A Study of Crack Detection Ultrasonic Attributes to Manage Leak Threats Associated With Short Crack-Like Flaws in ERW Pipelines

Inline Inspection (ILI) tools along with hydrostatic testing have been the primary identification and mitigation techniques for cracking threats on liquids pipelines. Each technique faces detection challenges in relation with the weld type, geometry, and feature types, sizes and orientations. Low frequency electric resistance welds (LF ERWs) are subject to a number of crack-like defects due to the ERW manufacturing process. These defects may include fatigue cracks, lack of fusion, burned metal defects, stitched welds, cold welds, cracks in hard HAZ, surface breaking hook cracks near the weld and selective seam corrosion [1]. Within a population of features in a pipeline, a subpopulation can exist of short, deep defects (>50% wt) that may be undersized by the ILI tool or not detected by a hydrostatic test due to the length of the flaw. For ILI tools, a length detection threshold is set based on the tool speed (which is dictated by the tool type and configuration). A feature may be undersized by the ILI tool if its length is below this tool threshold. For hydrostatic testing, through-wall flaws may be undetected if the flaw length is below the critical length for a significant leak. Through detailed ILI data analysis, Enbridge along with PII Pipeline Solutions has been able to consistently identify short and deep crack-related defects on LF ERW pipe through means other than feature dimensions provided by the ILI tool. In-ditch non-destructive examination and destructive laboratory testing has confirmed these features are critical and fall below current ILI tool’s detection thresholds. This paper discusses unique ILI data attributes that may identify a more severe feature than would conventional ILI sizing practices, and how the identification and selection procedure is being applied across Enbridge’s pipeline system. This analysis effort aligns with Enbridge’s goal to continuously improve its integrity management processes and further enhance the safety of its pipelines.