BP's main crude unit at Whiting shut for at least a month -sources

(Adds source comment, market reaction)

HOUSTON, Aug 11 (Reuters) - Heavy damage to the largest crude distillation unit at BP Plc's 413,500-barrel-per-day (bpd) Whiting, Indiana, refinery will require at least a month to repair, sources familiar with the refinery's plans said on Tuesday.

The sources stressed that the time frame for the CDU's restart was preliminary and may change.

"I would expect longer rather than shorter," one of the sources said.

Piping inside the 240,000 bpd CDU, called Pipestill 12, which processes heavy sour oil crude, was damaged in a malfunction on Saturday.

BP spokesman Scott Dean declined to discuss operations at the oil major's largest refinery in the United States.

News (Other OTC: NWSAL - news) on the length of the unit's outage was fiercely sought after by refined products and crude traders because of the impact the loss of production at the refinery could have on prices.

The Whiting crude unit outage was said to contribute to U.S (Other OTC: UBGXF - news) . crude's fall of $1.88, or more than 4 percent, to $43.08 a barrel, the lowest settlement since March 2009, and about $1 above the 2015 contract low on March 18.

RBOB gasoline in the New York Harbor was virtually unchanged from Monday at $1.6937 a gallon, but up 7 cents a gallion from Friday's finish.

Refining crack spreads climbed $2.00 a barrel to $28.00.

At the Whiting refinery, examination of the damaged crude unit was continuing on Tuesday, the sources said.

Pipestill 12 was the centerpiece of a $4 billion refit of the refinery to run more sour crude from Canada's tar sands fields in Alberta. The rebuilt Pipestill 12 came on-line in July 2013.

BP sold off refineries in Texas and California in 2013 to focus its U.S. refining operations on plants with easy access to Canadian crude.

Crude distillation units do the initial refining of crude oil coming into a refinery and produce feedstocks for all other units. (Reporting by Erwin Seba; Editing by Jonathan Oatis, Marguerita Choy and Andrew Hay)