In Situ Monitoring of Corrosion under Insulation Using Electrochemical and Mass Loss Measurements

Abstract

Corrosion under insulation (CUI) refers to the external corrosion of piping and vessels when they are encapsulated in thermal insulation. To date, very limited information (especially electrochemical data) is available for these “difficult-to-test” CUI conditions. This study was aimed at developing a novel electrochemical sensing method for in situ CUI monitoring and analysis. Pt-coated Ti wires were used to assemble a three-electrode electrochemical cell over a pipe surface covered by thermal insulation. The CUI behavior of X70 carbon steel (CS) and 304 stainless steel (SS) under various operating conditions was investigated using mass loss, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) measurements. It was found that both the consecutive wet and dry cycles and cyclic temperatures accelerated the progression of CUI. LPR and EIS measurements revealed that the accelerated CUI by thermal cycling was due to the reduced polarization resistance and deteriorated corrosion film. Enhanced pitting corrosion was observed on all tested samples after thermal cycling conditions, especially for CS samples. The proposed electrochemical technique demonstrated the ability to obtain comparable corrosion rates to conventional mass loss data. In addition to its potential for in situ CUI monitoring, this design could be further applied to rank alloys, coatings, and inhibitors under more complex exposure conditions.

Investigation of the Effect Chloride Ions on Carbon Steel in Closed Environments at Different Temperatures

“…As the rust layer under this condition was porous and thin, it could be inferred that the corrosion layer could not effectively hinder the diffusion process, resulting in localised corrosion. The fitting results proved that the electrical equivalent circuit (EEC) Figure 13 was suitable [31,32], and the analytical results were listed in Table 3 and Table 4, respectively. The fitting results proved that the electrical equivalent circuit (EEC) Figure 13 was suitable [31,32], and the analytical results were listed in Tables 3 and 4, respectively.…”

“…The fitting results proved that the electrical equivalent circuit (EEC) Figure 13 was suitable [31,32], and the analytical results were listed in Table 3 and Table 4, respectively. The fitting results proved that the electrical equivalent circuit (EEC) Figure 13 was suitable [31,32], and the analytical results were listed in Tables 3 and 4, respectively.…”

“…(c) (d) The fitting results proved that the electrical equivalent circuit (EEC) Figure 13 was suitable [31,32], and the analytical results were listed in Table 3 and Table 4, respectively. Q C is a constant phase element (CPE) of a corrosion product, R S is the solution resistance, and R C denotes the resistance of a corrosion product.…”

Prospect of Using Machine Learning-Based Microwave Nondestructive Testing Technique for Corrosion Under Insulation: A Review

“…In these industries, the corrosion is grown invisibly in the metal substrate under insulation due to the intrinsic coating imperfections, humidity, and water invasion that makes structural thinning [7][8][9]. This structure's weakness can lead to a catastrophic failure on asset integrity which has several adverse consequences, including production losses, maintenance cost, environmental pollution, and personnel risk in terms of health and safety [10][11][12]. Therefore, an accurate and quick inspection for CUI detection is required to avoid the aforementioned consequences and enhance the system's overall integrity.…”