CO2 corrosion behavior of simulated heat-affected zones for X80 pipeline steel

The CO2 corrosion behavior of the simulated heat-affected zones (HAZs) of X80 pipeline steel in 3.5 wt% NaCl aqueous solutions was surveyed using electrochemical measurements and welding thermal simulation technology combined with microstructural analysis. The results revealed that changes in the corrosion resistance of the HAZ sub-regions were associated with variations in the microstructural sensitivity to the CO2 corrosion behavior in the NaCl aqueous solutions. The weakening of the corrosion resistance in the coarse-grained HAZ was attributed to the larger grain size and coarsening martensite/austenite constituents in the matrix. The corrosion products on the metal surface can lead to a minor reduction in the corrosion rate. In addition, increasing H+ concentration and higher residual stress can destroy the dynamic balance on the metal surface, thereby eventually damaging the corrosion product film.