When welding, you need to comply with some regulations. For example, the welding site must be protected from direct attacks by wind, rain, snow, etc. The wind speed in the manual arc welding environment is not greater than 10m/s, and the gas shielded welding is 2m/s. The welding environment humidity is less than 90%, the temperature should be higher than -10℃. The performance of the welding equipment used must be maintained in good condition, and the measuring instruments must be certified and within the validity period. The contact between the welding power source and the component must be reliable, and the base metal cannot be damaged due to poor contact. To prevent arc ignition and quenching on the base metal outside the welding groove, if necessary, add arc ignition and quenching plates identical to those of the base metal at the beginning and end of the weld.
Before spot welding, the assembly gap, misalignment, etc. should be adjusted and inspected. Spot welding uses welding methods and processes consistent with actual construction. Stainless steel welded parts can be grooved using machining or a plasma cutting machine combined with a polishing machine. The groove surface must be kept smooth and assembled according to the drawing requirements. You can use a stainless steel wire brush to clean the groove surface and within 50mm on both sides; when using argon arc welding, acetone should also be used to scrub; when manual arc welding, anti-spatter agent should be brushed on both sides of the groove.
When processing and welding stainless steel, in order to control the welding stress and post-weld deformation, the welding sequence and specific requirements of the component welds must be implemented according to the construction plan or procedure and the welding process card. For single-sided welding and double-sided forming, priority should be given to using argon arc welding for the base and manual arc welding for the filling. When argon arc welding is performed, argon gas protection measures should be used on the reverse side. When double-sided welding, before back-sealing welding, grinding with a grinding wheel is required to remove root defects. In the case of multi-layer welding, low heat input should be used to prevent the lateral swing of the welding arc, the welding layer should be thin, and the interlayer temperature between welding passes should not be higher than 150°C, thereby reducing local overheating of the weldment. In multi-layer welding processes, visual inspection is required after each layer is welded to remove welding defects that will affect subsequent weld passes. The starting and ending points of each layer of passes should be staggered as much as possible, and the connection of the welding beads should be maintained with a smooth transition. When performing argon arc welding, the principle of supplying gas first, then starting the arc, and then extinguishing the arc and then stopping the gas is followed. The purity of the argon gas should be greater than 99.9%. During the entire process of weld assembly and welding, the contact between stainless steel and carbon steel should be strictly controlled. Stainless steel gaskets and wooden boards can be used for isolation, or paint can be painted on the surface of carbon steel for isolation. When removing defects, special tools for stainless steel construction should be used to avoid ferrite contamination. After welding is completed, the welder must carefully clean the weld surface and submit it for inspection.
