When a shell & tube exchanger starts losing efficiency, the first evidence is almost always in its pressure and flow data — not in the product outlet. Below are the questions our engineering team receives most often from plant operators, with the answers we usually give on site.
Because the fluid meets more resistance on its way through the exchanger, so the pump or fan has to work harder to push the same volume through the unit. Energy consumption climbs while the heat actually transferred stays flat or falls. Three conditions are responsible in most cases:
Practical trigger point: a pressure drop increase of more than 20–25% against the clean commissioning baseline deserves an inspection — it is not a normal seasonal fluctuation.
Because the exchanger is no longer transferring the heat it was designed for. Operators throttle the flow until the outlet temperature returns to set point, which restores the reading but hides the fault: the effective heat transfer coefficient has already degraded. The plant then runs below rated capacity and pays for the shortfall in output, not only in energy. If a unit needs a lower flow rate to hold the same outlet temperature, treat it as a capacity problem rather than a control tuning issue.
Part of the fluid short-circuits and leaves the unit without passing over the effective heat transfer surface, so the exchanger behaves like a smaller one. Typical causes:
Bypass is easy to miss because total flow and total pressure drop can both look almost normal while outlet temperatures drift apart.
| What You Observe | Most Likely Cause | Check To Run | Usual Action |
|---|---|---|---|
| Pressure drop rising, outlet temperature falling | Fouling or partial blockage | Compare with clean baseline; inspect tube ends and shell side | Chemical or mechanical cleaning; review strainers |
| Flow throttled to hold outlet temperature | Loss of heat transfer coefficient | Energy balance and U-value calculation | Cleaning, retubing or capacity re-rating |
| Outlet temperatures diverging at normal total flow | Bypass, baffle leakage or tube leakage | Pressure test between passes; borescope inspection | Replace gaskets and seals; plug or retube failed tubes |
| Pump or fan power rising at constant duty | Higher resistance in the flow path | Pump curve vs. measured head; vibration survey | Inspect internals; repair deformation |
Log pressure drop, flow rate and inlet/outlet temperatures at a fixed reference condition — same load, same ambient, same valve positions. When two of the symptoms above appear together, schedule the inspection before the next production campaign instead of waiting for a forced shutdown.
If the unit is repeatedly fouled, or the required duty has grown since commissioning, cleaning only buys time. A correctly specified replacement shell & tube exchanger is often more economical than a cleaning cycle every few months. Send us flow rate, inlet and outlet temperatures, allowable pressure drop and fluid properties — our engineers will size the replacement and confirm the packing and shipping plan to your port.
