Effects of oxidation-nitridation in the presence of water vapor on ASTM A335 P92 steel using SEM-EDS and XPS characterization techniques

This research studies the physical and chemical changes in steel ASTM A335 P92, produced from a typical refinery corrosion environment. The environment evaluated was oxidation-nitridation with the presence of water vapor. In this study five (5) exposure times were selected: 1, 20, 50, 100 and 200 hours; As well as two (2) analysis temperatures: 450 and 550°C. The working pressure used was one (1) atmosphere. Bearing in mind the kinetic study, the behaviour shown in ASTM A335 P92 steel describes an accelerated growth until 50 hours, after this time growth is less. For the tests carried out at 450°C, the kinetic constant was 2x10-8g²mm^-4h^-1, as well as for 550°C the calculated kinetic constant was 3.1×10-7g²mm^-4h^-1; through the SEM-EDS characterization techniques, it was possible to appreciate a good adhesion and homogeneity of the layers formed on the metal matrix until a time of exposure of 100 hours at 450 and 550°C, different from that evidenced to 200 hours of exposure where the layer formed near to the substrate showed detachment, this is attributed to the formation of hydroxides product of water vapor. Among the results obtained are the elemental composition, the presence of nitrides such as Si₃N₄, also NSiO₂ and NSi₂O, molybdenum oxides: MoO₂ and MoO₃ and iron oxides: FeO and Fe₂O₃ can be evidenced.