South Bow Corporation and the Pipeline and Hazardous Materials Safety Administration (PHMSA) have released findings from an independent root cause analysis of the April 2025 failure at Milepost 171 of the Keystone Pipeline near Fort Ransom, North Dakota. The investigation determined that the rupture originated from a fatigue crack in the pipe's long-seam weld that initiated during the transportation phase and was subsequently aggravated by hydrogen-induced brittleness accumulated over 15 years of operational service. While both the pipe material and welds met applicable industry standards at the time of manufacture, engineers identified that the seam weld geometry created localized stress concentrations that contributed to crack propagation.
Following the incident, South Bow has conducted an extensive integrity assessment program, completing seven in-line inspection runs and 51 direct excavation integrity digs across the affected pipeline segment. The inspections have identified no additional injurious conditions requiring immediate remediation. As part of PHMSA's Corrective Action Order, South Bow is implementing comprehensive remedial measures and deploying enhanced inspection technologies to prevent similar failures and ensure continued safe pipeline operations.
The findings underscore the importance of understanding long-term material degradation mechanisms in pipeline infrastructure and highlight the operator's commitment to exceeding regulatory requirements through proactive integrity management and technological advancement.