Exclusive: After setbacks, Motiva refinery faces lengthy 2014 work - sources

The biggest U.S. oil refinery could shut its main crude distillation unit for up to three months next year to replace a vibrating pipe that prevents the 325,000 barrel per day (bpd) unit from running at full capacity, sources familiar with operations said

That would be another blow to the Motiva Enterprises , 600,000 bpd plant since the $10 billion refinery, in Port Arthur, Texas, opened last year. Motiva is owned by Royal Dutch Shell and Saudi Aramco .

"In keeping with our disclosure policy, we cannot provide detail on the timing of maintenance at specific units, or how long it will take to complete maintenance activities," a Shell official said.

The fall of 2014 is likely the earliest time repair work could be carried out on the 16-inch pipe, which moves crude in the refinery's main unit, the VPS-5 unit, and suffers from excessive vibration, according to the sources.

This means the refinery would be without its main crude unit just as markets seek to build up inventories of distillate ahead of winter.

"It will have to be a larger pipe," said one of the sources. "It will be a fix of the fix they made after the caustic leak," said the source, referring to repairs following from a chemical leak in mid-2012.

The refinery has faced numerous problems.

Last year, it was forced to shut the main unit, the centerpiece of the massive expansion that made Port Arthur the biggest U.S. plant, for seven and a half months of work after a small chemical spill of undiluted caustic sodium hydroxide into the system that pitted and cracked thousands of feet of stainless steel pipe.

VPS-5 has only reached its rated capacity of 325,000 bpd one time and rarely run above 300,000 bpd. Most often it runs between 250,000 bpd and 280,000 bpd, and rates are next expected to go beyond that until the pipe is replaced, sources said, due to the vibrations caused by running at full throttle.

The vibration can cause leaks on the pipe, which had already been replaced once due to the caustic spill.

Plans to boost the crude unit's capacity by 20 percent by improving its efficiency were scrapped in March due to the pipe vibrations.

Replacement of the pipe would come after the refinery moves past two fires last week that shut three units.

Those fires, which affected a hydrocracker and a sulfur recovery unit, will take at least two weeks to recover from, sources said. The second fire prompted the idling of the main distillation unit called VPS-5 but did not damage it.

(Reporting by Erwin Seba; Editing by Terry Wade and Steve Orlofsky)