By Jack Xing, Technical Sales Director, YK Chanshine · Published October 30, 2026 · 13 min read
Short answer: A vertical crack in a steel ladle wall near the purging plug is usually one of three things: an opened joint (lining structure, expansion allowance, preheat), a crack through a brick (thermal shock or a brick flaw), or an edge erosion groove (weak brick edges plus gas-driven flow). A seam that runs through several courses in one line points to the joint before it points to the brick. Probe the depth, read what fills the gap, and cut a residual brick before you change the brick grade.
Why a Vertical Crack Near the Purging Plug Needs Its Own Diagnosis
Ladle wall wear is normally slow and even. A vertical crack is not. It is narrow, it runs straight up the wall, and it can be deep. We have seen reports of seams 50 mm deep in a lining that was otherwise in fair shape.
The usual reaction on the floor is to blame the brick. Sometimes that is right. More often the brick, the joint and the gas flow all share the blame, and which one leads decides what you change next. Swapping the brick grade when the real cause is a tight ring or a cold start burns a lining and teaches you nothing.
This guide is written from the factory side. We make MgO-C, MgO-Al2O3-C and Al2O3-MgO-C ladle bricks, and we get these photos from customers. Here is how we read them.
What we assume in this guide
- The crack is in the wall at or near the purging plug, not in the bottom.
- The lining is a bricked ladle wall, with working lining bricks against a permanent lining and a steel shell.
- You can reach the crack for a visual check, probe and photographs after the ladle is emptied and cooled.
Three Kinds of Vertical Cracks (They Look Alike from the Floor)
| Type | What you see | What it usually points to | First check |
|---|---|---|---|
| 1. Joint opening | Gap along the brick joint, often through several courses. Brick edges on both sides look intact. Steel or slag frozen inside | Lining structure, expansion allowance, shell condition, preheat | Where is the seam relative to key bricks and expansion joints? |
| 2. Crack through a brick | Crack crosses the body of one brick and stops at the joint. Neighbours look fine | Thermal shock, hot strength, a flaw in that brick | Break the brick open and look at the crack face |
| 3. Edge erosion groove | Brick corners rounded off, the joint becomes a trench, the wall looks “pillowed” | Weak edges, fines, flow erosion | Cut a residual brick and compare edge and centre density |
A real wall often shows two of these at once. A joint that opens lets steel in. Steel in the joint then attacks the edges of the bricks beside it. By the time you see a groove, the joint opening may be weeks old.
Why the Purging Plug Zone Is Harder on the Wall
Plume flow becomes wall flow
Argon from the plug drags steel upward. At the surface the steel spreads out and runs down the nearest wall. That wall sees faster, more turbulent flow than any other part of the lining. A joint or a soft brick edge is where this flow starts cutting.
Gas cooling and thermal cycling
Blowing cools the hot face beside the plug. When the gas stops, the face heats again. Every blow cycle is a small thermal cycle at the exact spot where the joint is already working hardest. Over many heats the joint opens a little more each time.
Open eye at the slag line
Where the plume breaks the surface, the slag layer is pushed aside. Bare steel reaches the wall at the slag line. If the crack is near the top of the plume zone, the lining also takes slag attack, and MgO-C bricks lose carbon faster there.
Steel in the joint acts as a wedge
Once a joint opens, steel gets in and freezes. On the next heat-up the bricks try to expand, but the frozen steel keeps the joint from closing. The stress on the brick edges goes up. Edges chip, the gap widens, and more steel gets in. This loop is the most common reason we see a seam grow deeper over a few weeks.
The Three Field Explanations We Hear from Plants
When a seam turns up, the refractory engineers we work with usually list three suspects. We take all three seriously, and each one can be tested.
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Fine powder at brick edges from forming
Corners are the hardest part of a brick to fill and press evenly. If fines collect at the edges, or the pressure does not reach the corners, the edge density drops. Soft edges erode first, and flow finds them.
How to test the edge-fines idea
Cut a residual brick near the seam. Take samples from the edge and from the centre. Measure bulk density and apparent porosity on both. A large gap between edge and centre is a forming problem. Agree an acceptance limit with the supplier before you judge the number.
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Too much recycled brick in the mix
Some reclaimed grain is normal in MgO-C bricks. The question is how much, how it is graded and whether the batch is recorded. Too much reclaimed material brings uneven grading, partly oxidized particles and more porosity, and the weak spots tend to sit at the corners.
How to test the recycled-brick idea
Ask the supplier for the recycled content range for that brick grade and for the batch record. Look at the cut face: scattered dull or oxidized-looking grains point to this.
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High thermal expansion under stress
A brick that expands a lot will push on its neighbours and on the shell. But expansion alone is not the fault. What matters is how much expansion the lining has room for.
A rough example. A ladle with a 3.5 m inner diameter has a ring circumference of about 11 m. If the hot face grows about 1% (the figure depends on the recipe), that is on the order of 100 mm of free growth around the ring. Mortar joints, expansion paper and a little shell growth take some of it. What is left becomes compression. Too much compression and the weakest joint spalls or buckles. Too little and the joints open when the ladle cools and steel walks in.
