TransCanada will meet the federal requirement of at least 26 inspections per year for the Keystone XL. According to Howard, aerial surveys will be conducted about once every two weeks, along with "'on foot' inspections [that] occur more frequently as part of our operators' regular tasks and routine."

The Keystone XL will not include a concrete cap like the one used for Longhorn.

Weimer said concrete caps could prevent excavation damage, a leading cause of serious pipeline accidents. But the cap may be of limited use along the Keystone, he said, because most of the pipeline runs through sparsely populated regions that are unlikely to see much construction activity.

The Longhorn pipeline is now owned by Magellan Midstream Partners, which plans to convert the line to carry crude oil. A Magellan spokesman said the company will continue to use and maintain all of Longhorn's safety features.

Keystone Protest Continues

On Feb 17, Keystone XL opponents will gather for their fourth large protest outside the White House in hopes of persuading President Obama to stop the project. For now there is little talk about what they will do if the pipeline is approved. Anthony Swift, a policy analyst for the Natural Resources Defense Council, said it's "premature" to discuss whether his organization would push for stronger pipeline protections if that happens.

As the debate over the project continues, the National Academy of Sciences is analyzing existing research studies to determine whether dilbit corrodes pipelines more quickly than conventional crude oil. But the National Academy report isn't due until next summer, and by then it will be too late for it to have much impact on the construction of the Keystone XL. The administration is expected to make its decision in early 2013, and TransCanada has said it is prepared to begin work immediately.