For a pipeline that is nearly half a century old, a river crossing can pose all manner of hazards. Bacteria and corrosion can attack from inside. Floodwater, scouring away the river bottom and heaving against the exposed pipe, can damage the outside. Pipes installed using old methods can be particularly vulnerable.
Sometimes, the result is catastrophe.
Last week, the Rangeland pipeline, built in 1966 and run by Plains Midstream Canada, ruptured beneath the flooding Red Deer River. It leaked 160,000 to 480,000 litres of oil, coating the banks with crude when the waters receded and leaving a large stain on Gleniffer Lake, a reservoir that supplies drinking water to Red Deer, Alberta’s third-largest city.
It may take many months to conclude what went wrong with the Rangeland pipe, and Plains has declined to comment on the cause, saying it is focusing on a cleanup effort that continued on Monday with more than 100 workers.
Today, companies building across major rivers typically use horizontal drills to burrow deep beneath the water – anywhere from eight to 30 metres – into stable rock. Those crossings are considered some of the safest parts of a pipeline. “Virtually all creeks and rivers are drilled under,” said Kevin O’Brien, president of IMV Projects Inc., a Calgary engineering firm that works on pipelines. Environmental regulations won’t even allow other methods “except in rare circumstances where not technically feasible.”
Techniques decades ago involved digging into the riverbed. Dredges, diggers and backhoes were all used, sometimes with the help of temporary dams, to open a trench for the pipe. Depending on the method, the pipe might be pulled into place, or coated in concrete, floated above the trench with barrels and then dropped down and covered with sediment.
The risks were numerous: Trenching in a flowing river meant it was difficult to create a clean bed for the pipe. Dropping it into place could introduce stress and strain, creating weak spots. And the cover was not always certain: The pipe might be buried two to three metres from the bottom of the river, but rivers are dynamic systems with the power to sweep away sediment, exposing the pipe. When they do, the force of the water can crack a pipe, or throw rocks that puncture its sides. In other cases, the trench was too shallow, compounding the problem.
“Some of those older ones, they weren’t too deep. They might have a couple, three feet of cover,” said Barry Singleton, senior vice-president of Singleton Associated Engineering Ltd., which designs pipelines. Even then, construction crews knew that what they were doing might not last.
“Lots of times they would install two crossings – they would install a spare,” Mr. Singleton said. “There were concerns back in the day.”
But external issues are only part of the potential problems. River crossings are low parts of the pipe, where water can collect, posing a risk of corrosion. Older pipes also may not be used as consistently – the Plains Rangeland system, for example, operated intermittently – which allows sediment to collect in low spots.
“Things start falling out [of the oil] and start stagnating,” said Izak Roux, technical manager for RAE Engineering and Inspection Ltd., which specializes in pipelines. A kind of mud layer can build up, and “then you can start having what we call a bacterial attack. This bacteria can eat right through the steel, and then you get a leak as well.”
Worse, many older pipes use sharp bends to get into and out of the riverbed. Those bends can make it impossible to push through cleaning tools called pigs. Neither Plains nor Alberta’s Energy Resources Conservation Board responded to questions on whether the Rangeland pipe is accessible to pigs.
But those pipes “constructed in the ‘50s and ‘60s, not all of them are piggable,” Mr. Roux said. “That’s basically the problem we have on the older lines.”