PetroChina will shut down its 200,000-barrel-per-day (bpd) Dushanzi refinery in northwestern Xinjiang from early August for a 50-day turnaround, an industry source said on Friday.

Previously, the maintenance was tentatively scheduled to be conducted in June or July.

It was not immediately clear why the overhaul was delayed.

But PetroChina will close almost half of the effective refining capacity in Lanzhou refinery, in Gansu province that neighbors Xinjiang, from June 20 for nearly one-month maintenance. The two refineries are the largest in northwestern China.

Dushanzi, processing mainly Kazakhstan crude oil, was fully commissioned in September 2009 after replacing several old crude oil units with a new 200,000-bpd unit and adding a 1-million-ton-per-year ethylene cracking unit.