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A federal pipeline safety office investigation says the trans-Alaska pipeline poses a risk to public safety and the environment and that issues tied to corrosion, inspection and pipeline restarts after shutdowns must be addressed.

The Pipeline and Hazardous Materials Safety Administration handed Alyeska Pipeline Service Co. a list of proposed corrective measures tied to challenges that have spun off from having too little oil in the 48-inch diameter, 800-mile pipeline.

The pipeline currently operates at less than one-third capacity from its peak of 2.1 million barrels per day.

Less through-put means decreased crude oil temperatures and conditions that lead to corrosion.

The cooler oil allows more buildup on pipeline walls of paraffin, a corrosion hazard. Alyeska inserts paraffin pigs _ a sort of tube with fins _ inside the pipe to scrape the walls. "Smart pigs" perform other pipeline maintenance jobs, such as the detection of abnormalities in metal, but the inline inspection tools are at risk of clogging by paraffin.

Lower temperatures also means water mixed in with crude oil is susceptible to freezing in Alaska's extreme cold if the pipeline is shut down, making re-starts of the pipeline after long shutdown more risky.

"There is a risk of water accumulation in low points freezing and creating ice plugs which could impede restart of TAPS and damage valves, instrumentation, and other pipeline components," the letter said. The water itself is another corrosion hazard

The proposed safety order follows a January leak at a North Slope pump station. A containment vault collected an estimated 13,326 gallons of oil that leaked from a pump station pipe but the pipeline was shut down for days and producers for a time were limited to extracting 5 percent of capacity.

The agency proposed 13 corrective measures, including replacement of any piping in the system that cannot be assessed with smart pigs or other technology it approves.

The agency wants an assessment of the need for using additional pig launchers and receivers. The agency called for an evaluation of the need for increased tank capacity at pump stations to assist in collecting oil during prolonged outages and the implementation of a cold restart.

The agency called for a revised cold restart plan to address a prolonged shutdown, and a demonstration that it can be put into effect.

Alyeska spokeswoman Michelle Egan said Friday the proposed safety order is part of the regulatory process.

"We're requesting a meeting with them to confer about the items that are in their letter," she said. "There are several that we disagree on and there are also several items in there that we have already begun."

The company, she said, is well aware of issues associated with fewer barrels of oil in the pipeline.

"We believe that the pipeline is safe and that there are challenges that are associated with such things as low through-put. It's a large, complex system that we manage within the risks," she said.

"The fact that we were able to restart the pipeline and resume operations not only with this event occurring but also with the cold conditions and the low through-put challenges that were posed, I think is symbolic of our ability to manage it," she said.

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