Maintenance and Repair, Materials and Workshop Practice
What this domain tests
This domain tests planned maintenance, defect diagnosis, workshop practice and materials selection: whether you can keep machinery within maker's tolerances and choose the right repair, fastener and material for the service.
Planned maintenance
- The planned maintenance system is driven by running hours and calendar intervals; work is raised, executed, signed off, and defects are carried forward rather than closed on paper.
- Condition monitoring decides when to intervene: vibration trends, oil analysis for wear metals, viscosity, water and base number, thermography and performance monitoring.
- Isolation and permit to work precede any opening of machinery: lock-off and tag-off, depressurise, drain, prove dead, and check for stored energy in springs, accumulators and suspended loads.
Tolerances and fits
- Bearing clearances are measured with feeler gauge, lead wire or plastigauge and compared with maker's limits; alignment after reassembly is checked by dial gauge or laser.
- Crankshaft deflection readings reveal bedplate and bearing condition; a change between readings, not the absolute value alone, is the signal.
- Torque is applied in the maker's sequence with a calibrated wrench; a reused gasket, a wrong grade bolt or over-torque produces a leak or a cracked flange.
Materials and corrosion
- Mild steel for structure, cast iron for blocks and housings, stainless steel for seawater-exposed fittings, bronzes for pump internals; dissimilar metals in seawater set up galvanic corrosion, so isolate with gaskets and sleeves.
- Crevice and pitting attack concentrate under deposits and gaskets; erosion-corrosion follows high velocity, especially at bends and impellers.
- Welding: manual metal arc for general repair, TIG for thin and stainless work, with correct electrode, preheat and post-weld treatment; dye penetrant, magnetic particle or ultrasonic testing proves the repair.
Worked example
An oil analysis reports iron at 85 ppm against a 30 ppm alarm limit, with viscosity up 15%. Reasoning: the trend across three samples matters more than one result. Iron with a viscosity rise suggests wear plus oxidation, or the wrong oil grade. Action: verify the sample point and grade, shorten the sampling interval, inspect filters and magnetic plugs, and plan an inspection at the next opportunity rather than an immediate overhaul.
Traps that cost marks
Over-torquing to stop a leak; fitting stainless bolts into a mild-steel flange; judging wear from a single oil sample; opening machinery without proving it depressurised; reusing gaskets or locking devices.
Key points
- Planned maintenance is closed out against running hours and calendar intervals, not on paper