The attacks on Tuesday, which were hours apart, sharply reduced crude oil supplies to Iraq's biggest refinery at Baiji.
The government is already struggling to build up stocks of refined oil products before winter.
The attacks did not lift oil prices, however, as speculation about a US election victory for Senator John Kerry triggered a 10% decline from last Monday's price peaks.
US crude was off nine cents at $50.04 a barrel at 1200 GMT.
Attacks against oil facilities in north and central Iraq have intensified in the past few weeks as US forces have attacked cities in central Iraq. Imports of refined products have also been disrupted.
The first pipeline attack on Monday night destroyed a section of the Iraq-Turkey export pipeline in the Riyadh area, 65km southwest of the oil producing centre of Kirkuk, officials at the state North Oil Company said.
It was followed by two attacks, including one in the Qushqaya region northwest of the city on a pipeline connected to the Bai Hassam oilfield and feeding the main export pipeline, officials said.
Reuters Television footage showed huge blazes with no fire crews to be seen.
"We cut off all flows for now. The Qushqaya fire is covering around 1 sq km. The export pipeline fire is also big. Technically, the system was shut down"
Iraqi oil official
"We cut off all flows for now. The Qushqaya fire is covering around 1 sq km. The export pipeline fire is also big," one official said.
"Technically, the system was shut down."
Iraq has been exporting some 300,000 barrels per day (bpd) in recent days via the pipeline to the Turkish Mediterranean port of Ceyhan, mainly from the Kirkuk oilfields in the north.
Shipping sources in Turkey said some crude still appeared to be flowing to Ceyhan, but at a reduced rate.
The oil is probably coming from smaller fields further north of the blast via the pumping station at Tikrit but it is unclear how long this can be sustained.
"The pumping has been sort of sporadic in the past week. It is down to about 140,000 bpd today," one shipper said.
But the sources said about 3.5 million barrels of Kirkuk crude are lying in storage tanks at Ceyhan, meaning tanker loadings can continue on schedule.
ExxonMobil's Framura tanker was due to lift 700,000 barrels later on Tuesday, shippers said.
Exports are continuing as normal
from the southern Basra terminal
The Kirkuk region produces 600,000-700,000 bpd out of the country's output of 2.6 million bpd. Exports were continuing normally via the southern Basra terminal.
Oil officials said relentless attacks since the war have cost the treasury billions of dollars in lost revenue.
Iraq's October exports were at 1.76 million bpd from Basra as well as Turkey, shipping lists showed on Tuesday.