The chemistry of feedwater control is well understood and there is a raft of legislation and guidance notes spelling out minimum requirements and testing regimes but they all fall short in specifying suitable methods of controlling the application of those chemicals.
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.
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.
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.
Pressure Systems Safety Regulations 2000 state that:-
'The primary objective is to deal with the dangers of stored energy'. The regulations are concerned with all matters affecting the mechanical integrity of those parts of the plant which contain pressure.
It is not necessary to know chemistry to appreciate the fundamentals of water treatment. Good water treatment practice is dependent on a suitable treatment regime for the whole system; from the cold feed to the returning condensate.