OTTAWA, O.N. – The Transportation Safety Board of Canada says a stress corrosion crack caused the rupture of a natural gas line near Prince George in 2018.

On October 9, 2018, a 36-inch natural gas pipeline operated by Westcoast Energy Inc, ruptured about 13km north of Prince George.

The Transportation Safety Board of Canada investigation found that the pipeline ruptured due to stress corrosion cracks on the outside surface of the pipe; and that the polyethylene tape coating applied to the exterior surface of the pipe as a measure to protect it from corrosion deteriorated over time.

This allowed soil moisture to come into contact with the pipe surface, leading to corrosion and cracking. Growing and merging over time, the cracks reduced the load-bearing capacity of the pipeline at normal operating pressures.

Aerial view of the area affected by the fire that resulted from the pipeline rupture (Source: RCMP, with TSB annotations)

The pipeline operator had a stress corrosion cracking hazard management plan in place for this pipeline. However, the extent of the existing cracking on the segment of pipe that ruptured was not identified. The model used to predict crack growth did not take into account all potential uncertainties in the predicted crack growth. This resulted in cracks growing at higher rates than the model predicted.

Additionally, an inspection of this pipeline segment scheduled for 2017 was deferred until the fall of 2018. As such, the existing cracks remained undetected.

There were no injuries; however, 125 people within a 2 km radius of the occurrence location were evacuated as a precaution.

See the full investigation report here.

Map showing Westcoast’s T-South natural gas pipeline network and the occurrence location (Source: Enbridge, with TSB annotations