Corrosion under insulation - testing of protective systems at high temperatures

Corrosion under insulation (CUI) has been a continuous challenge for StatoilHydro on- and off-shore operations, requiring continuous focus on maintenance work. Pilot scale accelerated testing has been performed to study and evaluated the effects of CUI on different coating systems and service conditions. A test loop has been constructed, where 115 mm o.d. pipe spools are combined in a loop which is internally heated using steam. The coated and insulated pipe spools are exposed at controlled internal temperatures and intermittently wetted by fresh seawater. Two test lines with 8 pipe spools have been run in parallel.
Different aspects of CUI, including methods of steel pretreatment, coating application conditions, coating types and insulation design have been studied. Special focus has been on high temperature service conditions and the effect of moist and intermittently wet condition. High temperature coatings have been compared with a traditional coating system and thermally sprayed aluminum coating. The effect of coating application during service with steel temperatures up to 150°C has been studied.
Due to the harsh exposure conditions, both tested coating systems were heavily degraded and a fair comparison of the two coating systems is difficult. A positive effect of distance insulation was the most significant result from the test, and both tested coating systems showed markedly improved quality using distance insulation The different application temperatures showed significant differences, and the results were in general better for the coatings applied at ambient conditions. Only minor differences were observed between the different steel pre-treatment methods.