Flow-accelerated corrosion has been studied by means of computational fluid dynamics (CFD) techniques and rotating cage (RC) autoclave tests according to ASTM G170. This study evaluated through CFD and laboratory tests the influence of RC geometry and baffles on the wall shear stress (τw) proposed by the aforementioned standard. The experimental were performed at 120 °C and 2 angular velocities (500 and 800 rpm) during 25 h in a solution with 600 mg/L of Cl- ions and 10-3 mol/L of sodium thiosulfate. Corrosion rates were obtained by ASTM G31 and the surfaces were evaluated by OM and XRD. Corrosion rate values and XRD analyses showed divergence between samples in different positions in the RC and between distinct regions in the same sample. The numerical simulations and the experimental tests showed a great influence of the baffles on τw. The conservatism in the values obtained with this technique is caused by excessive corrosion close to the samples edges and the non-uniformity of τw on the internal samples surfaces. Thus, the main conclusion of the study is related to the importance of better knowledge on experimental methodology and mathematical approximations for updating the criterion for the correct τw calculation on sample surfaces.

Abstract Niobium pentoxide (Nb2O5) has gained prominence as an anti-corrosive pigment. The performance of anti-corrosive coatings based on Nb2O5 was tested in an environment with an acid atmosphere and at high temperatures. For comparison, SAE 1020 carbon steel samples were coated with two anti-corrosive coatings based on Nb2O5: applied by thermal spray and epoxy paint. The samples were partially immersed in the laboratory for 720 h and 1440 h in a 40% (v/v) H2SO4 at 25°C, 60°C, and 80°C. An in-situ evaluation was carried out of chemical industry installations over 4383 h in microclimates with the presence of corrosive agents at temperatures up to 70°C. The results obtained showed that the Nb2O5 coatings applied by thermal spray offer better anti-corrosive performance under immersive conditions. In contrast, under conditions submitted to steam, both the Nb2O5 coatings applied by thermal spraying and epoxy-Nb2O5 paint show excellent anti-corrosive behavior.