Corrosion Under Insulation (CUI) is defined as a severe localized form of corrosion due to entrapped water and electrolytes under the insulation layer of piping and vessels. CUI is extremely critical since it takes place out of sight and may cause costly unexpected shut downs and accidents.Protection against CUI is a relatively novel area of knowledge. Although there are some standards or guides for specifying coatings for CUI protection (NACE SP 0198-2010 NORSOK M501 ed. 6) there is lack of broadly accepted test methods. The current standards do not necessarily agree on what the optimum solution is. Furthermore experimental findings may not be widely circulated as manufacturers endeavour to find innovative solutions while keeping competitive information confidential.There has been progress since 2004 when Fitzgerald suggested the use of organic coatings up to around 100C and other more costly solutions like thermal spray aluminium and Al-foil wrapping for higher temperatures. New coating types (high build silicones) have entered the marked and the use of epoxies has been extended to higher temperatures. Haraldsen investigated the performance of two such new high build silicones and compared to a “phenolic epoxy” and thermally sprayed aluminium. In this study the two high build silicones provided very little corrosion protection under wet conditions and heating up to 120 C.During the past three years Hempel has been labouring over the development of a liquid applied coating solution to provide protection against CUI. We have navigated a journey od discovery in both product development and performance evaluation. During this period we have accumulated experience in coating formulation test methods and the understanding of how to best prevent corrosion under insulation.In terms of composition we have evaluated the ability to provide protection against CUI of a number of chemistries.Epoxy Mastic: Two-component polyamide adduct cured epoxy paintNovolac Epoxy: Two-component amine adduct cured phenolic epoxy (novolac) coating with very good adhesion and high temperature water and chemical resistance.High Build Silicones: One component high build silicone for insulated and non-insulated steel up to 650°C.Thin Film Silicone: One component thin film silicone coating for use up to 600°C.In terms of test method development we have explored the suitability of existing test methods and developed novel test methods.Thus a number of experimental techniques were used to investigate and compare the temperature resistance and corrosion protection offered by the coatings.Crack resistance – dry exposure in oven at a range of temperatures. The ability of coatings to resist the thermal stress of the different coatings systems was evaluated.Salt spray exposure.Cyclic conditions testing. Specimens were exposed to cyclic conditions high temperatures cold water immersion hot water immersion etc.Combined Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC)-Cyclic heating/immersion on flat panels with an artificial damage was made down through the coating.Modified Houston pipe test which consisted of exposing pieces of coated pipe to cyclic immersion and dry out conditions at elevated temperature exposure using multiple insulation materials. As it was expected different type of coatings showed different behaviour in different test methods. Particularly challenging has been to use the results of accelerated testing to predict the field performance of the tested technologies.This paper is an account of the problems challenges and solutions that we have found during our development of a liquid coating solution to provide protection against CUI.
