Production from Statoil's Statfjord B platform has been reduced as a result of capacity problems in its sprinkler system.
The cutback was adopted on the North Sea installation at 14.30 on 6 August following a routine test of fire water piping in the gas compression module.
This showed that rust and wax had blocked the pipes, which form part of the overall fire protection system on the platform.
Production is currently running at 22,000 barrels per day, compared with a usual level of roughly 88,000 barrels, but should return to normal during 8 August.
"After the relevant module was shut down, we've cleared the pipes of rust particles and cleaned them with water under high pressure," says platform manager Klaus Kolloen.
This is the third time since May that various modules on Statfjord B have had to shut down because of inadequate sprinkler coverage.
A major programme has accordingly been launched on the field, which includes testing of all sprinkler systems in each platform.
Mr Kolloen says that complete fire-extinguishing coverage will be restored on Statfjord B when it resumes full production.