BOILERS CONDENSATE CORROSION FILTERS

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Abstract

Having spent many years at two coal-fired plants, the author knows the importance of condenser monitoring, and minimizing the occurrences and impacts of cooling water in-leakage. Introduction of impurities, and particularly such contaminants as chloride and sulfate, can cause severe corrosion problems in boilers. However, these corrosion mechanisms are greatly exacerbated by the presence of porous iron oxide deposits on waterwall tubes. Under-Deposit Corrosion During normal steam generator operation, condensate/feedwater piping and boiler tubes develop a layer of iron oxide, which, while being a corrosion product, protects the underlying base metal against further corrosion. This protective layer may be very tight, especially where oxygenated treatment (OT) is used (see Addendum article), but during periods of chemistry upsets, thermal transients, and forced outages, additional corrosion products are generated. And, from the major work often performed during scheduled maintenance outages, literally hundreds to thousands of pounds of loose particulates may collect in the condenser hotwell, condensate, and feedwater systems. As these particulates enter the boiler, they precipitate on the tubes, primarily on the hot side. Because these transported deposits are porous, they can establish wick boiling. In this mechanism, the bulk boiler water enters the deposits and migrates towards the tube surface where the water flashes to steam. Figure 1 illustrates wick boiling as it would appear inside a boiler tube wall.

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