This paper focuses on the corrosion behaviour of high strength flexible wire material immersed in de-aerated 3.5% NaCl solution under 40bar CO2 partial pressure at different test temperatures: 30°C, 40°C and 60°C; different CO2 fluxflux: 0.1ml/min/cm2 and 0.0008ml/min/cm2; different volume of solution to surface area of sample (V/S) ratios: 1ml/cm2 and 0.3ml/cm2 and test durations: 2 and 4 months. The tests were carried out in a lab-scale test system designed and built at TWI Ltd for the simulation of complex annulus environments. The corrosion rates and the maximum depth of the localized attack for tests at different temperatures were recorded as: 30°C>60°C>40°C. This is linked with the stability, structure and thickness of the precipitated iron carbonate scaling. The lowest corrosion rate was recorded for the test with the lowest V/S and slowest CO2 flux, linked with a thin and compact iron carbonate layer. The effect of the flow and degree of confinement are significant at high CO2 partial pressures.
Flexible pipes are frequently used both as flowlines and risers in the oil and gas industry. A flexible pipe has a complex structure consisting of layers of polymer and metallic materials. The armor wire layers – shielded with polymer materials from seawater on the outside and well fluid on the inside – are the load and pressure bearing parts. Due to diffusion from the well fluid and/or damage of the outer polymer layer, the annulus can be water-filled, and armor wire can corrode. In this work, the susceptibility to hydrogen embrittlement (HE) with the presence of atomic hydrogen due to cathodic polarization has been investigated for six different tensile armor wire materials. Samples were exposed to Slow Strain Rate testing (SSRT) in 3.5% NaCl solution and cathodic polarization to -1.1 and -1.4 VAg/AgCl at room temperature. Reference samples without hydrogen charging were tested in air for comparison. Stress-strain curves, reduction in area (RA) and the microstructure of the fracture surfaces were investigated. The HE susceptibility tended to increase with the carbon content, strength and hardness and the materials tended to be more brittle when charged to -1.4 VAg/AgCl than -1.1VAg/AgCl.