Company spokesman Grady Semmens said Monday the pipeline was safely restarted earlier in the day, but it will flow with reduced pressure for the next 24 hours while the company completes testing.
"Once the pipeline system is operating at full pressure, we will be curtailing October volumes and will return to contractual delivery levels in November," he said.
"We will be having direct discussions with our customers regarding the impact this will have on their deliveries to us
The line, which delivers about 500,000 barrels of crude each day from the oilsands to refineries in Illinois and a storage hub in Oklahoma, was shut as a precaution last Wednesday after a "small anomaly" was discovered on the outside of the pipe and tests showed public safety concerns.
The potential problems were detected in a section of the line between Missouri and Illinois. TransCanada had planned to restart the pipeline Saturday, but bad weather complicated efforts to move equipment into the area so workers could excavate the pipeline for inspection.
The temporary closure isn't expected to affect refinery production or retail gas prices because crude supplies are plentiful.
The shutdown comes amid delays over TransCanada's plans to build a $7 billion pipeline called the Keystone XL that would transport heavy tar-sands crude oil from Canada to Texas' Gulf Coast refineries.
Opponents warn the new pipeline would be carrying heavy, acidic crude oil that could more easily corrode a metal pipe and lead to a spill. TransCanada says its pipeline would be the safest ever built.
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