Adel Gazzaz, the Director of Iraq's Northern Oil Company said the first explosion started a fire on Friday on a pipeline linking the northern city of Kirkuk with al-Debs oil fields, further to the north.
A second blast started a fire on a parallel pipeline running at about five metres from the first.
Firefighters rushed to the area in an attempt to extinguish the fire, Gazzaz said.
The first explosion was caused by a bomb planted on the pipeline and the second pipeline blew up because of the heat, firefighters said.
Earlier during the day, hand grenades were hurled at a disused portion of an oil pipeline outside Kirkuk, starting a small fire.
Meanwhile, two employees of the Northern Oil Company have been killed and four wounded in a roadside explosion.
The explosion ripped a company bus on the road between Baiji and the town of Riyadh, 40 km west of Kirkuk, Ghazzaz said.
"Two people were killed and the other four seriously wounded," he said.
The victims were engineers and labourers going home to Kirkuk after finishing work.