ILI and NDE Characterization of Pipeline Manufacturing Flaws and Confirmation through Full-Scale Testing

ABSTRACT:

Pipeline-manufacturing flaws, such as slivers, can be difficult to accurately characterize and size during in-line inspection. After discovery of longitudinal flaws of varying depth and length, full-scale burst tests and metallography were conducted to confirm the size and morphology of the features. Metallography was performed on the samples to characterize the flaw morphology. Metallography indicated that the flaws present were consistent with original manufacturing mill slivers. The metallography also confirmed that the flaws showed no evidence of in-service growth. While flaw depths varied, the remaining wall thickness of the pipe was within API 5L minimum tolerances. Flaw depths measured via metallography were compared to those reported by the original ILI vendor (ILI), phased-array ultrasonic testing (PAUT), and RTD’s IWEX system. Flaw-depth measurements varied between systems but were consistently greater than those determined through metallography. Slivers are typically very shallow flaws; consequently, they can be difficult to accurately size under ideal conditions with typical NDT methods such as PAUT. Sizing the flaws in these samples was further complicated by the presence of inclusions and laminations typical of vintage pipeline steels. In this respect, the IWEX system was superior in that it allowed the user to visualize the flaw through the pipe wall. In this case, the flaw orientation was shown turning parallel to the pipe’s outer surface in the IWEX scans. Research indicated that manufacturing flaws such as slivers represent a minimal integrity concern in pipelines unless they grow during fatigue cycling, which is unusual. This assertion was confirmed through full-scale cycle and burst tests of the flaws.

Futch, D., Scrivner, R., Dotson, R., Pulsifer, A., “ILI and NDE Characterization of Pipeline Manufacturing Flaws and Confirmation through Full-Scale Testing,” Proceedings of The 29th International Pipeline Pigging & Integrity Management Conference, Houston, TX, February 27 – March 2, 2017.