Corrosion failure analysis of L485 natural gas pipeline in CO2 environment

• The work studies corrosion failure analysis of L485 pipeline in CO2 environment.
• The corrosion scale mainly consists of FeCO3.
• The actual corrosion rate is at the range of 1.413–1.978 mm/a.
• The Mn content of L485 steel exceeds the standard compared with API Spec 5L.
• Corrosion undergoes the bare metal, scale-covered, reaction destruction period.

The corrosion failure analysis of Qinhuangdao–Shenyang L485 natural gas pipeline in CO2 environment has been investigated in the present study. The morphology and composition of the corrosion scale are characterized by scanning electron microscopy, X-ray powder diffraction and energy-dispersive spectroscopy. The weight loss experiment is conducted to estimate the actual corrosion rate of L485 pipeline steel. A conceptual model is developed to illustrate the corrosion behavior by electrochemical test of potentiodynamic polarization curve. Results show that corrosion scale mainly consists of FeCO3, and the corrosion rate is in the range of 1.413–1.978 mm/a. The manganese content of L485 pipeline steel exceeds the standard compared with API Spec 5L. In addition, the corrosion behavior of L485 pipeline steel can undergo the periods of bare metal, scale-covered and reaction destruction.