Why Does Equipment Keep Pitting? Understanding Chloride Corrosion from Local Failure to Oilfield Protection
Explain how chloride ions break passive films and trigger autocatalytic pitting, how chloride differs from CO₂/H₂S corrosion, and how materials, chemistry, process control, and monitoring work together for protection.
Article Summary
Chloride ions are small and strongly electronegative. They compete with oxygen species for sites in passive films, penetrate film defects, form soluble chlorides, and initiate microscopic pits. Once a pit forms, the exposed metal becomes a small anode surrounded by a large cathode; hydrolysis lowers the local pH, chloride migrates into the pit, and a self-accelerating cycle develops beneath corrosion products.
Unlike the more predictable thinning associated with CO₂ or the hydrogen-cracking risk associated with H₂S, chloride corrosion is often hidden until perforation. Protection should be layered: select materials by chloride concentration, use strongly adsorbing inhibitor blends in high-salt service, control scale and microbes, clean deposits, and combine electrical, ultrasonic, and distributed monitoring for early warning.
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