5 min read | Maintenance & Reliability
Most PM schedules were written by someone who left the company years ago. Nobody questions them. They just get executed, quarter after quarter, whether the equipment needs it or not.
That's the problem with purely time-based maintenance. And it's why more plants are testing condition-based maintenance as a smarter alternative to calendar-driven change-outs.
Fixed-interval preventive maintenance made sesnse when you had no other way to predict equipment condition. You guessed at intervals based on OEM recommendations, ran the schedule, and hoped you were catching failures before they happened. Sometimes you were. Often, you were pulling components that still had plenty of service life left.
Why Fixed-Interval PM Fails More Than You Think
Time-based PM assumes failure is time-dependent. For some components, that's accurate. A V-belt on a 24/7 conveyor drive running at 1,750 RPM under consistent tension will wear in a fairly predictable pattern. A scheduled change-out makes sense there.
But most rotating equipment doesn't fail on a schedule. It fails based on load variation, contamination, lubrication quality, and installation precision. None of those factors care what month it is.
Here's what that looks like in practice. You pull a Dodge pillow block bearing at 90 days because the schedule says to. The bearing looks fine. Normal grease color, no pitting on the race, no unusual cage wear. You just replaced a component with six more weeks of service life and introduced a contamination risk on reassembly.
Sound familiar?
Industry research from SMRP practitioners consistently shows that 30 to 40 percent of components replaced during scheduled PM still have significant remaining service life. On a plant running 50 PM tasks per quarter, that's a substantial chunk of budget and downtime producing no reliability improvement.
But here's the part nobody talks about. Every time you open a bearing housing, you're introducing the chance of contamination, incorrect re-greasing, or misalignment on reassembly. That's not a knock on your maintenance team. Handling a component you didn't need to handle is an exposure you didn't need to take. Some plants find their "preventive" program is generating failures, not preventing them.
What Condition-Based Maintenance Actually Does
Condition-based maintenance doesn't replace your PM schedule. It tells you which parts of it are actually needed.
Instead of servicing at a fixed interval, you service when the data tells you to. Vibration signature, temperature trend, acoustic emission, oil analysis. You're watching for early degradation signals and intervening before failure, on your timeline instead of the equipment's.
For rotating assets like bearings and motors, this works because most failure modes don't happen instantly. Bearing fatigue develops over weeks. Misalignment-induced wear builds gradually. The early signals, like a slight rise in vibration at bearing defect frequencies or a 5 to 8 degree increase in housing temperature, show up long before the asset is actually in danger.
That's enough lead time to plan a coordinated outage rather than react to one at 2 AM on a Tuesday.
The OPTIFY IIoT sensor line from Regal Rexnord attaches directly to bearing housings and motor frames and monitors vibration, temperature, and speed continuously. For assets where unplanned failure has real production consequences, removing the guesswork is worth the investment.
Which Assets Belong on Your Condition Monitoring List
Not every asset needs a sensor on it. The overhead has to make sense.
Prioritize condition-based monitoring for assets that are:
- Critical to production. If it fails, the line stops. No manual workaround available.
- Expensive to replace or repair. A Dodge shaft-mounted reducer on a heavy aggregate conveyor or a large-frame Baldor motor in a continuous-duty application both qualify.
- Difficult to access. If inspection requires a full lockout/tagout and 30 or more minutes of disassembly, continuous monitoring removes that exposure entirely.
- Running failure modes that develop gradually. Bearing fatigue, misalignment wear, imbalance. These are detectable weeks in advance. Sudden failures from foreign object damage aren't, and CBM doesn't help there.
Keep fixed-interval PM on low-criticality assets, inexpensive quick-swap components, and anything subject to sudden failure modes that sensors can't anticipate.
Making the Shift Without Rebuilding Your Whole Program
You don't have to convert overnight. A focused approach works better anyway.
Start by ranking your five highest-consequence PM tasks. What happens if those assets fail unplanned? For each one, ask whether condition data is feasible to collect. If yes, run monitoring alongside your existing schedule for 90 days. Let the data show you when the PM would actually be needed. Then adjust the interval, or drop the task entirely if the asset stays within spec.
That's it. No big program. No consulting engagement. Just data applied to the five assets where it matters most.
One thing worth addressing first: if you're seeing failures between PM intervals rather than at them, condition monitoring won't fix that. The problem is likely installation quality or load specification. Reviewing the root causes of early bearing failure before redesigning your program will save you from building a CBM approach around a problem that sensors can't solve.
Frequently Asked Questions
What is condition-based maintenance vs preventive maintenance?
Preventive maintenance services equipment at fixed time or usage intervals, regardless of actual condition. Condition-based maintenance uses real-time data like vibration levels, temperature, or oil analysis to service equipment only when indicators suggest degradation is underway. CBM reduces unnecessary interventions while improving the ability to catch failures before they cause unplanned downtime.
Does condition-based maintenance replace preventive maintenance?
No. Most plants use both. Fixed-interval PM still makes sense for consumables, lubrication schedules, and components where failure is genuinely time-dependent. CBM adds precision for rotating equipment where degradation develops gradually, like bearings, couplings, and motor drives.
How do I identify which assets are good candidates for condition monitoring?
Start with criticality. If the asset's failure stops production, takes more than four hours to remediate, or has caused unplanned downtime more than once in the past 24 months, it's worth evaluating for condition monitoring. High replacement cost and difficult physical access are strong secondary qualifiers.
What data matters most for bearing condition monitoring?
Vibration analysis is the most reliable early indicator. Specific frequency signatures at bearing defect frequencies (BPFO, BPFI, BSF) appear weeks before physical failure in most cases. Temperature trending is a secondary indicator, useful for confirming lubrication adequacy and detecting thermal runaway before it causes housing damage.
How does my MRO stocking strategy connect to my maintenance approach?
Fixed-interval PM requires stocking spares to support scheduled change-outs on a calendar. Condition-based maintenance shifts that to ordering replacement parts based on actual detected degradation, which typically means lower safety stock and better cash flow on spares. Your MRO stocking strategy should reflect whichever approach you're running across your critical assets.
Ready to explore condition monitoring for your most critical assets? Browse the OPTIFY IIoT sensor line at MRO-PT.com. Most orders ship same or next day.
Written by the MRO-PT Team. We've supplied Dodge bearings, Baldor motors, and power transmission components to manufacturers for over 25 years.