Maintenance and Troubleshooting of Machinery and Equipment
This domain tests maintenance strategy selection, reliability numbers and fault-finding discipline. Expect calculation of MTBF, MTTR and availability, plus questions on condition monitoring and root-cause analysis.
Maintenance types
- Preventive: scheduled by time or running hours, replacing or servicing before failure.
- Predictive/condition-based: triggered by measured condition - vibration, thermography, oil analysis, ultrasound.
- Corrective: after failure. Reactive maintenance is only economic for cheap, non-critical items.
- The bathtub curve shows early-life, random and wear-out failure phases; each needs a different strategy.
Reliability arithmetic
MTBF = total operating hours ÷ number of failures. MTTR = total repair hours ÷ number of repairs. Availability = MTBF ÷ (MTBF + MTTR).
Fault-finding
Work from symptom to cause: gather the complaint, confirm it, list possible causes, test the cheapest and most likely first, then verify the repair. Use 5 Whys or a fishbone diagram across man, machine, material, method, measurement and environment. Repeated bearing failure usually points to misalignment, imbalance, lubrication or soft foot - not to the bearing.
Worked example. A pump runs 7200 h with 6 failures and 48 total repair hours. MTBF = 7200/6 = 1200 h; MTTR = 48/6 = 8 h; availability = 1200/1208 = 99.34 %.
Traps. Counting repair time inside MTBF; replacing the failed part without finding the cause; confusing preventive (scheduled) with predictive (condition-triggered); over-greasing a bearing and blowing the seal; ignoring alignment after a motor change.