CORROSION PERFORMANCE OF HIGH STRENGTH-LOW ALLOY STEELS IN AERATED AND CO_2 SATURATED LYMAN AND FLEMING SOLUTIONS

摘要

Aerated and CO_2 saturated Lyman and Fleming solutions were used as electrolytes to investigate the corrosion susceptibility of three high strength low alloy steels (HSLA) designated as Steel A, Steel B and Steel C. API 5L X65 carbon steel was used as reference specimen. Electrochemical Polarization (LPR and Tafel Extrapolation) and surface analysis (SEM/EDAX and XRD) techniques were used for this investigation. The results of linear polarization resistance (LPR) and potentiodynamic polarization corroborated each other presenting the corrosion performance (CP) of the steels in a descending order of CP _(steel c)> CP _(steei b) > CP _(X65)> CP _(steel a). The results also revealed a more severe corrosion attack averaging about 35% for all the steels in the aerated than in the CO_2 saturated Lyman/Fleming solutions. This was attributed to the absence of dissolve oxygen (DO) and the covering of the surface of the specimens by CO_2 gas in CO_2 saturated solution. On the other hand, the presence of DO which is a precursor for cathodic reduction and for the formation of calcareous deposits, initiated an early rapid corrosion attack culminating to higher corrosion rates within the 24 hours of this work. The chemical composition and microstructures of the steels contributed significantly to the witnessed corrosion behaviour. The API XL X65 carbon steel showed almost a comparable corrosion resistance with Steel A but differ significantly with Steel B and Steel C in both aerated and CO_2 saturated Lyman and Fleming solutions.