Welded steel pipes for low-pressure fluid transportation (GB/T3092-1993) are also known as general welded pipes, commonly known as black pipes. It is a welded steel pipe used for conveying water, gas, air, oil, heating steam and other general low pressure fluids and other purposes. The wall thickness of steel pipe can be divided into ordinary steel pipe and thickened steel pipe, and the nozzle end can be divided into non-threaded steel pipe (smooth pipe) and threaded steel pipe.