Setsu Yamamoto

DEVELOPMENT OF A WELDING MONITORING SYSTEM FOR IN-PROCESS QUALITY CONTROL OF THICK WALLED PIPE

The authors have developed a systematized in-process quality control system for arc welding of thick walled pipe utilizing visual sensors and computers. This system consisted of four main subsystems that monitor the welding conditions, monitor the weld pool shape, visualize the weld bead shape, and visualize inner defects, respectively. The welding condition monitoring system detects abnormal welding conditions using an electric signal. The weld pool shape monitoring system assesses the position among weld pool, the electrode, wire, and groove using a charge coupled device (CCD) camera and filters. The weld bead shape visualization system detects abnormal bead surface conditions using a three-dimensional (3D) visual technique. The inner defect visualization system was achieved using a laser-ultrasonic in-process testing (LUT) technique and synthesis aperture focus technique (SAFT). Each subsystem informs workers of unsuitable welding conditions to allow them to reestablish the suitable conditions. Furthermore, the in-process quality control system was applied to thick walled pipe welding to verify the practicality of this system for improving the quality and efficiency of welding operations.

LASER‐ULTRASONIC TESTING AND ITS APPLICATIONS TO NUCLEAR REACTOR INTERNALS

A new nondestructive testing technique for surface‐breaking microcracks in nuclear reactor components based on laser‐ultrasonics is developed. Surface acoustic wave generated by Q‐switched Nd:YAG laser and detected by frequency‐stabilized long pulse laser coupled with confocal Fabry‐Perot interferometer is used to detect and size the cracks. A frequency‐domain signal processing is developed to realize accurate sizing capability. The laser‐ultrasonic testing allows the detection of surface‐breaking microcrack having a depth of less than 0.1 mm, and the measurement of their depth with an accuracy of 0.2 mm when the depth exceeds 0.5 mm including stress corrosion cracking. The laser‐ultrasonic testing system combined with laser peening system, which is another laser‐based maintenance technology to improve surface stress, for inner surface of small diameter tube is developed. The generation laser in the laser‐ultrasonic testing system can be identical to the laser source of the laser peening. As an example op...