Inclusion behavior at the corrosion process of api 5L X65 pipes

High Strength Low Alloy steels (HSLA) are widely used on the oil and gas industry, for either transport or refining of natural gas and petrol. These materials are in constant exposure to hydrogen sulfide (H₂S), causing failure due to hydrogen induced cracking (HIC) or stress sulfide corrosion cracking (SSCC). The main objective of this paper is to analyze and compare the morphology and inclusions influence on the corrosion resistance of two different API 5L X65 pipes, one fit for sour service, and the other not. At first, inclusion characterization was done by optical and scanning electron microscopes. Corrosion tests were conducted according to NACE TM0284, using Solution A as electrolyte and afterwards injecting H₂S. The samples were also subjected to Linear Polarization in order to obtain the Polarization Resistance as function of immersion period. Optical and scanning electron microscopes were also used to characterize the corrosion morphology, and analyze possible inclusion influence. Results showed similar corrosion morphology on both steels, with preferential corrosion at the metal-inclusion interface. The Polarization Resistance test, as well as the microscopic examination, indicates better corrosion resistance for the sour material, which can be possibly attributed to the chemical composition difference of both steels, as well as different inclusion density.