Abstract
CUI (corrosion under insulation) is among the leading damage mechanisms active in oil refining and hydrocarbon facilities. Reportedly, 10% of the total maintenance budget of a typical refinery is spent on inspecting and fixing CUI damages. The mechanism of CUI is complex and influenced by many factors namely the design of the insulated system, insulation type, ambient conditions, condition of coatings and insulation materials, as well as operating parameters. This study addresses the quantified influence of cyclic temperatures on CUI in comparison with constant temperatures for various insulation designs namely the closed-contacting and contact-free with low-point drainage. It also investigates the CUI behaviors under moisture cycling (i.e., wet-dry conditions) of candidate insulation designs in comparison to a fully wet environment. To simulate this, corrosion rates were determined under Isothermal wet, isothermal wet-dry, cyclic wet, and cyclic wet-dry conditions using weight loss measurement as per applicable ASTM G189-07 standard. The influence of cyclic temperatures and wet-dry conditions were also studied using the linear polarization resistance method in the system with contact-free insulation. The corroded coupons were then characterized using a microscope and surface topography. The wet-dry conditions under both cyclic and constant temperatures caused more corrosion rates than those under wet conditions. Also, cyclic temperatures caused more corrosion rates than constant temperatures under both wet and wet-dry conditions.
