seamless steel pipes have hollow sections, and are applied to pipes for conveying fluids in quantity, such as pipes for conveying petroleum, natural gas, coal gas, water and some solid materials. Compared with round steel and other solid steel materials, steel pipes have lighter weight at the same bending and twisting strength, belong to economic section steel materials, and are widely used for manufacturing structural parts and mechanical parts, for example, annular parts of oil drill rods, automobile transmission shafts, bicycle frames, steel scaffoldings used in building construction and so on are manufactured by steel pipes, which can improve the material utilizing rate, simplify manufacturing processes and save materials and processing time, and have been widely manufactured by steel pipes.