Major diameter control manner of seam non tube and major diameter control unit null of seam non

摘要

PROBLEM TO BE SOLVED: To provide a method of controlling the outside diameter of a seamless pipe, which can maintain predicted accuracy of heat shrinkage factor at high accuracy not depending on pipe wall thickness and rolling schedule of each process. SOLUTION: In this method to control the outside diameter of a seamless pipe when the seamless pipe is rolled with sizing machine, cooled, and finished to a specified diameter after processes where a heated round billet is drilled to make a hollow pipe and rolled, each temperature distribution on inlet/outlet sides of the processes and on the inlet side of the sizing machine are sequentially determined on the basis of the temperature (S6) of the heated round billet, carrying time (S12) through the processes, and deformation strain volume (S16) through the processes (S14, 18). On the basis of the temperature distribution on the inlet side of the sizing machine and the deformation strain volume due to the target diameter to be rolled with the sizing machine, the temperature distribution of the seamless pipe on the outlet side of the sizing machine is predicted, and the target diameter is set so as to achieve approximate agreement between the target diameter at the average temperature which is calculated from the finished diameter and the target diameter.