Phased Array Non-Destructive Error Measurement in the Characterization of Axially and Circumferentially Oriented Crack and Weld Defects in Transmission Pipelines

Abstract Phased Array Ultrasonic Testing (PAUT) is among the most common non-destructive examination (NDE) methods for the characterization and sizing of pipeline defects. Where defects sized by PAUT cannot be removed by griding (internal/midwall defects or stacked defects) the practice of an operator was to add 1 mm depth to any PAUT reported values. If this assumed error is conservative, there may be significant impact to repair decisions, tool validation, and fatigue life calculations for crack defects or weld defects sized using PAUT. This impact is felt across the organization through higher integrity repair budget costs, an increase in required digs, and directly impacts workload for planning and execution groups. The purpose of the study was to verify whether the assumption to add 1mm depth to defects sized by PAUT was appropriate. A comparison of PAUT measured sizing to ground (true) depths was conducted on over five hundred individual defects during integrity repair programs completed between 2020 and 2022 on a 1960’s vintage 317 MPa grade and 4.78 mm nominal wall thickness NPS 12 pipeline. The pipeline was selected as a candidate for the study due to the significant amount of available NDE data, particularly for axial/circumferential crack and girth/longseam weld defects. The influence of variables including technician conducting work, defect orientation, defect type, and longseam/girth weld interaction on the accuracy of measurements were assessed.