Abstract
The production and transport of sour oil and gas always imply a risk of material damage and shutdown due to CO2/H2S corrosion, especially localized corrosion attack. In sour systems, the localized corrosion of carbon steel has become a progressively greater concern to the oil and gas industry as a result of production from increasingly H2S environments. The increased knowledge of localized corrosion mechanisms is necessary to develop efficient methods for prediction and mitigation. This paper describes a case history of a pipeline failure that resulted in a leak in a discharge line from a hydrocarbon well in an oilfield in southern Mexico. The physicochemical composition of the fluid was characterized "on site" by colorimetric techniques. The sample fluid was taken directly from an access nipple on the well. The corroded metal was placed in an inert medium and taken immediately to the laboratory. Characterization analyses of the corrosion products and layer on the metal’s surface were carried out by scanning electronic microscopy coupled to X-ray dispersive energy and X-ray diffractive systems. The microstructure of the base metal was then analyzed. The morphology of the attack and the layers of corrosion products formed around the area of failure were analyzed. A mechanism was proposed involving the effect of H2S correlated with the water cut, salt content, and operative conditions of the discharge line. The material analysis of the microstructure indicated that the material complied with the requirements for sour media services. The final results showed that the pipeline suffered localized corrosion at six-o’clock position due to deposit-accelerated corrosion.