Detection of circumferential cracks in heat exchanger tubes using pulsed eddy current testing

Heat exchanger tubes in industrial pressure vessels typically require periodic inspection, and detection of circumferential cracks is one of the foremost issues. In this study, the pulsed eddy current method was used for the detection, and new types of probes were designed. Transverse probes were designed to render the eddy currents perpendicular to circumferential cracks to improve detection sensitivity, and the corresponding numerical simulations showed that the eddy currents were approximately perpendicular to the circumferential cracks along more than half of the tube circumference. Thus, two probes could cover the entire circumference for more economical inspection to be achieved. The experiments were performed on copper and steel tubes. The results show that when compared to longitudinal probes, the designed transverse probes significantly improved the detection sensitivity towards circumferential cracks. Particularly, the effectiveness of the proposed method is shown regarding detection of deep defects with good sensitivity in steel tubes without saturation magnetization.