Inquiry into fire incident at Norwegian offshore gas platform draws to a close

Norwegian offshore safety regulator has finished investigating an incident involving a fire in a high-voltage transformer on an Equinor-operated platform in the Norwegian Sea, and followed it up with a task to the operator, seeking information on the way the identified nonconformity will be handled.

After completing its investigation of the fire incident in a high-voltage transformer on the Åsgard B platform, which occurred in November 2022, the Petroleum Safety Authority Norway (PSA) explained that the smoke and fire occurred as the result of overheating and a short circuit/arc flash in a dry-type high-voltage transformer in the utilities area on the lower deck of the gas production platform.

Thanks to this investigation, the offshore safety watchdog came to the conclusion that the direct cause of the fire was a short circuit/arc flash resulting from impairments to and/or degradation in the winding insulation over time.

In light of this, the underlying causes of the breakdown are thought to be accelerated degradation of winding insulation at the fault site as a result of overheating, and local failure and partial discharges because of transient surges from the 11 kV switchboard, while possible problems with the special configuration of the system for direct electric flowline heating could have contributed over time to internal impairments in the transformer.

While no one was injured, the incident caused a transformer breakdown and consequent loss of production, however, the PSA believes that the fire in the transformer room did not have a major accident potential. As the room has been designed to withstand fire, while little flammable material is present in the area, the regulator underscores that fire is unlikely to have spread beyond it.

“Had there been personnel in the room when the short circuit/arc flash occurred, they are unlikely to have been directly exposed except to noise and possible smoke during the seconds it takes to leave the room,” explained the Norwegian regulator.

During this investigation, the PSA identified breaches of the regulations, entailing one nonconformity related to following up and learning from incidents. In addition, the regulator observed two factors categorised as improvement points, which cover barriers and door-impaired A-60 firewall.

Following the completion of the safety watchdog’s investigation, Equinor has been asked to explain how the nonconformity will be addressed and provide an assessment of the observed improvement points.

Åsgard B is a semi-submersible floating platform on the Åsgard field with processing facilities for gas treatment and stabilisation of oil and condensates. It came on stream on 1 October 2000. This platform was the largest semi-submersible platform ever built for production in 2000, with a topside weighing 33,700 tonnes.

Located at Haltenbanken in the Norwegian Sea, about 200 kilometres from the Trøndelag coast and 50 kilometres south of the Heidrun field, the Åsgard field development concept includes the Åsgard A production vessel, the Åsgard B semi-submersible platform and the Åsgard C storage vessel. The field has been producing oil since May 1999 and gas since October 2000.

The Åsgard facilities currently receive oil and gas from seven different fields: Midgard, Smørbukk, Smørbukk South, Mikkel, Morvin, Smørbukk Northeast and Trestakk. Morvin – four wells and two subsea templates – and Mikkel – three wells and two subsea templates – are also tied into the infrastructure at Åsgard B.

The gas from the Åsgard field is routed by pipeline to Kårstø in Northern Rogaland County, where heavier components such as ethane, propane, butane and naphtha are separated out. From there, the dry gas is transported onward via the Europipe II pipeline to customers on the continent.