Boiler Water Treatment Primer


| January/February 1988



108 Garfield Avenue, Madison, New Jersey 07940

To paraphrase Coleridge's Rime (sic) of the Ancient Mariner, 'Water, water, everywhere nor any drop for the steam engine' is, every day, becoming more prophetic as our sources become contaminated. Just opening the nearest fire hydrant to fill the engine's tank could, in the long term, prove to be catastrophic. I am really not an 'expert' in the field of boiler water treatment but one who found it necessary to gain an understanding of the subject. Let me share that with you.

Impurities in water which form scale inside a boiler are hardness, silica and corrosion products. Scale is formed by impurities precipitating from solution directly on boiler plates and tubes or the suspended solids settling out and then being baked on these heat transfer surfaces. Scale causes failures of metal due to local overheating and also contributes to boiler corrosion.

The parameters of boiler design involved here are pressure and steam temperature i. e., saturated or superheated with pressure being the primary consideration. Since our interest is in traction engine and portable power boilers we will limit ourselves to the problems associated with 125 pound saturated steam operations.

By way of some background in the subject of water treatment, most waters available to Iron-Men will contain constituents that can be placed into three categories: temporary hardness, permanent hardness, and suspended solids. If the water source happens to be from a municipal supply and not some nearby creek then suspended solids can probably be neglected thus avoiding a costly and difficult coagulation type treatment step or, at least, a slow sand filter bed operation.

At a risk of over simplification we can define the two types of hardness by saying that temporary hardness elements in the water supply, and which cause excessive scale formation, are of a chemical nature that can be converted to compounds that will remain in solution in the boiler water through rather simple treatment steps to later be removed by hot blow-down on a regular basis. On the other hand, permanent hardness elements do respond to such simple treatment steps but require more difficult to achieve alkalinity control. If they are of sufficient amounts in the supply, they too can be a source of potential damage to the boiler. In general, the carbonates of calcium and magnesium constitute the temporary category while the sulphate form of calcium and magnesium constitute permanent hardness.