Quantitative comparison of anaerobic pitting patterns and damage risks by chloride versus Desulfovibrio vulgaris using a fast pitting-characterization method

• Compared anoxic carbon steel corrosion by chloride and a sulfate reducing bacterium.
• The SRB Desulfovibrio vulgaris induced more severe pitting than sea-water-level chloride.
• Validated application of fast pitting-parameter-quantitation method in all systems.
• Used/developed pitting diagrams to show pitting patterns and failure risks.
• Studied surface roughness effects; examined pit morphologies in different systems.

Anaerobic carbon steel corrosion induced by chloride and a sulfate reducing bacterium (SRB) Desulfovibrio vulgaris was compared using a fast pitting-characterization method based on Infinite Focus Microscopy. This method was found to be significantly less labor-intensive and more reproducible for determination of maximum and average pit depths and pitted area percentage than manual pit identification and measurement. Graphic diagrams were developed with these parameters to show pitting patterns and compare damage risks. Results showed that this SRB was more damaging than chloride by forming deep pit clusters with larger maximum pit depths. Pit geometry and size were also compared for the two corrosion causes. The fast pitting-characterization method was validated to work well for corrosion with different pitting patterns and pit geometries induced by the chloride and D. vulgaris systems.