Patent ID: 7093469

Claim:
A method of manufacturing seamless pipes while adjusting wall thickness based on measured values of wall thickness of a pipe, comprising: a step of measuring the wall thickness at a plurality of points in a circumferential direction in a cross section of the pipe in an axial direction; a first calculation step of calculating a complex Fourier component of each k-th-order thickness deviation of the wall thickness that changes periodically k times (k is a natural number) in one turn by performing a complex Fourier transform in the circumferential direction on a plurality of measured values of the wall thickness; a second calculation step of calculating a thickness deviation amount indicating a degree of thickness deviation of each k-th-order thickness deviation, from an absolute value of the calculated complex Fourier component; a third calculation step of calculating a position of a thick portion or thin portion of each k-th-order thickness deviation, from a phase of the calculated complex Fourier component; and an adjustment step of adjusting the wall thickness of the pipe, based on the thickness deviation amount and/or the position of the thick portion or thin portion, according to a method suited to each k-th-order thickness deviation.