Seamless steel pipe and welded steel pipe (seamless pipe) two categories. According to the shape of the cross-section can be divided into round tubes and shaped tubes, widely used round steel tube, but there are also some square, rectangular, semi-circular, hexagonal, equilateral triangle, octagonal and other special-shaped steel. For steel pipes subject to fluid pressure, hydraulic tests are required to test their pressure resistance and quality. No leaks, soaks, or expansions are acceptable under specified pressures. Some steel pipes are also subjected to crimping tests according to standards or demand-side requirements. , flaring tests, flattening tests, etc.