PDFAll furnace typesReading crack patterns: The comparison chart
Symptom, cause and required action side by side.
Only in the PDFSix damage patterns from real furnace inspections with classification: observe, plan or act immediately
To the articleDamage and causes4 min
Reading crack patterns: symptom, cause, need for action
Cracks are symptoms, not surprises. How the course, width and position of a crack reveal what lies behind it — and what needs to be done.
Almost every furnace inspection turns up cracks. The actual work does not consist in finding them, but in classifying them: which crack is normal, which is an early warning sign and which has to be treated immediately? The course of a crack reveals more than its width.
What the course reveals
- A fine network across the surface: typical drying and shrinkage cracks after the first heat-up. As a rule uncritical, provided they do not open up and show no discolouration.
- Straight, continuous cracks running with the component: a missing or blocked expansion joint. Here the lining has created for itself the joint that was missing from the design.
- Cracks along a change of material: differing expansion at the transition. Keep them under observation, but the cause lies in the build-up and cannot be remedied by filling.
- A crack with discolouration or efflorescence: medium has already passed through. This is no longer a crack pattern but an infiltration finding — action is needed regardless of the width.
The three questions for every crack
- Is it changing? Without a comparison photo from the last visit this cannot be answered — which is why every crack pattern should be photographed and dated.
- Does it go all the way through? A surface crack and a through-crack look the same from the inside. Thermography from the outside separates the two reliably.
- Where is it? The same crack is an immediate case in the bath line and a note for the next overhaul in the upper furnace.
A crack that was already there last time and has not changed is a different finding from the same crack appearing for the first time. Without documentation, every crack is a first finding.
At a glance
4 crack patterns
network, straight, at the transition, with discolouration
The course
more meaningful than the crack width
From practice
Matching references
Melting chamber overhaul in Austria
Targeted overhaul of a melting chamber in Austria – side walls partially repaired and floor restored using a pour-on process.
Maintenance uncovers a loss of capacity
Professional maintenance of an aluminium furnace uncovers faulty repairs by a previous contractor – after correction, around 20 tonnes more aluminium per month and noticeably reduced energy consumption.
Practice sheets on this topic
Technical newsletter
Get new practice sheets automatically
All PDFs on this page are free, without sign-up. If you want to know when a new sheet is added: one e-mail a month, unsubscribe anytime.
PDFAll furnace types
PDFAll furnace typesRepair or reline? The three findings
When a targeted repair is enough, and the three findings where only a relining will hold.
Only in the PDFDecision table with 6 findings, the 3 typical wrong decisions, 2 photos from a relining
To the article
PDFEnergy & CombustionRefractory on the tube wall: The inspection points
Protecting without blocking the heat: what matters when lining a boiler tube wall.
Only in the PDF7-point checklist for tube walls, the 3 typical mistakes, 2 photos from the boiler
To the articleMore insights from our projects
New insights from the job site every week – damage patterns, relinings and practical refractory know-how.
Planning a project?
Whether complete relining, repair or emergency — free initial consultation and a fast response.