CO2 Corrosion of Carbon Steel and 13Cr Steel in Particle-Laden Fluid

Corrosion tests were conducted on carbon steel (API(1) 5L X70) and 13Cr steel (AISI(2) 420) materials in a 3% NaCl solution containing sand particles (5000 to 9000 ppm) and saturated with CO2, at defined partial pressure (0 to 0.3 MPa) and temperature (30 to 60 C). The effect of residual O2 content (10 to 1500 ppb) was further examined. The following two flow geometries were studied: (1) undisturbed pipe flow and (2) submerged jet impinging (30 to 90 degrees) onto a flat plate. The effect of specimen surface treatment (shot blasting or pickling) was examined with dry-polished material as a reference. Weight loss and electrochemical measurements were applied to determine average and instantaneous corrosion rates respectively. The results are discussed relative to fluid flow conditions and the surface preparation/microstructure of the materials tested. No stable corrosion product layers retarding CO2 corrosion were formed within the testing time frame (<100 h). Consequently, no erosion-corrosion associated with physical degradation of protective layers occurred. Enhanced corrosion of C steel specimens by sand impingement has been related to the induced plastic deformation and disruption of the metal surface layer stimulating corrosion attack.