Anode consumption and coating breakdown on a X-mas tree installed at the Troll Field in the Norwegian North Sea was investigated after 5 years. A comparison with a spare tree and one tree being exposed for only 3-4 months was done. The epoxy coating has several blisters, in particular on stainless steel surfaces. Water inside the blisters has a pH of 13-14 indicating that the cathodic reaction occurs inside them. The anode
dimensions indicate an overall anode consumption of approximately
20%, while the design allows 27% after 5 years. This indicates that the original design is quite conservative. If the design had been done according to present day design rules, the conservatism would be reduced; an overall anode consumption of 23% is then likely (still less than allowed 27%).