When water is turned into steam, the minerals previously dissolved in the water are left behind and deposit a scale on the hot boiler surfaces. This scale, mostly calcium and magnesium, is an excellent insulator and slows the transfer of heat to the water. When boiler surfaces are covered with scale, heat normally absorbed by the water goes up the stack instead, and the tube metal temperature rises to the point of failure.

Water dissolves many substances. It never occurs in nature in a pure state, because groundwater picks up impurities as it migrates through rock strata. Surface water contains organic matter and insoluble suspended matter such as sand and silt. Even rain picks up oxygen and carbon dioxide as it falls to earth, so descaling is essential and must be planned.

The amount of scale dissolved in the feedwater is measured in parts per million (ppm). Its difficult to imagine the accumulation of scale for a 100-hp boiler producing 3,450 lb of steam per hour with the feedwater hardness at 50 ppm but its a significant issue and boiler failure occurs when the scale is allowed to accumulate.

Steel retains its strength up to 700 deg. F, and it starts to weaken above that point. At 1000 deg. F it has a hard time supporting its own weight. A boiler with a flame temperature of 3,000 deg. F survives because the water absorbs the heat from the metal fast enough so the temperature of the metal does not reach the danger point. If scale is allowed to accumulate, it creates an insulation between the metal and water and the metal temperature increases. if allowed to develop and descaling is not performed the metal will overheat causing blisters, bags and eventually a ruptured pressure part.


X Scale Limited recommends your condenser be cleaned bi-annually.  To learn more about our maintenance packages please contact us with your Boiler cleaning needs.