Boiler continued tube corrosion

During shutdowns, water can also condense on the fireside of the boiler. Each shutdown results in a recurrence of this condensation phenomenon. The moisture can combine with acidic residue on the tubes and cause severe corrosion. If allowed to continue, tube failures can occur. The problem is most pronounced in boilers burning sulfur-laden fuels, even when such fuels are burned only occasionally. 

In water-wall incinerators. The internal walls of the combustion chamber are lined with boiler tubes that are arranged vertically and welded together in continuous sections. When water walls are employed in place of refrac toiy materials, they are not only useful for the recovery of steam but also extremely effective in controlling furnace temperature without introducing excess air however, they are subject to corrosion by the hydrochloric acid produced from the burning of some plastic compounds and the molten ash containing salts (chlorides and sulfates) that attach to the tubes. 

Because of the complex and often corrosive environments in which the power plants operate, corrosion has been a serious problem. Corrosion continues to be a problem with electrical generators and turbines. Specifically, SCC in steam generators in PWR plants and boiler tube failures in fossil fuel plants continue to be problems. 

It is possible also for the caustic to concentrate at the waterline. Generally, the waterline area is always most sensitive to corrosion. Two types of failures are common in boilers and both are related to the effect of concentration of caustic. One which forms discontinuous microcracks and results in the bursting of tubes is called hydrogen damage, and the other which results in the formation of continuous microcracks leading to intergranular corrosion is called caustic cracking. Both are briefly discussed below ... 

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