The cause of the explosion on Monday was not clear. It was not immediately known whether the pipeline was the main oil export pipeline running to Turkey.
Fighters blew up another pipeline feeding the 350,000 barrels per day (bpd) Baiji refinery earlier on Monday. Crews managed to put out the fire, around 25km southwest of the oil centre of Kirkuk, security officials said.
The northern export pipeline passes near the area of the two explosions.
Officials at the state North Oil Company said before the second blast that export flows to Turkey's Ceyhan port were running at 300,000 bpd.
Iraq could export up to 600,000 bpd through the northern pipeline, depending on its condition and the level of storage tanks at Ceyhan.
In the south, exports were running normally with two tankers loading at the Basra offshore terminal, formally known as Mina al-Bakr, a shipping agent said.
The tanker Marcos was loading at the rate of 25,000 barrels per hour and the Apollo at 46,000 barrels per hour.
Three tankers were waiting to load, including one at the nearby Khor al-Amaya terminal.