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newSchoolWorks.com › VoTechWorks › Building & Construction › Nuclear Power Plant Technician / Operator Prep › Nuclear Plant Maintenance: Procedures, Equipment, and Reliability › Lesson 8
BLD-NUCL84-08 · Lesson 8 · 20.5 clock hours · demo

Predictive Maintenance: Vibration Analysis, Thermography, and Oil Sampling

Objective. Students will collect vibration data on a rotating equipment training stand, perform a thermal scan on a training electrical panel, and take an oil sample from a training gear box, then interpret each data set using provided acceptance criteria.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed professional engineer or master tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

What Is Predictive Maintenance?

Predictive maintenance (PdM) uses condition-monitoring data collected while equipment is running to forecast when a failure is likely to occur. Instead of replacing parts on a fixed schedule or waiting for a breakdown, technicians track trends over time and act only when the data shows a problem developing. In a nuclear plant, where reliability directly supports safety and continuous power generation, PdM is a cornerstone of the plant maintenance strategy.

The three techniques you will practice today—vibration analysis, infrared thermography, and oil sampling—are the most widely used PdM methods for rotating equipment and electrical systems.

Vibration Analysis

Rotating equipment such as pumps, motors, fans, and compressors produces vibration. A small amount of vibration is normal; an increase in amplitude or a change in frequency pattern signals a developing fault such as imbalance, misalignment, bearing wear, or looseness.

A portable vibration data collector with an accelerometer is held against, or magnetically attached to, a bearing housing. The instrument measures overall vibration velocity, typically in inches per second (in/s) peak or RMS. You compare your reading to the ISO vibration severity zones:

The exact boundary values depend on the machine class (size and mounting). Always use the correct machine class from the reference standard.

Safety: Wear appropriate PPE—safety glasses and hearing protection in equipment areas. Never reach across rotating shafts or couplings to place a probe. Apply lockout/tagout (LOTO) before any repair is attempted; PdM data is collected on running equipment only, and no maintenance action is taken without a work order and LOTO.

Recording data: Enter each reading in the predictive maintenance data log with the date, equipment tag number, measurement point location, and zone classification. Trend data over multiple readings; a single reading is less informative than a rising trend.

Infrared Thermography

All objects emit infrared radiation proportional to their temperature. A thermal imaging camera converts that radiation into a visible color-mapped image. In electrical systems, a poor connection or an overloaded component has elevated resistance, which generates excess heat that appears as a hot spot in the image.

During a thermographic inspection of an electrical panel:

1. The panel door is opened carefully (energized electrical work requires arc flash PPE per NFPA 70E—always verify the required PPE category for the voltage level before opening any enclosure).

2. Scan all connection points, breakers, and bus bars.

3. Identify any hot spot and record the temperature of the anomaly and the temperature of a similar component at ambient (background) conditions.

4. Calculate the temperature differential (ΔT): subtract ambient temperature from the anomaly temperature.

5. Classify severity using the thermographic inspection guideline's ΔT bands. A larger differential generally indicates a more urgent repair need.

Safety: Treat every electrical panel as energized until confirmed otherwise. Wear the PPE specified by your facility's arc flash hazard analysis. Never touch internal components while the panel is energized. Follow your site's energized electrical work permit procedure.

Oil Sampling

Lubricating oil degrades over time and carries debris from wear. A laboratory analysis of an oil sample reveals viscosity (whether the oil still lubricates properly), particle count and metal type (which parts are wearing), and water content (contamination). Trends in these values give early warning of bearing or gear deterioration long before audible noise or vibration changes appear.

Proper sampling technique is critical—a contaminated sample produces false results and may lead to unnecessary maintenance or, worse, a missed fault.

Procedure:

1. Verify the gear box is at normal operating temperature (warm oil carries particles in suspension; cool oil allows them to settle).

2. Use a clean vacuum sampling pump and fresh, clean tubing. Do not reuse tubing.

3. Insert the tubing to the mid-depth of the sump through the oil fill port or a dedicated sampling port.

4. Draw a sample directly into a clean, sealed sample bottle—do not pour from a drain plug catch.

5. Cap the bottle immediately.

6. Complete the sample submittal form: equipment ID, date, operating hours since last oil change, and any known abnormalities.

7. Ship to the laboratory in the provided mailer promptly.

When laboratory results return, compare viscosity to the oil specification, review the particle count and metal analysis for trending wear metals, and check water content against the acceptable limit. Any reading outside acceptance criteria triggers a maintenance work order.

