Analysis of the Keystone Cushing Extension Pipeline Rupture

On December 7, 2022, at approximately 9:01 p.m. CST, a significant rupture occurred on the Keystone Cushing Extension operated by TC Oil Pipeline Operations Inc. in Washington County, Kansas. The incident involved a 36-inch diameter pipeline that released an estimated 12,937 barrels of crude oil into Mill Creek. The rupture was detected by the TC Liquids Pipeline Control Center through a volume imbalance alarm, leading to an emergency shutdown just six minutes after the initial alarm.

The root cause of the rupture was identified as excessive bending stress due to external loading on a girth weld in a replaced fitting assembly. This assembly, known as TAG 98, was part of a 2010 warranty replacement program following the discovery of substandard fittings during hydrostatic testing. The failure was attributed to:

• Lack of Fusion (LOF) Defects: Small defects in the root bead of the girth weld where the weld did not fully penetrate the joint, leading to stress concentration points.
• Inadequate Soil Compaction: During the backfill process post-installation, the soil compaction was not sufficient, leading to bending stress on the pipeline from the weight of the overburden.
• Design Flaws: The shorter wall thickness taper transition in the weld joint design increased stress concentration at the weld.

The pipeline was operating within its allowed pressure limits under PHMSA Special Permit (SP) issued under § 190.341 on April 30, 2007, allowing operations at up to 80% of the Specified Minimum Yield Strength (SMYS). However, the segment where the failure occurred operated at no more than 72% SMYS as required by 49 C.F.R. § 195.106.

Immediate actions included:

• Emergency Shutdown: The pipeline was shut down and isolated within 19 minutes of the leak detection.
• Environmental Response: Oil recovery operations started promptly, with containment booms and underflow dams placed along Mill Creek to manage the spread of the oil. The cleanup involved vacuum equipment and manual removal as temperatures fluctuated.
• Pipeline Repair: The damaged section was replaced, and further inspections were conducted to identify and mitigate similar risks elsewhere in the pipeline system.
• Regulatory Response: The Pipeline and Hazardous Materials Safety Administration (PHMSA) issued a Corrective Action Order (CAO) under the authority of 49 U.S.C. § 60112 and 49 C.F.R. § 190.233, which required TC to take specific actions to ensure safety. These included a review and revision of backfill procedures, an evaluation of integrity threats across the pipeline, and an independent assessment of the geohazard program to understand if land movement contributed to the failure.

Total Cost of the Incident

The total cost associated with this incident was reported at approximately $600,793,659, covering cleanup, environmental remediation, and infrastructure repair.

Tips for Pipeline Operators to Prevent Similar Incidents

1. Ensure that all pipeline components meet or exceed design specifications before installation. Regularly audit and test manufacturer quality under standards like API Specification 5L.
2. Implement and strictly adhere to comprehensive backfilling procedures according to 49 C.F.R. § 195.246. Use mechanical compaction methods and avoid using frozen soil, which can lead to poor compaction and subsequent settlement.
3. Enhance welding procedures, especially for transition welds. Use counterbore and taper transitions for significant wall thickness changes to distribute stress more evenly, as suggested by MSS SP-75-2008 and TC's own welding procedure TES-WELD-AS-US.
4. Conduct thorough post-construction inspections with in-line inspection tools as mandated by 49 C.F.R. § 195.452. Establish baseline data for pipeline positioning and strain using technologies like IMU (Inertial Measurement Unit) to monitor for changes over time.
5. Monitor and manage pressure cycling and temperature changes that could fatigue pipeline materials over time, in compliance with 49 C.F.R. § 195.406. Implement strategies to minimize these cycles where possible.
6. Ensure robust emergency response plans are in place, with regular training and updates as required by 49 C.F.R. § 195.402. This includes having effective shutdown protocols and environmental response capabilities.
7. Meet not just the minimum regulatory requirements but consider going beyond in terms of safety and integrity management to prevent failures.
8. Maintain detailed records of all construction, maintenance, and inspection activities to aid in root cause analysis and prevent recurrence, adhering to 49 C.F.R. § 195.404.

This incident serves as a critical reminder of the complexities involved in pipeline operations and the need for continuous vigilance and improvement in safety practices.

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