A Study of Flexible Magnetic Camera for Welded Tubular Joint Inspection

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.