Classification of stainless steel tubes: stainless steel seamless steel tubes and stainless steel welded steel tubes (seamed steel tubes) are basically two categories. According to the outer diameter and shape of steel tubes, they can be divided into round tubes and special-shaped tubes. Round steel tubes are widely used, but there are also some special-shaped steel tubes such as square, rectangular, semicircular, hexagonal, equilateral triangle, and octagonal.