Bangkok to Los Anglese via Chengdu Airport and Nanjing Airport

Hi, I'm holding dual passports for Australian Passport (Citizen) and Thai passport. I'm traveling from Bangkok to LA via Chengdu Airport then refueling at Nanjing Airport during transit in 8.5 hours. do I need to apply transit visa or I'm qualify for 72 hours free transit? if I need to apply transit G type, which passport should I use (Australian OR Thai) ? Please advise me so I will go ahead with my application. Thanks..Aree (28/03/2016)