Characterization of oxide films grown by flow-accelerated corrosion using scanning electron microscope (SEM) and focused ion beam (FIB) techniques

Abstract

Flow-Accelerated corrosion (FAC) has remained an issue in steam raising power plants with FAC being the cause of enhanced degradation of plant piping and if the degradation continues it can develop into unexpected pipe wall failure. Therefore understanding the mechanisms of FAC is necessary in order to predict where it will occur and what can be done to mitigate it. To this end a morphology study was conducted on probes corroded by FAC in various conditions. By observing the changes in oxide layer morphology in response to changes in system conditions more information about the mechanisms of FAC can be inferred. The information gained from the morphology study was then used to update the UNB mechanistic model to improve the accuracy of its predictions. After updating the model, it was able to predict FAC rates and oxide thicknesses quite well in both neutral and ammoniated conditions for two different compositions of steel.