An Investigation of Corrosion Behaviors of Thermally Sprayed Aluminum (TSA) at Elevated Temperatures Under Thermal Insulations and Autoclave Immersion Conditions

Abstract

Thermally Sprayed Aluminum (TSA) protects against internal and external corrosion in many industrial applications. Even though TSA coating has been the subject of many studies, there is still a need to gain better insights into the degradation mechanisms of the TSA especially under immersion conditions and moisture-saturated thermal insulations. This study addresses the corrosion behavior of TSA in a CUI simulation setup (per ASTM G189-07) and autoclave immersion. The corrosion tests were conducted for three and four days under isothermal wet (IW) and cyclic wet (CW) conditions. Linear polarization resistance (LPR) scans were conducted during both (i.e., CUI simulation and autoclave immersion tests) to better understand the corrosion behaviors of TSA coating. Following corrosion testing, thorough microstructural examinations were conducted employing confocal laser microscopy, 3D topography, scanning electron microscopy (SEM), and Energy dispersive spectroscopy (EDS) to understand the microstructural and tribological changes resulting from corrosion testing. TSA coating under the insulation showed significant degradation via flashing moisture and active dissolution of iron at the insulation-metal interface. Unlike immersion conditions, the wear of TSA due to flashing moisture under thermal insulation created the crevices that caused the active corrosion of the steel substrate.