Chemical Engineering Interview Questions 2026: Reliance GET, IOCL and Process Roles

Chemical is a small branch with unusually high-paying recruiters. Only 18,009 candidates registered for GATE CH in 2025 - a fraction of mechanical or civil - yet the employers at the top of the branch are Reliance Industries, whose GET programme pays Rs 7.5-9 LPA, the refining and gas PSUs (IOCL, ONGC, GAIL, HPCL, BPCL, EIL) that recruit through GATE, specialty chemicals (Tata Chemicals, Deepak Nitrite, Aarti, UPL, Pidilite), pharma (Dr. Reddy's, Sun, Cipla), FMCG (HUL, P&G, ITC) and the EPC design houses (Toyo, Technip, L&T Hydrocarbon). The placement rate sits near 59%.

The interview universes are the private GET route and the PSU route after GATE, and both test the same spine: material and energy balances, fluid mechanics, heat and mass transfer, reaction engineering, thermodynamics and process control, plus the ability to draw and defend a process flow diagram. Experienced interviews add simulation, equipment design, HAZOP and plant operations.

How the interview actually runs

Reliance GET is the largest private hirer. It screens on eligibility (60% with no backlogs), runs an online cognitive and technical test, then a regional personal interview and a medical. The interview asks you to draw the PFD or P&ID of your project and explain every equipment choice, then probes safety basics. Specialty and pharma companies follow the same shape with more emphasis on batch processing, GMP and solvent handling.

PSU recruitment runs on the GATE score. IOCL weights GATE at 85% and the group discussion or group task plus personal interview at 15%; ONGC, GAIL, HPCL, BPCL and EIL run personal interviews after the shortlist. Recent thresholds put IOCL, ONGC and GAIL near 800+ GATE marks. The PSU interview covers mass transfer, heat exchangers, reaction engineering, pumps and compressors, refinery flow and process safety, and your project.

Fluid mechanics and mechanical operations questions

Q (fresher): What does the Reynolds number tell you? A: The ratio of inertial to viscous forces; pipe flow is laminar below about 2,100 and fully turbulent above roughly 4,000.
Q (fresher): What is the Fanning friction factor? A: The dimensionless wall-shear parameter equal to 16/Re in laminar flow and one quarter of the Darcy factor, used in the pressure-drop equation for pipes.
Q (fresher): What is NPSH and why do pumps cavitate? A: Net positive suction head is the margin between suction pressure and the liquid's vapour pressure; if the available value falls below the pump's required value, vapour bubbles form and collapse on the impeller.
Q (fresher): When do you choose a centrifugal pump over a positive displacement pump? A: For high flow at moderate head with low-viscosity liquids; positive displacement pumps suit high pressure, metering and viscous fluids.
Q (experienced): What NPSH margin do you design for? A: Available NPSH should exceed required by at least 1 m or 10% at rated flow, more for water and hot hydrocarbons, per API pump practice.

Heat transfer and heat exchanger questions

Q (fresher): What is LMTD and when do you correct it? A: The log mean of the terminal temperature differences, the driving force for a pure counter-current exchanger; multi-pass shell-and-tube units apply a correction factor F below one.
Q (fresher): Why do fouling factors matter? A: Deposits add resistance on both sides, so the design overall coefficient must include fouling allowances or the exchanger will be undersized after a few months of service.
Q (fresher): What is a TEMA type? A: The three-letter code that describes a shell-and-tube exchanger's front head, shell and rear head, such as AES or BEU, which fixes cleanability and thermal expansion handling.
Q (experienced): What is pinch analysis? A: A method that plots hot and cold composite curves to find the minimum approach temperature, the energy targets and the exchanger network that meets them without cross-pinch transfer.

Mass transfer and distillation questions

Q (fresher): What is the McCabe-Thiele method? A: A graphical binary distillation design that steps between the equilibrium curve and the operating lines to count theoretical stages for a given reflux ratio.
Q (fresher): What happens at minimum reflux? A: The operating line touches the equilibrium curve at a pinch and the number of stages becomes infinite; real columns run at 1.2 to 1.5 times minimum reflux.
Q (fresher): What is HETP? A: Height equivalent to a theoretical plate, the packing height that performs one equilibrium stage, used to size packed columns from a stage count.
Q (fresher): What causes flooding in a column? A: Vapour velocity high enough to hold up or carry over liquid, so pressure drop rises sharply and separation collapses; design runs at 70-80% of the flooding velocity.
Q (fresher): Why choose absorption over distillation? A: When the component to remove is dilute in a gas and a suitable solvent exists; absorption then costs less energy than boiling the whole stream.

