Hot annealed weld inspection

摘要

An eddy current system and method for hot annealed weld inspection is disclosed for use on metallic workpieces such as steel pipe. An annealer produces strong alternating fields to heat the weld. A nearby exciter coil produces test eddy currents within the workpiece at a carrier frequency. Detector circuitry including a demodulator and a detector coil senses defects within the workpiece as evidenced by nonuniformities in the test eddy currents, in response to which the detector coil produces a flaw indicating signal modulated on the carrier frequency. The carrier frequency is automatically maintained at a non-integral multiple of the annealer alternating frequency. A variable band pass filter between the demodulator and detector coil is automatically maintained with its pass band substantially centered upon the carrier frequency.