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Comparison of Phased Array Ultrasound to Conventional Ultrasound and Radiographic Testing for Bridge Welds

Phased array ultrasonic testing (PAUT) was performed on nine complete joint penetration (CJP) weld samples with internal and external weld discontinuities to develop a discontinuity sizing procedure using the backward tip diffraction technique. The weld samples include flat plate CJP welds, CJP T-joint welds, and a thickness transition weld. The discontinuity sizing results were compared to the physical size of the weld discontinuities by sectioning the weld samples. It was found that the response signal would vary greatly depending on the scanning face and index offset. Therefore, the combined results from first and second leg scans from each available scanning face were used to estimate the discontinuity size. While the estimated discontinuity size was typically quite close to the actual discontinuity height and length for planar discontinuities, some difficulties were encountered when there was limited access for scanning, which caused the discontinuity to be undersized. Oversizing was also possible due to beam spread at long sound paths or from misinterpretation of surface gouges. Additional research is necessary to refine this technique to determine the size of volumetric discontinuities using PAUT. Additional testing was performed using conventional ultrasonic testing (UT) and radiographic testing (RT) to compare with the PAUT results and the acceptability of each sample under various acceptance criteria. It was found that weld discontinuities that were rejectable under combined conventional UT and RT per AWS D1.5 may be acceptable under alternate PAUT acceptance criteria. This typically occurred when the weld discontinuity was volumetric in nature such as internal porosity since UT is not as effective at discerning the limits of volumetric discontinuities compared with planar discontinuities. The variation in acceptance criteria may also be attributed to the fact that line scanning with PAUT may not maximize the response amplitude compared with raster scanning for conventional ultrasound.

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