Corrosion Rate of Shipwreck Structural Steels under the Sea

The purpose of this study is to predict the time of oil leaking from shipwrecks due to corrosion. Generally speaking, the corrosion factors are dissolved oxygen, temperature, pH, salinity, current velocity, wave action, marine growth, bacteria and so on. The corrosion factors of ship structural steel at sea are clarified by the results of laboratory test. The results indicate that oxygen, temperature, current velocity, marine growth and bacteria have a strong influence as corrosion factor at sea. The 2 cases of immersion tests in the field at deep and shallow sea are carried out to investigate the corrosion rate of ship structural steels; one is the deep sea area of which depth is 2511 m and the other is shallow sea area of which depth is 28 m. The results of the corrosion rate obtained from above tests can be applied to predict the wastage of shipwrecks at deep and shallow sea. In the case of deep sea, the corrosion factor can be expressed by the dissolved oxygen only. This is because that temperature is almost constant around 0 degree and the current velocity does not exist. On the other hand, in the case of shallow sea, the factors of corrosion are dissolved oxygen, temperature and current velocity which influence dissolved oxygen. Moreover wave action, marine growth and bacteria are important corrosion factors at shallow sea.