South Bow sets out root causes of Milepost 171 incident

Executive Summary

• South Bow Corp. and PHMSA released an independent third‑party root cause analysis (RCA) of the Milepost 171 Keystone pipeline incident that occurred on April 8, 2025.
• The RCA identified a fatigue crack originating in a long‑seam weld, exacerbated by hydrogen‑induced brittleness, as the primary failure mechanism.
• South Bow has completed seven inline inspection runs and 51 integrity digs, with additional inspections and digs scheduled for 2026, and has submitted a remedial work plan to PHMSA for approval.

Key Details

• Incident Overview: Failure occurred at MP‑171 of the Keystone pipeline near Fort Ransom, ND; pipe and welds met industry design, material, and mechanical standards; pipeline was operating within design pressure at time of incident.
• Root Cause Findings:
• Fatigue crack originated along a manufactured long‑seam weld; seam geometry created stress concentration that likely initiated the crack during transportation from the mill.
• Multiple inline inspections (three generations of ultrasonic shear‑wave technology from two vendors) had previously been performed on the pipe section.
• Presence of hydrogen contributed to material brittleness and accelerated crack growth over ~15 years of normal operation.
• Remedial Actions Completed:
• Seven inline inspection runs completed.
• 51 integrity digs conducted with preliminary results showing no injurious issues.
• Modified inspection process now overlays data from prior tool runs and improves data analysis methods.
• Future Work:
• Additional inline inspection tool runs and integrity digs scheduled throughout 2026 as part of a comprehensive program addressing RCA recommendations.
• Ongoing collaboration with inspection technology vendors to enhance tool performance, validate methods, and develop new technologies.
• Regulatory Interaction:
• Submitted remedial work plan to PHMSA per corrective action order; plan includes completed actions and outlines further steps to meet RCA recommendations.
• CEO Statement: Bevin Wirzba (CEO) emphasized commitment to learning from the incident, implementing remedial measures, and maintaining transparency with regulators, customers, and industry peers.

Notable Quotes

“This was a complex set of unique circumstances. We are committed to learning from this incident and are already implementing remedial measures and enhancements across our systems to prevent future incidents,” – Bevin Wirzba, CEO, South Bow Corp.