As a boiler generates steam, impurities found within the boiler feed water do not evaporate and begin to concentrate in the boiler. As the concentration of these impurities (known as dissolved solids) increases further, it begins to affect the phase-change process of water into steam by increasing the stability of the bubbles at the (boiling) water-steam interface.

Depending on a boiler’s capacity (kg/hr) and operating pressure (barg), stable steam bubbles start to accumulate in the steam space within the boiler chamber. If untreated, these bubbles are carried forward into the steam main, causing the raised steam to be exceptionally wet and contain boiler water and suspended solids. This leads to the steam main and ancillaries – such as control valves, steam traps and flowmeters – being contaminated with impurities, which consequently affect their service life.

Whilst the formation of stable steam bubbles (also known as foaming) can be caused by high levels of contaminants produced by oils and fats, the most common cause of carryover is due to increases in the Total Dissolved Solids (TDS) levels in the boiler water. Assuming other contaminant sources are properly managed, careful monitoring and control of boiler water TDS levels would ensure that the risks of foaming and carryover are minimised.