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The ultra-thick seamless steel tubes are prone to abnormal bore shape when rolled by conventional symmetric roll pass. Therefore, in this paper, a new type of asymmetric pass is designed to overcome this defect. Also, comparative analysis concerned with mechanical analysis, finite element simulations, and industrial experiments is carried out to test the differences between the two types of roll passes. Results show that the contrast is remarkable in terms of billet movement, bore roundness, and the evenness of stress and strain. By adopting the asymmetric roll passes, the roller is able to drive the tube rotating continuously around the tube axis. Through this self-rotary motion of the tube, the uniformity of stress and strain gets greatly improved; thus, the roundness of ultra-thick seamless tubes also gets obvious improvements. [ABSTRACT FROM AUTHOR]