Abstract
In many service applications excursions in solution chemistry, temporary loss of inhibitor, or transient increases in temperature may give rise to localised corrosion in an otherwise inhibited system. It is important to demonstrate that inhibition will be effective in retarding propagation of localised corrosion when normal conditions, appropriate to prevention of general corrosion, are restored. To test this requirement, the use of a ‘pencil’ type of artificial pit has been investigated using simple simulations of a cooling water and of an oil production formation water. The results demonstrate the effectiveness of this technique and show that nitrite, as an example of a cooling water inhibitor, can be effective in retarding propagation with the appropriate dosage, a result that is not too surprising as it will act as a competing anion. Tests in simulated oil production formation waters at 50 °C demonstrated that an imidazoline-based inhibitor can decrease pit growth kinetics in nearly neutral CO2-saturated solution but does not appear to be so effective with oxygen contamination of that solution or in mildly acidic CO2-saturated solution.
