ss Great Britain iron hull: modelling corrosion to define storage relative humidity

Abstract

Brunel’s wrought iron ship Steam Ship Great Britain is corroding in its dry dock in Bristol. Corrosion control will involve sealing and desiccating the dock. The corroding iron hull forms chloride rich βFeOOH and during desiccation ferrous chloride is likely to form. βFeOOH/iron and FeCl2.4H2O/iron were subjected to controlled relative humidity (±1%) and corrosion thresholds were experimentally determined. Iron in contact with these compounds corroded above the thresholds but not below them. Iron did not to corrode in the presence of FeCl2.2H2O. The stability of this compound to moisture was determined. Corrosion was extremely slow just above corrosion thresholds, but increased significantly as relative humidity values rose to 30%. These results are being used to set an operational relative humidity for the desiccated environment around the ss Great Britain and to offer new conservation options for other historic ships. Keyword: iron, corrosion, ferrous chloride, β-ferric oxyhydroxide, relative humidity, storage.