Boiler Feedwater Problems: Diagnosis & Solutions

Why Feedwater Quality Matters

Every kilogram of steam that leaves the boiler is a kilogram of water that must be replaced by feedwater. If the feedwater contains impurities — hardness, dissolved gases, dissolved solids, oil — those impurities enter the boiler and accumulate. Over time, they cause scale, corrosion, foaming, and carryover. The quality of the feedwater is the single most important factor in boiler reliability.

Problem 1: Hardness (Calcium & Magnesium)

Symptoms: Scale on boiler tubes, reduced heat transfer, rising stack temperature, tube failures.

Solution:

• Install or repair a water softener (sodium zeolite ion exchange) — the primary defence for most boilers
• For high-pressure boilers, use demineralisation or reverse osmosis
• Internally treat with phosphate or chelant chemicals to keep residual hardness in suspension as sludge
• Test feedwater hardness daily — target: 0 ppm (completely soft)

Problem 2: Dissolved Oxygen

Symptoms: Pitting corrosion on boiler tubes — small, deep pits often hidden under rust nodules.

Solution:

• Install or repair a deaerator — heats feedwater to saturation to release dissolved gases. Target: less than 7 ppb oxygen.
• Dose oxygen scavenger: sodium sulfite for low-pressure, hydrazine/carbohydrazide for high-pressure boilers
• Test sulfite residual in boiler water daily — target: 20–40 ppm excess sulfite
• Check the deaerator vent — it should be releasing a small amount of steam (evidence that gases are being vented)

Problem 3: High TDS

Symptoms: Foaming, carryover, unstable boiler water level, contamination of downstream steam.

Solution:

• Increase surface blowdown to reduce TDS below the limit for the operating pressure
• Install automatic TDS-controlled blowdown (conductivity controller)
• Maximise condensate return — returned condensate has very low TDS, diluting the feedwater
• For high-pressure boilers, consider reverse osmosis or demineralisation of makeup water

Problem 4: Oil Contamination

Symptoms: Severe foaming, carryover, discoloured boiler water, oily film on the gauge glass.

Solution:

• Identify and fix the source — check process heat exchangers for tube leaks, compressor seals, and lubrication systems
• Install an oil separator on the condensate return line
• Dump contaminated condensate to drain — do not return it to the boiler
• Add a dispersant chemical to break the oil film on the water surface
• If contamination is severe, drain and refill the boiler with clean water

Problem 5: Low pH (Acidic Water)

Symptoms: Generalised corrosion of boiler steel, thinning of tube walls, rust in the gauge glass.

Solution:

• Dose caustic soda (NaOH) to raise pH — target boiler water pH of 10–12
• Check for CO₂ in the condensate (carbonic acid) — dose neutralising amines in the steam line
• Check the deaerator — if it's not removing CO₂, the gas dissolves in condensate and forms acid
• Test feedwater and condensate pH every shift

Feedwater Testing Programme