R&D and Application of Φ820 mm Retained-mandrel Precision Pipe Mill

Based on the characteristics of the large-sized hot-rolled seamless steel tube，described in the paper are the equipment composition of the Φ820 mm retained-mandrel precision pipe-rolling plant，and the main aspects of the new type CTP mill and the retained-mandrel precision pipe mill proper，including the manufacturing process flows，major technical parameters and characteristics，etc. Also described are the geometric dimensional tolerances of the products as rolled. Relevant inspection results show that without being subjected to the sizing process，the tube as manufactured via such processes as piercing plus finish-rolling with retained-mandrel mill or piercing plus secondary piercing and finish-rolling with retained-mandrel mill has the O.D. tolerance better than that of the finished tube （O.D. tolerance≤±0.5%D），while the W.T. tolerance is within the specified tolerance scope of the finished tube （W.T. tolerance ±5%S~±8%S）.