HKIE Professional Assessment - Chemical Discipline common mistakes
HKIE Professional Assessment - Chemical Discipline · Understand the traps and how to avoid them.
When asked to recommend a relief device or flare header size, the candidate performs a hydraulic or orifice calculation and stops there, never stating the governing scenario, the design basis (fire, blocked outlet, control valve failure, runaway reaction) or the applicable code clause and set-pressure margin.
Candidates treat the question as a pure calculation exercise because the numbers are given, and they have memorised sizing equations without the surrounding design-basis workflow. Under time pressure the calculation feels like the 'answer', so the scenario selection and code justification get dropped.
What to do instead
Before any number, write one sentence naming the worst-credible scenario and why it governs, then state the code basis (e.g. ASME VIII / API 521 style approach), the set pressure, accumulation limit and any inlet/outlet line loss allowance. Only then compute. Practise three-scenario comparisons (fire vs blocked outlet vs runaway) so scenario selection becomes automatic.
In HAZOP-style questions the candidate lists generic hazards ('fire', 'leak', 'overpressure') instead of working the guideword-plus-parameter matrix (no flow, more flow, less temperature, reverse flow, as well as) against specific nodes, and fails to record cause-consequence-safeguard-action in a structured way.
Candidates confuse HAZOP with a hazard identification brainstorm. They have read about guidewords but never practised applying them node by node, so they default to listing outcomes rather than deviations.
What to do instead
Answer in a table: node, parameter, guideword, deviation, credible cause, consequence, existing safeguard, risk, recommendation. Force yourself to generate at least one deviation per guideword for the given node, and explicitly distinguish cause from consequence - examiners deduct for conflating them.
The candidate presents a conceptual process design or flowsheet without a mass and energy balance closure, without stating stream purities and recoveries, and without identifying the recycle, purge and utility streams - jumping straight to equipment selection.
Flowsheet sketching is visually satisfying and quick, so candidates spend their time drawing rather than closing balances. Many have only seen flowsheets as finished diagrams and have not internalised that the balance is the design.
What to do instead
Always present a balance table with overall and component closures, degrees-of-freedom count, recycle/purge justification (why the purge rate is what it is), and utility duties. State key purities and recoveries as design specifications. If data is missing, state the assumption explicitly and its sensitivity.
When asked about corrosion or material selection, the candidate names a generic alloy ('use stainless steel') without specifying the grade, the corrosion mechanism at play, the environment (chlorides, temperature, pH, H2S partial pressure), or the inspection/monitoring strategy and corrosion allowance.
Material selection is taught as a lookup table in many courses, so candidates recall family names rather than grade-specific behaviour. They also under-weight the mechanism-first reasoning that drives grade choice.
What to do instead
Structure answers as: mechanism (e.g. chloride stress corrosion cracking, sour service per NACE/ISO 15156, high-temperature sulphidation) → controlling variables → candidate grades with trade-offs → corrosion allowance or mitigation (coating, CP, inhibitor) → inspection method and interval (UT, RT, coupons, probes). Name the standard.
In control and instrumentation questions the candidate draws a feedback loop but cannot justify the chosen controlled variable, manipulated variable, or controller action (direct/reverse), and does not address failure position of valves, loop integrity or alarm management.
Candidates learn PID tuning rules in isolation and rarely practise mapping a process narrative onto loop structure. The 'why this variable' reasoning is the part most often skipped in study.
What to do instead
For every loop, state: objective, controlled variable, manipulated variable, disturbance variables, valve fail-safe position, and whether action is direct or reverse. Add a sentence on what happens on instrument failure and how the operator is alerted. For safety-critical loops, mention independence from the BPCS and the trip set point.
On economics and project questions the candidate quotes a payback or NPV number without stating the basis: discount rate, project life, currency and year of estimate, contingency, escalation, or whether the figure is real or nominal - and ignores contracting strategy and risk allocation.
Financial formulas are easy to reproduce mechanically, and candidates focus on getting a number rather than on the assumptions that make it meaningful. Contractual and risk-allocation content is often studied last and thinly.
What to do instead
Always tabulate assumptions before the result: estimate class and accuracy range, cost year and index, discount rate, life, tax and depreciation treatment, contingency and owner costs. State whether cash flows are real or nominal. Then add one paragraph on contract form (lump sum vs reimbursable vs EPC) and how it allocates the dominant risks.
On ethics and professional-practice questions the candidate answers with personal opinion or general virtue language ('be honest', 'act professionally') rather than identifying the specific duty owed, to whom, the relevant code or statutory obligation, the conflict of interest, and the escalation route.
Candidates treat ethics as a soft topic and do not realise it is marked against a framework. They also lack familiarity with the institution's code of conduct and local statutory duties, so they cannot anchor the answer.
What to do instead
Answer with a four-part structure: facts and the technical/professional issue; duties owed (public safety, employer, client, profession) and which prevails; the specific code clause or statutory requirement engaged; and the concrete action and escalation path (raise internally, document, decline to certify, report to authority). Practise with short scenarios.
The candidate answers a scale-up or simulation question by treating a CFD or process-simulation result as validated truth, without discussing model assumptions, mesh or thermodynamic model selection, convergence, experimental validation, or the regime change between pilot and plant (mixing, heat transfer area per volume, residence time distribution).
Software output looks authoritative and candidates are trained to operate tools rather than critique them. Scale-dependent phenomena are hard to visualise, so they get omitted.
What to do instead
For any simulation answer, state the governing equations and closure/thermodynamic model chosen and why, the boundary conditions, convergence and sensitivity checks, and the validation data. For scale-up, explicitly list which dimensionless groups or ratios are held constant and which cannot be, and what that means for yield, selectivity or heat removal.
On reaction engineering and catalysis questions the candidate reports conversion or rate without addressing selectivity, deactivation, heat management, or intrinsic versus apparent kinetics - and does not check whether the observed rate is transport-limited.
Conversion is the easiest quantity to calculate and the most commonly examined, so it crowds out selectivity and transport reasoning. Candidates also under-practise the diagnostic tests (e.g. variable particle size, temperature dependence) that reveal transport artefacts.
What to do instead
For every reactor answer, report conversion and selectivity together, state the thermal regime (isothermal, adiabatic, hot spot risk) and the heat removal mechanism. Check for transport limitation using the standard criteria (particle-size variation, activation energy comparison, internal effectiveness). Add a line on catalyst life and regeneration.
On separation and unit-operation questions the candidate sizes a column or exchanger from a single shortcut method and never states the design margin, turndown, flooding or fouling allowance, or the operating limits - and does not reconcile the shortcut result with a stage-by-stage or rating check.
Shortcut methods (Fenske–Underwood–Gilliland, LMTD) are quick and feel complete. Candidates rarely practise the follow-up questions about turndown, fouling and hydraulic limits that distinguish a design from a calculation.
What to do instead
Present shortcut results as a first estimate, then state the rigorous check performed, the design margin (e.g. percentage above flooding, exchanger area margin for fouling), turndown range, and the limiting hydraulic or thermal constraint. State fouling factors and cleaning strategy explicitly, and name the performance test that would confirm the design.