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 other-shaped pipes; and by application into general welding pipes, galvanized welding pipes, oxygen welding pipes, wire sleeve pipes, metric welding pipes, roller tubes, deep well pump pipes, automotive pipes, transformer pipes, welding thin-walled pipes, welding non-standard pipes, and spiral-welded pipes.