The most common source of corrosion in boiler systems is the amount of dissolved oxygen that remains in the boiler feedwater after treatment. Oxygen scavenging chemicals normally Sodium Sulphite, is added to the stored feedwater.
Modern Steam Boilers have a high heat transfer rate: impurities in the feedwater can cause scale or chemical deposits to form and reduce the rate of heat transfer from the tube walls to the water, overheating the metal surfaces whilst reducing the steam output.
Even though we add chemicals to the feedwater to protect the boiler from scale and corrosion, they do add to the ‘Total Dissolved Solids’ (TDS) content. As steam is produced, the dissolved solids remain in the boiler and concentrate up.