US Patent 7174761 Method of manufacturing a seamless pipe

When manufacturing a seamless pipe by carrying out elongation rolling and sizing on a mother tube for forming a seamless pipe, the occurrence of portions of thickness variation in the seamless pipe is suppressed by previously identifying the portions of wall thickness variation where the thickness varies in the circumferential direction of the seamless pipe, and carrying out elongation rolling so that the thickness of the portions of the mother tube corresponding to the portions of wall thickness variation of the seamless pipe are different in thickness at the completion of elongation rolling from that of other portions of the mother tube. As a result, local variations in wall thickness in the circumferential direction of a seamless pipe are prevented.