51313-02715-Localized Corrosion Due to Galvanic Coupling Between FeS-Covered and Uncovered Areas

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Product Number: 51313-02715-SG

ISBN: 02715 2013 CP

Author: Angeire Huggins

Publication Date: 2013

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Galvanic coupling effects have been attributed to the presence of corrosion product films of different nature on the pipe surface (e.g. FeCO3 vs. FeS-covered areas; bare surface vs. FeCO3-covered areas; bare surface vs. FeS-covered areas). Such galvanic effects have been claimed to cause accelerated material degradation in particular localized corrosion in CO2/H2S oil and gas production systems. It has been traditionally considered that FeS products on the metal surface which are electronically conductive act cathodically to the uncovered steel areas which would then corrode preferentially. However the driving force for localized corrosion could also be the difference in the local environment between covered and uncovered areas. Insufficient and inconclusive experimental evidence is available in the open literature in part due to the inexistence of reliable testing methods and protocols to evaluate possible galvanic effects when coupling metal samples with different surface films and/or surface conditions. An experimental methodology was developed and implemented based on a modified H-Cell where customization of the environment for each cell is possible leading to different metal surface conditions. Both cells are connected by a custom-made salt bridge which prevents cross contamination between and minimizes the IR drop effects. This paper presents the approach and methodology developed as well as proof-of-concept results showing galvanic effects between electrodes with different corrosion products or exposed to electrolytes having different concentrations of CO2 and H2S.