Scaling occurs as water is heated and converted into steam. The boiler
functions as a distillation unit, taking pure water out as steam and leaving
behind concentrated minerals and other contaminants in the boiler. Scale forms
as a result of the precipitation of normally soluble solids that become
insoluble as temperature increases. Some examples of boiler scale are calcium
carbonate, calcium sulfate and calcium silicate.
is a general term that indicates the conversion of a metal into a soluble
compound. In the case of boiler metal, corrosion is the conversion of steel
into rust. In a boiler, two types of corrosion are prevalent. There is
oxygen-pitting corrosion, seen on the tubes and in the preboiler section. And
there is low-pH corrosion, seen in the condensate return system. Corrosion of
either type can lead to failure of critical parts of the boiler system,
deposition of corrosion products in critical heat exchange areas, and overall
- Carryover. Carryover is caused by either priming or foaming. Priming is the sudden violent eruption of boiler water that is carried along with steam out of the boiler. It usually is caused by mechanical conditions. Priming can cause deposits in and around the main steam header valve in a short period of time. Foaming causes carryover by forming a stable froth on the boiler water that then is carried out with the steam. Over a period of time, deposits due to foaming can completely plug a steam or condensate line.