Effect of Corrosion on the Buckling Capacity of Tubular Members
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The majority of the offshore installations around the world are operating beyond their design life. These installations are subjected to a harsh marine environment and often have significant damages from corrosion. Corrosion can significantly affect the ultimate strength of tubular jacket members including the buckling resistance. A number of studies have been performed in the past on the effect of corrosion on the buckling resistance of tubular members. However, most of these studies were either based on limited experimental tests or numerical analyses of few cases resulting in semi-empirical relations. Moreover, none of the earlier proposed empirical relations considered the effect of initial imperfections. Also, there are no available guidelines and recommendations in the currently available design codes. To fulfil this research gap, a new formula is proposed to consider the effect of patch corrosion on the buckling resistance of tubular members. The proposed formula is verified with results from finite element analyses performed on several members and for varying corrosion patch parameters. The members are selected to represent the most relevant European buckling curve for tubular members. Based on this study, it is concluded that corrosion reduces the buckling resistance significantly. It is also concluded that the angular extent and thickness wastage of the corrosion patch are more critical for the buckling resistance compared to its height. The proposed formula is also applied to an existing offshore jacket structure. The buckling capacity of jacket members in the splash zone reduces significantly with ageing. This reduction is around 10% for the leg member and 22% for the brace member with a design life of 20 years. The significance and applicability of the proposed formula is therefore highlighted through this case study. Finally, it is concluded that the proposed formula can be easily applied by practising engineers for an accurate estimation of the residual buckling resistance of corroded tubular members, without the need for any advanced numerical analyses.
Master's thesis in Structural Engineering