CUI is well understood, yet pervasive. Despite long-established mitigation methods, it costs the process industry millions of euros annually. Effective prevention based on life-cycle costs can slash the cost of downtime, maintenance repair, and inspection. Carbon steel under wet insulation undergoes nonuniform general corrosion and/or highly localised pitting. Austenitic stainless steels mainly suffer pitting and CSCC. The mechanism: Figure 1 shows through-wall corrosion under insulation in a carbon-steel storage tank. It occurred near the tank bottom where the coating failed, exposing the carbon steel to wet corrosive conditions under the insulation. Carbon ...