Fatigue Analysis Of Ice-resistant Offshore Platform Under The Condition Of Corrosion

Ice-resistant Jacket platform is the most important form in developing ocean oil of cold region, which is generally used in Liaodong bay. But it is indicated that ice-induced vibration of ice-resistant platforms is quite intensive, and directly endangers the structural safety according to the monitored data on several platforms in the Liaodong Bay of Bohai Sea in past years. Ice load is the most preponderant factor to the working offshore platform in ice region. Ice induced vibrations will result in severe structural damage. Besides, the metal uniform corrosion caused by environment can also make structural mechanism performance decline. The essence of fatigue under corrosion condition is the interaction of electrochemical process and mechanical process. Combined effect is far more than the simple superposition of the two effects above,and it will bring great decline of fatigue life.Evaluation of fatigue life is often considered without corrosive effect, which will make the result higher than it is. Considering corrosion effect, corrosion rate can be regarded as an average random variable, which treates the decrease of thickness as a linear variation with the time changing. However, current corrosion experiment data indicate that single linear model cannot describe the complex metallic corrosion behavior well.According to environmental conditions and mechanical characteristics, it is necessary to develop extensive research on corrosion of platform and fatigue life. Based on the proper nonlinear uniform corrosion model, we calculate the leg equivalent remaining thickness under the condition of corrosion, and analyse the fatigue problem under corrosion. According to the field data of ice load history and ice-induced response ,we establish the ice fatigue environmental model of the JZ20-2 area in the Bohai Sea, fully considering the effect of structural dynamic characteristics caused by corrosion. The ice-induced fatigue life of JZ20-2NW platform is done with the spectral method in details to make the design economical and rational.