To ensure leak-proof welds on stainless steel hot water pipes, comprehensive control is needed across multiple aspects, including welding process, material selection, operating procedures, post-weld treatment, and inspection and maintenance.
Welding process is fundamental. When welding stainless steel hot water pipes, argon arc welding should be prioritized due to its stable arc and concentrated heat, which reduces impurities in the weld and improves weld quality. For thicker stainless steel hot water pipes, a combination of argon arc welding for the root pass and manual arc welding for the fill and cover passes can be used. The root pass ensures root penetration, while the fill and cover passes ensure weld formation and strength. During welding, the interpass temperature must be strictly controlled, generally below 150℃, to avoid coarse weld grains caused by excessive temperature, which reduces corrosion resistance and mechanical properties. Simultaneously, a lower heat input should be used to reduce the heat-affected zone and prevent cracking due to excessive thermal stress.
Material selection is equally crucial. High-quality stainless steel matching the base material should be used for both the stainless steel hot water pipe and the welding materials to ensure consistent chemical composition and mechanical properties. Welding wire must be clean, and welding rods must be baked to remove moisture and impurities, preventing defects such as porosity during welding. For example, ultra-low carbon or stabilizer-free filler materials can prevent intergranular corrosion and improve the corrosion resistance of the weld. Furthermore, use specialized grinding wheels and stainless steel tools for cutting and grinding, avoiding direct flame heating to protect the corrosion resistance of the stainless steel.
Operating procedures are crucial. Before welding, the bevel must be finely machined and cleaned. The machining dimensions, precision, and surface quality of the bevel should meet relevant standards. The bevel surface and at least 200mm on both sides should be thoroughly cleaned to remove burrs, slag, rust, oil, oxide film, paint, and other harmful foreign matter. For materials with high requirements, non-destructive testing, such as dye penetrant testing, is also necessary to detect and remove defects such as cracks. During assembly, the assembly gap should be controlled within 1.5-2mm. TIG welding with three-point tack welding should be used, with weld points at the 3 o'clock, 9 o'clock, and 12 o'clock positions, and a weld length of 10-15mm. Thorough penetration and no defects are required, with misalignment not exceeding 1.5-2mm. Forced assembly is prohibited. The inner walls of the joint must be flush. Tack welding must be free of air, slag inclusions, tungsten inclusions, and cracks.
Post-weld treatment improves quality. After welding, the weld should be ground, pickled, shot-peened, brushed, or polished to remove residue and weld discoloration, resulting in a bright surface and improved corrosion resistance. Simultaneously, a pressure test should be conducted to confirm no leakage before use. Pressure testing verifies the sealing and strength of the welded joint and is a crucial step in ensuring welding quality.
Environmental factors must also be considered. The welding environment should be well-ventilated, free of flammable and explosive materials, and with clean and unobstructed passageways. Welding should not be performed when the relative humidity of the welding environment exceeds 90% or the wind speed exceeds 2 m/s, to avoid affecting the weld quality. For stainless steel and low-alloy steel, welding should only be performed when the temperature is below -5℃, and for carbon steel, when the temperature is below -20℃, with appropriate measures taken.
Regular inspection and maintenance can extend the service life. During use, welded joints in stainless steel hot water pipes require regular inspection and maintenance to promptly identify and address potential leaks. For example, non-destructive testing methods, such as radiography or ultrasonic testing, can be used to randomly inspect the welds to ensure that the weld quality consistently meets standard requirements.
