KUALA LUMPUR, June 21 (Reuters) - Hengyuan Refining Company Bhd expects an impact to its revenue following an unplanned shutdown of its long residue catalytic cracking unit (LRCCU), the firm said in a bourse filing late Thursday.

Hengyuan said it plans to shut down the unit for inspection and repairs after a leakage was found at its carbon monoxide boiler on Wednesday. The LRCCU is used to convert high-boiling point hydrocarbon fractions of crude oil into high-value consumer petroleum products.

Production at the Port Dickson-based refinery on Malaysia's west coast will be affected during the shutdown period.

"Given current uncertainties, the financial impact of this incident cannot be reliably estimated at this point, but is expected to be material for the company," Hengyuan said.

The company said it will launch measures to ensure there's no major disruption of production supply to its customers during the shutdown period.

Hengyuan is a subsidiary of China's Shandong Hengyuan Petrochemical Co. The Port Dickson refinery has a licensed capacity of 156,000 barrels per day.

(Reporting by Rozanna Latiff; Editing by Sherry Jacob-Phillips)