Seamless steel pipes are widely used. General-purpose seamless steel pipes are rolled from ordinary carbon structural steel, low-alloy structural steel or alloy structural steel, and have the largest output. They are mainly used as pipelines or structural parts for conveying fluids. 2. According to different purposes, it is divided into three types of supply: a. According to chemical composition and mechanical properties; b. According to mechanical properties; c. According to water pressure test. For steel pipes supplied in accordance with category a and b, if they are used to withstand liquid pressure, they shall also be subjected to a hydraulic test. 3. Special-purpose seamless pipes include seamless pipes for boilers, chemical and electric power, seamless steel pipes for geology, and seamless pipes for petroleum.