Alaska oil spill may signal wider problems-state

By Yereth Rosen

ANCHORAGE, Alaska, Dec 19 (Reuters) - Alaska officials are investigating the cause of a pipeline rupture on the North Slope earlier this week that they say could be a sign of more widespread corrosion problems at the state's aging fields.

The 4,284-gallon spill from the ConocoPhillips (COP.N: Quote, Profile, Research, Stock Buzz) line on the Kuparuk field was caused by rare rust on the outside of the pipe beneath a layer of insulation, according to preliminary findings by the company and the Alaska Department of Environmental Conservation.

"It's definitely gotten our attention because it's a different type of corrosion. Is this an indicator of what's going on throughout the field, or not?" said Leslie Pearson, emergency preparation and response program manager for the Department of Environmental Conservation.

Other recent leaks from North Slope pipelines have been from internal corrosion after inadequate internal 'pigging' inspections, including the small hole in BP's (BP.L: Quote, Profile, Research, Stock Buzz) western Prudhoe Bay line that caused a 200,000-gallon oil spill in March 2006, the North Slope's biggest.

The Conoco spill was discovered early Sunday morning and cleanup crews have been working since to remove the spilled oil, which soaked through the thin snow layer and was sprayed by high winds, Pearson said.

External pipeline corrosion is not unheard of on the North Slope but it usually occurs at weld sites and along the bottom of the pipe, Pearson said. The Conoco line rusted through along the side of the pipeline, away from any welds.

Pearson said the department was still trying to find out the age of the pipeline, and whether others at Kuparuk or elsewhere are of the same vintage.

"We're not going to make the assumption that it could not be going on elsewhere, given this incident," she said.