Analyses of the Failures of Hull Structure Plating Caused by Corrosion

There are a lot of different factors of hull structure degradation such as cracks, damage, fatigue or corrosion. Fatigue and corrosion were the most thoroughly examined in the previous studies. Corrosion is a more dominant form of degradation that causes the reduction of the original thickness of materials over time, which can be expressed through weight loss, in millimeter or percentage of thickness diminution of steel plates. Corrosion process can reduce carrying capacity and longitudinal strength of vessels, cause different types of failures or lead to the pollution of surrounding areas. This study analyzes the corrosion of a structural element of a fuel tank on the old bulk carrier that has been in operation for 25 years. The database consists of thickness measures expressed as percentage of diminution of the original plate thickness and the analysis of the chemical composition of a corroded and replaced steel plate. The study examined the total of 350 measured data after 5, 10, 15, 20 and 25 years of ship exploitation. Similarly, the research observed the chemical composition of the replaced steel plate. Linear corrosion models were developed while the chemical composition was analyzed by means of Energy Dispersive X-ray analysis of the samples from both sides of the corroded plate. The obtained results indicated that the degree of corrosion significantly varies depending on the environment of the plate. Furthermore, the formed linear corrosion model adequately follows the empirical data and value of 1,55 %/year.