Validation of Current Approaches for Pipeline Girth Weld Discontinuity Sizing Accuracy

Edison Welding Institute (EWI) collected third party, independent data and statistically characterized the systematic and random errors in girth weld discontinuity sizing, as measured by mechanized ultrasonic testing using the pulse/echo and time of flight diffraction techniques, as well as phased array ultrasonic technology, in support of pipeline reliability assessments. The results of this study provided statistical information for improving the safety of pipelines and will help to align girth weld discontinuity acceptance criteria with current design trends, thus facilitating their incorporation into new codes. It was found that the best accuracy was achieved at the blind trials using shape focused multiprobes with sizing algorithms. When using non-focused multiprobes, it was found that discontinuity height was typically undersized. Phased array technology demonstrated superior sizing accuracy in the open trial but was below the expected level of accuracy in the blind trials. In the best case, only 45% of the discontinuity population will be sized within 0.5 mm (0.02 in.) accuracy. The majority of the discontinuities will be sized within 2 mm (0.08 in.) accuracy. It was recommended that additional research be conducted to analyze the latest trial results. Mechanized ultrasonic testing systems, procedures and operators should not be considered as an integral approach. The additional research should include new open and blind sizing trials to bring the phased array technology to a higher level of demonstrated accuracy. It is also necessary to investigate probability of detection for phased array technology.