Flexible pipes used in oil and gas production are composed of densely packed steel wires enclosed in an annulus confined by inner and outer polymer sheaths. Lighter hydrocarbons, water, CO2 and H2S from the bore may diffuse through the inner liner and form a corrosive environment in the confined space between the sheaths. Generally, low corrosion rates (<0.01 mm/y) are experienced. This is attributed to the large steel surface to water volume ratio giving rapid accumulation of dissolved corrosion products and precipitation of protective corrosion product films. When H2S is present, the films also consist of FeS.

The consumption rate of H2S and the stability and protective properties of mixed corrosion product films were studied in experiments where the H2S/CO2 ratio and supersaturation of dissolved corrosion products were varied. The experiments were performed at ambient pressure, 25 °C and with a gas mix containing N2, 0.02 MPa CO2, and 0.005 kPa, 0.01 kPa and 1 kPa H2S respectively.

Subject
Films, Piping, Precipitation (solids), Hydrogen concentration, Corrosion rate, Annulus, Iron sulfides, Protective films, Partial pressures, Corrosion products, Film formation, Steel, Corrosion protection
Keywords:
Corrosion, flexible pipe, CO2, H2S
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2020
Association for Materials Protection and Performance (AMPP)
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