Comparison of Non-Destructive Examination Techniques for Crack Inspection

Abstract

Effective and efficient crack management programs for liquids pipelines require consistent, high quality non-destructive examination (NDE) to allow validation of crack in-line inspection (ILI) results. Enbridge leveraged multiple NDE techniques on a 26-inch flash-welded pipe as part of a crack management program. This line is challenging to inspect given the presence of irregular geometry of the weld. In addition, the majority of the flaws are located on the internal surface, so buffing to obtain accurate measurements in the ditch is not possible. As such, to ensure a robust validation of crack ILI performance on the line, phased array ultrasonic testing (PAUT), time-of-flight diffraction (TOFD), and a full matrix capture (FMC) technology were all used as part of the validation dig program. PAUT and FMC were used on most of the flaws characterized as part of the dig program providing a relatively large data set for further analysis. Encoded scans on the flash welded long seam weld were collected in the ditch and additional analyses were performed off-site to characterize and size the flaws. Buff-sizing where possible and coupon cutouts were selected and completed to assist with providing an additional source of truth. Secondary review of results by an NDE specialist improved the quality of the results and identified locations for rescanning due to data quality concerns. Physical defect examinations completed after destructive testing of sample coupon cutouts were utilized to generate a correlation between the actual defect size from fracture surface observation and the field measurements using various NDE methods. This paper will review the findings from the program, including quality-related learnings implemented into standard NDE procedures as well as comparisons of detection and sizing from each methodology. Finally, a summary of the benefits and limitations of each technique based on the experience from a challenging inspection program will be summarized.

In-Line Inspection (ILI) Techniques for Subsea Pipelines: State-of-the-Art

“…It boasts the capability to detect cracks as small as 25 mm in length with a minimum depth of 1 mm. and research have predominantly focused on the external inspection of pipeline welds [78][79][80], with relatively few examples of its use in Inline Inspection (ILI). But the application of PAUT technology in ILI has a well-established history.…”