CHIEF ENGINEER Unit 14 Condition Monitoring Q2 Answer

With reference to condition monitoring:
(a) explain how vibration analysis can be used as part of a planned maintenance system;(7)
(b) list SIX tests that can be carried out on crankcase oil in order to determine its suitability for further service.(3)

Vibration analysis is a key condition monitoring technique that helps detect faults in rotating machinery before they lead to failure.

Baseline measurement – A vibration signature (frequency spectrum) is recorded for each piece of machinery when operating normally.
Trend monitoring – Regular measurements are taken and compared with baseline to detect deterioration.
Identification of faults by frequency – Each type of fault produces vibration at characteristic frequencies:
- Unbalance → vibration at shaft rotational frequency.
- Misalignment → vibration at multiples of running speed.
- Bearing defects → high frequency “spikes” from pitting or spalling.
- Gear faults → sidebands around gear mesh frequencies.
Severity analysis – Amplitude of vibration indicates severity and urgency of maintenance action.
Early fault detection – Problems can be detected at an early stage before catastrophic failure.
Maintenance planning – Repairs or replacements can be scheduled at a convenient time, reducing downtime.
Life extension of machinery – Monitoring ensures components are only overhauled when required, avoiding unnecessary work and cost.

Six common tests used to check oil condition:

Viscosity test – ensures the oil has not thickened or thinned beyond acceptable limits.
Base Number (BN) test – measures alkalinity reserve to neutralise acids.
Acid Number (AN) test – indicates oxidation or contamination by acids.
Water content test – detects ingress from cooling water leaks.
Metal content analysis (spectrometric analysis) – identifies wear metals (e.g., Fe, Cu, Pb, Sn) from engine parts.
Contaminant analysis – checks for soot, fuel dilution, or dirt particles.