CUI (corrosion under insulation) is reportedly a contributor to the failure of insulated piping and process equipment. Protective coatings are among various effective measures to manage the CUI of industrial assets. Phenolic epoxy is among the widely used coatings under thermal insulations. This research work involves CUI testing of phenolic epoxy coating for 192 hours as per applicable ASTM standard G189-07 using cyclic wet operating conditions. The resulting weight loss from the test was converted to corrosion rate followed by microscopic checks. The as-coated (i.e., new) surface and post-test coatings were characterized using microscope and surface topography to account for damage modes and surface roughness. Phenolic epoxy coating under contacting insulation suffered a higher material loss rate, dis-bonding, and holiday defects tendency in comparison to contact-free insulation with low-point drainage.
CUI (Corrosion under insulation) refers to localized corrosion under thermal insulations, which pose integrity risks to the hydrocarbon facilities. 1 CUI is reportedly a driver behind 40-60% of failures in the facility piping. Smaller-sized piping (i.e., diameter < 4") are even more prone to CUI, whereas reportedly 81% of failures in small-sized piping are due to CUI. 2 CUI-related failures and associated efforts comprise 10% of a facility's maintenance budget. Management of CUI risks has always been challenging as it involves maneuvering numerous governing factors. The key driving factor behind CUI is the aerated moisture that comes from soaked thermal insulations. 3 The type and condition of insulation materials have a significant impact on their moisture absorption tendency and subsequent CUI rate(s). In addition to triggering CUI, the absorbed moisture deteriorates thermal insulations via increasing the thermal conductance. Reportedly, moisture content of 5% within stone wool insulation causes a 25% increase in thermal loss(es). 4
Recommended practice suggests the use of low point drains to release the trapped moisture and reduce the time of wetness for thermally insulated systems. 5 A previous study by Rana et al. addresses the influence of low point drains and insulation stand-offs on moisture removal behavior of stone wool insulation. 6 Contact-free insulations help to keep the insulation off the pipe; which reduces the probability of moisture trapping that may otherwise result in permanent attachment of moisture to the metal's surface via surface tension and capillary action. Previous studies by Rana et al. and Pojtanabuntoeng et al. have reported the influence of contact-free insulation design and low point drains on the CUI performance of uncoated carbon steel. 7-8 CUI rates of carbon steel were found substantially lower when applied with contact-free insulation, and low point drains. 7
