Patent ID: 8383978

Claim:
A steel pipe weld zone heating apparatus for making a tubular steel pipe by bending a moving steel plate into cylindrical shape, the apparatus comprising: a variable frequency alternating current power supply, having a frequency variable within a predetermined frequency range, configured to generate joule heat by passing alternating current near end faces of the bent steel plate, and continuously melt and pressure-weld a weld zone of the bent steel plate, forming the steel pipe, a first imaging unit installed opposite an end face weld zone of the bent steel plate that detects self-emitted light of the weld zone, and outputs a brightness image; a weld zone temperature distribution computation unit that performs image processing based on the brightness image, and applies emitted light temperature measurement to compute the plate-thickness temperature distribution of the weld zone; and a heating control unit configured to use criteria predefined from dimensions and electromagnetic properties of the bent steel plate to evaluate a relationship between the alternating current frequency and a plate-thickness temperature distribution, and to determine the frequency of the alternating current based on the plate-thickness temperature distribution; wherein the variable frequency alternating current power supply is configured to pass alternating current of the frequency determined by the heating control unit through the bent steel plate.