HKIE Professional Assessment - Mechanical Discipline cheat sheet

Steady-flow energy equation: q − w = Δh + ΔKE + ΔPE; for adiabatic nozzle/ diffuser w = 0 and h₁ + V₁²/2 = h₂ + V₂²/2.

Carnot efficiency η = 1 − T_L/T_H with absolute temperatures; no real cycle between the same reservoirs can exceed it.

Reynolds number Re = ρVD/μ = VD/ν; pipe flow is laminar below about 2,000 and fully turbulent above about 4,000 in circular pipes.

Darcy–Weisbach head loss h_f = f(L/D)(V²/2g); friction factor f from Moody chart using relative roughness ε/D and Re.

Bernoulli with losses: p₁/γ + V₁²/2g + z₁ = p₂/γ + V₂²/2g + z₂ + h_L; pump head added on the left side.

Bending stress σ = My/I; maximum at extreme fibre y = c; section modulus Z = I/c gives σ = M/Z.

Euler buckling load P_cr = π²EI/(KL)²; effective length factor K depends on end restraint (K = 1 pinned–pinned, 0.5 fixed–fixed, 2 fixed–free).

Single-degree-of-freedom vibration: natural frequency ω_n = √(k/m), damping ratio ζ = c/(2√(km)), resonance near ω/ω_n = 1.

Design factor (safety factor) = failure strength / allowable stress; applied to yield for ductile members and to ultimate for brittle members.

Ashby material index method: express objective (mass, stiffness, strength) as a function of material properties, then select the material maximising or minimising that index.

Stiffness-limited light beam index E^(1/2)/ρ for a bending beam of fixed length and stiffness; strength-limited index σ_y^(2/3)/ρ.

Ductile-to-brittle transition: carbon steels show a Charpy transition temperature; specify steel with transition temperature below the minimum service temperature.

Galvanic corrosion risk rises with the potential difference between dissimilar metals; avoid coupling stainless steel to aluminium in wet environments or insulate the joint.

Tolerance stack-up: worst-case arithmetic sum of tolerances versus statistical (root-sum-square) method; specify fits per ISO 286 hole-basis or shaft-basis systems.

Weld symbols follow ISO 2553; a fillet weld leg length and throat thickness relate by throat = 0.707 × leg.

Pressure vessel design to BS EN 13445 or ASME VIII uses minimum thickness t = pD/(2SE − p) plus corrosion allowance for cylindrical shells.

Fit-up and alignment tolerances for rotating machinery are checked with dial gauges or laser alignment; allowable shaft offset and angularity are typically below 0.05 mm for high-speed sets.

Commissioning sequence: static checks, pressure/leak testing, flushing, no-load run, load test, performance verification, then handover with as-built records.

Hydrostatic test pressure for pipework is commonly 1.5 times design pressure (or per the applicable code), held for a defined duration with no pressure loss.

Preventive maintenance intervals derive from manufacturer data, failure history and criticality; condition monitoring (vibration, thermography, oil analysis) drives predictive maintenance.

Vibration severity for rotating machines is judged against ISO 10816/20816 zone boundaries (A/B/C/D) measured as RMS velocity in mm/s.

Non-destructive testing methods: dye penetrant (surface-breaking defects), magnetic particle (ferromagnetic surface/near-surface), ultrasonic (internal), radiography (internal volumetric).

Balancing grades follow ISO 1940-1; permissible residual unbalance e_per × rotor mass per balance quality grade G.

Factory acceptance test (FAT) and site acceptance test (SAT) are separate gates; FAT results do not replace site commissioning verification.

Sensible heat gain Q_s = 1.23 × airflow (L/s) × ΔT (°C) for air at standard conditions; latent heat uses moisture content difference.

Cooling coil apparatus dew point and bypass factor determine supply air condition; room load ratio fixes the supply air temperature difference.

Fan and pump laws: flow ∝ speed, head ∝ speed², power ∝ speed³; affinity laws underpin variable-speed control savings.

Coefficient of performance COP = cooling output / electrical input; chiller efficiency in kW/tonne or COP, with IPLV for part-load performance.

Hong Kong energy code (Building (Energy Efficiency) Regulation and BEC) sets maximum allowable power densities and requires energy audits for prescribed buildings.

