Deviations in CUI Corrosion Rate Predictions for TSA Coated Carbon Steel – A Comparison of Experimental vs RBI Approach

Abstract Thermally Sprayed Aluminum (TSA) coatings are used in industry for the protection against corrosive environments. Corrosion Under Insulation (CUI) programs often deploy TSA as it has improved physical properties (hardness, adhesion, etc.) as well as higher corrosion resistance in comparison to traditional epoxy coatings. Unlike Epoxy coatings, in-service inspections of TSA can be challenging due to the heterogenous thickness profile and surface porosity. This study presents an outlook of corrosion rates of TSA coating from an experimental and Risk-based inspection (RBI) standpoint. The corrosion rates of TSA coating from a published experimental study were compared with RBI calculated corrosion rates. Corrosion rates that were extracted from the experimental studies were under two sets of testing conditions namely (a) CUI simulation test based on ASTM G189-07 test at high temperature (170°C) over a duration of 3 days and (b) quick immersion in fresh water (for 48 hours) followed by outdoor ageing test at ambient temperature over a duration of 1 year. Followed by the comparisons between experimental and RBI calculated corrosion rates, it highlights the deviations reasonings and possible ways for the alignment of the TSA corrosion rates as observed from experimental studies to those assumed with RBI models.