How does resistance welded pipe achieve welding through resistance heating?
Resistance welded pipe uses the resistance heat generated when current passes through the edge of metal strip for welding. When high-frequency current passes through the edge to be welded, the local temperature rises rapidly to a molten state due to the contact resistance and material resistance. Under the action of the pressure roller, the molten metal is squeezed to form a weld. The whole process does not require filling materials, and the welding speed is fast and efficient. This process is suitable for continuous production and is widely used in pipeline manufacturing.
What is the difference between high-frequency resistance welding (HFW) and ordinary resistance welding?
High-frequency resistance welding (HFW) uses high-frequency current (usually 100-800kHz), and the skin effect concentrates heat on the surface of the material, with faster welding speed and smaller heat-affected zone. Ordinary resistance welding uses low-frequency current, with a larger welding depth but lower efficiency. HFW welds have higher quality and are suitable for thin-walled pipes and precision pipe production. In addition, HFW has lower energy consumption and has become the mainstream process for modern welded pipes.
What are the main process steps of resistance welded pipes?
The production process of electric resistance welded pipe includes uncoiling, leveling, forming, welding, internal and external burr removal, cooling, sizing, cutting and testing. In the forming stage, the strip is rolled into a tube by multiple rollers; in the welding stage, the connection is completed by current and pressure; and the subsequent treatment ensures dimensional accuracy and surface quality. The whole process is highly automated and can continuously produce welded pipes up to hundreds of meters long.
Why do electric resistance welded pipes need to be deburred?
During the welding process, molten metal may overflow to form internal and external burrs, affecting the flow of fluid in the pipe or subsequent connection. Deburring removes excess metal by cutting or grinding to ensure the smoothness of the inner wall and the consistency of the outer diameter. In addition, burrs may become the starting point of corrosion, and removal can increase the life of the pipe. Automated deburring equipment can complete this process online to ensure production efficiency.
What factors affect the welding quality of electric resistance welded pipes?
Welding current, pressure, speed and material composition are key factors. Insufficient current will lead to incomplete fusion, and too high current may burn through; insufficient pressure will make the weld strength low, and too high pressure may cause deformation. Strip edge cleanliness and oxide content also affect welding quality. In addition, cooling rate and subsequent heat treatment have a significant impact on weld microstructure and mechanical properties.
