CUI (Corrosion Under Insulation) is among the key damage mechanisms affecting equipment and piping in hydrocarbon processing facilities, as well as pipelines. The key reason behind CUI is the contact of soaked insulations with the metal(s). Insulation stand-offs and membranes can keep the soaked insulation off the pipe and mitigate CUI risk. This research study addresses the CUI simulation tests to characterize the corrosion behaviors of carbon steel under isothermal wet and cyclic wet conditions, in the presence of insulation stand-offs, low point drains, and Teflon membranes. The corroded coupons were characterized using microscope and surface topography to investigate the damage modes namely pitting, uniform corrosion, localized damage. Insulation stand-offs with low point drains showed uniform corrosion in comparison to closed-contacting insulation, which mainly caused localized corrosion and pitting. Teflon membrane with low point drains caused the least corrosion rate among candidate configurations and did not show any noticeable surface damage from pitting or even uniform corrosion.


Corrosion under thermal insulations namely CUI (Corrosion under insulation) is among the key damage mechanisms which poses integrity risk to the hydrocarbon facilities. 1 CUI is reportedly known as the reason behind 40-60% of failures in the facility piping whereas small bore piping (i.e., NPS < 4") are even more sensitive to CUI failures, where up to 81% of reported failures in small-sized piping are known to be from CUI. 2 Monetary spending to inspect and fix CUI-related failures cost 10% of overall maintenance budget in a typical medium-sized oil refinery. 2 CUI risk is influenced by numerous operational and environmental factors which impedes its management in a typical AIM (Asset integrity management) program. The key driving factor behind CUI is the aerated moisture on the metals that comes from soaked thermal insulations. 3 The type and condition of insulation materials have significant impact on their moisture absorption tendency and subsequent CUI rate(s). Other than triggering CUI, the absorbed moisture degrades 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

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