Effect of Polymer and Ceramic Crevice Formers on the Crevice Corrosion of Ni-Cr-Mo Alloy 22

One important factor affecting crevice corrosion of passive metals is the crevice geometry, e.g., the gap of the crevice. The crevice geometry can be affected by the properties of the materials used as the crevice formers, i.e., a polymeric crevice former can conform to the surface roughness of a metal specimen, which helps the creation of a tighter crevice gap. The objective of this work was to investigate the effects of crevice former materials on the evolution of crevice corrosion damage of Alloy 22 (UNS N06022). The factors that may limit the initiation and slow or stop the propagation of crevice corrosion are addressed. Crevice formers made from ceramic, polymers, and polytetrafluoroethylene (PTFE) tape-covered ceramic are compared in controlled crevice corrosion tests, which are performed under highly aggressive, accelerated conditions. Results show that crevice corrosion of Alloy 22 is affected by the crevice former materials and by the surface finishes of the crevice former and specimen. Four stages of crevice corrosion were observed: initiation, propagation, stifling (corrosion slowed), and arrest (corrosion stopped). In some cases, the corroded alloy can become repassivated after undergoing an amount of corrosion.