Strength of thick-walled circular steel tubes with pitting corrosion under axial compression and bending moment

In this research the behavior of thick-walled Circular Steel Tubes (CSTs) with corrosion under axial compression and bending moment have been studied. There are several factors leading to corrosion in steel structures, especially in marine structures that results in strength reduction of whole structure. Steel tubes are widely used in construction of on-shore and off-shore structures such as, oil rigs and platforms, oil and gas transmission lines. Current study focuses on strength reduction of steel tubes with “pitting corrosion”. To this end numerical analyses using finite element software, Abaqus, have been performed. Therefore, utilizing verified models, the simultaneous effects of bending, axial load and corrosion on CSTs have been evaluated. Accordingly, by considering the dimensional characteristics of typical tubular legs of off-shore jackets, a set of parametric study has been undertaken. Pitting corrosion has been characterized in the analyses by relative mass loss ratio index, in companion with morphological indexes of the corrosion, i.e. density and depth of the pits. In accordance with the results obtained and based on the AISC360-22 formula for calculating the load bearing capacity of uncorroded CSTs under combined axial compression and bending moment, two adjustment factors were introduced to scaled down the AISC360-22 formula for accounting the degradation due to the pits. The obtained factors for the relative mass loss ratios vary between 10 to 30 percent showed an average lost bearing capacity of 20 to 50 percent as compared with intact CSTs, with a more profound detrimental effect for deeper pits. The comparison of the proposed method for estimating the lost capacity of the corroded CSTs under combined aforementioned actions in two distinct scenarios, revealed the maximum difference of 11 percent with those obtained from finite element analyses. This showed the applicability of the proposed method.