How to Inspect and Repair Wear Liners in Cyclones and Ducts

In graphite grinding plants, cyclones and dust ducts suffer severe abrasive wear from high-speed graphite dust and particle flow. Wear liners (rubber, polyurethane, ceramic, cast basalt, or wear-resistant steel) protect the base metal from erosion, prevent dust leakage, and avoid system blockages. Below is a step-by-step inspection and repair procedure tailored to abrasive dust service, with safety and graphite-process specific requirements.

1. Pre-Work Safety & Preparation

1.1 Safety Lockout (LOTO)

• Shut down the cyclone, duct fan, dust collector, and upstream grinding equipment; lock and tag all power and air sources.
• Ventilate the workshop for 15–20 minutes to reduce residual graphite dust concentration.
• Wear full PPE: anti-static overalls, dust respirator, safety helmet, cut-resistant gloves, and steel-toe boots.
• Prohibit dry sweeping or compressed air blowing during inspection (avoids dust cloud explosion risk).

1.2 Tools Required

• Ultrasonic thickness gauge, tapping hammer, flashlight/explosion-proof lamp
• Wear repair materials: ceramic patches, polyurethane repair compound, rubber lining adhesive, wear-resistant putty
• Measuring tape, marker, grinding tool, sealing compound, torque wrench
• Digital camera for recording wear locations

2. Inspection of Wear Liners

2.1 Key Wear Zones (High-Failure Areas)

These areas suffer the strongest particle impact and scouring—focus inspection here first:

2.2 Inspection Methods & Acceptance Standards

1) Visual Inspection

• Check for cracks, peeling, blistering, holes, or exposure of base metal (immediate repair required if found).
• Look for graphite dust buildup behind liners (indicates liner detachment or gaps).
• Check for dust leakage at flanges and liner joints (sign of severe wear or poor sealing).

2) Tap Test (Quick Detachment Check)

• Tap the liner surface with a rubber hammer:
  • Clear, crisp sound: liner is well-bonded
  • Hollow/muffled sound: liner is detached, bulged, or hollowed (must repair/replace)

3) Thickness Measurement (Quantitative Inspection)

• Use an ultrasonic thickness gauge to measure liner thickness at 10–15 points per component.
• Scrap/Repair Threshold:
  • Rubber/PU liners: wear loss ≥ 50% of original thickness
  • Ceramic/cast basalt liners: thickness loss ≥ 30% or chipping > 10 mm
  • Wear-resistant steel liners: thickness loss ≥ 40%

4) Inspection Frequency

• Daily: Visual check for dust leakage and obvious damage
• Weekly: Tap test for liner detachment
• Monthly: Full thickness measurement and detailed inspection
• Quarterly: Comprehensive disassembly inspection for cyclone apex and duct elbows

3. Repair of Wear Liners

Choose repair methods based on wear severity and liner material (common in graphite plants: rubber, PU, ceramic, wear steel).

3.1 Minor Wear Repair (Small Cracks, Thin Spots, Small Chipping)

Suitable for damage area < 10% of total liner surface

1. Clean the worn area with a wet cloth to remove graphite dust and grease (no dry grinding).
2. Roughen the surface slightly to improve adhesion.
3. Apply wear-resistant repair compound / polyurethane patch to fill gaps or cover thin areas.
4. Smooth the surface and cure for 4–12 hours (per product instructions) before restarting.

3.2 Moderate Wear Repair (Partial Peeling, Medium-Sized Holes)

1. Cut and remove the damaged liner section completely.
2. Clean the base metal surface and apply primer adhesive.
3. Install a pre-cut replacement liner patch (matching original material and thickness).
4. Seal edges with high-temperature sealant to prevent dust penetration.
5. Clamp or bolt the patch firmly and cure fully.

3.3 Severe Wear Repair (Full Peeling, Large Holes, Base Metal Exposure)

1. Remove all worn/damaged liners and clean rust/oxide from the base metal.
2. Install full new liner sheets (ceramic tiles recommended for high-wear zones like cyclone inlets).
3. For cyclones: ensure the cone liner has no steps or gaps (avoids material buildup and blockages).
4. For ducts: maintain smooth inner walls to keep air velocity ≥ 12–16 m/s (prevents graphite dust deposition).
5. Torque all bolts evenly and seal all joints to eliminate dust leakage.

3.4 Replacement of High-Wear Components

• Cyclone apex/underflow spout: replace every 6–12 months (most worn part)
• Duct elbows: replace liners every 8–12 months
• Use ceramic-lined composite bends for long service life in graphite dust service

4. Post-Repair Inspection & Commissioning

1. Check liner smoothness, adhesion, and sealing (no gaps or protrusions).
2. Test run the dust collection system for 10–15 minutes to check for:
   • Dust leakage at flanges/liner joints
   • Abnormal airflow or pressure drop
   • Unusual vibration from uneven liners
3. Verify duct air velocity and cyclone pressure drop return to normal levels.
4. Record repair location, material used, thickness, and date for traceability.

5. Prolong Liner Service Life (Graphite Plant Special Tips)

1. Maintain duct air velocity ≥ 12 m/s to reduce particle impact wear.
2. Avoid sudden airflow changes that increase erosion.
3. Use anti-static liners to prevent graphite dust adhesion and static buildup.
4. Regularly clean graphite dust deposits on liner surfaces (wet cleaning only).
5. Align cyclone inlets and ducts to reduce turbulent scouring.