Barnes, P E

Engelberg, Dirk L

Lyon, Stuart b

High strength carbon steel wires are used in flexible risers to act as pressure and tensile armours for the fatigue loads and pressures sustained by the riser. The armours are contained within an annular space where the presence of condensed water and gases such as CO2, H2S and CH4 maintain a corrosive environment. Consequently, the high strength steel wires can suffer from corrosion fatigue under cyclic loading conditions. Previous work has shown that fatigue cracks initiate from corrosion pits that form on the surface of the carbon steel wire [1].Digital Image Correlation has been used to explore the formation and development of local surface strain fields around localised corrosion pits of high strength steel wire in a seawater environment. This technique has not been used before on steel exposed to seawater and successful application therefore required the development of a suitable corrosion scale on the surface to optimise imaging conditions. Corrosion pits have been grown on the surface of the steel using chrono-amperometry and chrono-potentiometry.The effect of pit size and population on the localised strain development of a high strength carbon steel sample under tensile loading has been explored. This has been achieved by growing single pits of different diameter and multiple pits in different size areas. Statistical analysis of the DIC results demonstrates that there is an increase in localised strain for the multiple pitted areas than for the single pits. This validates that multiple corrosion pits increase the localised strain field on the steel surface

In-situ Surface Strain Mapping of Pitting Corrosion in a High Strength Carbon Steel

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