2022 pipeline explosion in northern Alberta caused by corrosion: TSB

The April 7, 2022, explosion site of a Nova Gas Transmission Ltd.-operated pipeline west of Fox Creek is seen in this aerial photograph. (Source: Transportation Safety Board of Canada)

A pipeline explosion in northwestern Alberta two years ago was the result of the pipe's walls corroding, the Transportation Safety Board of Canada (TSB) has concluded.

On April 7, 2022, a natural gas pipeline about 64 kilometres west of Fox Creek ruptured, creating a 3.3-metre deep crater in the earth. The leaking gas ignited. Over the course of four hours, a total of 3.75 million cubic metres of natural gas leaked and burned 1.2 hectares.

According to the TSB report released Tuesday, a structure meant to protect the pipe surface from corrosion – called an impressed current cathodic protection system – did not do what was intended, leading to the degradation of the pipe's exterior coating.

The pipe corroded at an accelerated rate because of stray current interference from a nearby out-of-service pipe operated by a different company.

A TSB investigator listed the area's soil resistivity and an incomplete electrical bond between the neighbouring pipelines – which is used to mitigate stray current interference – as additional factors. The bond was not checked for five months, meaning the stray current interference went unmitigated for that long.

When the pipeline corroded to the point of failure, it was about one year before its next scheduled in-line inspection in February 2023.

At the site of the explosion, investigators recovered pieces of pipe that were as thin as .49 millimetres – only about 12 per cent of the wall's original thickness.

No one was hurt, the nearest body of water was unaffected, and no evacuations were needed.

The fire "self-extinguished," the TSB said, shortly after valves on either side of the rupture were manually closed.

Pipeline operator Nova Gas Transmission Ltd., a subsidiary of TransCanada PipeLines Limited, replaced the damaged sections of the pipeline and began to shut the line down permanently.

The TSB noted Canada does not have a system for organizing information about pipeline cathodic protection systems, which it says presents a risk if pipeline operators are not fully aware of the operating characteristics of infrastructure in proximity to their pipelines.