This experiment is based on the ASTM F746 Standard Test Method for Pitting or Crevice Corrosion of Metallic Surgical Implants. It automates data collection for this test method, which was developed using manual control methods.
This technique actually determines the Critical Repassivation Potential. This is the potential at which a pitting specimen will not repassivate. The specimen is induced to pit (the stimulation phase) by applying a large anodic potential. After pitting has started, the potential is dropped to a test potential to see if the sample will repassivate at that potential. The first potential tested is Ecorr. If the specimen repassivates, the process of stimulation and repassivation is repeated at a more anodic potential. Each repassivation phase increases the potential to the next multiple of 0.05 V. The experiment ends when, during a repassivation phase, the current exceeds a limit indicative of pitting or, when the sample does not pit during a stimulation phase.
Although the CPP experiment originated in biomedical studies, it can be used to investigate localized corrosion in most industries.