What phenomenon occurs at the low temperature area of boilers?

The phenomenon that occurs at the low temperature area of boilers is cold end corrosion. This occurs because the lower temperature zones of a boiler can lead to condensation of flue gases, which contain corrosive substances such as sulfuric acid. When the flue gases condense on the cooler surfaces of the boiler, it provides a moist environment that can corrode materials over time, particularly in areas where certain metals are present.

Cold end corrosion is particularly problematic in systems that operate at lower temperatures, as they may not be adequately heated to prevent condensation. Addressing this issue often involves maintaining higher temperatures in these areas, using appropriate materials, or implementing protective measures such as chemical treatments to inhibit corrosion.

The other options, while relevant to boiler operations, do not specifically relate to the low temperature zones. High pressure formation typically occurs in high temperature areas, thermal expansion is a characteristic of all materials but not constrained to low temperatures, and steam fluctuation usually pertains to changes in steam pressure or temperature in different operating conditions rather than a direct result of low temperatures in the boiler.