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Stainless steel tee welding connection, need to pay attention to the following issues before welding, welding process and after welding:
Before welding
Material inspection: confirm that the material and specifications of the stainless steel tee and pipe meet the design requirements, check the quality certification documents of the material, and ensure that the chemical composition and mechanical properties of the material meet the requirements for use. At the same time, check the material surface for cracks, pores, slag and other defects, if any defects should be treated or replaced.
Beveling: According to the wall thickness of tee and pipe, choose the suitable form of beveling, such as V-type, U-type and so on. Bevel processing should ensure accurate size, flat surface, no burrs and oxides to ensure good fusion during welding.
Cleaning and protection: Before welding, you need to use acetone, alcohol and other organic solvents to clean up the welding parts and nearby surfaces of oil, rust, moisture and other impurities, to prevent these impurities in the welding process to produce porosity, slag and other defects. At the same time, in order to prevent the welding process generated by the spatter damage to the stainless steel surface, can be coated with anti-spatter agent near the welding parts.
Welding equipment and materials preparation: according to the material of stainless steel and welding process requirements, select the appropriate welding equipment, such as argon arc welding machine, welding rod arc welding machine. Welding materials such as welding rods, wires, etc. should be matched with the base material, and the quality should meet the requirements of the relevant standards. For example, when welding 304 stainless steel tee, usually use ER308L or E308L-16 and other types of wire or welding rod.
Welding process
Welding parameter selection: according to the wall thickness of stainless steel tee and pipe, material and welding position and other factors, reasonable selection of welding current, voltage, welding speed and other parameters. Generally speaking, when welding stainless steel, the current should not be too large, so as not to cause overheating, resulting in coarse grain, reducing the performance of the welded joints; welding speed should be moderate, too fast may lead to poor weld molding, too slow will make the heat-affected zone expansion.
Welding techniques: the use of correct welding techniques, such as argon arc welding, should maintain the welding torch and the surface of the weldment angle and distance uniformity, wire feeding speed to match the welding speed to ensure that the weld is formed beautiful and stable quality. For thicker weldments, multi-layer multi-channel welding can be used, the thickness of each layer of the weld should not be too thick, and pay attention to the interlayer cleanup, removal of slag and spatter before the next layer of welding.
Argon protection: To prevent stainless steel from being oxidized during the welding process, especially for some important pipelines or weld quality requirements of high occasions, the need for argon protection during welding. That is, before welding, to the tee and pipe internal argon gas, exclude the air, in the welding process, to maintain a continuous supply of argon gas, so that the weld metal in the argon protection under the cooling solidification, so as to obtain good welding quality.
After welding
Weld appearance inspection: after welding is completed, first check the appearance of the weld to see if the weld is well formed, with or without biting edges, pores, cracks, unfused and other defects. The surface of the weld should be smooth, the transition should be even, and the width and residual height of the weld should meet the requirements of relevant standards. If there is any appearance defect, it should be repaired in time.
Non-destructive testing of weld: According to the requirements of pipeline use and relevant standards, non-destructive testing of weld, such as ray testing, ultrasonic testing, magnetic particle testing, etc., in order to detect whether there are defects inside the weld. Nondestructive testing should be carried out after the weld is cooled down to room temperature, and the test results should meet the corresponding quality acceptance standards.
Weld heat treatment: For some thick-walled stainless steel tees or occasions with high performance requirements for welded joints, post-weld heat treatment may be required. The purpose of heat treatment is to eliminate welding residual stress, improve the organizational properties of the weld and heat-affected zone, and improve the toughness and corrosion resistance of welded joints. Common heat treatment methods are high temperature tempering, solution treatment, etc., the specific treatment process should be determined according to the material and welding process.
Surface treatment: after the completion of welding, the weld and nearby areas should be surface treatment, such as pickling, passivation and so on. Pickling can remove the oxide skin and impurities on the surface of the weld, passivation can form a dense passivation film on the surface of stainless steel to improve the corrosion resistance of stainless steel. After surface treatment, the surface should be cleaned to avoid residual acid and other corrosion of stainless steel.