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Corrosion under Insulation: Case Studies and Challenges in the Use of Corrosion Inhibitors

Corrosion Under Insulation (CUI) is a significant concern in the oil and gas industry. This paper presents several case studies of CUI, including instances of External Chloride Stress Corrosion Cracking (ECSCC). In our facilities, applying insulation material sprayed with a specific corrosion inhibitor to the internal surface is considered a temporary solution for equipment where CUI is a concern due to damaged coatings. In our previous study, this non-combustible corrosion inhibitor containing phosphate and nitrite showed effective corrosion inhibition in carbon steel even when rusted. However, we considered that an Active Path Corrosion can be occurred under loaded stress portions. To replicate chloride-concentrated environments under insulation, a 70-day immersion test was conducted using U-bend type test specimens of carbon steel in a NaCl solution with the inhibitor. The tested specimens with the inhibitor maintained a metallic appearance without stress corrosion cracking. However, crevice corrosion was observed. These results suggest that the corrosion inhibitor may have limited effectiveness in chloride-concentrated environments. We concluded that it is beneficial to perform cleaning before applying the insulation with corrosion inhibitor and to implement other permanent measures before chloride concentration significantly increases.
Product Number: 51324-20778-SG
Author: Takehiro Toyoda; Yoshiyasu Kushima; Koji Watanabe; Toshiyuki Sunaba
Publication Date: 2024