How to test the expansion idea
Ask for the expansion curve of the brick, then check how much allowance the lining design actually provides.
Field Checks Before the Next Heat
Look: where is the seam?
Record its height, its distance from the plug, and its angle. Does it run through several courses in one line? Is it on a key brick, an expansion joint or a ring closure? Take a wide photo that shows the plug and the seam together.
Probe: how deep, how wide?
Push a thin steel strip into the gap. Record the depth and the width at three heights, and photograph the strip in place. Do it again after a few heats. A seam that deepens week by week is a process problem. A seam that stays the same is a lining problem.
What to record
Read: what is inside the gap?
Frozen steel
The gap was open while the ladle held steel. It is likely older.
Slag
The gap opened near the slag line, or after the steel was gone.
Clean, dark faces
A recent crack.
Oxidized or rusty faces
The gap has been open for some time and has seen air.
Cut: what does a residual brick tell you?
Take a residual brick from the seam area and cut it. Look at the decarburized depth, any layering, and the density from edge to centre. A cut face tells you in an hour what a week of discussion cannot.
A Six-Step Diagnosis You Can Run in One Shift
- Locate the seam: height, distance and angle from the plug, nearest key brick or expansion joint.
- Classify it: joint opening, crack through a brick, or edge erosion groove.
- Probe depth and width at three heights.
- Read the gap: frozen steel, slag, clean or oxidized faces.
- Cut a brick and compare edge and centre.
- Check the records: preheat curve, argon flow, ladle turnaround, heat count, shell condition.
Reading the result: observation, likely cause, confirmation, fix
| What you observe | Likely cause | How to confirm | Fix to try first |
|---|---|---|---|
| Seam on a key brick or ring closure, through several courses, brick edges still sharp | Lining structure or expansion allowance | Check joint widths on the drawing and in the lining record | Review joint spacing, expansion allowance and ring closure |
| Seam appears after the first one or two heats of a new lining | Preheat or first heat-up | Compare the preheat log with the supplier curve | Slower, controlled preheat, repeat on the next lining |
| Seam appears after a long idle or cold start | Thermal cycling at the joint | Check ladle turnaround and cold time | Keep ladles hot, avoid long idle, reheat gently |
| Edges soft and dusty when cut, density drops from centre to edge | Forming or grading | Edge and centre density, porosity, recycled content record | Talk to the supplier, set an edge density check |
| Seam deepens heat by heat, worst at the plume | Flow erosion on a weak line | Repeat the steel-strip probe, check argon flow and blow time | Adjust blowing practice, consider a stronger grade at the zone |
| Crack through a single brick, fresh dark faces | Thermal shock or a flaw in that brick | Break it open, check for lamination and oxidation | Review preheat and brick lot, replace the brick |
| Shell hot spot or deformation near the seam | Shell condition | Thermal imaging, shell geometry check | Repair the shell before relining |
What to Do Now, and What to Change in the Next Lining
This week
- Decide whether the ladle should keep running. Compare the seam depth with the remaining lining thickness. A seam that reaches the permanent lining, or shows steel near the shell, is a stop. Follow your plant safety rules, and ask your own refractory engineer for the final decision.
- Record the seam. Photos, probe numbers and heat count. Repeat the probe at the same points.
- Be careful with a patch. Gunning or patching a joint is a short-term measure. If the cause is still there, the seam returns.
- Replace the affected bricks if the lining must go on. Re-lay with the correct joint allowance. Do not wedge new bricks in tight.
In the next lining
- Joint strategy: agree the joint width, mortar, and expansion allowance with the brick supplier at the drawing stage, and review where the key bricks and the closure sit relative to the plug.
- Brick grade at the plug zone: a higher-grade MgO-C, or MgO-Al2O3-C or Al2O3-MgO-C, may be right for this zone. Pick it from the cut brick and the process data, not from habit.
- Brick quality: ask for edge density checks, dimension tolerance and a recycled-content statement.
- Preheat: use the supplier curve for the first heat-up, log it, and keep the log.
- Process: review blowing practice and ladle turnaround. A good lining still suffers in a bad cycle.
Brick grades for the purging plug wall: a comparison
Typical commercial descriptions. Actual TDS values differ by supplier.
