It has taken on the air of fact among those seeking to halt pipelines designed to carry crude from the oil sands. The diluted bitumen those pipelines would carry, critics say, is more corrosive than "normal" crude. In other words, the chemical nature of oil sands crude places the steel it travels through at risk.
But a new study conducted by federal scientists finds exactly the opposite: Diluted bitumen is not more corrosive. In fact, when comparing four types of dilbit, as it's called, with seven other kinds of oil, the dilbit is among the least corrosive.
The study is a major strike against a key argument made by opponents of pipelines such as TransCanada Corp.'s Keystone XL and Enbridge Inc.'s Northern Gateway.
Just last week, Quebec Environment Minister Daniel Breton argued that Alberta crude was found to be more corrosive on older pipelines and could result in spills, as he warned Quebec could oppose a plan to pipe western oil through the province to eastern markets.
The challenge to those claims comes from work conducted by a Natural Resources Canada lab in Hamilton.
It builds on efforts that have seen government researchers test the corrosive qualities of oil since 1993. For the latest study, conducted this year, they compared various types of oil with a salt solution, which corroded pipeline steel at a rate of nearly 20 milli-inches per year. Anything below four is considered non-corrosive. The dilbit came in at three and below.
In fact, "we are not seeing any corrosion rate which is more than around four ... in all the around 100 crude oils we have tested so far" in two decades of work, said Sankara Papavinasam, a research scientist with Natural Resources Canada.
As for dilbit, "we did not see any difference whatsoever. We could not differentiate" it from other types of oil.
Dilbit also tends to be a more acidic crude, but "we did not see any correlation between TAN" – that refers to Total Acid Number – "and the corrosion rate under pipeline operating conditions," said Mr. Papavinasam.
Alex Pourbaix, president of energy and oil pipelines for TransCanada, said the study could be "meaningful" to efforts to get Keystone XL built.
"All of these things coming out make it more difficult for the opponents of this pipeline to continue spinning the misrepresentations and exaggerations that they have been prone to," he said.
The NRC tests were carried out at room temperature, roughly matching the 10 to 20 degrees Celsius that is normal for oil moving through pipelines. But TransCanada, for instance, suggests Keystone XL will operate at temperatures up to 54 degrees. That's significantly above the conditions used by federal scientists, and the variance is enough that environmental groups continue to be skeptical, saying dilbit could still be more corrosive at higher temperatures – as it is, conclusively, in refineries, which operate at 500 degrees Celsius and above.
"The temperature issue is a key one," said Anthony Swift, an energy analyst at the New York-based Natural Resources Defense Council. Mr. Swift was the lead author on a report that made public the notion that dilbit could be risky. That February 2011 publication, whose information has often been repeated by pipeline opponents and even U.S. legislators, concludes that "There are many indications that DilBit is significantly more corrosive to pipeline systems than conventional crude."
Asked if the federal study would persuade him to acknowledge that science has found differently, Mr. Swift said: "if it does, we will." He reiterated that temperature creates concerns both for internal and external corrosion, and that friction from the oil travelling through the pipe also serves to elevate the temperature.
But in some ways, the science already has spoken, and Mr. Swift's concerns are not shared by at least one of the scientists tasked by the U.S. government to provide a definitive evaluation of the dangers of dilbit. Frank Cheng holds the Canada Research Chair in Pipeline Engineering at the University of Calgary. He is the sole Canadian researcher among 12 experts chosen by the National Academy of Sciences to examine the corrosive properties of oil sands crude for the U.S. Congress. Their report is due at the end of 2013; it is primarily a literature survey, and will rely in part on the Natural Resources Canada work.
It is true, Mr. Cheng said, that higher temperatures produce more corrosion, and dilbit pipelines typically operate at 50 to 60 degrees Celsius, he said. But the difference in corrosion rates at 60 degrees and 20 degrees "in my opinion is minor. So it's not significant," he said. As for friction heating? Mr. Cheng's inquiries, including a field trip to speak with pipeline operators, have generated a similar finding: it happens. But it is not, he said, "an issue."