Study On Approach Of Corrosion Fatigue Life Assessment For Marine Structures

Ocean engineering structures will suffer from the combined effects of corrosion and fatigue during their service, which promotes each other obviously. However, the corrosion and fatigue issues are always considered separately or added simply ignoring the nature of the corrosion fatigue, with the common problem that the tolerance of the fatigue strength results is difficult to control, even in the presence of the magnitude.As the complexity of the marine environment is hard to be simulated by the laboratory, only the real sea coupon corrosion data can be applied to actual engineering structures. In this paper, we analyzed the real sea coupon corrosion data of eight kinds of marine engineering steel, and built a power function model of the corrosion depth and the exposure time. By analyzing the electrochemical experiments and the corrosion control factors, we proved the feasibility of the application of the sea coupon corrosion data under the stress applied conditions. Basing on the corrosion thermodynamics and the kinetic equation, we analyzed the mechanical and chemical effects of the metal and built a new nonlinear corrosion model considering the mechanical factors.The spectral analysis method is commonly used in the field of marine engineering fatigue strength assessment. Combined with the recommended spectral analysis methods of ABS specifications and the new non-linear corrosion model, this paper proposed a new method to assess the corrosion fatigue damage in marine engineering structures. Throughout the evaluation process, the finite element model need to be revised based on the corrosion damage all the time. Using APDL and MATLAB, we parameterized and modularized the assessment process and developed a set of marine engineering structure corrosion fatigue evaluation software. The software takes into account the complexity of the assessment of regional plate thickness and types of corrosion inconsistent that may appear in the actual project. Hence, the software is very versatile.The presented evaluation method is based on the corrosion fatigue mechanism, considering the coupling effect of fatigue and corrosion, and is much more in accordance with the practical. By comparing the calculated results of the structural fatigue damage using the new method and the method that doesn’t consider the mechanical factors, the difference becomes more obvious with the increases of the corrosion years. Therefore, for a long period of service and the overall high stress level of the structure in marine engineering structures, the new method can assess the corrosion fatigue life more accurately.