Revamps 2026 Issue

though the equipment, failure modes, and fixes are all quite different. In each situation, the problem was not that the original design was careless or that the engineering team missed something obvious. The problem was that real operating conditions introduced complexities that aver - age-case design calculations simply do not capture. Once those complexities took hold, the exchanger started behav - ing in ways nobody had anticipated. In the winterisation case, the critical parameter was one that thermal ratings do not always report directly: the local TWT at the cold end of the bundle. An exchanger can be meeting its overall heat duty perfectly well while simulta- neously running TWTs below the pour point in a localised zone, and that is all it takes for wax deposition to begin. In the vibration case, the numbers looked acceptable at the design stage. It was only when the unit was running under actual two-phase flow conditions, with local cross- flow velocities that deviated significantly from the bulk average, that the vulnerability became apparent. Similarly, fouling in crude preheat train exchangers is ulti - mately a thermal-hydraulic problem, driven by the combined effect of low tube-side velocity and high wall temperatures accelerating deposit formation. Addressing it requires moving beyond routine turnaround cleaning toward a data-driven approach that identifies the worst-performing exchangers. What all three cases reinforce is that heat transfer anal- ysis in critical services needs to go deeper than average duty calculations. Local velocity distributions matter. Phase behaviour matters. Transient temperature profiles during

start-up and shutdown matter at least as much as steady- state operating points. These are not exotic considerations reserved for academic analysis;they are the details that separate exchangers that run reliably for years from those that generate recurring maintenance calls and unplanned outages. The root cause is usually somewhere upstream, in the thermal-hydraulic conditions the exchanger is actu - ally seeing versus what it was designed for. Finding that disconnect and addressing it properly is what makes the difference between a fix that holds and one that buys six more months before the same problem returns. Sadhna Singh is Chief General Manager and Head of the Heat Transfer Department at Engineers India Limited (EIL). She has more than 35 years of extensive experience in the thermal design, engineering, and optimisation of fired and unfired process equipment for the hydro - carbon, petrochemical, and fertiliser industries. Singh has authored several technical papers published in reputed oil and gas journals, is a sought-after speaker at national and international conferences, and holds multiple patents in the field of heat transfer design. She holds a bachelor’s degree in chemical engineering. Harshita Gupta is an Executive MBA and is currently working as Senior Manager at Engineers India Limited (EIL). She has more than 13 years of professional experience in the thermal design and engineering of heat exchangers, air coolers, ejectors, and refinery preheat networks. Gupta has been actively involved in optimisation studies, brownfield revamp projects, troubleshooting of critical process equipment, and indigenous technology development for refinery and petrochemical applications. She holds a bachelor’s degree in chemical engineering.

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FCC UNIT TURNAROUNDS DEPROPANISER UPSIZING

CORROSION PREVENTION

IMPROVED FRACTIONATION

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09/09/2026 10:18:34

Revamps 2026