Equinor is facing more headaches with its beleaguered Johan Castberg project off Norway after the discovery of a critical software issue that could seriously impact on-field operations of the scheme's under-construction floating production, storage and offloading unit.

The error in the software provided by classification giant DNV GL has the potential to lead to significant underestimation of fatigue damage on weathervaning units, the Norwegian state-controlled operator said in a document shared with safety regulator officials and seen by Upstream.