Failure Analysis and Corrosion Resistance of Carbon Steel Pipelines in Concentrated Sulfuric Acid

This study examines the waste sulfuric acid pipeline within the waste acid system from a certain petrochemical company, specifically, related to its sulfuric acid alkylation process. The current study sought to investigate the corrosion perforation mechanism of pipelines and revealed the synergistic effects of sulfuric acid temperature and concentration on the corrosion behavior of 20# carbon steel. The corrosion features of the failed part were analyzed by scanning electron microscopy, X-ray energy-dispersive spectroscopy, and X-ray diffraction. The corrosion rates of 20# carbon steel in sulfuric acid at different concentrations (80%, 90%, 98%) and working temperatures (20 °C, 40 °C) were measured using the immersion corrosion method, potentiodynamic polarization curves, and electrochemical impedance spectroscopy. The results indicate that the failed pipeline exhibited multi-form corrosion characteristics, with both uniform and localized corrosion occurring simultaneously in concentrated sulfuric acid. The lowest corrosion rate was 0.0795 mm/a in 98% H2SO4 at 40 °C. The sulfuric acid concentration and working temperature exhibited synergistic effects on the corrosion behavior of 20# carbon steel. The corrosion rates increased with concentration in the range of 80–90% H2SO4 but reached a minimum of 98% due to passive film formation. In a nutshell, we established that elevated temperatures accelerated corrosion in low-concentration systems, but triggered localized active dissolution in high-concentration systems by disrupting the passive film on the surface of the steel.