Lifetime Predictions for Carbon Steel in Natural Fresh Water

Corrosion rates of carbon steel exposed at multiple locations in a fresh water harbor were monitored over 3 years. Measurement techniques included (linear) polarization resistance (LPR)*, pit depth and weight loss.  All corrosion rates are reported in units of mils-per-year (MPY) for direct comparison. The estimated corrosion rates varied among the techniques with the fastest penetration rate predicted by the LPR measurements. There were no obvious relationships between the predicted rates, e.g. MPY calculated from weight loss were not directly related to MPY calculated from pit depth. Corrosion rate was not linear with time.  Localized corrosion (pitting) in the first year exposure was more aggressive than in subsequent years. Pit depth varied among the locations. The corrosion rate calculated from weight loss remained remarkably constant at all exposure sites over 3 years.