The steel pipe has a hollow section and its length is much larger than the diameter or circumference of the steel. According to the cross-sectional shape, it is divided into round, square, rectangular and special-shaped steel pipes; according to the material, it is divided into The inner and outer surfaces of the pipeline must be smooth, free of cracks, cracks, material coverage, and non-metallic inclusions. After removing the defects generated in the production process, small scratches, bumps, dents, thin layers of welding slag or traces are allowed to prevent the wall thickness from falling to the minimum allowed range. The weld must be compact, continuous, and free of cracks or other defects, which will reduce the weld resistance of the base metal.