SACA Predictive Maintenance and Condition Monitoring — Questions and Answers
Question 1: What is the key difference between Predictive Maintenance (PdM) and Preventive Maintenance (PM)?
- PdM is performed after a failure occurs; PM is performed on a fixed schedule
- PdM uses real-time condition data to service equipment only when degradation is detected; PM services equipment on a fixed time or cycle interval regardless of condition (Correct answer)
- PM uses sensor data to predict failures; PdM relies entirely on historical MTBF data
- PdM is less expensive to implement than PM because it requires no sensors
Correct answer: PdM uses real-time condition data to service equipment only when degradation is detected; PM services equipment on a fixed time or cycle interval regardless of condition
Predictive Maintenance monitors actual equipment condition (vibration, temperature, oil quality) and triggers maintenance only when indicators approach failure thresholds, avoiding unnecessary work. Preventive Maintenance follows a calendar or run-hour schedule regardless of actual equipment health, which can lead to over-maintenance.
Question 2: A maintenance technician uses a vibration analyzer and finds a dominant frequency peak at exactly 1× running speed. This signature most likely indicates:
- Bearing outer race defect
- Gear mesh frequency problem
- Mass imbalance in the rotating component (Correct answer)
- Looseness in the bearing housing
Correct answer: Mass imbalance in the rotating component
A dominant vibration peak at 1× running speed (1× RPM) is the classic signature of mass imbalance — the center of mass is offset from the center of rotation, creating a once-per-revolution centrifugal force. Bearing defects produce sub- or super-harmonic frequencies; gear mesh appears at (teeth × RPM) frequency.
Question 3: Infrared thermography is used in a PdM program primarily to detect:
- Shaft misalignment through vibration harmonics
- Abnormal heat patterns indicating electrical resistance problems, bearing failures, or refractory degradation (Correct answer)
- Lubricant viscosity changes through spectral oil analysis
- Ultrasonic emissions from compressed air leaks
Correct answer: Abnormal heat patterns indicating electrical resistance problems, bearing failures, or refractory degradation
Infrared thermography detects thermal anomalies non-intrusively. Hot spots on electrical panels indicate high-resistance connections; elevated bearing temperatures signal lubrication failure or wear; cold spots in refractory lining reveal thermal breaches. It is a key non-contact PdM tool.
Question 4: What does the P-F curve in predictive maintenance represent?
- The relationship between production output (P) and failure frequency (F) over time
- The interval between the point where a potential failure (P) can be detected and the point of functional failure (F) (Correct answer)
- A plot of preventive (P) vs. failure-based (F) maintenance costs over asset life
- The power factor (P) vs. frequency (F) curve of a motor under varying load
Correct answer: The interval between the point where a potential failure (P) can be detected and the point of functional failure (F)
The P-F curve shows that most failures don't happen instantaneously — a detectable degradation signal (P) appears well before actual functional failure (F). The P-F interval is the window available for PdM intervention. Monitoring technologies must detect the failure at the P point to allow planned maintenance before F.
Question 5: Oil analysis as a PdM technique is BEST suited for detecting which type of equipment problem?
- Electrical insulation breakdown in motor windings
- Structural resonance in machine frames
- Internal wear, contamination, and lubricant degradation in gearboxes and hydraulic systems (Correct answer)
- Pipe wall thickness reduction from external corrosion
Correct answer: Internal wear, contamination, and lubricant degradation in gearboxes and hydraulic systems
Oil analysis detects wear metals (iron, copper, chromium particles) that indicate internal component wear, identifies contaminants (water, dirt, coolant), and measures lubricant properties (viscosity, TAN/TBN) to assess whether the oil is still serviceable — ideal for gearboxes, hydraulic systems, and compressors.
Question 6: Which metric is used in reliability engineering to quantify the average time between failures for a repairable system?
- MTTR (Mean Time To Repair)
- OEE (Overall Equipment Effectiveness)
- MTBF (Mean Time Between Failures) (Correct answer)
- MTTF (Mean Time To Failure)
Correct answer: MTBF (Mean Time Between Failures)
MTBF (Mean Time Between Failures) is the average operating time between successive failures for a repairable system. It is a key reliability KPI used to set maintenance intervals and justify PdM investments. MTTF applies to non-repairable items; MTTR measures repair duration; OEE measures production efficiency.
SACA Predictive Maintenance and Condition Monitoring
What is the key difference between Predictive Maintenance (PdM) and Preventive Maintenance (PM)?