ConocoPhillips, the second-largest U.S. refiner, shut a coker March 17 at its Santa Maria plant in Arroyo Grande for about a month of scheduled repairs, a United Steelworkers representative said.

The coker will be shut until about April 20, Steve Sullivan, an international representative for the USW, said in an interview with Bloomberg News. Sullivan is based at the USW’s District 12 office in Concord.

The two refineries are linked by a 200-mile pipeline and have a combined processing capacity of 120,000 barrels a day, according to the company’s Web site. Cokers convert heavy refinery streams into light products such as naphtha and heating oil.

Are you a subscriber? If not, sign up today and get four free issues of the Pacific Coast Business Times!