Flexible pipes - corrosion fatigue testing under representative annulus conditions

Paper ID: C2025-00106 ABSTRACT: The fatigue life of armor wires in flexible pipes and the shape of generated SN curves are affected by the corrosion rate, the steel surface condition and the annulus/test environment. An experimental program was performed to develop a procedure for the preparation of the test specimens and the test environment to be used in corrosion fatigue testing. The procedure includes a pre-corrosion phase and a fatigue-exposure phase. To optimize the pre-corrosion phase, a series of corrosion experiments were performed at different CO2 partial pressures, pH’s, concentrations of dissolved corrosion product, bicarbonate additions and concentrations of H2S. The target concentration (super saturation) of dissolved corrosion products to be used during the fatigue exposure was studied in combined corrosion and FeCO3 precipitation experiments. These experiments which were performed at different CO2 partial pressures and with seawater and condensed water (1.65 g/L NaCl) showed that a high supersaturation (>100) of dissolved FeCO3 was required to maintain a low corrosion rate (< 0.01 mm/y).
The paper discusses the experimental approach and the main results obtained in the corrosion and FeCO3 precipitation experiments.