UPDATE 1-India's Chennai Petro to shut refinery units in Aug

(Adds details, background)

NEW DELHI, July 25 (Reuters) - India's Chennai Petroleum Corp (CHPC.BO: Quote, Profile, Research) will shut units at its 190,000 barrels per day refinery in the southern state of Tamil Nadu in August for planned maintenance, cutting output by up to 33 percent in the month.

It will shut a diesel hydro de-sulphurisation unit (DHDS) and a 60,000 barrels per day crude distillation unit (CDU) at the Chennai plant for most of August.

"We will shut the DHDS from August 4 for four weeks, and one to two days after that we will take a three-week shutdown of a three million tonnes (a year) CDU," Managing Director K.K. Acharya told Reuters on Friday in a telephone interview.

The closures would reduce throughput by 27-33 percent but Chennai Petroleum would continue to export normal volumes of both naphtha and fuel oil, Acharya said.

Chennai Petroleum, a subsidiary of the country's biggest oil retailer Indian Oil Corp (IOC.BO: Quote, Profile, Research), operates two refineries in Tamil Nadu with a total capacity of 210,000 bpd.

An IOC official, who did not wish to be identified, said the planned shutdown of the diesel unit had forced it to buy "extra light" grades like N'Kossa, Mallitah and Marib Light.

"We will export the normal 0.8 million tonnes of naphtha this year. There will be no impact on fuel oil exports, but our September-loading cargo could be delayed. It will be a late offer," Acharya said.

Chennai Petroleum offers a 30,000-35,000 tonne cargo of naphtha in a month for loading in the next month, and one 30,000-tonne parcel of fuel oil on average every three weeks. (Reporting by Nidhi Verma, Editing by Mark Williams)