Third-party reports investigating the causes of a 3,500-barrel oil spill from the Keystone pipeline in North Dakota in April 2025 have been made public. The spill occurred at Milepost 171 near Fort Ransom, with 3,110 barrels recovered.

Root Cause Analysis Findings

An independent root cause analysis (RCA) by Anderson & Associates, submitted in June 2025, concluded the pipe failure resulted from a fatigue crack originating along the pipe's manufactured long-seam weld. The primary contributor was the seam weld geometry, which created a stress concentration. This crack likely initiated during transportation from the pipe mill, before construction and 15 years of subsequent operation. The report noted that multiple prior in-line inspections using advanced ultrasonic technology from different vendors had been completed on that pipe section.

Contributing Factors: Hydrogen and Inspection Limitations

The RCA found that the presence of hydrogen contributed to material brittleness and increased the fatigue crack growth rate, a process known as hydrogen-induced cracking. Possible hydrogen sources include corrosion, excessive cathodic protection, and welding. A subsequent study by Blade Energy Partners, submitted in September 2025, corroborated these findings. It concluded weld geometry enabled crack initiation and propagation during transport, while in-line inspection tools failed to detect the crack's evolution, exhibiting no crack-like signal at the rupture location. Blade Energy also found that fatigue crack propagation during operation was enhanced by the weld's heat-affected zone microstructure and exacerbated by hydrogen damage, potentially from minor water, diluted bitumen, and the tar sands environment.

Company Response and Remedial Measures

South Bow Corporation stated the incident involved a unique set of circumstances but is committed to implementing remedial measures. Actions taken include seven in-line inspection runs and 51 integrity digs, with preliminary results showing no injurious issues. The company has modified its in-line inspection process by overlaying data from previous tool runs and improving data analysis methods. It continues to work with technology vendors to advance tool performance and develop new technologies. Blade Energy's report recommended evaluating alternative detection technologies like phased array ultrasound, and noted hydrostatic testing as a potential but problematic alternative.

Regulatory and Financial Context

As part of a corrective action order from the Pipeline & Hazardous Materials Safety Administration (PHMSA), South Bow has submitted a remedial work plan for approval. Financially, costs linked to the spill totaled $55 million, which are largely expected to be recovered through insurance. The company has maintained its contractual commitment to transport 585,000 barrels per day. The Keystone Pipeline spans approximately 4,300 kilometers from Alberta, Canada, to Texas, US.