Background
A cement plant in Shandong Province, China had a policy of replacing all conveyor belts on a fixed time-based schedule β every 3 years regardless of condition. An incoming maintenance manager reviewed the policy and questioned whether it was optimal.
The plant had 24 conveyors ranging from limestone quarry overland conveyors to clinker and packing lines. Under the 3-year cycle, 7β8 belts were replaced each year at significant cost. Some belts looked nearly new at replacement; others had clearly been close to end of life.
Assessment Process
The maintenance manager commissioned a condition assessment of all 24 belts rather than proceeding with the next scheduled round of replacements. The assessment method:
Visual inspection (all belts): - Cover surface condition: cracking, blistering, abrasion depth - Edge condition: fraying, damage - Splice condition: cover delamination, step separation - Belt tracking evidence: uneven edge wear indicating chronic mistracking
Cover thickness measurement (belts with visible wear): Using a calibrated ultrasonic thickness gauge, top cover thickness was measured at 5 positions across the belt width and at 10-meter intervals along the belt length. Original cover thickness was known from installation records.
Classification: Each belt was classified into one of four categories: - A β Replace now: Cover wear approaching carcass (<2mm remaining) or structural damage - B β Replace within 12 months: Significant wear but adequate life remaining for one more year - C β Replace at next scheduled cycle: Moderate wear, life consistent with schedule - D β Extended service: Minimal wear, condition justifies extending beyond schedule
Results
| Category | Number of Belts | Action |
|---|---|---|
| A β Replace now | 3 | Immediate replacement |
| B β Replace within 12 months | 5 | Plan for year 1 budget |
| C β Replace at schedule | 9 | Maintain current schedule |
| D β Extended service | 7 | Extend to 4β5 year cycle |
Key findings: - The 3 Category A belts needed urgent replacement β they would not have lasted to the next scheduled cycle and were at risk of in-service failure - 7 Category D belts (29% of the fleet) were in excellent condition and had been wastefully replaced on the fixed 3-year cycle for years - The quarry overland conveyor (EP500, heavy abrasion service) genuinely needed 3-year replacement; the packing line belts (EP150, light duty) had negligible wear at 3 years
Economic Impact
Previous approach (all belts on 3-year cycle): - Average 8 replacements per year - 7 of these were at schedule; 1 was emergency (the Category A belts caught early would have been emergencies under the old system)
Condition-based approach: - Year 1: 3 urgent + 5 planned = 8 replacements (similar, but better-timed) - Year 2: 4 planned (no urgent) - Year 3: 6 planned - Average: 6 replacements per year β 25% reduction
The 7 Category D belts extended to 5-year cycles instead of 3-year cycles saved approximately 2.3 belt replacements per year at the marginal cost of periodic thickness measurement checks.
Ongoing System
Following the initial assessment, the plant implemented condition-based belt maintenance: - Annual thickness measurement on all belts - Category review and replacement planning based on actual condition - Emergency replacement budget retained for unexpected failures
The maintenance manager noted that the annual measurement exercise also improved the team's understanding of which conveyors were the highest-wear (and therefore needed attention to abrasion cause, not just replacement frequency).
Key Points
Fixed time-based belt replacement wastes money on low-wear belts and misses early failures on high-wear ones. Condition-based assessment is more accurate in both directions.
Cover thickness measurement is the key metric. Visual inspection alone misses subsurface wear. Ultrasonic thickness gauges are inexpensive and give reliable remaining-life data.
Different conveyors have very different wear rates. A quarry overland conveyor and a packing plant belt in the same cement plant may have 5β10Γ different wear rates. Applying the same replacement interval to both wastes money on the light-duty belt and risks failure on the heavy-duty one.
Elephant Rubber provided technical consultation on belt condition assessment methodology for this project and supplied the replacement belts.