Prediction and Measurement of Pitting Damage Functions for Condensing Heat Exchangers

Pitting corrosion is a form of localized attack resulting in rapid penetration into a metal substrate. It is one of the most destructive and insidious forms of corrosion that occurs in industrial systems. Traditionally, the damage function (i.e, the number of pits vs the pit depth) is measured experimentally, and the development of damage has been described using empirical models. In general, the empirical models are successful because the distribution functions employed display great mathematical flexibility, but they require a significant database to achieve reliability. In fact, they really are successful only when the answer is known in advance. In this study, a deterministic method was developed to predict localized corrosion damage functions for condensing heat exchangers. The method incorporated calculations for the composition of the condensed environment and the electrochemical corrosion potential (E_corr) of the alloy and included mechanistic treatments of pit nucleation and growth. The roles of important environmental parameters such as chloride concentration ([Cl⁻]) and partial pressure of oxygen (⁠$PO2$⁠) in the flue gas were accounted for by the model. The predicted damage functions agreed well with the experimental data.