Bitumen, a heavier form of petroleum, is too thick to flow in a pipeline at ground temperature, so it needs to be thinned with a very light petroleum product called diluent. The resulting homogeneous mixture is referred to as “diluted bitumen” or dilbit. Trans Mountain has safely been transporting diluted bitumen for 30 years.

Diluent is typically either light crude, such as ‘synthetic crude’, or ‘condensate’, which is extracted from the ground along with natural gas. When mixed with bitumen the resulting material, dilbit, therefore has a makeup of light and heavy hydrocarbon molecules. The resulting density is the average of the materials blended.

Does dilbit sink or float if spilled in water?

With a maximum density of 0.94, diluted bitumen is lighter than freshwater (density 1.00) and seawater (density 1.03). This means dilbit spilled into fresh, brackish or saltwater will float on the surface of the water unless another mechanism, such as wave action, mixes it into the water column, as would be the case for any oil. Only after extensive weathering may some portion become submerged or sink in freshwater, without invoking additional parameters that can modify the density of the spilled product.

Bench-top and wave tank testing carried out by a number of research organizations (see below) indicates dilbit is not likely to sink due to weathering alone within a short to medium timeframe. The evidence notes that multiple factors, such as the interaction between density, viscosity, potential emulsion formation, and environmental conditions must collectively be examined together in considering the fate of spilled oil, including the possibility of sinking.

Trans Mountain’s strict set of tariff rules and regulations outline the requirements that need to be met to ship products down our line. These rules include the specification that all product shipped have a maximum density of 0.94.

How is dilbit cleaned up in the event of a marine spill?

As dilbit is much like most medium to heavy crude oils it can be recovered using a variety of skimmer systems. As dilbit weathers, the oil viscosity increases significantly however skimmers designed for more viscous oils, including brush, belt and mechanical systems, can continue to effectively recover weathered oil (demonstrated in up to 10 days of weathering in tank tests).

In the case of any spill, response time is critical. A rapid response means the spilled product has less time to disperse and to weather, ultimately making the cleanup process more efficient and more predictable.

For more information on marine response click here.

Is bitumen more corrosive than other crude oils?

Transporting diluted bitumen is as safe as transporting other types of crude oil and it does not pose a greater risk of corrosion than pipelines carrying other types of petroleum products. The only significant difference between diluted bitumen and conventional crude is that diluted bitumen carries diluent. Neither the properties of diluent or bitumen carry any characteristics that would cause more corrosion. See this fact sheet for more information.

Diluted Bitumen Studies and Fact Sheets

The following are scientific studies and fact sheets on diluted bitumen:

Comparison of the Behaviour of Spilled Conventional and Non-Conventional Oils through Laboratory and Meso-Scale Testing 

The Behaviour and Environmental Impacts of Crude Oil Released into Aqueous Environments View Report

A Study of Fate and Behaviour of Diluted Bitumen Oils on Marine Waters View Report

A Comparison of the Properties of Diluted Bitumen Crudes with other Oils View Report

Properties, Composition and Marine Spill Behaviour, Fate and Transport of Two Diluted Bitumen Products from the Canadian Oil Sands View Report

Effects of Diluted Bitumen on Crude Oil Transmission Pipelines View Report 

Report on Dilbit Corrosivity View Report

Bitumen-Derived Crude and Corrosivity View Report

Crude quality Inc. Report Regarding the U.S. Department of State Supplementary Draft Environmental Impact Statement View Report

Alberta Innovates - Comparison of the Corrosivity of Dilbit and Conventional Crude View Report

CEPA Corrosion Fact Sheet View

CEPA Diluted Bitumen Fact Sheet View

Diluted Bitumen-Derived Crude Oil: Relative Pipeline Impacts View Report