Why This Guide Matters (Even If You Think You Already Know)
Let’s be honest – most steel mills neglect slag pots until something cracks or a trunnion looks suspicious. Then it becomes an emergency: production stops, you scramble for a replacement, and safety managers lose sleep.
We’ve seen the same pattern at over 100 steel plants. The good news: most premature slag pot failures are preventable with simple, low-cost maintenance. This guide gives you practical steps – no fancy equipment, no expensive consultants.
*Based on real feedback from Womic Steel customers over 12 years, plus input from maintenance engineers who’ve kept slag pots running for 10,000+ cycles.*
Part 1: The Real Reasons Slag Pots Die (Not What Suppliers Tell You)
| Cause of Failure | % of Cases (Womic field data) | Typical Timeline |
| Thermal fatigue cracks (rim & sidewall) | 42% | 2–4 years |
| Trunnion root cracks | 28% | 3–5 years |
| Slag freeze on / mechanical damage | 18% | Any time |
| Wall thinning / erosion | 8% | 4–6 years |
| Original casting defect | 4% | <1 year |
Key insight: Thermal fatigue is #1. It happens because slag pots go from red-hot (1,600°C) to relatively cool (300–500°C) 10–20 times per day. Each cycle expands and contracts the metal. Over time, tiny cracks start at the rim and propagate downward.
What makes it worse:
● Uneven cooling (water splashed on one side)
● Long hold times with partial slag (creates hot spots)
● Poor trunnion design (sharp radius = stress concentration)
● The good news – with a few simple changes, you can add 1,000–2,000 cycles to every pot.
Part 2: Daily & Weekly Checks (Everyone Can Do)
You don’t need NDT certified technicians for these. Train your crane operators or shift supervisors. Takes 5 minutes per pot.
Every Shift – Visual Inspection
| What to Look For | What It Means | Action |
| New crack at rim, especially near trunnions | Early thermal fatigue | Mark with chalk, check weekly |
| Dent or deformation on bottom | Hard impact during dumping | Inspect for hidden cracks; adjust dumping procedure |
| Slag stuck on inner wall (>50mm thick) | Coating worn or wrong slope | Schedule cleaning; consider recoating |
| Trunnion surface wear >3mm depth | Crane hook mismatch or misalignment | Measure and report; may need trunnion buildup welding |
| Paint blistering or peeling | Overheating in that zone | Monitor temperature |
Every Week – Simple Tap Test
Use a 500g ball pein hammer. Tap the pot in 5 zones: rim (4 quadrants), sidewall, bottom, both trunnions.
Clear ringing sound → OK
Dull or hollow sound → Possible internal crack or lamination → Mark for UT inspection
This old-school method works surprisingly well. One customer found three pots with internal cracks before they became visible.
Every Week – Trunnion Rotation Check
If your crane hooks have rotation capability, slowly rotate the pot while suspended. Listen for grinding or uneven movement. If rotation is stiff, trunnion bores may be worn or distorted.
Part 3: Monthly & Quarterly Inspections (Simple Tools)
These require basic measuring tools – tape measure, caliper, straight edge.
Measure Rim Roundness
Place a straight edge across the rim diameter. Measure gap at 4 points.
Acceptable: Deviation ≤15mm from round.
If >15mm: The pot is warping. Rotate it to less-duty station or schedule repair.
Check Wall Thickness (No UT? Do This)
You can’t measure exact thickness without UT, but you can detect gross erosion or internal cracks by:
● Wet the pot surface with water – if a crack is through-wall, water will seep out slowly on the outside after the pot cools.
● Compare as-built weight – weigh a new pot of same design. If your used pot is >5% lighter, suspect wall thinning.
● Trunnion Bore Wear
Measure the diameter of trunnion bores with inside caliper.
Wear limit: 3mm increase from original.
Beyond that, bushing or buildup welding is needed.
Part 4: Annual Professional Inspection (Why You Shouldn't Skip It)
Once a year, bring in a qualified NDT technician. Minimum scope:
| Test | Location | Standard |
| Ultrasonic thickness mapping | 20 points per pot | ASME or ISO |
| Magnetic particle (MT) | Trunnion root radius, rim 100mm band | ASTM E709 |
| Dye penetrant (PT) | Any suspect area | ASTM E165 |
Cost: ~$300–500 per pot.
Payback: Detecting a crack early allows repair while the pot is still in service. Replacing a pot that fails catastrophically costs 10x more in downtime alone.
Real case: A Turkish mill skipped annual inspection for 3 years. In 2022, a trunnion failed during lifting – the 30-ton pot dropped 2 meters. No injuries, but production stopped for 18 hours. Plus the cost of replacing the pot and repairing the floor.
