The welding process for welding B-type pipes for heater cores usually includes the following steps:
1.Welding preparation
Material cleaning: Use stainless steel wire brushes, files, and other tools to remove oil stains, rust, impurities, and other contaminants from the surface of the B-type pipe to be welded, such as the connection between the pipe end and the header, revealing a metallic luster. If necessary, organic solvents such as acetone can be used to further remove oil.
Welding material selection: Choose the appropriate welding material based on the material of the B-type pipe. For example, if it is a B-type pipe made of carbon steel material, corresponding carbon steel welding rods such as E4303 can be selected; If it is made of stainless steel material, stainless steel welding rods such as E308-16 should be selected.
Welding equipment debugging: Check whether the welding equipment is running normally, adjust the welding current, voltage and other parameters. For arc welding equipment, it is necessary to ensure that the gas flow rate is appropriate and the purity of argon gas is above 99.97%.
Groove processing: Select the appropriate groove form, such as V-shaped groove, based on the diameter and wall thickness of the B-type pipe. The dimensions of groove angle, blunt edge, and joint clearance should meet the welding process requirements. Generally, the groove surface angle is 60 °± 5 °, the blunt edge is 0-2mm, and the joint clearance is 2-4mm.
Positioning welding: Assemble the B-type pipe with components such as the header to ensure accurate positioning. Fixed by positioning welding, the length and quantity of positioning welds vary depending on the pipe diameter. When the pipe diameter is less than or equal to 100mm, the length of positioning welds should be 5-10mm, and there should be no less than 3 positioning welds; When the pipe diameter is greater than 100mm, the length of the positioning weld should be greater than 15mm.
2.Welding operation
Bottom welding: Start an arc on the surface of the groove, then bring the arc to the starting position, and weld along the weld seam after the blunt edge is melted through. Using the arc breaking method or continuous arc method for welding, pay attention to observing the size of the molten pool and the breakdown situation to ensure good fusion at the root of the weld, without defects such as incomplete penetration or slag inclusion.
Fill welding: After the base welding is completed, fill welding is performed. Single or multi pass welding can be used according to the specific situation, and continuous arc welding can be used. The strip transportation method can use crescent or sawtooth swinging, and the amplitude should be increased layer by layer. It is important to pause slightly on both sides of the groove to ensure the width and height of the weld seam, and to avoid slag inclusion caused by grooves between the weld beads.
Cover welding: When covering welding, the current used should be slightly smaller to maintain a uniform shape and size of the molten pool. The angle between the welding rod and the welding direction should be kept at around 75 °. When the welding rod swings to the edge of the groove, it should pause briefly to avoid undercutting.
3.Post weld treatment
Weld cleaning: After welding is completed, promptly clean the surface of the weld from impurities such as slag and splashes, using tools such as wire brushes and grinding machines for cleaning.
Appearance inspection: Check whether the appearance of the weld meets the requirements. The weld should be uniform, smooth, and free of defects such as pores, cracks, undercutting, and lack of fusion. The excess height of the weld should be within the specified range, generally 0-2mm, and locally not higher than 3mm. The width of the cover weld should be 0.5-2.0mm wider on each side of the groove opening.
Non destructive testing: According to relevant standards and requirements, non-destructive testing is carried out on welds, such as magnetic particle testing, penetrant testing, or ultrasonic testing, to check for defects inside the weld.
Heat treatment: If the material of the B-type pipe is high alloy steel or other materials that are prone to welding stress, or if the welding process requires heat treatment, the weld seam needs to be heat treated, such as tempering, normalizing, etc., to eliminate welding stress and improve the mechanical properties of the weld seam.
