Equinor ordered to correct several regulation breaches on offshore platform

23 May 2022

The Petroleum Safety Authority Norway (PSA) has identified breaches of regulations following the completion of its investigation into an incident involving the discovery of cracks in the outer shell of second-stage gas coolers on Equinor’s Troll C offshore platform in October 2021. The PSA has given Equinor an order to correct six breaches of its regulations.

Troll C platform - Image: Øyvind Hagen / Equinor

Cracking in a gas compressor cooler was identified on 24 October 2021. During an inspection of the Troll C facility in the Norwegian North Sea to check the status of an ongoing job, a black substance was identified under a second-stage gas cooler.

Further investigations established that the substance was asphaltene (a heavy crude oil component), which had leaked out through cracks in the cooler’s outer shell. This was also found to be the case for a similar cooler in the parallel process train.

The incident caused no harm to people or the natural environment, but resulted in a production shutdown and substantial repair work. In the PSA’s view, the incident could have developed under slightly altered circumstances into a major gas leak through brittle fracturing in the outer shell of one of the gas coolers. The coolers held hydrocarbon gas under a pressure of 60 bar.

The gas coolers are a shell and tube type, comprising an outer shell in 22%Cr duplex steel where gas circulates and an inner tubing bundle in titanium filled with coolant (seawater). The outer shell has a specified thickness of 36 millimetres. The coolers are protected by fire insulation on tank and flanges.

Technical material investigations concluded that the cracks were through-wall and caused by chloride stress corrosion cracking (CSCC), which had begun externally. The condition had developed over time, and it is difficult to date when cracks began to develop. Underlying causes of the incident include the design/construction of the coolers and their follow-up during the operational phase.

The PSA investigation identified several breaches of the regulations, including:

- Lack of risk reduction related to material degradation
- Maintenance deficiencies
- Deficiencies in consequence classification
- Failure to use information
- Deficiencies in governing documents
- Late notification

In addition, two conditions were observed which have been categorised as improvement points:

- Maintenance programme
- Documentation of passive fire protection