The best defence against crevice corrosion is to limit the potential for crevices in the first place. Crevice corrosion is driven by the choice of metal, the operating conditions and environment, and the presence of a crevice or crevice-former.
Where different conditions develop between a crevice and the bulk surface, an electrochemical cell forms and corrosion begins. Inside the crevice, conditions become far more aggressive than in the bulk, because acidic species concentrate and the oxygen that would otherwise support re-passivation of the protective passive film is absent.
How to reduce the risk
The most common source of crevices is around bolted connections, underneath bolts or washers. Tight corners, dead spots in the flow of liquid through a component, and surface damage such as deep scratches or gouges can all act in the same way. Practical measures include:
- Limiting bolted connections and joints
- Producing components with radiused corners rather than sharp angles
- Designing components to experience more uniform flow
- Polishing surfaces to remove crevice-forming damage