After chain making, proof load testing is used to evaluate if the chains are mechanically qualified. However, proof load testing may bring elongation in the chain links that may affect the corrosion performance of mooring chains in seawater. The influence of deformation and microorganisms on the corrosion properties of chain steel in seawater were investigated together with industry. As part of the Localized Mooring Chain Corrosion (LMCC) JIP project, chain links were prepared according to industrial standards. Some steel samples were elongated to a maximum of 6%. The steel samples were tested by immersion in artificial seawater with and without the addition of microorganisms. Their corrosion behavior was studied using electrochemical impedance spectroscopy (EIS). The corrosion morphology was investigated using three dimentional microscopy. The results indicate that elongation has an adverse effect on the corrosion resistance of the steel in seawater. With the addition of microorganisms localized corrosion is enhanced.