Phased Array Ultrasonic Testing (PAUT) Weld Flaw Sizing
Ultrasonic weld inspection using phased array ultrasonic testing (PAUT) is used to detect and size weld defects across many different industries and is incorporated in American Welding Society (AWS) structural and bridge welding codes and American Society for Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC). In one or two encoded scans, PAUT can generate 2-D and 3-D weld defect profiles. In this article, the basic principles of phased array weld defect sizing are presented on the Olympus MX-2 platform. The basic phased array A-scan, S-scan, and C-scan data are discussed along with how to use phased array measurement cursors to size weld flaws.
Comparing Conventional Ultrasonic and Phased Array Sizing Techniques
Weld defect sizing is performed differently between conventional ultrasonic testing (UT) and phased array ultrasonic testing (PAUT). In conventional ultrasonic testing, the -6 db sizing technique is used generally used. This is a manual process that requires the inspector to find the maximum reflection amplitude from the weld defect and then moving the transducer in the scan axis and index axis directions until the maximum reflection amplitude is decreased by 6 dB or 50%. The scan axis length provides the length of the weld defect. While moving the transducer in the index axis direction, the depth of the weld defect is recorded at the upper and lower 6 dB points to provide weld defect height or dimension in the thickness direction. These are the two most important dimensions for fracture critical analyses. Weld defect sizing using phased array technology is always performed digitally in the height direction using the S-scan. Along the weld axis, it may be performed manually or digitally depending on if the scan was encoded.