On the mitigation of corrosion under insulation (CUI) of mild steel using local cathodic protection

"Corrosion under insulation (CUI) is a severe form of localized corrosion, which detrimentally affects insulated engineering equipment typically used in oil and gas production. The undetected or unmitigated progression of CUI in oil and gas equipment could result in consequences, e.g., the metal perforation of steel piping and gas leakage in LNG plants. A strategy based on cathodic protection (CP) could be a practically feasible means to protect steel piping from CUI. CP was assessed to protect insulated steel specimens using sacrificial zinc anodes. The conditions to effectively impart CP through the moist insulation were considered. The so-called throwing power or protection achieved using sacrificial zinc anodes coupled with mild steel specimens in moist insulation was estimated using copper electroplating. The results validated that the efficacy of CP depends upon the ionic resistivity of the moist insulation and the moisture content (by volume) must be >25% for efficient ionic conductivity through the insulation. The maximum throwing power of CP through the insulation was obtained when zinc was in direct physical contact with mild steel, with 1:10 zinc to mild steel area ratio."