Investigation of Corrosion Under Insulation (CUI) using microelectrodes

Corrosion under insulation (CUI) presents a substantial and pervasive challenge in a wide range of industrial sectors, both onshore and offshore. The severity and prevalence of CUI exhibit geographical dependencies, with heightened risks associated with facilities situated in proximity to coastal regions. The potential consequences of CUI are profound, encompassing significant structural damage to insulated pipes and tanks, thereby posing threats to both personnel safety and uninterrupted production processes. Despite its significance, the evaluation of CUI through electrochemical techniques remains an area that has yet to reach its full potential in terms of development and application.
This research initiative is focused on assessing the CUI rates, with particular emphasis on the top (12 o'clock) and bottom (6 o'clock) positions of ASTM A 106Gr B. This effort employs an innovative approach that involves the use of three microelectrodes in conjunction with the Linear Polarisation Resistance technique (LPR).
The electrochemical analyses performed in this study have unveiled noteworthy disparities in corrosion rates between the top and bottom samples, as determined by LPR. The corrosion rate estimates obtained through mass loss measurements consistently surpass those obtained via LPR. This trend holds regardless of the specific environmental conditions, including temperature, pH levels, or the analytic technique employed. This observed trend may be affected by the Stern-Geary coefficient (β) value, which is approximated to be 26 mV/decade in this research.
Moreover, this research examining of surface morphology and the underlying corrosion mechanisms. This examination leverages advanced analytical tools such as scanning electron microscopy, X-ray diffraction (XRD), and Raman spectroscopy. The data collected from the XRD was used to evaluate the Protective Ability Index (PAI) of the corrosion layer formed under thermal insulation. The results showed a good correlation between the CUI rate and the PAI.