Patent ID: 7333925

Claim:
A thickness deviation information derivation apparatus for deriving information about a thickness deviation that occurs in a pipe, based on measured values of wall thickness of the pipe, comprising: first calculating means for 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 a circumferential direction on measured values of the wall thickness at a plurality of points in a cross section of the pipe in an axial direction; second calculating means for 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; and third calculating means for 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.