Boiler water treatment is one of the most critical aspects of industrial plant maintenance. Untreated or poorly treated boiler feedwater leads to three primary failure mechanisms: oxygen corrosion (pitting), scale deposition (reduced heat transfer), and carryover (damage to turbine blades and downstream equipment). A comprehensive treatment program addresses all three simultaneously through integrated chemical dosing.
Oxygen scavenging is the first line of defense against corrosion. Dissolved oxygen in feedwater — even at levels as low as 7 ppb — causes pitting corrosion that can perforate boiler tubes within months. Mechanical deaeration removes the bulk of dissolved oxygen (down to ~7 ppb for spray-type deaerators), but chemical oxygen scavengers are required to reach the < 5 ppb level needed for reliable boiler protection. Hydrazine (N₂H₄) and its derivatives remain the most effective scavengers for high-pressure systems (> 60 bar), reacting stoichiometrically with oxygen: N₂H₄ + O₂ → N₂ + 2H₂O.
pH control in the boiler and condensate systems prevents acid corrosion and minimizes the solubility of protective magnetite (Fe₃O₄) films. The target pH for boiler water is typically 10.5–11.5 for low-pressure systems and 9.0–9.5 for high-pressure systems. Caustic soda (NaOH) or coordinated phosphate programs are used to maintain these levels. In the condensate return system, neutralizing amines such as cyclohexylamine or morpholine are dosed to maintain a condensate pH of 8.5–9.0, preventing carbonic acid corrosion.
Scale prevention requires controlling hardness, silica, and total dissolved solids (TDS) in the boiler water. External softening or demineralization of makeup water is essential. Internal treatment with phosphate-based programs precipitates residual calcium as non-adherent sludge rather than hard scale. Regular blowdown removes accumulated sludge and controls TDS. The blowdown rate should be calculated to maintain conductivity below the manufacturer's limit — typically 3,500 µS/cm for low-pressure and 150 µS/cm for high-pressure boilers.