The NRC findings echo those of an earlier report by Penspen Integrity, commissioned by the Canadian Energy Pipeline Association (CEPA), which found that diluted bitumen (dilbit, or synbit—bitumen extracted from oil sands and diluted with lighter crudes or synthetic crudes for transport through pipelines) is not more corrosive than comparable heavy sour crudes in pipelines—and in cases may be less corrosive. (Earlier post.)

The NRC committee was not asked to address whether the consequences of a diluted bitumen release differ from those of other crude oils.

Bitumen is a dense and viscous form of petroleum that will flow in oil pipelines only when it is diluted with lighter oils. Diluted bitumen has been imported from western Canada for more than 30 years and is transported through numerous pipelines in the United States.

With bitumen imports from Canada’s oil sands on the rise, Congress passed legislation in January 2012 calling upon the secretary of transportation to determine whether any increase in the risk of a release exists for pipelines transporting diluted bitumen. The US Department of Transportation asked the Research Council to convene an expert committee to analyze one aspect of this risk: whether pipelines transporting diluted bitumen have a greater likelihood of release compared with pipelines transporting other crude oils.

The study committee reviewed pipeline incident statistics and reports of investigations; analyzed data on the chemical and physical properties of diluted bitumen; examined the technical literature; consulted experts in pipeline failure mechanisms such as corrosion and cracking; queried pipeline operators on their operations and maintenance practices; and solicited comments from the public.

The committee did not find any causes of pipeline failure unique to the transport of diluted bitumen. In addition, it found no physical or chemical properties outside the range of other crude oils and no evidence that pipeline operators manage or maintain their systems any differently when transporting diluted bitumen compared with other heavy crude oils.

Diluted bitumen has density and viscosity ranges that are comparable with those of other crude oils. It moves through pipelines in a manner similar to other crude oils with respect to flow rate, pressure, and operating temperature. There’s nothing extraordinary about pipeline shipments of diluted bitumen to make them more likely than other crude oils to cause releases.

—Mark Barteau, professor of chemical engineering at the University of Michigan and chair of the committee that wrote the report

The report also says that shipments of diluted bitumen do not contain higher concentrations of water, sediment, dissolved gases, or other agents that cause or exacerbate internal corrosion, including microbiologically influenced corrosion, and the organic acids in diluted bitumen are not corrosive to steel at pipeline operating temperatures.

In addition, the committee found no properties in diluted bitumen that could make transmission pipelines more vulnerable to erosion, external corrosion and cracking, or damage from mechanical forces.

The study was sponsored by the Pipeline and Hazardous Materials Safety Administration of the US Department of Transportation.

The National Research Council is the principle operating arm of the National Academy of Sciences and the National Academy of Engineering.

Resources

• National Research Council. TRB Special Report 311: Effects of Diluted Bitumen on Crude Oil Transmission Pipelines. Washington, DC: The National Academies Press, 2013