The Petroleum Safety Authority Norway (PSA) said it had identified regulatory breaches in relation to cracked gas coolers on board the Troll C platform, and ordered national oil company Equinor to rectify six non-compliances .

During an inspection of the Troll C platform on October 24, 2021, platform operator employees found a black substance under a gas cooler in the gas export compressor system. Upon investigation, the substance turned out to be asphaltene, which had leaked from the cooler through cracks in its outer casing. A similar chiller in another process train also showed signs of cracking.

The coolers were of the shell and tube type, with a gas-filled stainless steel outer shell and an inner bundle of seawater-filled titanium tubes. They were installed in 1999 and were original equipment on board of the platform.

An engineering analysis of the hull revealed that chloride stress corrosion cracking – a common vulnerability for petchem piping – had started on the outer side of the tank, below its insulating jacket, and had penetrated through the steel wall. 1.4 inches thick. The cracks occurred over time and the exact timing of formation could not be determined.

Illustrations courtesy of Equinor / PSA Norway

PSA was first informed of the incident on November 1, more than a week after the damage was discovered. The incident had no impact on personnel or the environment, but the platform had to stop production and carry out major repairs. If things had gone differently, PSA estimates, the fracturing could have evolved into a major gas leak from a pressurized ship at around 870 PSI.

PSA identified six nonconformities in its order, including maintenance flaws, failure to use available information about a common corrosion problem and late notification to regulators. “Generally, little attention has been given to the [gas coolers] by the Equinor organization on land or at sea during the operating period. Several interviewees said coolers were “off the radar” and the risk of [corrosion] has not been actively evaluated by the company,” PSA concluded.