Seamless steel pipe is made of whole metal and has no seams on its surface. According to the production method, seamless pipe is divided into hot-rolled pipe, cold-rolled pipe, cold-drawn pipe, extruded pipe, pipe jacking and so on. According to the cross-section shape, seamless steel pipe can be divided into two kinds: circular and irregular. The irregular pipe has many complex shapes, such as square, ellipse, triangle, hexagonal, melon seed, star and finned pipe. The maximum diameter is 650 mm and the minimum diameter is 0.3 mm. Depending on the use, there are thick-walled and thin-walled tubes. Seamless steel pipes are mainly used for petroleum geological drilling pipes, cracking pipes for petrochemical industry, boiler pipes, bearing pipes and high-precision structural steel pipes for automobiles, tractors and aviation.