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Manufacturing defect, ineffective cathodic protection led to fatal 2019 pipeline explosion

15 September 2022

The US National Transportation Safety Board (NTSB) announced on September 14 that the rupturing of a 30-inch natural gas pipeline owned by Enbridge Inc. and a subsequent fire caused the 2019 death of one person and the destruction of five homes near Danville, Kentucky.

Post-rupture aerial view of the accident area - Google Earth image, NTSB graphic overlay by Christy Spangler
Post-rupture aerial view of the accident area - Google Earth image, NTSB graphic overlay by Christy Spangler

The accident occurred when a 30-inch pipeline, owned and operated by Enbridge Inc., ruptured and released natural gas that ignited on August 1, 2019. Fourteen other residences were damaged, and the fire burned around 30 acres of land.

NTSB investigators determined that the combination of a pre-existing manufacturing defect – known as a hard spot – together with a degraded pipeline coating and ineffective cathodic protection, led to hydrogen-induced cracking at the outer surface of the pipe.

Contributing to the accident, according to the NTSB, was Enbridge’s integrity management program, which did not accurately assess the condition of the pipeline or estimate the risk from interacting threats. The report said Enbridge underestimated the risk posed by hard spots because its processes and procedures were inconsistent with PHMSA guidance and industry knowledge of hard spot threat interaction.

Investigators noted Enbridge and its predecessors increased cathodic protection voltages on the affected pipeline segment to compensate for the increased external corrosion. Buried steel pipelines will corrode because of the presence of moisture and ground water in the soil. Cathodic protection is an electrochemical method used to prevent corrosion on buried pipelines where the applied coating has been damaged, exposing bare pipeline metal to the soil.

Based on the results of its investigation, the NTSB issued six safety recommendations, three to the Pipeline and Hazardous Materials Safety Administration and three to Enbridge Inc. The safety recommendations address:

- Incomplete evaluation of the risks caused by a change of gas flow direction;
- Limitations in data analysis related to in-line inspection tool usage;
- Incomplete assessment of threats and threat interactions;
- Missed opportunities in training and requalification practices.

The Pipeline Accident Report 22/02 is available online and can be ready by clicking here

The accident docket, which contains interviews, photos, and other factual material can be seen by clicking here.

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