To assess the influence of temperature on the pitting corrosion susceptibility of metallic materials intended to be used in industrial applications involving corrosive streams several methodologies are followed. The pitting resistance equivalent number (PREN), an empirical relationship purely based on the mass fraction of some alloying elements in the material is commonly used as a general indication for pitting resistance. The critical pitting temperature (CPT) is also frequently used to benchmark the susceptibility to localized corrosion of metallic materials. ASTM G48 and G150 standards describe the test methodologies for determining the CPT of stainless steels and nickel alloys in chloride-bearing solutions. However, standardized electrolytes do not always simulate accurately expected service conditions and have limited thermal stability, therefore, they might lead to conservative values. On the other hand, electrochemical methods can be used for characterizing the pitting susceptibility and repassivation behavior of alloys at expected service conditions, also at high temperatures. In the present study, the pitting corrosion resistance of eight metallic materials typically used in oilfield technology was characterized electrochemically in chloride solutions at temperatures ranking between room temperature and 150 °C and compared to the corresponding reported PREN and CPT-values. The intention is to demonstrate the lack of correlation between the real pitting resistance of most of these materials at elevated temperatures and the conclusions that might be drawn using PREN and CPT-values for predicting pitting susceptibility in service.
Several industrial applications including the chemical industry and oilfield technology involve frequently halide-containing streams at elevated temperatures, that challenge the pitting corrosion resistance of metallic materials. Pitting susceptibility becomes not only a reject criterion for materials selection during the design stages of engineering components used in these applications. It also constitutes a significant limiting factor to the service life of these components once in service. Therefore, the characterization of the pitting corrosion resistance of metallic materials including the influence that operational factors can have on material's susceptibility is crucial. Temperature is one of these critical factors that influences pitting corrosion of metallic materials.1 It is well known that the susceptibility to pitting corrosion of metallic materials increases with increasing temperature.2,3 The temperature dependence of the pitting resistance changes with the metallurgical properties of the metallic material including its composition as well as with the environmental conditions the material is expected to be subjected to, and these relationships are not always known.