Safety: Gear box oil may be hot; use heat-resistant gloves. Dispose of used tubing and spilled oil per your plant's waste-handling procedure.

Entering Data and Closing the Loop

PdM has no value unless data reaches the people who act on it. Every reading—vibration, thermal image, or oil sample result—must be entered into the predictive maintenance data log or the plant's computerized maintenance management system (CMMS) with complete identification. The maintenance supervisor reviews trends and decides whether to generate a work order. You complete the loop by accurate, timely documentation.

Key terms9

Overall vibration velocityA single number summarizing the amplitude of vibration at a measurement point, typically expressed in inches per second (in/s); used to compare against ISO severity zone boundaries.
ISO vibration severity zones (A/B/C/D)A classification system from ISO standards that assigns vibration levels to four zones—good, satisfactory, unsatisfactory, and unacceptable—based on machine class and measured velocity.
Temperature differential (ΔT)The difference in temperature between an identified hot spot and a reference component operating under similar conditions; used to classify the severity of an electrical anomaly found by thermography.
Infrared thermographyA non-contact inspection technique that uses a thermal imaging camera to detect surface temperature variations, revealing heat-generating faults such as loose or corroded electrical connections.
Vacuum sampling pumpA hand-operated or motorized device that creates suction to draw a representative oil sample from mid-sump depth through clean tubing into a sealed sample bottle, minimizing contamination.
Particle countA laboratory measurement of the number and size of solid particles per unit volume of oil; elevated counts or wear-metal identification indicate internal component degradation.
Predictive maintenance data logA written or electronic record that documents condition-monitoring measurements over time, enabling trend analysis and providing the basis for generating maintenance work orders.
Lockout/tagout (LOTO)An OSHA-required energy-control procedure that de-energizes and physically secures equipment before repair or maintenance, preventing unexpected startup; PdM data collection is performed on running equipment and never substitutes for LOTO before work.
ViscosityA measure of an oil's resistance to flow; laboratory analysis compares the measured viscosity against the equipment manufacturer's acceptable range to determine whether the oil still provides adequate lubrication.

Worked examples4

1. A bearing on Pump P-101 reads 0.18 in/s RMS overall velocity. The applicable ISO machine class boundary values are: Zone A/B boundary = 0.10 in/s, Zone B/C boundary = 0.25 in/s, Zone C/D boundary = 0.40 in/s. What zone does this reading fall in, and what action is indicated?
  1. Step 1 – Locate the reading on the zone scale. The reading is 0.18 in/s.
  2. Step 2 – Compare to boundaries: 0.10 < 0.18 < 0.25. The reading is above the A/B boundary (0.10) but below the B/C boundary (0.25).
  3. Step 3 – Assign zone: the reading falls in Zone B (Satisfactory).
  4. Step 4 – Determine action: Zone B is acceptable for continuous operation. Record the value in the data log and continue trending.
Answer: Zone B (Satisfactory); no immediate repair required—document and continue trend monitoring.
2. During a thermographic scan of a motor control center, a terminal lug reads 67 °F above the ambient temperature of an identical lug on the same bus. The thermographic inspection guideline classifies ΔT 1–10 °F as low, 11–30 °F as moderate, 31–60 °F as serious, and above 60 °F as critical. What is the severity classification?
  1. Step 1 – Identify the ΔT: hot spot temperature minus ambient reference = 67 °F.
  2. Step 2 – Compare 67 °F to the guideline bands: the 'critical' band begins above 60 °F.
  3. Step 3 – Since 67 °F exceeds 60 °F, classify as Critical.
  4. Step 4 – Record the anomaly location, the hot spot temperature reading, the ambient reference temperature, and the ΔT on the thermographic inspection form and generate a priority maintenance work order.
Answer: Critical (ΔT = 67 °F, exceeding the >60 °F critical threshold); immediate maintenance work order required.
3. A vibration data collector is used to measure the same bearing three times in sequence. The readings are 0.22 in/s, 0.21 in/s, and 0.23 in/s. The instructor's baseline for that point is 0.20 in/s. The pass/fail check requires student readings to be within 10% of the baseline. Do all three readings pass?
  1. Step 1 – Calculate the 10% tolerance band: 10% of 0.20 = 0.020 in/s.
  2. Step 2 – Acceptable range: 0.20 − 0.020 = 0.180 in/s (lower limit); 0.20 + 0.020 = 0.220 in/s (upper limit).
  3. Step 3 – Check each reading: 0.22 in/s ≤ 0.220 → pass; 0.21 in/s ≤ 0.220 → pass; 0.23 in/s > 0.220 → fail.
  4. Step 4 – Two of three readings pass; the third reading (0.23 in/s) is outside the ±10% band and does not pass. Re-measure at that bearing location.
Answer: Readings of 0.22 in/s and 0.21 in/s pass; 0.23 in/s fails (exceeds upper limit of 0.220 in/s by 0.01 in/s).
4. An oil sample from Gear Box GB-204 shows a water content of 0.12% by volume. The equipment manufacturer's acceptable limit is 0.05% water by volume. By how much does the result exceed the limit, expressed as a percentage above the limit, and what is the required next step?
  1. Step 1 – Identify the measured value: 0.12% water.
  2. Step 2 – Identify the limit: 0.05% water.
  3. Step 3 – Calculate the exceedance: 0.12 − 0.05 = 0.07% above the limit.
  4. Step 4 – Calculate percentage above limit: (0.07 ÷ 0.05) × 100 = 140% above the acceptance limit.
  5. Step 5 – Because the result exceeds the acceptance criterion, document in the data log and generate a maintenance work order to investigate the source of water ingress and schedule an oil change.
Answer: Water content exceeds the limit by 0.07 percentage points (140% above the limit); a maintenance work order must be generated.

