ABSTRACT Corrosion in oil and gas pipelines poses operational and safety challenges, especially where temperature gradients lead to different corrosion behaviors. Although mixed H₂S/CO₂ corrosion has been studied, few works isolate the effects of H₂S/N₂ and CO₂ on top‐of‐the‐line (TLC) and bottom‐of‐the‐line (BLC) corrosion. This study investigates API 5L X65 carbon steel under sweet (CO₂) and sour (H₂S/N₂) environments, focusing on steel position and environmental chemistry. Samples were exposed in situ for 7 days at 12°C steel and 30°C liquid temperatures. Analyses included weight loss (ASTM G1‐03), surface morphology/composition (SEM/EDX), and phase identification (XRD). Results show nearly identical TLC and BLC corrosion rates in the sweet environment, while BLC corrosion is much higher in the sour case. SEM/EDX and XRD reveal flaky oxide scales under CO₂ and dense, multilayered FeS scales under H₂S/N₂, with NaCl deposits contributing to localized BLC attack. Findings underscore the role of chemistry and steel position in corrosion mechanisms and provide insights for mitigation and pipeline design.
Taqiuddin et al. (Sun,) studied this question.