CRE Equipment and Tools Knowledge 2 — Questions and Answers
Question 1: Which condition monitoring technique is MOST effective for detecting early-stage bearing defects in rotating machinery?
- Infrared thermography
- Vibration spectrum analysis (Correct answer)
- Oil pressure gauging
- Visual inspection
Correct answer: Vibration spectrum analysis
Vibration spectrum analysis can detect characteristic bearing defect frequencies (BPFI, BPFO, BSF, FTF) long before failure becomes visible or thermal.
Question 2: A laser shaft alignment tool reports an angular misalignment of 0.8 mrad. This value primarily affects which failure mode?
- Corrosion fatigue
- Coupling and bearing wear from bending loads (Correct answer)
- Cavitation in seals
- Thermal expansion cracking
Correct answer: Coupling and bearing wear from bending loads
Angular misalignment introduces cyclic bending loads on couplings and bearings, accelerating wear and fatigue damage.
Question 3: When using an ultrasonic thickness gauge, the measured value is lower than the nominal wall thickness. What is the MOST likely cause?
- Excessive lubrication on the probe
- Internal corrosion or erosion reducing wall thickness (Correct answer)
- Probe frequency too high
- Surface roughness on the outside
Correct answer: Internal corrosion or erosion reducing wall thickness
Internal corrosion or erosion removes material from the inner surface, reducing the measured wall thickness without visible external damage.
Question 4: In oil analysis, a high ISO cleanliness code (e.g., 22/20/17) compared to the target (16/14/11) indicates:
- Oil is within acceptable contamination limits
- Excessive particulate contamination requiring filtration or oil change (Correct answer)
- Water contamination only
- Additive depletion without particulates
Correct answer: Excessive particulate contamination requiring filtration or oil change
A higher ISO cleanliness code means more particles per milliliter, signaling contamination that can accelerate bearing and gear wear.
Question 5: A motor current signature analysis (MCSA) tool detects sidebands at frequencies of line frequency ± 2sf. What does this pattern indicate?
- Voltage unbalance
- Broken rotor bars (Correct answer)
- Stator winding short
- Overloading
Correct answer: Broken rotor bars
Broken rotor bars produce characteristic sidebands at f_line ± 2sf (where s = slip, f = supply frequency) in the motor current spectrum.
Question 6: Which NDT method is BEST suited for detecting surface and near-surface cracks in ferromagnetic components without removing coatings?
- Radiographic testing (RT)
- Magnetic particle inspection (MPI)
- Dye penetrant testing (DPT)
- Eddy current testing (ECT) (Correct answer)
Correct answer: Eddy current testing (ECT)
Eddy current testing can detect near-surface flaws through non-conductive coatings without requiring their removal.
Question 7: A vibration analyzer shows a dominant peak at exactly 1× running speed that increases significantly when the rotor speed changes. The MOST likely cause is:
- Bearing outer race defect
- Rotor imbalance (Correct answer)
- Looseness
- Gear mesh frequency
Correct answer: Rotor imbalance
Rotor imbalance produces a dominant 1× running speed vibration whose amplitude is proportional to the square of speed.
CRE Equipment and Tools Knowledge 2
Which condition monitoring technique is MOST effective for detecting early-stage bearing defects in rotating machinery?