Classification of steel pipes: steel pipes are divided into two categories: seamless steel pipes and welded steel pipes (with seam pipes). According to the shape of the section, it can be divided into round pipes and special-shaped pipes. Circular steel pipes are widely used, but there are also some square, rectangular, semi-circular, hexagonal, equilateral triangle, octagonal and other special-shaped steel pipes. For steel pipes subjected to fluid pressure, hydraulic tests are carried out to check the pressure resistance and quality. No leakage occurs under the specified pressure. Wetting or expansion is qualified. Some steel pipes are also subjected to the crimping test according to the standard or the requirements of the purchaser. Flaring test, flattening test, etc.