Analytical and Experimental Approaches for the Sizing of Fatigue Cracks in Inconel Welds by Eddy Current Examination

Cracks by SCC (stress corrosion cracking) and high cycle fatigue were detected at the welded joints of nickel based alloy of reactor vessel, pressurizer and core internal of nuclear power plants in recent years. To ensure the integrity of plants, it is necessary to improve NDT (non-destructive testing) techniques for reliable detection and evaluation of defects in the nickel-base alloy. Basic studies on the flaw detection and characterization by eddy current examination of inconel, a typical nickel-base alloy, are carried out. Specimens made of inconel and inconel weld metal are prepared, fabricated with EDM (Electro-Discharge Machining) notches and fatigue cracks. The detecting and sizing capability of eddy current method is investigated through analytical and experimental approaches. Numerical analysis helps in choosing an appropriate probe and examination condition, and evaluating a crack from the measured signals. All or part of a planar crack is reconstructed using an inversion approach. The result from ECT (eddy current testing) is compared with that of UT (ultrasonic testing). The research presented in this paper shows that by choosing a proper testing situation, eddy current examination is feasible for the detection and sizing of surface-breaking cracks in inconel welds.