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Applicability Study of Inhibitors to Corrosion Under Insulation

Corrosion Under Insulation (CUI) is the corrosion of piping or equipment under insulation that occurs when moisture ingresses the interface between insulation and piping or equipment, helping to form corrosion cells. CUI is one of the costliest problems shared by the oil and gas industries. One reason this problem has been a perennial challenge is that CUI is difficult to detect because it occurs under the insulation. And since it occurs regardless of the type of fluid in the pipe, every part of the plant would be included in the monitoring scope.

Product Number: 51323-19244-SG
Author: Takehiro Toyoda, Ayano Yasui, Hirotaka Mizukami, Yukinori Yanase, Toshiyuki Sunaba
Publication Date: 2023
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Corrosion Under Insulation (CUI) is one of the most significant corrosion issues in oil and gas production facilities. One way to address this issue is to use insulation materials with corrosion inhibitors. In this study, under the simulated CUI conditions in the laboratory, the performances of some corrosion inhibitors were evaluated on carbon steel. Immersion tests of polished metal surface specimens and corroded ones were conducted in the solutions controlled 18,000 ppm chloride ions (3.0 wt.% NaCl) at 50°C, and the mass loss values were compared. In addition, potentiodynamic polarization measurements were performed to presume these inhibition mechanisms. One nonflammable inhibitor known to contain phosphates and nitrites showed good anti-corrosion performance on both the polished metal surface specimens and the corroded ones. The primary inhibition mechanism was considered to be the formation of the protective film on the steel surfaces. On the other hand, it was deemed that localized corrosion was a possible concern in spots where the inhibitor did not act sufficiently. Therefore, applying corrosion inhibitors to insulation materials is expected to be one of the corrosion control techniques for preventing further CUI as a temporary expedient until other permanent repairs are carried out.

Corrosion Under Insulation (CUI) is one of the most significant corrosion issues in oil and gas production facilities. One way to address this issue is to use insulation materials with corrosion inhibitors. In this study, under the simulated CUI conditions in the laboratory, the performances of some corrosion inhibitors were evaluated on carbon steel. Immersion tests of polished metal surface specimens and corroded ones were conducted in the solutions controlled 18,000 ppm chloride ions (3.0 wt.% NaCl) at 50°C, and the mass loss values were compared. In addition, potentiodynamic polarization measurements were performed to presume these inhibition mechanisms. One nonflammable inhibitor known to contain phosphates and nitrites showed good anti-corrosion performance on both the polished metal surface specimens and the corroded ones. The primary inhibition mechanism was considered to be the formation of the protective film on the steel surfaces. On the other hand, it was deemed that localized corrosion was a possible concern in spots where the inhibitor did not act sufficiently. Therefore, applying corrosion inhibitors to insulation materials is expected to be one of the corrosion control techniques for preventing further CUI as a temporary expedient until other permanent repairs are carried out.

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