Corrosão em armaduras de tração de dutos flexíveis em diferentes pressões parciais de H2S

Abstract

Flexible pipelines are widely used in the oil and gas industry because their versatility allows for complex installations and high depth for prospecting and transporting oil in offshore installations. The permeation of contaminants, such as marine solution and H2S, through the layers of the structure of these pipelines can lead to premature failure of tensile armours due to processes involving corrosion. In this work, adaptations of NACE TM 0177 and NACE TM 0284 standards were used associated with electrochemical technique to evaluate the corrosion process and corrosion scales to formed on the steel surfaces when exposed to different H2S partial pressures. An electrochemical cell was employed to measure the open circuit potential of the prestrained specimens for a period of 15 days. In addition, coupons of the same material were used to evaluate the corrosion rates by mass loss measurements, and the corrosion products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and electrochemical technique of linear potentiodynamic polarization. It was found that the H2S partial pressure and the pH can influence corrosion rate and the degree of protection given to the steel by the scales. The layers formed on the steel surface are composed by monosulfides (mackinawite and troilite). The results obtained showed the importance for the industry to adopt a standardization in corrosion tests for flexible pipes to ensure reproducibility on the results for materials from the same batch.