Why is boiler condensate prone to corrosion? [Basic Knowledge]

Is higher purity more prone to corrosion? Reasons for managing boiler water at around pH 11.

■Why is steam and condensate prone to corrosion? Boiler steam has a low level of impurities, making it easy for iron ions and copper ions to dissolve. Generally, high-purity water with few impurities has a poor buffering capacity to neutralize acids, and even a small amount of acidic components can significantly lower the pH, thereby increasing its corrosive nature that can dissolve metals. ■Why does the pH of condensate decrease? Condensate that has been heat exchanged and condensed tends to dissolve oxygen and carbon dioxide (CO2) easily. When CO2 dissolves in water, it forms carbonic acid, which lowers the pH. This decrease in pH is a cause of corrosion in piping. ■Why does maintaining alkalinity help prevent corrosion? Maintaining the pH of boiler water between 11.0 and 11.8 is considered desirable for corrosion prevention. In the alkaline range, a dense oxide film (magnetite) forms on the surface of iron, which is thought to protect the metal and suppress corrosion. ■What are some often-overlooked points of caution? Since the steam line is not included in the annual boiler performance inspection items, it requires attention from the management side. Please feel free to consult us first.

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