PSA issues findings on North Sea Troll platform gas cooler cracks

Offshore staff

OSLO, Norway — The Norwegian Petroleum Safety Authority (PSA) has served Equinor with an order after investigating an incident at the Troll C platform in the North Sea.

In October 2021, an inspection revealed cracking in a gas compressor cooler, with asphaltene (a heavy crude component) also found to have leaked out through cracks in a second-stage gas cooler’s outer shell.

The same process was occurring in a cooler in the parallel process train.

While there was no damage to the natural environment, the discovery led to a production shutdown with a need for repairs.

Under slightly altered circumstances, the PSA determined a major gas leak could have developed through brittle fracturing in the outer shell of one of the gas coolers.

The coolers, which held hydrocarbon gas under a pressure of 60 bar, are a shell and tube type, comprising an outer shell in 22%Cr duplex steel in which gas circulates, and an inner tubing bundle in titanium filled with coolant (seawater).

They are protected by fire insulation on the tank and flanges.

Material investigations concluded that the cracks were through-wall and instigated by chloride stress corrosion cracking, which had begun externally. Underlying causes included the design/construction of the coolers and their follow-up during the operational phase.

The PSA has ordered Equinor to ensure a level of maintenance for the HTA and HTB coolers on Troll C so they are capable of performing their required functions in all phases of their operating lives. Equinor also must make sure that failure modes related to corrosion under insulation on stainless steel materials are systematically prevented through maintenance programs on all the company’s Norwegian offshore facilities and at its onshore plants.

Deadline for compliance is Dec. 1, 2022.

5/17/2022