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Water Treatment
Boiler water chemistry including scale, corrosion, blowdown, and chemical treatment.
Why Water Treatment Matters
Untreated water causes three major problems in boilers: scale, corrosion, and carryover. Proper water treatment extends boiler life and maintains efficiency.
- Scale: mineral deposits that insulate tube surfaces and cause overheating
- Corrosion: chemical attack on metal surfaces, primarily from oxygen and low pH
- Carryover: water droplets carried with steam, causing water hammer and equipment damage
Scale as thin as 1/32" can reduce heat transfer efficiency by up to 12%.
Scale and Deposits
Scale forms when dissolved minerals precipitate out of solution as water is heated. It is the most common boiler problem.
- Caused by calcium and magnesium hardness in the water
- Acts as insulation between flame and water
- Causes tube overheating, blistering, and eventual failure
- Removed by: blowdown, chemical treatment, or mechanical cleaning
- Prevention: water softening, proper blowdown, phosphate treatment
Corrosion
Corrosion is chemical or electrochemical attack on boiler metal surfaces.
- Oxygen corrosion (pitting): dissolved O₂ attacks metal — treated with sodium sulfite
- Caustic embrittlement: concentrated NaOH attacks metal at stress points (rivets, tube rolls)
- Low pH corrosion: acidic water attacks metal — maintain pH 10.5–11.5 in boiler water
- CO₂ corrosion: in condensate lines — treated with amines
Blowdown
Blowdown removes concentrated dissolved and suspended solids from the boiler water.
- Bottom blowdown: removes sludge and sediment from the mud drum
- Surface blowdown: removes floating solids and controls TDS (Total Dissolved Solids)
- Blowdown rate = feedwater solids ÷ (boiler solids − feedwater solids)
- Excessive blowdown wastes energy and water
- Insufficient blowdown causes scale buildup and carryover
Always blow down before taking a water sample for testing.
Chemical Treatment
Chemical treatment programs maintain safe water chemistry inside the boiler.
- Sodium sulfite: oxygen scavenger — removes dissolved O₂
- Phosphate: reacts with calcium/magnesium to form non-adherent sludge instead of hard scale
- Caustic soda (NaOH): raises pH and alkalinity
- Amines: protect condensate lines from CO₂ corrosion
- Test boiler water regularly: pH, TDS, hardness, sulfite residual, alkalinity