A series of experiments were conducted to investigate the applicability of unsaturated AC magnetic flux leakage testing for fatigue crack detection at the paint-coated welded joints. Fatigue cracks were generated at the weld toes of Tshaped joints by applying cyclic bending loads. The signals were measured at the weld toe parts by the unsaturated AC magnetic flux leakage testing with a highsensitive sensor. The ratio of the measured signal magnitude at the cracked welded joints to the initial signal magnitude measured at sound welded joints was defined as the evaluation index. The fatigue cracks could be detected over the assumed 1 mm and 2 mm thick paint coating when the signal magnitude ratio was larger than 1.1.
