The crucial Forties oil and gas pipeline in the North Sea was shut for a second time in two months on Wednesday.
The latest shutdown has raised concerns about the reliability of infrastructure.
Pipeline operator Ineos said it aimed to restart the pipeline overnight.
In a statement the company said: “Ineos FPS confirms that a feed control valve closed at its Kinneil facility at around 10.20am today (Wednesday, February 7).
“Automated safety systems operated as expected to safely close the main pipeline system.
“We have now identified the issue that caused this and are hoping to resolve it this evening.
“We then plan to start-up again overnight.”
The pipeline, which pumps about 450,000 barrels per day of oil, was shut down in mid-December for about three weeks when a crack was discovered.