Influence of temperature on corrosion behavior of N80 Steel in multiple thermal fluid environment

Abstract

Abstract During offshore oil production, O2 could be introduced into the multiple thermal fluid, and the temperature of the wellbore can reach up to 200°C, which may result severe corrosion of tubing. However, the corrosion mechanism of downhole pipes in such aggressive environment remains unclear in the high-temperature and high-pressure CO2-O2-H2O mixed environment. Herein, we investigated the corrosion behaviour of N80 steel with different temperatures in CO2-O2-H2O environment. The influence of temperature on composition and structure of the corrosion product film of N80 steel was characterized by scanning electron microscope, energy-dispersive spectroscopy and X-ray diffraction. The results show that the corrosion rates of N80 steel performed a downward trend with the increase of the temperature, but it increased slightly at 180°C. The corrosion rate of N80 steel was up to 1.6 mm/y at 60°C, owing to the damage to corrosion product film by O2 and reduced its protection at lower temperature. As the temperature increased, the formation of Fe3O4 enhanced the protection of the inner corrosion product film, thereby greatly reducing the corrosion rate. However, the product of (FeCa)CO3 in the corrosion film completely lost its protection at 180°C, and the corrosion rate increased slightly to 0.84 mm/y. With the temperature increased to 240°C the corrosion rate of N80 steel reduced to 0.24 mm/y on account of the formation of dense and complete Fe3O4.