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Kinder Morgan and various authorities contend that dilbit’s acidity is no problem. Studies by Canada’s CanmetENERGY agency found that “corrosion rates were very low” in pipelines transporting dilbit, “and did not correlate with [total acid numbers]." “We’ve transported bitumen in pipe for about 30 years,” says Trans America engineer Mike Davies, “and haven’t experienced any integrity issues. It’s not corrosive and not abrasive, and the difference in acidity is not significant.”
But that difference is certainly substantial. According to one industry tabulation, dilbit is five-plus times as acidic as benchmark Mexican Maya crude. It’s no more viscous than heavy, sour Canadian conventional crudes, but it's on average about twice as acidic and a third more sulfurous. Another way of looking at it: the share of acid by weight in dilbit is a fifth to half that in commercial vinegar, a liquid customarily deemed too corrosive to store in metal.
Heat is the other big question in piping dilbit, and it’s also a controversial one. Higher heat amplifies liquids’ corrosiveness; according to an industry rule of thumb the corrosion rate doubles with each additional 10 degrees Celsius. All oil gets warmed by friction as it pushes down a pipe; the question is how much.
Tar sands opponents contend that dilbit gets much hotter than conventional crude, thanks to more abrasive grit and higher pressures needed to move it. Not so, Kinder Morgan once again insists: “Dilbit products shipped in our pipeline do not get warmer than conventional crude,” Davies declares. “We monitor temperatures within the pipeline and there is little difference between crude types. Overall temperatures do vary seasonally. In winter temperatures are typically 10 C or less, and in summer they are typically 20 C or less. There is no need to undertake any cooling measures.”
Scientific data on pipeline friction seems to be skimpy. It’s one of the questions being examined by a panel of the U.S. National Academy of Sciences deputed to determine the risks of pipeline damage from dilbit.
The pipeline industry meanwhile prides itself on not suffering any “releases of oil caused by internal corrosion from pipelines carrying dilbit” for the 10 years leading up to mid-2012. But it’s had ample mishaps of other sorts, including several on the Trans Mountain line.
In 2007 a construction backhoe broke a pipe at the Burnaby depot, sending oil pouring into Burrard Inlet and forcing the evacuation of some 50 homes. In January 2011 Trans Mountain operators ignored warning alarms for a reported three-and-a-half hours while some 25,000 gallons of oil spilled through a failed gasket at its Sumas tank farm. Canada’s National Energy Board scored Kinder Morgan for many operational failings. And last month at Vancouver (though not at Kinder Morgan’s facility) a ship crashed into Westshore Terminals, North America’s largest coal port, spilling a heap of coal and dust into the fish-rich Fraser Delta. At least it wasn’t oil, terminal officials said, trying to look on the bright side. That would be harder to clean up.
Even harder if it were dilbit. The problem lies partly in bitumen’s stickiness — in air, it dries like varnish on rocks and other surfaces — and partly in its weight. Conventional crude is lighter than water; it mostly floats to the surface, where it can evaporate and be skimmed. Straight bitumen is denser; it sinks to the bottom and penetrates sediments and substrates. Diluted bitumen has about the same density as water, which makes it hang in the water column.
The industry maintains that dilbit is so thoroughly homogenized, the bitumen and diluents can’t separate. That may be true when it's contained, but it didn’t hold in July 2010 when an Enbridge pipe carrying dilbit ruptured near Marshall, Michigan, causing the costliest pipeline spill in U.S. history.
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