Part 5: Repair – What Can Be Fixed (and What Cannot)
Can Be Repaired (Cost-Effective)
| Defect | Repair Method | Success Rate |
| Shallow crack (<20mm deep) | Grind out, smooth radius | Very high |
| Worn trunnion surface | Build-up welding + machine | High (if done with qualified welder) |
| Dent or gouge | Grind smooth; no filler needed | High |
| Coating failure | Re-apply anti-stick coating | Very high |
| Wall thinning (<15% of original) | Accept as is; monitor | N/A |
Can Be Repaired with Caution
| Defect | Repair Method | Risk |
| Deep crack (>20mm but not through-wall) | Gouge out, weld, stress relieve | Medium (may re-crack) |
| Trunnion root crack | Full penetration weld repair, then UT examine | Medium – requires qualified welder and PWHT |
| Warped rim | Heat straightening (limited success) | High – may cause new stresses |
Cannot Be Repaired (Discard / Re-melt)
● Through-wall crack longer than 200mm
● Trunnion completely broken or missing
● Severe wall thinning (>25% original)
● Multiple cracks forming a network (alligator skin)
● Pot that has been welded more than 3 times
Rule of thumb: If you’re unsure, send photos to your slag pot supplier. Most reputable suppliers will give free assessment.
Part 6: Coating Maintenance – The Most Overlooked Factor
Slag sticking (freeze-on) is a major productivity killer. It adds cycle time, requires manual breaking, and damages the inner surface.
How to know your coating needs attention:
● Slag sticks more than 50mm thick after dumping
● You need to hammer the pot to release slag
● You see bare metal in the bowl after cleaning
Simple maintenance:
● Every 3 months, touch up with high-temperature anti-stick coating (available as aerosol or brush-on).
● Every 12 months, fully recoat the inner bowl (sandblast to Sa 2.5, apply 2 coats of ceramic-epoxy).
● Cost of recoating: ~$800–1,500 per pot.
● Return: Reduces freeze-on by 70%, cuts cleaning time, extends pot life.
Part 7: Storage & Handling Best Practices
Most mills store slag pots outdoors. That’s fine, but follow these rules:
| Do | Don’t |
| Store on wooden planks or concrete pads | Store directly on wet ground |
| Cover pots with tarps during rain/snow | Allow water to pool inside the bowl |
| Rotate pots in service (use oldest first) | Keep the same pot in service for months |
| Keep pots grouped by size/age | Mix badly worn pots with new ones |
| Mark each pot with ID, weight, and inspection date | Rely on memory |
Why rotation matters: If you always use the same 3 pots and leave 5 in storage, the 3 will wear out quickly while the 5 deteriorate from weather. Rotate weekly.
Part 8: Training Your Team – Simple Checklist Poster
We recommend printing this checklist and hanging it near the slag pot storage area.
Slag Pot Daily Check (5 minutes)
● Walk around pot – any new cracks?
● Tap rim with hammer – clear ring?
● Trunnions – any wear, dents, or cracks?
● Inner bowl – slag stuck more than 50mm?
● Paint – any blistering?
If YES to any → Tag pot, inform supervisor.
Weekly Checklist (30 minutes for all pots)
● Measure rim roundness (straight edge)
● Check trunnion bore wear (caliper)
● Weigh a sample pot (compare to new weight)
● Inspect coating condition
A well-trained team is your best defense against catastrophic failure.
Part 9: When to Call a Professional
You don’t need to be an expert, but you should know when to ask for help. Contact your slag pot supplier when:
● You find a crack longer than 100mm or deeper than 20mm
● Trunnion wear exceeds 5mm in diameter
● Pot weight has dropped by more than 8% from new
● You need repair welding (don’t let any welder do it – requires preheat and PWHT)
● You’re unsure about the inspection results
Womic Steel offers:
● On-site inspection training (1 day, at your plant)
● Remote video consultation
● Repair welding procedure specification (WPS)
● Replacement coating kits
Part 10: Summary – Your 12-Month Action Plan
| Month | Action |
| Month 1 | Train operators on daily checklist. Inspect all pots. Tag any suspect. |
| Month 2 | Schedule UT thickness mapping for oldest pots. |
| Month 3 | Recoat inner bowls of 3 worst pots. Test performance. |
| Month 6 | Measure trunnion wear, rim roundness. Rotate pot usage. |
| Month 9 | Repeat UT on pots that were borderline. |
| Month 12 | Full annual NDT. Plan replacements for next year. |
Final Word – The Most Cost-Effective Maintenance Is Prevention
Every time you avoid a slag pot replacement, you save tens of thousands of dollars. Every time you prevent a trunnion failure, you avoid a potential safety incident.
You don’t need expensive technology – you need discipline and a simple system. Use this guide, adapt it to your plant, and watch your pot life increase by 20–40%.
Need help setting up your slag pot inspection program?
Womic Steel offers a free 1-hour remote consultation. We’ll review your current pots, failure history, and operating conditions – then give you specific recommendations.
Victor: +86 15575100681 (WhatsApp/WeChat)
Jack: +86 18390957568 (WhatsApp/WeChat)
Email: sales@womicsteel.com
Website: www.womicsteel.com
Womic Steel – We don’t just manufacture slag pots; we help you get the most out of them.
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