| Category | MgO-C brick | MgO-Al2O3-C brick | Al2O3-MgO-C brick |
|---|---|---|---|
| Main raw materials | Fused or sintered magnesia, graphite | Magnesia, alumina or spinel, graphite | Alumina-rich aggregate, magnesia, graphite |
| Typical carbon | About 10 to 18% | About 8 to 14% | About 6 to 12% |
| Strengths | Slag resistance, good thermal shock behaviour | Better thermal shock behaviour in some recipes, forms spinel in service | Good thermal shock behaviour, suited where slag is less basic |
| Watch out for | Carbon loss at the slag line and open eye | Recipe-dependent expansion | Less slag resistance against strongly basic slag |
| Typical position | Slag line, high-wear walls | Walls and areas with thermal cycling | Lower wall, bottom areas |
| Question for the supplier | Edge density, fines control, antioxidant system | Spinel content, expansion curve | Alumina source, matrix, steel grade fit |
What to Ask for in a Ladle Brick TDS
| Property | Typical range for ladle MgO-C wall bricks | Why it matters for a vertical crack |
|---|---|---|
| MgO and impurities | MgO often 76 to 90%, depending on carbon level | Low SiO2 and CaO help hot strength and slag resistance |
| Fixed carbon | About 10 to 18% | Thermal shock resistance and slag non-wetting. Too little weakens both |
| Apparent porosity after coking | About 3 to 6% | Lower porosity limits steel and slag penetration into the edges |
| Bulk density | About 2.9 to 3.2 g/cm³ | Density at the edge is as important as the average |
| Cold crushing strength | About 35 to 50 MPa | Edge chipping resistance |
| Hot modulus of rupture | Depends on recipe. Ask for the test temperature and atmosphere | Resistance to cracking under thermal stress |
| Thermal expansion curve | Ask for the curve, not one number | Decides how much allowance the lining needs |
| Dimension tolerance | Agreed per drawing | Poor tolerance means uneven joints |
| Edge versus centre density | Agree a method and a limit with the supplier | Direct test for weak edges |
Do not stop at the one-line summary on a data sheet. Ask for the test method and, for density, where in the brick the sample was cut.
How YK Chanshine Supports a Vertical Crack Investigation
We make our own MgO-C, MgO-Al2O3-C and Al2O3-MgO-C ladle bricks, so we can look at a crack from both sides: the brick and the lining.
What we can do with your photos and records:
- Review your photos and probe numbers and tell you which of the three types we think it is, and what we would check next.
- Compare your current brick TDS with the cut brick results and the expansion allowance in your drawing.
- Supply a customized brick design for the plug zone: grade, shape, key bricks, tolerance and joint design.
- Run an edge-density check on a retained sample of our own bricks when the same lot is involved.
- Send free samples and a customized trial order for a zone trial on your ladle.
We cannot promise that a new brick grade will fix a seam caused by a tight ring or a cold start. What we can do is tell you early, from the evidence, which fix to try first.
Related reading on our site: our guide on slag line life with custom MgO-C bricks, the ladle casting vs. brick lining cost per tonne review, our magnesia carbon brick supplier page and our ladle refractories range.
Frequently Asked Questions (FAQ): Vertical Cracks in Ladle Refractories
Is a vertical crack in a ladle wall always a brick defect?
No. It can be a lining problem (joint, ring closure, expansion allowance), a process problem (blowing practice, cold starts, preheat), or a brick problem (edge density, grading, a flawed brick). Probing, reading the gap and cutting a residual brick tell you which.
How deep is too deep?
There is no single number. Compare the seam depth with the remaining thickness. A seam that reaches the permanent lining, or shows steel near the shell, is a stop. Below that, the trend matters more than one reading, so probe at the same points after each heat.
Can a ladle keep running with a vertical crack?
That is a decision for your plant safety rules and your refractory engineer. We can give a view on the cause. We cannot approve a ladle for service from photographs.
Why does the crack appear next to the purging plug and not elsewhere?
The plume turns into fast wall flow beside the plug. Gas also cools the hot face and heating returns when the gas stops. Both load the joints more than anywhere else in the lining.
Does too much recycled brick in an MgO-C brick cause cracks?
It can weaken the edges, which then erode faster. Some recycled content is normal. Ask for the range for your brick grade and the batch record, and check the cut face for dull or oxidized grains.
Is a higher thermal expansion always worse?
No. What matters is the expansion compared with the allowance in the lining. A lining with generous allowance can run a higher-expansion brick. A tight ring can fail with a low-expansion brick too.
Is filling the crack with mortar or patching mix a permanent fix?
Usually not. It slows the loss for a while. If the joint opened because of ring tightness, preheat or cold cycles, the seam comes back.
How does preheating affect vertical cracks?
Resin-bonded bricks release gas on the first heat-up, and the lining has to expand evenly. A fast or uneven first heat can open joints or crack bricks before the first steel. Follow the supplier curve and keep the log.
Would MgO-Al2O3-C or Al2O3-MgO-C bricks help at the purging plug?
Sometimes. They can handle thermal cycling better in some recipes. But if the cause is the joint or the process, a new grade will not fix it. Decide from the evidence.
How do I tell edge erosion from a thermal crack?
Edge erosion rounds the brick corners and turns the joint into a trench. A thermal crack is a sharp line, often across a single brick. A cut face shows the difference.
What should I send to the brick supplier?
Photos with the plug in frame, probe numbers at three heights, the heat count at first sign, brick grade and lot, preheat log, argon practice, ladle turnaround, and a residual brick if you can.
Send Us Your Photos, Wear Profiles & Operating Data
Send photos, steel-strip probe measurements, brick grade/lot, preheat logs, and purging gas flow practice. Our engineering desk replies with a root-cause diagnostic and an engineered lining optimization plan within 24 to 48 hours.