Boiler Failure Library
A guide to boiler failure modes — tube rupture, refractory failure, scaling, corrosion, low-water damage, and combustion problems. Each includes symptoms, causes, and prevention.
Understanding Boiler Failures
Boiler failures range from efficiency-robbing scaling to catastrophic tube ruptures. Many failures are preventable through proper water treatment, regular inspection, and correct operation.
Tube Rupture
Tube rupture is the most serious boiler failure — it can shut down the plant and cause injury. Tubes rupture from overheating (water-side scaling, low water), corrosion, or fatigue.
- Symptoms: Sudden loss of pressure, steam and water discharge from the casing, loud noise, water level drop, and emergency shutdown.
- Root causes: Scale buildup on the water side insulates the tube, causing overheating and rupture. Low water level exposes tubes to furnace temperature. Corrosion thins the tube wall. Thermal fatigue from rapid temperature changes.
- Prevention: Maintain rigorous water treatment (zero hardness, correct TDS, oxygen scavenger), blow down regularly, maintain water level controls and test low-water cutoffs monthly, avoid rapid start-up/shutdown, and inspect tubes annually.
Inspection tip
Inspect tubes annually — measure wall thickness with UT, check for scale on the water side, look for blistering or discoloration. Test low-water cutoff by blowing down the float column.
Refractory Failure
Refractory lining protects the boiler casing and furnace from extreme temperatures. Cracks and spalling reduce efficiency and can cause casing overheating.
- Symptoms: Hot spots on the boiler casing, visible cracks or gaps in the refractory, pieces of refractory in the furnace, and reduced efficiency.
- Root causes: Thermal cycling (rapid heating/cooling causes cracking), improper curing at initial startup, mechanical vibration, flame impingement (localised overheating), and ageing.
- Prevention: Follow proper refractory cure procedure at startup, avoid rapid temperature changes, ensure burner is tuned to prevent flame impingement, and repair cracks promptly.
Inspection tip
Inspect refractory during annual shutdown — look for cracks, spalling, and gaps around burner openings and doors. Tap the surface with a hammer — sound areas ring; damaged areas sound dull.
Scaling
Scale is the deposition of hardness minerals (calcium, magnesium) on the water side of tubes. It reduces heat transfer, increases fuel consumption, and causes tube overheating.
- Symptoms: Increased stack temperature (reduced efficiency), increased fuel consumption for the same steam output, and hot spots on tubes.
- Root causes: Inadequate water treatment (hardness in feedwater), insufficient blowdown (TDS too high), and faulty softener or deaerator.
- Prevention: Maintain water treatment: zero hardness in feedwater, TDS within limits, blowdown at correct frequency, test feedwater daily, and service the softener regularly.
Inspection tip
Inspect the water side of tubes during shutdown — scale appears as a white or tan crust. Measure scale thickness — even 1mm of scale can reduce heat transfer by 10%.
Oxygen Corrosion (Pitting)
Dissolved oxygen in boiler water causes pitting corrosion — deep, localised pits that can perforate tubes and drums.
- Symptoms: Pits on the water side of tubes and drums (look like small deep holes with a brown ring), rusty water, and tube thinning.
- Root causes: Inadequate deaeration (oxygen not removed from feedwater), insufficient oxygen scavenger dosing, air leaks in the suction side of the feed pump, and storage tank not properly vented.
- Prevention: Maintain deaerator performance, dose oxygen scavenger (sulphite or hydrazine) to maintain a residual, test for dissolved oxygen in feedwater, and seal air leaks in the feed system.
Inspection tip
Inspect the water side for pitting during shutdown — pits are small (1–3mm diameter), deep, and often have a brown ring of iron oxide. Test feedwater for dissolved oxygen.
Low-Water Damage
When the water level drops below the furnace tubes, they overheat rapidly and can rupture. This is one of the most dangerous boiler failures.
- Symptoms: Low-water alarm, tubes glowing red through the inspection port, steam leaks from tubes, and emergency shutdown.
- Root causes: Low-water cutoff failure (most common), feed pump failure, loss of feedwater supply, operator error, and rapid steaming without feedwater makeup.
- Prevention: Install redundant low-water cutoffs (two independent devices), test low-water cutoffs daily (blow down the float column), maintain feedwater system reliability, and train operators on emergency procedures.
Inspection tip
Test low-water cutoffs daily by blowing down the float column — the burner must shut down. Inspect tubes for overheating damage (blistering, sagging, or rupture).
Carryover and Foaming
Carryover is the discharge of water droplets into the steam line. Foaming is the formation of a stable foam layer on the water surface. Both contaminate steam and damage downstream equipment.
- Symptoms: Wet steam (water in steam line), fluctuating water level gauge, steam line hammering, and contaminated process.
- Root causes: High TDS in boiler water (causes foaming), high water level (too close to steam outlet), sudden load changes (cause surging), and oil or organic contamination.
- Prevention: Maintain TDS within limits by blowdown, maintain correct water level (not too high), avoid sudden load changes, and prevent oil contamination of feedwater.
Inspection tip
Observe the water gauge glass — the level should be steady. If it surges, suspect foaming. Check TDS with a conductivity meter. Inspect steam traps for water carryover.
How CHI can help
Ask CHI about boiler failure diagnosis and to recommend water treatment adjustments to prevent scaling and corrosion. The CHI assistant can help you diagnose failure modes from symptoms, recommend inspection methods, and suggest preventive maintenance actions to avoid similar failures.