Failure here means loss of containment (a leak between sides or to atmosphere), loss of integrity (thinned or cracked pressure parts), or a bundle that can no longer make duty because tubes are plugged, collapsed, or cut by vibration. Performance fade from fouling is a maintenance event unless it drives a metal-temperature or corrosion failure. Diagnose the mechanism before you buy a duplicate.
Tube leaks: corrosion, erosion, and joints
Tubes fail through the wall from process corrosion, cooling-water pitting, under-deposit attack, or erosion at inlets and U-bends. Tube-to-tubesheet joints fail from inadequate expansion/weld, cyclic load, or corrosion in the crevice. Cross-contamination is the plant symptom; the metallurgical report is the cause. Plugging is a stop-gap within remaining area and vibration limits. Repeated leaks in the same rows point to impingement, inlet erosion, or a dead zone — not 'bad tubes' as a class.
Flow-induced vibration
Shell-side cross-flow can excite vortex shedding, fluidelastic instability, or acoustic resonance. Tubes wear at baffle holes, collide, and fatigue. Failures cluster at U-bends, inlet spans, and tubes in the window. Root cause is usually span, velocity, or missing supports — a thermal layout that never ran a vibration screen. Replacing tubes to the same baffle spacing repeats the failure. See the article on tube vibration and baffle spacing.
If tubes are polished or cut at baffle locations, do not 'upsize ΔP' by raising flow without a vibration review. You will finish the rest of the bundle.
Thermal expansion and fatigue
Fixed-tubesheet units without adequate expansion provision crack tube-to-tubesheet welds or yield tubes when metal-temperature difference is larger than design — batch plants and steam-out cycles are frequent offenders. Expansion joints fail from over-cycle, corrosion of the bellows, or condensate/chloride collection in the convolution. U-bends can fatigue if vibration and cycling combine. Start-up and steam-out cases belong on the datasheet if they exist.
Fouling-driven damage
Deposits are not only a U problem. Under-deposit corrosion, overheating of tubes when boiling is blanketed, and high local velocity in remaining open lanes all damage metal. A condenser with blocked vents collects non-condensables and loses duty; a reboiler with fouled boiling surface can bump heat flux onto remaining tubes. Cleaning without inspecting for thinning misses the failure that fouling hid.
Gaskets, pass partitions, and nozzles
- Channel and pass-partition gasket blow-by: mixes tube-side passes or leaks to atmosphere; often after a clean-out with reused gaskets or uneven bolt-up.
- Shell cover / floating-head gaskets (on units that have them): shell-side leaks; Ohm does not build floating heads, but plants operating them should treat those joints as wear items.
- Nozzle cracks: piping loads not on the original design, water hammer, or thin reinforcement.
- Impingement failure: first-row tubes cut when ρv² was ignored.
What to inspect after a failure
Map leak locations on a tubesheet sketch. Photograph baffle wear, inlet impingement, and expansion-joint condition. Review actual flows and temperatures versus the datasheet, including turndown. Check water chemistry and process contaminants. Decide whether the replacement needs a different rear end (expansion joint or U-tube), different MOC, different velocity, or a vibration redesign — not only a new bundle to the old drawing.
RFQ for a replacement that does not repeat
Send the original datasheet and GA, failure description (location, time in service, photos), current process case, and what you want changed. Use /rfq?product=heat-exchangers. Ohm can fabricate a replacement in the types we manufacture (fixed-tubesheet ± expansion joint, U-tube, double-pipe, kettle) to the named code. We will not claim a floating-head rebuild we do not make.
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