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Nondestructive testing (NDT), which is applied to the manufacturing/installation of power generation facilities and preventive maintenance, is one of the key element technologies that are essential for "safety and quality assurance" as diagnosis and maintenance technology. Radiography testing (RT) is the main testing method; however, ultrasonic testing (UT) is applied together with RT in most cases. This significantly impacts process delays and economic losses. Therefore, in the industrial field, the introduction and utilization of phased array UT (PAUT) have been aggressively demanded as a new nondestructive volumetric examination technology that can reduce the dependency on RT and possibly replace it. PAUT not only makes it easier to test specimens with complex shapes that are difficult to test with conventional UT, but it also enables high-speed testing because it can electronically control the scanning of the ultrasonic beam. However, in the case of applying PAUT to the testing of a weld zone with a curved shape, such as a piping elbow weld zone, it is not easy to secure the objective and achieve reliable test data because contact with the probe is difficult. Therefore, in this study, flexible PAUT probe was developed that was capable of testing piping elbow weld zones, and its effectiveness was verified by comparing it with the use of a wedge, which is normally used for the testing of pipes with curved structures. Welding specimens were fabricated (including natural defects) in accordance with ASME standards, and artificial notches were machined. The possibility of overcoming the application limit of the current PAUT technology and further improving the reliability of the inspection results were confirmed through signal acquisition and an analysis according to the probe contact position (elbow or pipe surface).
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