This paper deals with investigation and characterization of weld circumferential thin cracks in austenitic stainless steel (AISI 304) pipe with eddy current nondestructive testing technique (EC-NDT). During welding process, the heat source applied to the AISI 304 was not uniform, accompanied by a change of the physical property. To take into consideration this change, the relative magnetic permeability was considered as a gradiently changed variable in the weld and the heat affected zone (HAZ), which was generated by the Monte Carlo Method based on pseudo random number generation (PRNG). Numerical simulations were performed by means of MATLAB software using 2D finite element method to solve the problem. To verify, results from the modeling works were conducted and contrasted with findings from experimental ones. Indeed, the results of comparison agreed well. In addition, they show that considering this changing of this magnetic property allows distinguishing the thin cracks in the weld area.

In this paper, a nondestructive inspection system is proposed to detect and quantitatively evaluate the size of the near- and far-side damages on the tube, membrane, and weld of the water-cooled wall in the fluidized bed boiler. The shape and size of the surface damages can be evaluated from the magnetic flux density distribution measured by the magnetic sensor array on one side from the center of the magnetizer. The magnetic sensors were arrayed on a curved shape probe according to the tube’s cross-sectional shape, membrane, and weld. On the other hand, the couplant was doped to the water-cooled wall, and a thin film was formed thereon by polyethylene terephthalate. Then, the measured signal of the flexible ultrasonic probe was used to detect and evaluate the depth of the damages. The combination of the magnetic and ultrasonic methods helps to detect and evaluate both near and far-side damages. Near-side damages with a minimum depth of 0.3 mm were detected, and the depth from the surface of the far-side damage was evaluated with a standard deviation of 0.089 mm.

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Liquid penetrant testing (PT), magnetic particle testing (MT) and ultrasonic testing (UT) have been used as nondestructive testing methods for the welded tubular joints of reactor cooling systems. The PT and the MT that are applied to the surface test of the specimen have been experiencing problems such as specimen contamination, hazardous chemical exposure risk for the inspector, and the inspector’s extended time in the nuclear power plant due to the long testing time (increased risk of radiation exposure). This study is about the applicability of an alternative nondestructive examination (ANDE) method to solve the aforementioned problems. According to the requirements of ANDE, the NDE technology should be applied with the same or better sensitivity and shorter inspection time than the conventional inspection methods of PT and MT. In order to satisfy these requirements, a flexible-type multi-sensor array was developed in order to scan a certain welding area and complete the inspection in a short time. The static and time-varying magnetic fields were applied to the test specimen and the magnetic flux density distribution was measured by solid state magnetic sensors. Each sensor is arranged with a spatial resolution of less than 2 mm, and the shape can be varied according to the shape of the bead. By using the measured data, the magnetic flux density distribution according to the presence or absence of defects and shapes can be visualized in real time, and stored into the database.