As the alkalinity of boiler water decreases, what happens to the severity of dissolved oxygen attack?

The severity of dissolved oxygen attack increases as the alkalinity of boiler water decreases due to the essential role that alkalinity plays in controlling pH levels and the formation of protective layers on metal surfaces. When alkalinity is high, the boiler water has better-buffering capacity, which helps maintain a stable and relatively neutral pH. This stable pH is crucial because a more acidic environment can corrode metal surfaces.

When alkalinity decreases, the pH can drop, leading to an increase in corrosive conditions that dissolve protective oxide layers on the metal surfaces of the boiler. This not only exposes the base metal to the water but also allows for increased levels of dissolved oxygen, which exacerbates corrosion. Thus, a decrease in alkalinity creates an environment where corrosion reactions proceed more aggressively, making the boiler system more susceptible to damage from dissolved oxygen.