Square pipe is divided into seamless steel pipe and welded steel pipe (welded pipe) two categories. According to the section shape can be divided into square and rectangular pipe, widely used is the circular steel pipe, but there are also some semicircular, hexagonal, equilateral triangle, octagonal shaped steel pipe.For the stainless steel square pipe under fluid pressure to carry out hydraulic tests to test its pressure capacity and quality, under the specified pressure does not leak, wet or expansion for qualified, some steel pipe also according to the standard or demander requirements for flange test, flaring test, flattening test.Round steel preparation → heating → hot rolling perforation → cutting head → pickling → grinding → lubrication → cold rolling processing → degreasing → solution heat treatment → straightening → pipe cutting → pickling → finished product inspection.Metals can react with oxygen in the atmosphere to form an oxide film on the surface. The iron oxide formed on ordinary carbon steel will continue to oxidize, so that the corrosion continues to expand, and eventually the formation of holes. This can be done by electroplating the carbon steel with paint or an oxidation-resistant metal, but the coating is only a thin film. If the coating is damaged, the steel underneath will begin to rust again. Whether the stainless steel tube is corroded is related to the chromium content in the steel, when the chromium content in the steel reaches 12%, in the atmosphere, the surface of the stainless steel tube generated a layer of passivation, dense chromium rich oxide and protect the surface, can prevent further reoxidation. This oxide layer is extremely thin, through which the natural luster of the steel surface can be seen, giving stainless steel its unique surface. If the chromium film is destroyed, the chromium in the steel and the oxygen in the atmosphere to form a passivation film, continue to play a protective role. In some special circumstances, stainless steel will also appear some local corrosion and failure, but stainless steel is different from carbon steel, will not appear uniform corrosion and failure, so the corrosion margin for stainless steel tube is meaningless.