Effect of Additives on Denting Corrosion in a Heated Crevice Environment: Chloride Ions and NiB

Abstract

The influences of chloride ion concentration and crevice geometry on the rate of denting corrosion of carbon steel in a solution containing copper ions were investigated. The results indicate that the denting rate increased with an increase in chloride ion concentration and crevice gap size. X-ray diffraction patterns suggest that hematite was formed at low chloride ion concentrations, whereas maghemite and magnetite were formed at high chloride ion concentrations. Nickel boride (NiB) was tested as a denting inhibitor under acid-chloride test conditions. The denting rate decreased dramatically with the addition of NiB powder in a solution containing 35,000 ppm of NaCl in both short-term (2 week) and long-term (12 week) experiments. Scanning electron microscope images revealed that the corrosion product obtained with a high chloride concentration with NiB powder was analogous to that obtained with a low chloride concentration without NiB powder.