The ultimate successful utilization of stainless steels and related alloys in marine and other chloride containing environments will depend on a more complete understanding of the factors affecting crevice corrosion. To this end, numerous test methods have been devised to investigate the effects of various metallurgical and environmental parameters. While not totally ignored in past research, more recent investigations have also emphasized the importance of crevice geometry considerations. For example, mathematical modelling of chemistry changes in the crevice electrolyte indicates a strong dependency on crevice gap and crevice depth dimensions. In addition, the bulk environment chloride level will affect the ultimate crevice electrolyte pH and chloride level. Accordingly, a given stainless steel may encounter a range of crevice solutions of varying pH and chloride level dependent upon the crevice geometry and bulk environment conditions encountered.
Two experimental approaches for studying crevice corrosion are presented. A remote crevice assembly and a compartmentalized cell have been used to study both the initiation and propagation phases of crevice corrosion. Both methods make use of two specimen components consisting of physically separated but electrically connected anodes (crevice portion) and cathode members. Accordingly, corrosion potential and current data along with conventional mass loss and penetration data can be gathered. A significant feature of these methods is that neither requires the application of current from an external source. Both initiation and propagation of crevice corrosion occur spontaneously. The two techniques differ slightly in that the remote crevice assembly requires creation of a physical crevice on the anode while the compartmentalized cell approach uses a nonoccluded anode in a simulated crevice electrolyte. With the compartmentalized cell, crevice electrolytes are simulated based on the predictions of a mathematical model of crevice corrosion.
Results from recent tests investigating the effects of variations in crevice tightness, bulk solution composition, and crevice solution pH are described in the present article. Remote crevice assembly research has focused on efforts to provide a consistent and reproducible condition of crevice tightness on the anode. The compartmentalized cell research has dealt with the effects of changes in both bulk environment conditions and crevice solution pH. Insights gained on the relative influence of these various factors on crevice corrosion lend credence to the testing concepts embodied by both the remote crevice assembly and the compartmentalized cell.