Module 12 · Maintenance and Troubleshooting3 min read
Boiler Tube Failures: Causes and How to Read Them
A failed tube is evidence. Its shape, its surface and where it sits in the boiler tell you why it failed — and whether the next one is already on its way. Replacing the tube without reading it invites a repeat.
You'll learn
- Name the main tube failure mechanisms
- Tell short-term from long-term overheating
- Link water-side failures to water treatment
- Follow a root-cause routine after a failure
Before this: Scale and corrosion, Shell, drums, furnace and tubes
BeginnerThe idea in plain words, and where you meet it. No maths.
Why tubes fail
A tube is a thin wall between hot gas and water. It survives because water carries heat away fast. Anything that stops that cooling — scale, low water, poor circulation — or that thins the wall — corrosion, erosion — leads to failure.
- Overheating: the metal runs hotter than it is designed for.
- Water-side corrosion: oxygen, caustic or acid attack inside the tube.
- Fire-side damage: erosion by ash and soot blowers, and dew-point corrosion.
- Mechanical: fatigue from cycling and vibration, and poor welds.
IntermediateThe formula, its units, and a worked example on real plant numbers.
Reading the failure
| Mechanism | What it looks like | Usual cause |
|---|---|---|
| Short-term overheating | Wide, thin-lipped “fish-mouth” rupture, little scale | Sudden loss of cooling: low water, blocked tube, starved circulation |
| Long-term overheating (creep) | Thick-lipped, small rupture with bulging and heavy oxide | Months above design temperature, often under scale |
| Oxygen pitting | Discrete pits with tubercles, often near feed inlet or economizer | Poor deaeration, idle boiler left wet without protection |
| Caustic gouging | Smooth gouges under deposits | Caustic concentrating under deposits at high heat flux |
| Erosion | Thinned, polished surface facing the gas or soot blower | High-ash fuel, high gas velocity, misaligned soot blower |
| Dew-point corrosion | Wastage on the cold end: economizer inlet, air heater | Metal below acid dew point |
| Fatigue | Fine transverse cracks at attachments or bends | Thermal cycling, vibration, restrained expansion |
ExpertThe fine print: where the simple model breaks, and what it costs.
After a failure
- Make safe and report as the law requires; a tube failure releasing steam is an accident under the Boilers Act.
- Keep the failed section — do not cut it up for convenience. Record where it was, its orientation, and the conditions before the failure.
- Measure wall thickness nearby and in similar positions; one failure often means others are close.
- Check the logs and water records for the weeks before: low level events, TDS excursions, feedwater oxygen, load swings.
- Fix the cause — water treatment, circulation, firing, soot blower alignment — not only the tube.
Key takeaways
- Tubes fail when cooling is lost or the wall is thinned.
- Thin-lipped fish-mouth: sudden overheating. Thick-lipped with oxide: long-term creep.
- Pitting, gouging and scale trace back to water treatment.
- Keep the failed tube, measure nearby tubes, read the logs, and fix the cause.