METHOD FOR DIAGNOSING FACTOR FOR THICKNESS DEVIATION OF SEAMLESS PIPE

摘要

PURPOSE:To diagnose exactly the factors for the thickness deviation of a pipe by measuring the wall thickness in the various parts along the axial direction of the pipe at plural circumferential points thereof and detecting the specific factors contributing to generating the change in the wall thickness from the distribution and period of the thickness deviation, and the max. and min. values of the circumferential thickness deviation. CONSTITUTION:The wall thicknesses in the various parts in the axial length direction of the seamless pipe are measured at the plural circumferential point thereof by using an electromagnetic ultrasonic method. The functions of the wall thickness distributions in the axial length direction are determined with the optional two points in the circumferential direction in accordance with the measured values. The cross-correlation functions are drived from these functions of the wall thickness distributions. Whether the peak value in the prescribed region of the cross-correlation functions exceeds a predetermined reference value or not is judged. The average values of the wall thickness in the axial length direction of the measured values described above are calculated and whether the difference between the max. value and min. value in the circumferential direction among the average values exceeds the predetermined other reference value or not is judged. The exact diagnosis of the factors for the thickness deviation is thus made possible and the adequate disposition is executed with a good timing.