Reaction engineering and thermodynamics questions

Q (fresher): CSTR or PFR for a positive-order reaction? A: A PFR needs less volume for the same conversion because concentration, and hence rate, stays high along its length; a CSTR operates at the low outlet concentration throughout.
Q (fresher): What is residence time distribution used for? A: Diagnosing dead zones, bypassing and channelling in real reactors from the exit-age curve of a tracer pulse.
Q (fresher): What does Raoult's law assume? A: Ideal liquid and vapour, so the partial pressure of each component equals its vapour pressure times its liquid mole fraction; deviations are handled with activity coefficients.
Q (fresher): What is a runaway reaction? A: An exothermic reaction whose heat release exceeds the cooling capacity, so temperature and rate rise together; design prevents it with heat-removal margins, inhibitors and relief.
Q (experienced): Which property package do you pick in a simulator? A: Peng-Robinson for hydrocarbons and gases, NRTL or UNIQUAC for polar and non-ideal liquids, and electrolyte NRTL for aqueous ionic systems; the wrong package is the most common source of a wrong answer.

Process control, P&ID, HAZOP and safety questions

Q (fresher): What is a transfer function? A: The Laplace-domain ratio of output to input deviation variables for a linear system with zero initial conditions, the basis for tuning and stability analysis.
Q (fresher): When do you use cascade control? A: When a fast inner disturbance, such as steam pressure, would otherwise upset a slow outer variable, such as reactor temperature; the inner loop rejects it before it propagates.
Q (fresher): What is split-range control? A: One controller output driving two valves over different ranges, for example inert make-up below 50% and vent above, to hold a blanket pressure.
Q (fresher): What is a HAZOP? A: A structured review that applies guidewords such as no, more, less and reverse to each node of the P&ID to find deviations, causes, consequences and safeguards.
Q (experienced): What does SIL mean for a safety instrumented function? A: The safety integrity level under IEC 61511, a target probability of failure on demand determined by LOPA, which fixes redundancy, proof-test intervals and hardware fault tolerance.
Q (experienced): How do you size a pressure safety valve? A: From the governing relief scenario - fire, blocked outlet, control valve failure or thermal expansion - using API 520 for the orifice and API 521 for the scenario and the flare load.
Q (experienced): What is a permit-to-work? A: Written authorisation for non-routine work such as hot work, confined-space entry or electrical isolation, specifying isolations, gas tests and PPE, valid for one shift.

What experienced engineers get asked

Process design engineers (2-10 years) are interviewed on simulation in Aspen Plus, HYSYS or DWSIM - property packages, convergence, recycle tears, rigorous versus shortcut columns - on exchanger and column sizing, on vessels to ASME Section VIII and tanks to API 650, on pumps to API 610 and piping to ASME B31.3, on relief and flare per API 520/521, on HAZOP leadership and SIL determination, and on materials selection with NACE requirements for sour service.

Plant and production engineers are interviewed on start-up and shutdown sequences, DCS operation and alarm management, refinery and petrochemical unit flows, process safety management elements, management of change, turnarounds and risk-based inspection under API 580/581, debottlenecking and specific energy consumption. Pharma roles add cGMP, validation and data integrity. Lead roles add HSE regulation - Factories Act, MSIHC rules, CPCB consents, OISD standards - and incident investigation.

The PSU interview after GATE

IOCL runs a group discussion or group task before the personal interview; ONGC, GAIL, HPCL and BPCL go straight to the interview. Panels are refinery and plant engineers who ask you to reason through unit operations - why a distillation column floods, how a reactor is protected from runaway, what limits an exchanger - and who push on your project until they find its softest assumption. Expect a few questions on the organisation's refineries, pipelines and current projects, and on why a PSU.

A 4-week plan

Week 1: Fluid mechanics, mechanical operations, heat transfer and material and energy balance from the Chemical Core section, 40 questions a day.
Week 2: Mass transfer, reaction engineering, thermodynamics and process control; redraw your project's PFD and P&ID from memory and take the free 2-minute readiness check on your stream.
Week 3: Process Design section for simulation, equipment design, HAZOP and piping if you target design roles; Plant Operations for refinery flows, process safety and reliability if you target production, safety or PSU roles.
Week 4: Recruiter pages for Reliance and IOCL, group-discussion practice, timed aptitude, and two full mock interviews at your target level.

All of the questions above are drawn from placd's Chemical Engineering banks, about 1,000 questions across the core, process-design and plant-operations sections with explanations. Start at the department hub, placd.in/engineering/chemical, browse topics such as placd.in/questions/chem-core/mass-transfer, placd.in/questions/chem-core/chemical-reaction-engineering and placd.in/questions/chem-process/hazop-and-process-safety, and sit the scored AI mock interview on Pro at placd.in/products/mock-interview (take the free readiness check first), with the interviewer asking from the chemical bank when you pick a process role.