The client wanted a safety case to extend the operating life of a power station boiler gas seal by several years. The component is a seal plate through which a steam penetration passes into the boiler casing. The gas seal operates at a high temperature in a carbon dioxide environment and following a review of the effects of corrosion, concerns were highlighted over possible thinning. Owing to its location, inspection of the component was deemed impractical. Previous assessments had considered only the uncorroded state, and it was considered that creep damage to the corroded state could undermine the proposal to extend the plant life.