The math in this lesson1

Learners place vibration readings in in/s on a zone scale to assign condition zones.
N-Q.1
Brush up in the math halls at newSchoolWorks.com:
In class: Using a portable vibration data collector, students measure overall vibration velocity at three bearing locations on a training motor-pump set, compare readings to the applicable ISO vibration severity zone boundaries, and determine whether the reading falls in the 'good,' 'satisfactory,' 'unsatisfactory,' or 'unacceptable' zone; findings are entered into the predictive maintenance data log. · Instructor demonstrates use of a thermal imaging camera on a training electrical panel with one intentionally warm connection; students scan the same panel, identify the thermal anomaly, record the temperature differential, and classify severity using the provided thermographic inspection guideline (temperature rise above ambient bands). · Students draw an oil sample from a training gear box using a vacuum sampling pump and clean tubing, fill the sample bottle correctly, complete the sample submittal form with equipment identification and operating hours, and explain orally how the laboratory results (viscosity, particle count, water content) would trigger a maintenance work order.
Materials: Portable vibration data collector with accelerometer, training motor-pump stand, thermal imaging camera, training electrical panel with warm connection fault, vacuum oil sampling pump, clean sampling tubing, sample bottles, sample submittal forms, ISO vibration severity standard reference (general), thermographic inspection guideline, predictive maintenance data log forms
Check: Vibration readings within 10% of instructor-measured baseline values and correctly zoned; thermal anomaly correctly identified and temperature differential recorded; oil sample bottle filled and labeled without contamination as confirmed by instructor observation; all three tasks must be satisfactory to pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

OSHA 10 – Hazardous Energy Control
1. When using a portable vibration data collector on a running motor-pump set, which safety requirement must be met BEFORE any corrective repair work begins on that equipment?
NUCP Uniform Curriculum – Predictive Maintenance
2. A pump bearing reads 0.31 in/s RMS. The ISO machine class boundaries are: A/B = 0.10, B/C = 0.25, C/D = 0.40 in/s. What is the correct zone classification?
NUCP Uniform Curriculum – Predictive Maintenance
3. Why must an oil sample for laboratory analysis be drawn from mid-sump depth rather than from the drain plug?
NUCP Uniform Curriculum – Predictive Maintenance
4. A thermal image shows a circuit breaker at 95 °F and identical breakers nearby at 71 °F. What is the temperature differential (ΔT)?
NUCP Uniform Curriculum – Maintenance Practices
5. What is the primary purpose of recording equipment operating hours on an oil sample submittal form?
OSHA 10 – Electrical Safety
6. Which personal protective equipment is required before opening an energized low-voltage electrical panel for a thermographic scan, according to NFPA 70E?
NUCP Uniform Curriculum – Predictive Maintenance
7. In the context of predictive maintenance, what does a rising trend in vibration velocity readings over successive monthly data points indicate, even if each individual reading remains in Zone B?
NUCP Uniform Curriculum – Predictive Maintenance
8. Which of the following laboratory oil analysis results would most directly indicate internal metallic wear inside a gear box?
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