The relationship between fracture toughness of CO2 corrosion scale and corrosion rate of X65 pipeline steel under supercritical CO2 condition

Corrosion experiments were performed with X65 pipeline steel under static supercritical carbon dioxide (SC CO2) conditions at 50, 80, 110 and 130 °C. The morphology, structure, chemical composition and fracture toughness of CO2 corrosion scales formed on the surface of X65 pipeline steel at various temperatures were investigated by means of Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDS). The corrosion rates were measured using weight-loss method. The fracture toughness of CO2 corrosion scale formed at different temperatures was investigated by means of nanoindentation and Vicker's indentation on a polished cross-section of the CO2 corrosion scale. The results showed that the corrosion rates increased from 50 °C to 80 °C and then decreased from 80 °C to 130 °C. As the temperature increased, the fracture toughness of CO2 corrosion scale first decreased and then increased, and the lowest fracture toughness was found at 80 °C. The corrosion rate (CR) has a quantitative relationship with the fracture toughness (KIC)CR=(3.25/KIC3/2)−0.908.

► No studies by far have been done on fracture toughness of scale in this field.
► For the first time we measured the fracture toughness of scale in this field.
► We first gave quantitive relationship of corrosion rate and fracture toughness.