Scientists find conventional crudes similarly corrosive to oil sands mix

Activists opposed to the Keystone XL pipeline believe the crude it would carry would make it more prone to leaks than the existing 52,475 miles of pipelines the United States has to transport conventional crude oil.

Their fears have been underscored by a statistic: Alberta has two pipeline failures per 1,000 miles of pipeline every year. In comparison, the United States has 1.7 failures for every 1,000-mile stretch, according to the Pipeline and Hazardous Materials Safety Administration. The difference, it is thought, is that Alberta's pipelines transport diluted bitumen, also called dilbit.

Dilbit refers to a heavy oil sands crude, called bitumen, mixed with a diluent to reduce the viscosity of the material and ease flow down a pipeline. It contains higher levels of some corrosive chemicals than some conventionally produced crudes, so there is worry that Keystone XL could be more vulnerable to internal corrosion than other pipelines.

But scientists are finding that some heavy conventional crudes are just as corrosive as dilbit or more corrosive. This implies that comparing dilbit to conventional crudes is an oversimplification, since "conventional" is an umbrella term for so many different hydrocarbons. Some of the research was presented at recent conferences and to a National Academy of Sciences (NAS) panel that will deliver a report on internal corrosion next year.

The insides of a pipeline corrode when water and sand sediment settle at the bottom of a pipe that is bending, going uphill or crossing under a river. Bugs also settle into the water and begin to eat away at the metal. And certain acids and hydrogen sulfides present in both conventional oils and dilbit can speed up the erosion when they come in contact with water. So pipelines are designed to minimize the stagnation of water and sediment.


To avoid corrosion, companies have to ensure that 99.5 percent of the liquid in a pipeline is oil and only 0.5 percent is water and sediment.

"Oil does not corrode pipeline," said John Zhou, executive director of environmental management at Alberta Innovates, a research collaboration between the government and industry. "In order for corrosion to occur, you have to have water and you have to have hydrogen sulfide to accumulate in certain spots of the pipeline."

The accumulation can happen in both conventional crude pipelines and dilbit lines, he said.

The reason Alberta has a slightly higher pipeline failure rate than the United States is that the province keeps a better record of spills, said Zhou. Alberta requires companies to report all spills, regardless of size, whereas the United States only notes spills larger than 5 barrels.

Corrosion comparisons

Water enters Alberta's oil sands system through steam. Operators pump vapor into underground reservoirs to melt the tar-like bitumen and bring it to the surface. During the process, temperatures can rise as high as 480 degrees Farenheit, at which point some of the sulfides in bitumen convert to corrosive hydrogen sulfide (H2S), Zhou said.

But even so, studies at the Alberta Innovates laboratory have shown that dilbit contains less H2S than some conventionally produced heavy crudes in Canada, said Zhou. The results have not yet been published in a journal.

It bears noting, however, that the H2S in dilbit far exceeds the levels found in conventional oils in the United States, including heavy crudes imported from Venezuela. In measurements made by Intertek, a laboratory that submitted its results to the NAS panel that were obtained by EnergyWire, all crudes measured in the United States contained less than 10 H2S particles per million other particles, a measure called parts per million, or ppm.

Light, sweet crude such as West Texas Intermediate (WTI), the benchmark crude in the United States, had less than 10 ppm of H2S. Oklahoma sour, a conventionally produced crude, also had less than 10 ppm.

In comparison, dilbit from Cold Lake in Alberta contained 300 ppm of the gas. A blend of conventional oil and dilbit, called Western Canada Select (WCS), contained 400 ppm.

Levels of H2S were highest in some conventionally produced heavy crudes in Canada. Bow River (BR) crude, a conventionally produced heavy oil, contained more than 2,000 ppm of hydrogen sulfide. So did the Midale Sour and the Mixed Sour blends (MSO).

Acid test

KXL watchers have expressed concern that dilbit contains more acidic compounds than most conventional oils. But the acidic compounds do not pose a threat at the temperatures at which pipelines operate, said Sankara Papavinasam, a researcher at Natural Resources Canada's CANMET Materials Technology Laboratory.

The lab exposed pipelines to dilbit and water at 150 degrees Fahrenheit, close to the temperature of transport of dilbit pipelines, for about 14 days.

They found that at these temperatures, the acid in dilbit does not correlate with greater corrosion of pipeline, said Papavinasam. The results were presented at a conference in Toronto last month.

Papavinasam said that internal corrosion results from the settling of water and sediment, a problem that can be handled by better pipeline design.

Real-world research

Another activist concern is that laboratory-based research does not take into account the combined effect of multiple stresses that a pipeline undergoes in the real world. That is what happened when Enbridge Energy pipeline Line 6B, which carries dilbit, leaked about 900,000 gallons of oil into the Kalamazoo River in Michigan in 2010.

The National Transportation Safety Board found that the failure happened in part because Enbridge had evaluated external corrosion and stress corrosion as separate issues and did not look into how they would interact, said Anthony Swift, an attorney with the Natural Resources Defense Council.

"There is a danger of taking out one risk and viewing it in isolation," said Swift, who first raised the possibility that dilbit might be more corrosive than conventional crudes in a report.

The issue could be put to rest if a section of Line 6B could be inspected, wrote Robert Whitesides, treasurer for the Kalamazoo River Watershed Council, in an email to an NAS panel. Enbridge will be retiring sections of the pipeline traversing Michigan and Indiana and installing new pipelines. The company currently plans to leave the older sections buried in the ground. Line 6B is unique since it has been carrying dilbit for many years and could be a real-word laboratory for studying the effect of dilbit.

Public concern about dilbit pipelines elevates risk, and governments need to be more careful in approving them, said Oliver Moghissi, vice president at the independent risk assessment firm Det Norske Veritas (DNV), to the NAS panel. The added regulations are warranted even though research has shown that dilbit lines are not more vulnerable to internal corrosion than other pipelines, he said.

Pipeline and Hazardous Materials Safety Administration officials also acknowledged to the NAS panel that the composition of dilbit is similar to that of other U.S. crudes and "no additional corrosiveness or abrasiveness issues found."

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