Abstract
Flexible pipes used in oil and gas production are composed of densely packed steel wires enclosed in an annulus confined by inner and outer thermoplastic sheaths. Water, CO2 and H2S from the bore may diffuse through the thermoplastic sheaths and form a corrosive environment in the confined space between the sheaths. Oxygen in seawater or air can also enter the annulus if the outer sheath is damaged. The large steel surface to water volume ratio in the annulus and a limited ingress of corrosive species give a complex corrosive environment. Experiments in sweet environments show that large amounts of dissolved corrosion products can accumulate and eventually give protective FeCO3 based corrosion product films and low corrosion rates. If O2 enters the annulus through damage in the outer sheath, the corrosion rate increases as the protective corrosion product films are destabilized when FeCO3 reacts and form oxides.
