Characterization of Erosion Resistance of Iron Carbonate (FeCO₃) Scale

When CO₂ corrosion takes place, iron carbonate scale (FeCO₃) may form under certain conditions. The role of an FeCO₃ layer in reducing corrosion rates in sand–free environments has been studied by many investigators. However, the protection offered by FeCO₃ scale when sand is produced is not well defined. This paper describes work conducted to characterize the resistance of iron carbonate (FeCO₃) scale to erosion by solid particle impingement. Dry and wet FeCO₃ scales were subjected to direct impingement by sand at various impingement angles. Scales were pre-formed in a flow loop at 65-93° C, from 6.1-6.5 pH, and 2.4 bar CO₂ pressure and then removed from the flow loop for direct impingement testing. The erosion pattern of the scale was characterized by scanning electron microscopy (SEM). Specimens with iron carbonate scale were partially eroded with sand at an impact angle of 60 degrees and then examined using SEM to study erosion mechanisms. The main conclusions drawn from this research were as follows: 1) The erosion resistance of the FeCO₃ scale in these tests is about 30-50 times lower than for mild steel (G10180), 2) The erosion resistance of wetted scale was not found to be statistically different from that of dry scale, and 3) The erosion behavior of iron carbonate scale appears to be closer to the behavior of brittle materials than that of ductile materials. The knowledge collected in this research is being used to characterize the erosion resistances of the scales for the purpose of predicting the erosion-corrosion rates in sand production conditions with FeCO₃ scales.