PURPOSE: To improve hot online the dimensional accuracy of a seamless steel pipe by determining the helix angle in the axial direction of a thickness deviation from the fluctuation in the wall thickness of a blank pipe detected during hot rolling, estimating the factor at which the thickness deviation arises in accordance with the detected helix angle and eliminating the thickness deviation.
CONSTITUTION: The relation between the factor for thickness deviation and a helix angle β corresponding to the same is beforehand determined by experiment in the production of a seamless steel pipe by a Mannessman plug mill process. The line connecting the max. wall thickness parts in the respective sections of the pierced blank pipe 4 is the straight line grading at the helix angle β in this case. The fluctuation in the wall thickness in the longitudinal direction of the pipe 4 is detected during actual hot rolling, and the detected fluctuation in the wall thickness is analyzed to calculate the helix angle β. The factor at which the thickness deviation arises is estimated by using the relation determined beforehand and the thickness deviation is online eliminated.
SAYAMA YASUHIRO