The steam purity required for any given boiler system is dictated by the use of the steam. Steam of inadequate purity can cause deposition and corrosion in superheaters, steam lines, control valves and turbines. Steam contaminants can also adversely affect catalyst performance and product purity. The ASME “Consensus on Operating Practices for the Control of Feedwater and Boiler Water Chemistry in Modern Industrial Boilers” and “Consensus on Operating Practices for Control of Water and Steam Chemistry in Combined Cycle and Cogeneration Power Plants” provide steam purity targets for typical industrial uses of steam.

The purity of steam is usually monitored by measuring the cation conductivity or sodium content of condensed steam samples. In special situations, as noted in the Combined Cycle and Cogeneration document, silica and∕or cation conductivity will be measured.