Boiler water problems

Harmful substances in Boiler Feedwater

The mineral and organic substances present in natural water supplies vary greatly in their relative proportions, but are principally comprised under the carbonates, sulphates and chlorides of lime, magnesia and sodium, iron and aluminum salts, silicates, mineral and organic acids, and the gases oxygen and carbon dioxide.

Scale is formed from the carbonates and sulphates of lime and magnesia, and from the oxides of iron, aluminum and silicon and it will result in:

• Reduction in the boiler efficiency because of the decreased rate of heat transfer.
• Overheating and burning of tubes resulting in tube failure.

Scales are dangerous long before it reaches this thickness. A very thin scale can cause tube failure due to overheating. Scale has about one-fortyeighth of the heat conductivity of steel.
A scale thickness of about 1 mm (0.04") can be sufficient to reduce the heat transportation to a dangerous point; when the water inside the tube cannot receive and carry away the heat fast enough from the tube metal to keep its temperature below its fusion temperature, resulting in the tubes "burning-out".