Online monitoring of carbon steel corrosion under different commercial coatings was conducted, utilizing coupled multielectrode sensors. The experimental results showed that the coupled multielectrode corrosion sensor is an effective tool for detecting initial defects and real-time degradation of the coatings. Because of their high sensitivity, the coupled multielectrode sensors may also be used as a quick and convenient tool for optimizing the selection of proper coatings for different applications.


Coatings are used to prevent metallic substrates from corrosion in many industries?including infrastructure, transportation, military, and industrial process equipment. In the United States alone, the total annual cost of coating applications in 1997 was estimated to be between $33.5 billion and $167.5 billion, according to a recent NACE report.1 The corrosion protection provided by the coatings depends on the quality of the coatings. If the coating is deteriorated or damaged in a given environment, corrosion may take place under the coating or at the flawed location. Such corrosion can cause severe problems?even catastrophic failures?if it is not identified and mitigated at an early stage. Because

corrosion beneath a coating is not easily detected, an effective monitoring technique is required to detect it at an early stage, in order to eradicate or control the undercoat corrosion. Periodically, inspection tools, such as holiday detectors, are used to evaluate the coating on a metallic substrate. An online monitoring technique may provide a real-time indication of the coating performance and serve as an early warning of degradation. Therefore, an online corrosion monitor is an ideal tool for detecting and

controlling undercoat corrosion.

Coupled multielectrode corrosion sensors have been used as in situ or online monitors for

Non-uniform and localized corrosions, in laboratories and industrial applications.2-5 These applications have demonstrated that the sensors can be used to continuously monitor corrosion, not only in aqueous solutions, but also under solid deposits, such as bio-deposits and salt deposits.3,4 .

In this study, coupled multielectrode corrosion sensors and a newly developed Multielectrode Corrosion Analyzer System were used as an online monitor to detect corrosions under coatings. The detailed experimental setup is described. The results of corrosion measurements on carbon steel under different coatings are presented.

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