Corrosion under insulation (CUI) has been a continuous challenge for on- and off-shore installations,
requiring continuous focus on maintenance work. Pilot scale accelerated testing has been performed to
study and evaluate the effects of CUI on different coating systems and service conditions. A test loop
has been constructed, where 115 mm o.d. pipe spools were combined in a loop which is internally
heated using steam. The coated and insulated pipe spools were 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 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.
Key Words: Corrosion, insulation, high temperature, CUI