PM vs Run-to-Failure Comparator
Decide whether a PM program is worth running on an asset at all, or whether running it to failure costs less once the unplanned-downtime premium is priced in.
Resources
How this works
A PM program's annual cost is its visit cost times how often it runs, plus whatever failures still get through despite it. Running an asset to failure instead has no visit cost, only failure cost, but every one of those failures is unplanned, and an unplanned hour of downtime typically costs more than a planned PM hour, since there is no time to stage parts, labor, or a production workaround. This engine prices that premium explicitly rather than treating a failure hour and a PM hour as the same cost.
This is a different question from picking a PM interval. It asks whether to run a scheduled maintenance program on this asset at all. Once the answer is yes, Preventive Maintenance Interval Planner finds the right interval to run it at.
Key terms
- PM program: a scheduled maintenance visit at a fixed interval, priced at a fully burdened cost per visit.
- Run to failure: no scheduled maintenance, the asset is fixed or replaced only when it actually fails.
- Unplanned-downtime premium: how much more an hour of unplanned failure downtime costs than an hour of planned PM downtime, since there is no time to prepare for it.
- Residual failures with PM: failures that still happen occasionally even while a PM program is running, since PM reduces but rarely eliminates failure risk.
Assumptions
- Failure rate under each policy is a single point estimate, not a hazard-rate curve
- PM visit cost is constant regardless of interval length
- One asset, two named policies, compared at a time
Limitations
- Does not solve for the PM interval itself, that is Preventive Maintenance Interval Planner
- Does not model Weibull or age-based failure distributions
- Does not account for PM-induced failures (maintenance that itself causes downtime)
Sources
Standard reliability-centered-maintenance cost framing, consistent with NIST Handbook 135, the same capital and cost-screening source used elsewhere on this platform.
Worked example
A PM visit every 30 days at $800 fully burdened runs $9,733 a year. Without any PM, this asset is expected to fail 4 times a year, each costing 5 hours of downtime at $300/hour plus $200 in repair cost. Priced without an unplanned-downtime premium, that is $1,700 per failure, $6,800 a year, which makes running to failure look cheaper. But a failure is unplanned, and at a realistic 150% premium over planned PM downtime, each failure actually costs $3,950, $15,800 a year, well above the PM program's $9,733. Ignoring the premium would have wrongly favored skipping PM.
Common use cases
- Deciding whether a low-criticality asset needs a PM program at all
- Justifying an existing PM program's cost against a run-to-failure alternative
- Screening a new asset before setting up its first maintenance plan
- Feeding a positive PM verdict into Preventive Maintenance Interval Planner to find the right interval