The Petroleum Safety Authority Norway (PSA) says that it has identified regulatory breaches in connection with cracked gas coolers aboard the platform Troll C, and it has given state oil company Equinor an order to rectify six nonconformities.
During an inspection of the Troll C platform on October 24, 2021, the platform operator's employees found a black substance underneath a gas cooler in the gas export compressor system. On investigation, the substance turned out to be asphaltene, which had escaped from the cooler through cracks in its outer shell. A similar cooler in another process train had signs of cracking as well.
The coolers were of the shell and tube type, with a stainless steel outer shell filled with gas and an inner bundle of titanium tubes filled with seawater coolant. They were installed in 1999 and were original equipment aboard the platform.
A technical analysis of the shell revealed that chloride stress corrosion cracking - a common vulnerability for petchem pipework - had started on the outer side of the tank, underneath its insulating jacket, and had penetrated through the 1.4 inch thick steel wall. The cracks occurred over time, and the exact timeline for formation could not be determined.
Illustrations courtesy Equinor / PSA Norway
PSA was first notified of the incident on November 1, more than a week after the damage was discovered. The incident had no effect on personnel or the environment, but the platform had to shut down production and carry out extensive repairs. If things had gone differently, PSA believes, the fracturing could have evolved into a major gas leak from a vessel pressurized at about 870 PSI.
PSA identified six nonconformities in its order, including maintenance deficiencies, failure to use available information about a common corrosion issue, and late notification for regulators. "Generally speaking, little attention has been paid to the [gas coolers] by Equinor’s organization on land or offshore during the operating period. Several interviewees said that the coolers have been 'off the radar,' and the risk of [corrosion] has not been actively assessed by the company," PSA concluded.
