Modeling of Thermal Cycling on Water Accumulation for Corrosion Under Insulation (C2026-00234)

Zhenjin Zhu, TK Akins

This paper develops a model to investigate the impact of thermal cycling on water accumulation for corrosion under insulation (CUI) on process piping. In this paper, a thermal insulation system consists of external jacketing, thermal insulation layer, annular space and coating. Temperature profile and heat loss are predicted through solving transient heat conductive equation with a convective boundary condition at jacketing surface. Thermal conductivities of insulation material and annular space are dependent on the absorbed and accumulated water amount. The source of liquid water is dominated by condensation of water vapor diffused through jacketing joints and openings. Water accumulation is quantified from changes of water vapor solubility based on frequency and magnitude of thermal cycling. Spread and retention of liquid water depend on water amount, hydrophobicity of insulation material and system configuration. A relationship between wet-dry cycles and thermal cycling is constructed. Coating breakdown is judged through comparing local temperature and wettability with coating specification for immersion service. Cumulative corrosion metal loss during wet cycles is predicted based on oxygen corrosion rate, concentration of leachable ions from insulation material and surface temperature. The identified sites and predicted corrosion severity help develop preventive and mitigative measures for effective CUI risk control.