Seamless steel pipes are a type of welded steel pipe, referring to pipes where the weld is parallel to the longitudinal axis of the pipe. They are categorized by wall thickness into thin-walled and thick-walled seamless pipes; by shape into round, square, or special-shaped pipes; and by application into general-purpose welded pipes, galvanized welded pipes, oxygen-blown welded pipes, wire conduit, metric welded pipes, roller tube, deep well pump pipes, automotive pipes, transformer pipes, welding thin-walled pipes, welding special-shaped pipes, and spiral-welded pipes.