Condition-Based vs Time-Based Maintenance - A Cost Comparison

The argument for condition-based maintenance over time-based schedules is made in general terms constantly. "You replace components before their time" and "you can catch failures earlier" are true statements, but they don't tell a plant manager what the actual cost difference is over a realistic operating period. This is our attempt to put real numbers to that comparison for a typical heavy manufacturing scenario.

The Baseline Scenario

We modeled a mid-scale conveyor and materials handling system at a steel processing facility: 28 conveyor drives covering raw material handling, product transfer, and finished goods discharge. Total installed motor power: approximately 1,800 kW across the 28 units. Mix of Dodge Tigear and Falk Quadrive gear reducers with SEW-Eurodrive and Baldor motors in the 30–90 kW range.

The maintenance team had been running a time-based schedule: bearing replacement at 12,000 operating hours on all conveyor head pulleys, oil changes at 6,000 hours on gearboxes, full motor inspection and regreasing at 4,000 hours. This is a reasonably standard schedule for this type of equipment — not neglectful, but also not condition-informed.

Time-Based Maintenance: Year One Through Five

On the 28-drive system, the 12,000-hour bearing schedule triggers approximately 14 bearing replacements per year across the fleet, assuming average utilization of 6,000 operating hours per year per drive. At a typical installed replacement cost of $480 per bearing position (parts plus labor), that's $6,720 annually in scheduled bearing work.

Gearbox oil changes at 6,000 hours: 28 changes per year across the fleet. At $180 per change including oil and disposal: $5,040 per year. Motor inspections at 4,000 hours: 42 per year. At $120 per inspection: $5,040 per year. Total scheduled maintenance cost: approximately $16,800 per year.

The problem isn't the scheduled cost — it's the failures that happen between schedules. Based on the facility's historical data over the three years prior to our deployment, they averaged 4.2 unplanned drive failures per year. Average cost per failure (parts, emergency labor, production loss, and recovery): $34,600. Annual unplanned failure cost: $145,320.

Total annual maintenance cost under time-based schedule: $162,120. Over five years: $810,600.

Condition-Based Maintenance: The Same System

Deploying continuous vibration monitoring on the 28 drives required 56 accelerometers (two positions per drive — motor-side and load-side bearing), gearbox temperature sensors, and two edge gateways. Hardware and installation: $52,400. Annual licensing: $14,400. Five-year total system cost: $124,400.

With condition-based maintenance, bearing replacements are driven by actual bearing condition rather than a fixed schedule. Based on our 847-asset dataset, condition-monitoring typically reduces scheduled bearing replacements by 40–55% because a significant share of bearings that would have been replaced on schedule are still in good condition. Applying a 45% reduction: from 14 scheduled replacements per year to 7.7. Annual scheduled bearing cost drops from $6,720 to $3,696.

The bigger impact is on unplanned failures. In the 18 months post-deployment at this facility, unplanned drive failures dropped from 4.2 per year to 0.4 per year. That's 3.8 fewer unplanned failures annually. At $34,600 per failure, that's $131,480 per year in avoided costs. Over five years: $657,400 in avoided unplanned failure costs.

Five-year cost under condition-based maintenance: system cost ($124,400) plus reduced scheduled maintenance ($85,440 for 5 years) plus residual unplanned failures ($69,200 for 5 years at 0.4/year) = $279,040.

The Five-Year Comparison

Time-based schedule, five years: $810,600. Condition-based, five years: $279,040. Net savings: $531,560. That's a 2.3x return on the monitoring system investment over five years, just on this 28-drive system.

These numbers are specific to this facility's failure history and production profile. A plant with fewer unplanned failures on the time-based schedule will see a smaller absolute savings. A plant running more costly equipment — large rotating machinery in steel or cement applications — will see larger per-failure costs and correspondingly larger savings.

Where the Comparison Gets More Complicated

The numbers above don't capture second-order effects, some of which favor condition-based and some of which complicate it.

In favor: planned maintenance windows are schedulable. When you get a 72-hour warning on a bearing, you can time the repair for a planned production gap, a weekend, or a low-demand shift. Unplanned failures don't give you that choice. The ability to schedule interventions reduces overtime costs, parts expediting costs, and cascading production impacts significantly beyond what the per-failure cost model captures.

Complicating: condition monitoring generates more data and more alerts, which require trained personnel to interpret and act on. Plants that install monitoring without investing in training tend to either ignore alerts (defeating the purpose) or over-respond to every vibration trend (generating unnecessary maintenance work). The labor cost of alert management is real and needs to be factored in.

Also: transition from time-based to condition-based maintenance requires updating the CMMS trigger logic, retraining technicians, and changing the culture around "if it ain't broke" — which is harder than it sounds at facilities that have run on the same schedule for 15 years.

What the Numbers Actually Tell You

The economics favor condition-based maintenance clearly, but the economics are not the hardest part. The hardest part is that time-based schedules are easy to plan, easy to budget, and easy to defend. Condition-based maintenance requires judgment, responsiveness, and organizational change. The ROI is there. Getting from here to there takes deliberate effort on the process side, not just the technology side.