Delaware State Fire Marshal Grover Ingle said Tuesday that gas leaking from the pipe was ignited by high temperatures from nearby equipment, resulting in the May 17 fire and explosion.
The state's findings coincide with results from an internal investigation conducted by Sunoco, which said it has stepped up inspection efforts at all of its facilities as the result of the incident.
Authorities said the corrosion resulted from unseen moisture that collected between the bottom of the pipe and a loose steel support on which it rested.
