Largest U.S. refinery shuts key crude unit, starts overhaul-sources

* Motiva overhauling CDU, coker at Port Arthur, Texas, refinery (Adds company comment, paragraph 5; background, paragraph 10.)

By Erwin Seba

HOUSTON, Feb 5 (Reuters) - The largest U.S. refinery began a planned one-month overhaul on Monday of its key crude oil processing unit, said three sources familiar with plant operations.

Motiva Enterprises Llc finished shutting down the large crude distillation unit (CDU) at its 603,000-barrel-per-day (bpd) Port Arthur, Texas, refinery on Sunday night to start the work on Monday, the sources said.

The 325,000-bpd VPS-5 CDU is scheduled to remain shut through February for the overhaul, its first since the unit began full production in 2013, the sources said.

Motiva also took down the coking unit associated with the CDU. The 110,000-bpd DCU-2 coker will be shut through mid-March for a planned overhaul, the sources said.

Motiva spokeswoman Angela Goodwin confirmed that Motiva began planned maintenance on Monday at the Port Arthur Refinery, but declined to identify the units involved.

Both units were part of a $10 billion expansion of the Port Arthur Refinery between 2007 and 2012 that more than doubled the plant's capacity to over 600,000 bpd.

VPS-5 suffered disastrous piping damage in early June 2012 from chemical corrosion, about six weeks after beginning initial production following construction. The damage required eight months of repairs.

The lengthy shutdown of the marquee crude unit strained what was then a 50-50 partnership between Royal Dutch Shell Plc (LSE: 0LN9.L - news) and Saudi Aramco.

Aramco became the sole owner of Motiva and the Port Arthur Refinery in a negotiated breakup of the partnership on May 1, 2017.

The Motiva Port Arthur Refinery accounts for 3 percent of U.S. refining capacity.

Most refinery units are shut for a full overhaul about every five years.

VPS-5 is the largest of three CDUs at the Port Arthur Refinery. The other two remain in operation.

The CDUs do the primary refining of crude oil and supply hydrocarbon feedstock for all other units.

The coker converts residual crude from VPS-5 into motor fuel feedstock and petroleum coke, which can be used as a coal substitute. (Reporting by Erwin Seba; editing by Bernadette Baum and Jonathan Oatis)