The influence of H2S on the microstructure of API 5 L X65 pipeline steel

Abstract

Pipelines and equipment made from microalloyed steels used in oil and gas production are exposed to aggressive environments: marine water on the exterior and hydrogen sulfide (H₂S)-rich environments inside. This study evaluated the corrosion behavior of two microalloyed steels (API 5 L X65) in solutions simulating internal and external pipeline conditions based on the NACE TM0284–11 standard. Potentiodynamic polarization was used to measure corrosion rates, and Scanning Electron Microscopy (SEM) with energy-dispersive X-ray Spectroscopy (EDS) characterized the microstructure and corrosion products. The results showed that solution B led to lower corrosion rates due to iron sulfide phase formation, while the steel without segregation bands exhibited superior performance in both solutions. Corrosion mechanisms were discussed based on experimental findings, thermodynamics, and kinetics.