Effect of dissolved oxygen on galvanic corrosion of low-voltage steel couples in seawater

Abstract

The repair of marine structures often involves coupling steel grades with minimal potential differences (<60 mV). This study systematically investigates the galvanic corrosion of 907A, 921A and Steel 1 in artificial seawater under varying dissolved oxygen (DO) levels. The key finding reveals that severe galvanic corrosion occurs despite the small potential difference, challenging conventional assumptions. Electrochemical measurements, weight loss assessments and morphological analyses demonstrate that 907A consistently acts as the anode, with its corrosion rate increasing dramatically as DO levels rise. Furthermore, the galvanic effect shifts 907A's corrosion behaviour from uniform to localised pitting, significantly elevating the risk of failure. A primary innovation of this study is the successful validation of the polarisation curve superposition method for predicting corrosion trends in this tri-metallic system, with predictions closely matching experimental results. This work underscores the underestimated corrosion risk associated with low-potential-difference couples in oxygen-fluctuating marine environments and provides a validated predictive tool to enhance the design and corrosion protection of marine structures.