Manufacturing method and manufacturing apparatus of pipe, thickness deviation information derivation apparatus, and computer program

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 plurality of cross sections of the pipe in an axial direction;
• a step of calculating a complex Fourier component of each k-th-order thickness deviation of 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 in the plurality of the cross sections in the axial direction;
• a 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, for the plurality of the cross sections in the axial direction;
• a step of calculating a phase of each k-th-order thickness deviation, from the calculated complex Fourier component, for the plurality of the cross sections in the axial direction;
• a step of calculating a complex Fourier component for each frequency representing the number of times the thickness deviation is twisted per unit length in a longitudinal direction of the pipe, by performing a complex Fourier transform on a complex function in which a complex number whose absolute value and phase are the thickness deviation and the phase calculated for each k-th-order thickness deviation, respectively, is a function of position in the longitudinal direction of the pipe;
• a step of determining whether the values of the complex Fourier component in a plurality of predetermined frequency ranges are larger or not based on a predetermined boundary value;
• and
• a step of adjusting the wall thickness of the pipe according to a method suited to each k-th-order thickness deviation and each frequency range, when it is determined that the value of the complex Fourier component is larger in any of the frequency ranges.

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 plurality of cross sections of the pipe in an axial direction;
• a first calculation step of calculating a complex Fourier component of a first-order thickness deviation of the wall thickness that changes periodically once in one turn by performing a complex Fourier transform in the circumferential direction on a plurality of measured values of the wall thickness in the plurality of the cross sections in the axial direction;
• a second calculation step of calculating a thickness deviation amount indicating a degree of thickness deviation of the first-order thickness deviation, from an absolute value of the calculated complex Fourier component, for the plurality of the cross sections in the axial direction;
• a third calculation step of calculating a phase of the first-order thickness deviation, from the calculated complex Fourier component, for the plurality of the cross sections in the axial direction;
• a fourth calculation step of calculating a complex Fourier component for each frequency representing the number of times the thickness deviation is twisted per unit length in a longitudinal direction of the pipe, by performing a complex Fourier transform on a complex function in which a complex number whose absolute value and phase are the thickness deviation amount and the phase thus calculated, respectively, is a function of position in the longitudinal direction of the pipe;
• a determination step of determining whether the values of the complex Fourier component in a plurality of predetermined frequency ranges are larger or not based on a predetermined boundary value;
• and
• an adjustment step of adjusting manufacturing conditions of the pipe, when it is determined that the value of the complex Fourier component is larger in any of the frequency ranges, according to a method suited to the frequency range.

A manufacturing apparatus for manufacturing seamless pipes while adjusting wall thickness based on measured values of wall thickness of a pipe, comprising:

• means for measuring the wall thickness at a plurality of points in a circumferential direction in a cross section of the pipe in an axial direction;
• 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 the circumferential direction on a plurality of measured values of the wall thickness;
• 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;
• 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;
• and
• adjusting means for adjusting the wall thickness of the pipe to be manufactured, 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.

A manufacturing apparatus for manufacturing seamless pipes while adjusting wall thickness based on measured values of wall thickness of a pipe, comprising:

• means for measuring the wall thickness at a plurality of points in a circumferential direction in a plurality of cross sections of the pipe in an axial direction;
• first calculating means for calculating a complex Fourier component of a first-order thickness deviation of the wall thickness that changes periodically once in one turn by performing a complex Fourier transform in the circumferential direction on a plurality of measured values of the wall thickness in the plurality of the cross sections in the axial direction;
• second calculating means for calculating a thickness deviation amount indicating a degree of thickness deviation of the first-order thickness deviation, from an absolute value of the calculated complex Fourier component, for the plurality of the cross sections in the axial direction;
• third calculating means for calculating a phase of the first-order thickness deviation, from the calculated complex Fourier component, for the plurality of the cross sections in the axial direction;
• fourth calculating means for calculating a complex Fourier component for each frequency representing the number of times the thickness deviation is twisted per unit length in a longitudinal direction of the pipe, by taking a relationship between the thickness deviation amount and the phase thus calculated as a function of position in the longitudinal direction of the pipe and performing a complex Fourier transform over a plurality of the functions;
• determining means for determining whether values of the complex Fourier component in a plurality of predetermined frequency ranges are larger or not based on a predetermined boundary value;
• and
• adjusting means for adjusting manufacturing conditions of the pipe, when it is determined that the value of the complex Fourier component is larger in any of the frequency ranges, according to a method suited to the frequency range.