The Forties pipeline, which carries 40% of North Sea oil and gas, is to be shut down while workers repair a crack.
Oil prices climbed on the announcement, with Brent crude up 2% to just under $65 a barrel – a fresh two and a half year high.
Ineos, which operates the Forties network, said a small hairline crack in the pipe was found last week during a routine inspection south of Aberdeen.
A cordon was set up and residents placed in temporary accommodation while the pipeline pressure was reduced and a full assessment made.
In a statement, Ineos said: “Despite reducing the pressure the crack has extended, and as a consequence the incident management team has now decided that a controlled shutdown of the pipeline is the safest way to proceed.
“This will allow for a suitable repair method to be worked up based on the latest inspection data, while reducing the risk of injury to staff and the environment.
“As always, safety remains our top priority and local residents, Forties Pipeline System users and other stakeholders are all being kept fully informed of the situation as it develops.”
Ineos said that up to now, no oil or gas seepage had been detected and that the pipe was being closely monitored.
The crack in the three-foot wide pipe has widened to 155mm (6 inches), the company said.
Ineos director Tom Crotty said the work would probably take a “couple of weeks” but he did not believe there would be any impact on the public.
Additional oil and gas will instead be shipped in from overseas.
Ineos bought the pipeline system from BP earlier this year in a deal worth up to $250m (£187m).
The 235-mile pipeline transports oil extracted from thousands of feet beneath the seabed 105 miles to the Cruden Bay terminal, near Peterhead, and then a further 129 miles to Kinneil processing plant next to the refinery and petrochemicals complex at Grangemouth.
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Oil prices tend to rise on any sign of a squeeze in supply.
Brent crude had already been trading around its highest levels since the summer of 2015 before the Ineos announcement.