RAM Preventive & Predictive Maintenance 2 — Questions and Answers
Question 1: Which statistical distribution is most commonly used to model equipment wear-out failures when establishing time-based preventive maintenance intervals?
- Exponential distribution
- Weibull distribution (Correct answer)
- Normal distribution
- Poisson distribution
Correct answer: Weibull distribution
The Weibull distribution is preferred for wear-out failure modeling because its shape parameter (β) allows it to represent increasing, constant, or decreasing failure rates.
Question 2: A predictive maintenance program detects a bearing vibration signature showing sidebands around the fundamental frequency. This pattern most likely indicates:
- Mass imbalance in the rotating shaft
- Modulation caused by gear mesh or bearing defects (Correct answer)
- Looseness in the bearing housing
- Resonance at the natural frequency of the structure
Correct answer: Modulation caused by gear mesh or bearing defects
Sidebands around a fundamental frequency are characteristic of amplitude or frequency modulation, typically caused by gear mesh problems or bearing defect frequencies.
Question 3: What is the primary purpose of an oil analysis ferrography test in predictive maintenance?
- Measure lubricant viscosity at operating temperature
- Identify wear particle morphology and concentration to diagnose failure mode (Correct answer)
- Determine the remaining useful life of the oil additive package
- Detect water contamination in the lubricant
Correct answer: Identify wear particle morphology and concentration to diagnose failure mode
Ferrography separates and examines wear particles by size and shape, allowing analysts to identify the type of wear occurring (sliding, fatigue, cutting) and its severity.
Question 4: Under a condition-based maintenance (CBM) strategy, a maintenance action is triggered when:
- A fixed calendar interval elapses
- A predetermined number of operating hours is reached
- A monitored parameter crosses a defined alert or action threshold (Correct answer)
- Equipment fails to perform its required function
Correct answer: A monitored parameter crosses a defined alert or action threshold
CBM initiates maintenance based on the actual condition of equipment, measured by physical parameters like vibration, temperature, or wear debris, compared against set thresholds.
Question 5: When calculating the P-F interval in predictive maintenance, 'P' represents the point where:
- Planned maintenance is scheduled to occur
- A potential failure can first be detected (Correct answer)
- Performance degradation becomes economically significant
- A functional failure has just occurred
Correct answer: A potential failure can first be detected
In the P-F curve, P is the point at which a potential failure becomes detectable by inspection or monitoring, before it progresses to functional failure at F.
Question 6: Which maintenance concept recognizes that most equipment does NOT exhibit an increasing failure rate with age, and therefore time-based overhauls may not improve reliability?
- Reliability-Centered Maintenance (RCM) (Correct answer)
- Total Productive Maintenance (TPM)
- Corrective maintenance optimization
- Mean Time Between Maintenance (MTBM) scheduling
Correct answer: Reliability-Centered Maintenance (RCM)
RCM analysis, particularly from the Nowlan & Heap aircraft study, showed that only a minority of failure modes exhibit age-related wear-out, challenging the assumption that periodic overhauls always improve reliability.
Question 7: An infrared thermography survey of an electrical switchgear panel identifies a connection at 95°C while surrounding connections are at 35°C. According to NETA guidelines, this delta-T of 60°C indicates:
- Normal operating condition requiring no action
- A minor deficiency requiring monitoring at the next scheduled inspection
- A serious deficiency requiring repair as soon as possible (Correct answer)
- An imminent failure requiring immediate de-energization
Correct answer: A serious deficiency requiring repair as soon as possible
NETA MTS guidelines classify a temperature differential of 40°C or greater on electrical connections as a 'serious' condition requiring repair as soon as possible before the next scheduled outage.
RAM Preventive & Predictive Maintenance 2
Which statistical distribution is most commonly used to model equipment wear-out failures when establishing time-based preventive maintenance intervals?