Steel pipes have hollow sections and are much longer than their diameter or circumference. According to the cross-sectional shape, it is divided into round, square, rectangular and special-shaped steel pipes; according to the material, it is divided into carbon structural steel pipes, low alloy structural steel pipes, alloy steel pipes and composite steel pipes. Seamless steel pipes are further divided into hot-rolled and cold-rolled (drawn) steel pipes. ) two types, welded steel pipes are divided into straight seam welded steel pipes and spiral seam welded steel pipes: according to the production method, they are divided into seamless steel pipes and seamed steel pipes. Seamed steel pipes are divided into two types: straight seam steel pipes and spiral seam pipes.