The validity of the higher harmonic imaging technique for detecting and imaging IGSCC cracks in Ni-based alloy welds is demonstrated. The higher harmonic measurement makes use of the waveform distortion which is generated at contact interfaces like IGSCC under large amplitude tone-burst waves. Using analog high pass filters, higher harmonics less than 1% of the fundamental amplitude that are extracted from the received waves scattered at IGSCC cracks. The higher harmonics are not affected by acoustic impedance mismatch, therefore, they are free from grain scattering noise. Also, they are selectively generated at defects of the kissing bond type, which are difficult to detect by conventional ultrasonic methods. With this higher harmonic technique, we can clearly image IGSCC cracks introduced in buttered and weld region of SUS316L/low carbon steel joints.

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