Abstract: Briefly described in the article are the development and application of the rotary-expanding process. Detailed are such aspects of the rotary expander,covering structure,roll arrangement and roll-setting mode and features as well as the manufacture process flow and deformation characteristics. An initial investigation is made into the quality and quality-affecting factors of the products as made from the trial production of the Φ720 mm rotary expander plant as located in Tianjin Steel Pipe Group Corp. Ltd. The said trial production demonstrates that the rotary expander is capable of producing light-wall tubes with D/S ratio over 50. Part of the products as rolled by the mill are the first of their kinds in the domestic circles,and the product quality is close to or even up to the physical quality of similar products as produced overseas.