Pitting Initiation and Propagation Mechanism

The main mode of attack is pitting of Cu-Ni 90/10 tubes. Pit-like attack in condenser tubes is often caused by impingement that occurs at sites where large air bubbles impinge on the tube surface and break into small bubbles on impact, causing local destruction of 

Anodic reactions Equation (la,b) lead to dissolution of metal (copper-nickel 90/10). At the beginning of pit initiation, the reactions of Equation (2a,b) might take place, 

The results of this study indicate that pit initiation takes place in areas where the oxide film is broken or damaged under a stagnant environment in the presence of sufficient moisture and oxygen. It is possible that pit propagation could occur without oxygen, and that it is accelerated by the copper redeposit reaction. In such a case, preventing pit initiation becomes very important. 

Janssen, Corrosion Control in a Refinery Sea Water Cooling System, Materials Protection, 1(10), 42-53 (1962). 

Matthewman and GJ. Evans, Power Station Condensers, Corrosion Technology, 1964, 15-17. 

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