Free Engineering Tool #034
Remaining Life from Vibration Trend
Estimate remaining useful life (RUL) based on vibration trending data. Project time to alarm and danger levels using linear, exponential, or power law growth models.
Results
Projected Vibration Levels
⚠️ Confidence Note: This estimate assumes the current growth pattern continues unchanged. Actual remaining life depends on fault mechanism, operating conditions, load changes, and maintenance actions. Use as guidance for planning — not as a guarantee. More data points and consistent measurement conditions improve accuracy.
Linear Growth Model
Assumes vibration increases at a constant rate:
Linear model is appropriate for gradual wear processes like unbalance growth from erosion or buildup.
Exponential Growth Model
Assumes vibration growth rate is proportional to current level (damage accelerates):
Exponential model best represents bearing degradation and fatigue crack propagation where damage creates more damage.
Power Law Model
Generalized model that can represent both sub-linear and super-linear growth:
Power law is useful for mixed degradation modes. The exponent p determines growth behavior: p<1 is decelerating, p=1 is linear, p>1 is accelerating.
Which Model to Choose?
| Model | Best For | Behavior |
|---|---|---|
| Linear | Gradual wear, erosion, buildup | Constant rate of change |
| Exponential | Bearing damage, crack growth | Accelerating — most conservative |
| Power Law | Mixed/unknown mechanisms | Flexible — adapts to data shape |
Practical Example
Given: V_baseline = 2.5 mm/s, V_current = 4.2 mm/s, elapsed = 90 days, alarm = 7.1 mm/s
Exponential model:
k = ln(4.2 / 2.5) / 90 = ln(1.68) / 90 = 0.5188 / 90 = 0.00577 /day
Time to alarm: t_alarm = ln(7.1 / 2.5) / 0.00577 = 1.0438 / 0.00577 = 181 days from baseline
Remaining = 181 – 90 = 91 days from now to alarm level
P-F Interval: The time between detectable fault initiation (P) and functional failure (F) determines how much warning you get. For rolling element bearings, the P-F interval is typically 1–9 months depending on speed, load, and lubrication conditions.
Vibration trending provides a reasonable estimate when the fault mechanism produces a consistent growth pattern. Key factors for reliability:
- More data points over a longer period improve accuracy
- Consistent measurement conditions (same point, direction, load, speed)
- Understanding the failure mode helps select the right growth model
- Bearing degradation typically follows exponential growth
- Gradual wear (erosion, buildup) tends to follow linear growth
Treat estimates as planning guidance, not precise predictions. Always err on the side of caution.
Linear growth: Vibration increases at a constant rate (e.g., +0.5 mm/s per month). The time to reach any level is easy to predict. Common for gradual wear processes.
Exponential growth: The rate of increase accelerates over time. Early stages show slow change; later stages show rapid deterioration. Common for bearing damage and fatigue crack propagation.
Why it matters: Exponential growth is more dangerous because it can appear stable for a long time, then deteriorate rapidly. The "hockey stick" curve means the window between detectable change and failure can be short.
General guidelines based on ISO 20816 / ISO 10816 philosophy:
- Plan action when vibration reaches Zone B/C boundary (alarm level) or has increased 50% above baseline
- Schedule maintenance when trend projection shows alarm will be reached within the next planned shutdown window
- Urgent action when vibration reaches Zone C/D boundary (danger level) or has doubled from baseline
- Immediate shutdown when danger level is exceeded or sudden step change occurs
The key principle: schedule corrective action while you still have time to plan, source parts, and execute safely.
Factors that reduce prediction accuracy:
- Inconsistent measurement: Different probe positions, mounting methods, or sensor types
- Variable operating conditions: Load, speed, or temperature changes between measurements
- Step changes: Sudden events (impacts, process upsets) that shift the baseline
- Wrong growth model: Using linear when actual growth is exponential, or vice versa
- Insufficient data: Fewer than 3–4 data points makes trend fitting unreliable
- Multiple fault mechanisms: If more than one fault is developing, the combined trend may not follow a simple model
Recommended measurement intervals based on machine criticality:
- Critical machines: Continuous online monitoring (24/7)
- Important machines: Weekly to monthly route-based measurements
- General machines: Monthly to quarterly
When a trend is rising:
- Zone A→B transition: Increase to weekly
- Approaching alarm: Increase to daily or install temporary online monitoring
- Above alarm: Continuous monitoring until maintenance
The measurement interval must be shorter than the P-F interval (time from detectable fault to functional failure) divided by at least 3, to ensure you capture the trend and have time to act.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional vibration monitoring with trending and alarm management. Predict failures before they happen. Used in 50+ countries.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
