It only took days to get the gas flowing again. It'll take a lot longer to find out why it stopped flowing in the first place.
With the restoration of natural gas service underway southeast of Winnipeg, TransCanada PipeLines must now figure out what caused an explosion along one of the lines it first strung through the Red River Valley more than 50 years ago.
At about 1 a.m. Saturday, a fireball erupted near the village of Otterburne at a valve station on TransCanada's Emerson Lateral line, a series of three parallel lines that carry gas from the Calgary-based energy company's east-west main line down to the Canada-U.S. border.
1. Stress corrosion cracking
Pipelines buried in a corrosive environment -- for example, acidic soil -- can develop tiny cracks that get worse over time and can eventually cause a section of pipeline to fail. Coatings were added to the exterior of pipes to prevent this from happening, while inspection techniques were developed to seek out the tiny cracks. Pipes are also outfitted with cathodic protection, a length of metal intended to rust instead of the pipe itself. The sacrificial metal -- essentially, an electrochemical battery -- attracts ions that otherwise would be attracted to the pipe.
2. Environmentally assisted cracking
A shift in the ground can bend a gas pipeline to the point at which it can rupture, as investigators learned following a 1996 explosion near St. Norbert. In that case, the stress caused by a slumping riverbank exacerbated a pre-existing pipe defect that may have been present in the pipe since it was laid in 1962.
TransCanada Pipelines inspected all of its river crossings following the 1996 incident. In other parts of North America, shifts in the ground can be caused by earthquakes, sinkholes or melting permafrost.
3. Human action
People who dig near natural gas pipelines can cause damage, either unwittingly or on purpose. The RCMP do not believe anything suspicious led to Saturday's explosion near Otterburne. TransCanada Pipelines said it tries to reduce the possibility of accidental damage to pipelines by placing the lines away from existing towns and cities. If human settlement does encroach on pipelines, sections may be covered in slabs, fenced off or even relocated.
-- additional sources: Transportation Safety Board, TransCanada Pipelines and Free Press files
The explosion and resulting fire left behind a crater that appears to be about 10 metres wide, based on aerial photographs taken Monday.
It also created more unease about oil-and-gas transportation in a country already sensitized to petro-disaster by oil-train accidents in Quebec and New Brunswick.
The cause of the Otterburne blast won't be known for weeks at the very earliest. Investigators from the Transportation Safety Board, along with National Energy Board staffers and TransCanada officials, first must examine the remains of the pipeline as well as the soil around it for physical and chemical clues as to what transpired.
"We simply do not know at this time," said Karl Johansson, TransCanada's executive vice-president and the head of its natural-gas division, speaking to reporters in Ile-des-Chênes on Monday.
"It's going to take time before we can figure out the cause of this fire and it's going to take some evaluation and analysis before we can give you an answer on what exactly has occurred."
The last time a TransCanada line exploded in this province -- in 2002, near the western Manitoba village of Brookdale -- the cause was determined to be stress corrosion cracking, or the chemical weakening of the pipe.
The explosion prior to that, near St. Norbert in 1996, was caused by the interaction of a slumping riverbank and a pre-existing defect in the pipe.
This weekend's incident is unusual because it took place at a valve station, where the flow of gas can be controlled. "We haven't seen an instance like this at a valve site for a very, very long time," Johansson said.
All that is known right now is one of three pipes in the Emerson Lateral line caught fire and exploded, damaging a second line and leading to a temporary reduction in flow to a third.
The first line to explode, a 76-centimetre-wide pipe, was built in 1960. Johansson said the pipe gets inspected from the outside every year, both visually, through aerial images, and chemically, with methane-sniffing equipment.
The line was last inspected from the inside in 2009 and no problems were found. Internal inspections are conducted by deploying devices known as "smart pigs" into the lines. These machines use electrical sensors and sound waves to discover defects ranging from disbonded outer coating -- a layer of tar or asphalt that protects the pipe from corrosion -- to cracks in the pipe.
Mark Yeomans, TransCanada's vice-president of pipeline integrity, said the pipe that blew up was also outfitted with cathodic protection, which is a sacrificial metal wire that helps prevent the pipe from corroding.
"TransCanada is considered one of the experts in stress corrosion cracking and natural gas pipelines," said Johansson, opining a rigorous inspection and maintenance regime can extend the life of a pipe to many decades. "Properly maintained, we don't have a period of time when we would pull those lines out."
Corrosion may not be to blame, however. The TransCanada officials said it's too soon to even speculate about the cause of the explosion. They said their staff are directed every step of the way in their investigation by the Transportation Safety Board and National Energy Board, which have at least five people on the ground right now.
"TransCanada takes this very, very seriously," Johansson said.