Development History edit the first phase (1904- 1934) in this period MPM technology is not mature. The second phase (1934- 1950) and even a floating mandrel square tube technology mature period. The third phase (1961- 1978), the floating core holding Pipe Mill at the height of the fourth phase (1978- 1992), a total of 11 sets of the world's big stopper (MPM) and two sets of semi-stopper formula (MRK) MPM to form plants. Welded steel pipe welded steel blanks is optional large square tube steel or steel, welding technology is not the same because it is divided into stove pipe, welded (ERW) pipe and active arc welded pipe. Because welding is not the same as two divided Longitudinal and spiral welded pipe. Its end shape is divided into circular pipe and shaped (square, flat, etc.) pipe. Pipe material and its use is not the same and is divided into the following varieties: GB / T3091-1993 (low pressure liquid delivery galvanized welded steel pipe). Mainly used for transporting water, gas, air, oil and heating hot water or steam is typically low pressure fluid and other useful tube. Which represents raw material Q235A grade steel. GB / T3092-1993 (low pressure liquid delivery galvanized welded steel pipe). Mainly used for transporting water, gas, air, oil and heating hot water or steam is typically low pressure fluids and other useful tube. Which represents raw material: Q235A grade steel. GB / T14291-1992 (mine fluid delivery welded steel pipe). Mainly used for mine air pressure, drainage, gas discharge shaft with a straight seam welded steel pipe. Which represents raw material Q235A, grade B steel. GB / T14980-1994 (low pressure fluid delivery with a large diameter welded steel pipe). Mainly used for transporting water, sewage, gas, air, steam heating and other low pressure fluids and other uses. Which represents raw material Q235A grade steel. Buying hot-rolled square tube square tube, exhibition of Commerce Bo, Hefei square tube provided by the Hefei exhibition Bo Trading Company. Hefei Show Bo Trading Company (www.hfzhanbo.com) (www.hfzhanbo.com) is Hefei, steel leaders, over the years, the company implement the scientific management, innovation and development, the principle of honesty and trustworthiness, and satisfy customers needs. In the exhibition of Commerce Bo leadership with the staff warmly welcome all inquiries negotiations to create the exhibition of Commerce Bo better future.