Reliability & Equipment Costs

Keeping machines working at low cost. Learn time definitions (availability, utilisation, efficiency), MTBF and MTTR, overall equipment effectiveness (OEE), preventive vs predictive maintenance, component life, and owning and operating cost per tonne.

A truck that is broken down produces nothing but still costs money. Mines track every hour of every machine to find losses. Maintenance can be 30–50 % of operating cost, so reliability engineering has a direct effect on profit.

An analogy

Equipment time is like a pie: breakdowns, standby, delays and slow operation each take a slice — what's left is productive time.

Time model

Calendar time splits into scheduled/unscheduled maintenance (down), standby (available but not used), operating delays (shift change, refuelling, blasting) and productive time. Consistent definitions allow benchmarking (GMG time usage model).

Maintenance strategies

Reactive (run to failure), preventive (time/hours-based), condition-based and predictive (oil analysis, vibration, thermography, payload and engine data). Component change-outs (engines, wheel motors) are planned from life data.

Costs

Owning costs: depreciation, interest, insurance. Operating costs: fuel/energy, tyres, maintenance parts and labour, operators. Tyres alone can be 10–20 % of truck operating cost.

Reliability engineering

Weibull analysis of failures, reliability-centred maintenance (RCM), FMECA, and digital twins that predict remaining useful life. Replacement decisions use life-cycle cost analysis.

Formulas

• Availability: A = MTBF / (MTBF + MTTR)
• OEE: OEE = A × U × performance (rate/payload)
• Productive hours: h_prod = calendar h × A × U
• Cost per tonne: $/t = (owning + operating $/h) / (t/h)

Worked example: Availability

Given: MTBF 90 h, MTTR 6 h

Find: A.

• A = 90/96 = 93.75 %

Answer: ≈ 94 %

Worked example: Cost per tonne

Given: Truck owning + operating $400/h; Productivity 677 t/h per operating hour

Find: $/t.

• $/t = 400/677 = $0.59/t

Answer: ≈ $0.59 per tonne hauled

Common mistakes

• Wrong: Inconsistent time definitions. — Right: Use a standard time usage model.
• Wrong: Maximising availability at any cost. — Right: Balance maintenance cost against lost production value.

Applications

• Maintenance planning: Scheduled shutdowns and component change-outs.
• Benchmarking: Comparing fleets across sites.
• Replacement decisions: Life-cycle cost of rebuild vs replace.

Key takeaways

• A = MTBF/(MTBF + MTTR).
• OEE = A × U × P.
• $/t = hourly cost / productivity.
• Predictive maintenance pays off.

Going further

• Weibull analysis: Failure distributions and optimal replacement.
• RCM & FMECA: Structured maintenance strategy design.
• Prognostics: Remaining useful life from sensor data.