Fire services installations in Hong Kong are governed by the Fire Services Department Circular Letters and Codes of Practice for minimum fire service installations and equipment.

Plumbing and drainage design follows the Water Supplies Department requirements and the Building (Plumbing) Regulations; soil and waste stacks require venting to protect trap seals.

Smoke control: pressurised staircases and smoke extraction systems are designed to maintain tenability; fan sizing must account for leakage through closed doors.

Buildings Ordinance (Cap. 123) and its subsidiary regulations govern building works; Buildings Department codes of practice give deemed-to-satisfy design rules.

Builders' lift and escalator installations are regulated under the Lifts and Escalators Ordinance (Cap. 618), with registration of contractors and periodic examination.

Pressure equipment and gas installations fall under the Gas Safety Ordinance (Cap. 51) and related regulations; registered gas contractors must carry out installation work.

The Factories and Industrial Undertakings Ordinance (Cap. 59) and subsidiary regulations (including safety management) set duties on contractors and employers.

Registration of engineers is under the Engineers Registration Ordinance (Cap. 409); the HKIE assesses professional competence for corporate membership and the professional assessment.

Fire safety in buildings is covered by the Code of Practice for Fire Safety in Buildings, covering means of escape, fire resisting construction and access for firefighting.

Occupational safety legislation requires risk assessments, safe systems of work and reporting of accidents to the Labour Department under the relevant regulations.

Statutory submissions for building services works require coordination with Buildings Department, Fire Services Department and Water Supplies Department approvals.

Risk assessment hierarchy of control: eliminate, substitute, engineering controls, administrative controls, then personal protective equipment as last resort.

Risk score = likelihood × severity; ALARP principle requires reducing risk so far as is reasonably practicable.

Confined space entry requires a permit, atmospheric testing for oxygen (19.5–23.5%), flammable gas and toxic gas, plus rescue arrangements and standby person.

Incident investigation models: Swiss cheese (Reason) model and 5-why / root cause analysis; findings should address system failures, not only individual error.

Lifting operations require a lifting plan, competent person, certified lifting gear and exclusion zones; SWL must not be exceeded.

Environmental impact assessment under the Environmental Impact Assessment Ordinance (Cap. 499) requires a permit for designated projects.

Noise control under the Noise Control Ordinance (Cap. 400) covers construction noise permits, restricted hours and prescribed noise standards.

Waste management follows the Waste Disposal Ordinance (Cap. 354); construction and demolition waste should be reduced, reused and recycled before disposal.

Critical path method: float = late start − early start; activities on the critical path have zero total float and drive project duration.

Earned value: CV = EV − AC, SV = EV − PV, CPI = EV/AC, SPI = EV/PV; CPI below 1 indicates cost overrun.

Standard contract forms in Hong Kong include the HKIA/HKIS Standard Form of Building Contract and the Government General Conditions of Contract; risk allocation differs between them.

Variation valuation follows the contract's rates and prices; where no rate applies, a fair valuation based on reasonable cost plus profit is used.

Quality assurance uses the plan–do–check–act cycle; inspection and test plans (ITP) define hold points and witness points for verification.

Stakeholder communication plan records audience, message, channel, frequency and owner; reporting lines must match the project organisation structure.

Liquidated damages must be a genuine pre-estimate of loss, not a penalty, to be enforceable.

Programme float ownership and extension of time entitlement depend on the contract; concurrent delay treatment should be stated in the contract.

Core ethical duties: competence, honesty, public safety and health first, confidentiality, avoidance of conflicts of interest, and fair dealing.

Whistleblowing duty: where a serious risk to public safety exists, the engineer should escalate internally and, if unresolved, to the appropriate authority.

Sustainable design applies life-cycle assessment; embodied carbon plus operational carbon gives whole-life carbon for a system.

Energy efficiency hierarchy: reduce demand, improve conversion efficiency, recover waste energy, then use low-carbon supply.

Declaring conflicts of interest in writing and withdrawing from decisions where impartiality is compromised is a standard professional requirement.

Continuing professional development (CPD) is expected of registered engineers to maintain competence in a changing technical and regulatory environment.

Signing and certifying work implies personal responsibility for its technical adequacy; only sign within your own competence.

Environmental and social impacts should be considered at concept stage, when the greatest opportunity to influence whole-life performance exists.