Stress-strain model of lower corroded steel plates of normal strength for fitness-for-purpose analyses

This study investigates the mechanical properties of specimens made of normal strength steel subjected to lower marine immersed corrosion degradation levels (below 25 %). The specimens were corroded in laboratory conditions, and only natural factors were controlled to raise the corrosion rate (reaching the level of 1 mm/year). Three different thicknesses of plates made of normal strength of shipbuilding steel are investigated (between 5 and 8 mm). The standard tensile tests are performed for estimating the stress-strain behaviour of corroded specimens. Non-corroded specimens were tested to establish the initial mechanical properties and uncertainty level as a reference. Further, the corroded specimens were tested too. Based on that, the changes in mechanical properties (i.e. yield stress, Young modulus, ultimate tensile stress and total elongation) were analysed. It was found, that for degradation level reaching 25%, approximately 10% reduction of yield stress was observed. A new parameter, defining the area reduction, was established as more closely related to the mechanical properties deterioration than the commonly used a mean degradation level. The bilinear stress-strain model of corroded steel plates was proposed for the fitness-for-purpose analyses in the structural integrity assessment.