PROCESS FOR MANUFACTURING SEAMLESS PIPE

摘要

A process for manufacturing a seamless pipe, in which cracking at pipe end portions can be effectively prevented in the stretch rolling step by means of a mandrel mill. The process for manufacturing a seamless pipe is characterized by including the steps of carrying out stretch rolling of a pipe by means of a first rolling stand allowing the groove ellipticity defined by disposed grooved roll to satisfy the requirements of the following formula (1) and carrying out stretch rolling of the pipe by means of a second rolling stand allowing the ratio of S/R1 wherein S means an offset extent and R1 means a curvature radius of groove bottom defined by disposed grooved roll to satisfy the requirements of the following formula (2). 1.2=groove ellipticity=1.4 (1) S/R1=-0.35 Ln(X)+1.43 (2) wherein X of the formula (2) means the groove bottom draft (%) at the second rolling stand.