(Compares with estimates; adds details, background)
Jan 31 (Reuters) - U.S. refiner Phillips 66 missed analysts' estimates for quarterly profit on Friday, hit by lower margins and higher turnaround activity at its refineries.
Turnarounds, which are planned capital projects, are a core part of the refining business and help prevent unexpected shutdowns and accidents.
The company said adjusted earnings at its refining segment plunged nearly 83% to $345 million in the quarter, as the refiner's crack spread, or the difference between the price of crude oil and finished products, fell in the quarter.
Refiners in the U.S. have been facing challenges to obtain low-cost heavy crude, as prices have been hit by production cuts from Canada's Alberta province, the Organization of Petroleum Exporting Countries as well as U.S. sanctions on Venezuela and Iran.
Adjusted earnings fell to $689 million, or $1.54 per share, in the fourth quarter ended Dec. 31, from $2.26 billion, or $4.87 per share, a year earlier.
Analysts on average had expected profit of $1.56 per share, according to IBES data from Refinitiv. (Reporting by Shradha Singh in Bengaluru; Editing by Amy Caren Daniel)