Movement of the solution over the metal surface often does what to pitting?

• A. Reduces, prevent
• B. Increases, promote
• C. Aids, worsens
• D. Circulates, induces

Answer: (A)

When the solution moves across the metal surface, it improves mass transport at the interface. That means aggressive species near the surface are more effectively flushed away and protective reactions, like the oxide/passive film, are better maintained by fresh oxidants such as oxygen. With the passive film staying intact and corrosive ions not concentrating at a local spot, pits are less likely to form or propagate. So, flow tends to lessen both initiation and growth of pits, making pitting less likely under flowing conditions.