Study of the corrosion mechanisms of steels corroded without and with cathodic protection on the site of metal wrecks sunk during the Second World War (HF)
Thousands of metal wrecks dating from the first two world conflicts lie along the French coast. These wrecks degrade under the effect of corrosion and collapse under the simultaneous effect of the increasing weight of the marine concretions and the reduction of the thicknesses of the structures by corrosion. The degradation of submerged metal wrecks has major consequences for cultural and historical heritage, since with their collapse a whole part of our history is erased. In addition, they can be the source of the release of polluting compounds and metals. The degradation of wrecks can therefore have dramatic consequences not only for heritage but also for the environment. To protect these wrecks and prevent them from disappearing completely, the project proposes to implement cathodic protection treatments on these wrecks. Cathodic protection is recognized as an effective method to protect steel from corrosion. Cathodic protection, commonly used in off-shore environments, in naval and port contexts, is well mastered for new materials launched. However, implementing it on submerged metal structures already colonized and covered with thick layers of corrosion products is a real scientific and technical challenge. To do this, the project has a twofold objective: on the one hand to gain a better understanding of the degradation mechanisms of wrecks, on the other hand to implement cathodic protection treatments on the wrecks. The specific methodology developed during the project consists of working on two wrecks located in two different environments: one in the English Channel and the other in the Mediterranean. These wrecks will be studied from the metal core to corrosion products and the links they develop with its environments close to the sedimentary layers to the characterization of biodiversity with or without cathodic protection. The first results obtained during on-site measurements of wrecks coupled with laboratory experiments concerning the electrical current requirements for cathodic protection have already been initiated. The characterization using a multi-scale approach for the study of the layers of corrosion products and the biodiversity on samples taken from the two wrecks (sheet metal from the wrecks, sediments, water) are in progress.