The tube bundle is the heat transfer core of a shell and tube heat exchanger: the assembly of tubes, tubesheets, baffles, tie rods and spacers inside the shell. Built to TEMA construction rules — Class R, C or B — the bundle determines thermal performance and remains the part that wears, fouls and is eventually replaced.
Bundles are supplied both as components for new exchangers built to API 660 and as replacement units for existing shells. For replacement work, the bundle must match the original shell inside diameter, bundle face length and nozzle positions; tube layout, pitch and material follow the service conditions of the installed unit.
TEMA and API 660 address different layers. TEMA fixes construction details — minimum tubesheet thickness, baffle and tie rod requirements, tolerances — while API 660 adds design, inspection and documentation requirements on top of it. A replacement bundle quoted "to TEMA" should state the class (R, C or B) explicitly, since the class drives wall thickness and examination coverage.
Four configurations cover most duties, identified by the TEMA rear-head letter:
For replacement projects, the existing rear-head type defines the bundle construction. A split-ring bundle cannot simply be substituted with a pull-through design without modifying the shell cover and gasket geometry.
Tubes. Seamless carbon steel to SA179, SA192 or SA210 Gr.A1; welded and seamless stainless to SA249 / SA213; duplex and titanium for corrosive service. Outer diameters of 19.05 mm (¾") and 25.4 mm (1") cover most layouts.
Tubesheets. Forged plates to SA266 Gr.2 or SA182, or carbon steel plates with corrosion-resistant weld overlay (316L, Alloy 625) where the process side demands it. Thickness is taken as the greater of the TEMA and ASME calculation results.
Baffles and support plates. Segmental baffles with a typical cut of 20–25% and spacing sized for shell-side velocity and pressure drop. Double-segmental, disc-and-doughnut and rod baffle layouts are used where vibration or fouling governs. In condensers, support plates replace baffles where pressure drop is the constraint.
Tie rods and spacers. Quantity and diameter follow the TEMA tables against shell diameter; they hold baffle position and keep the bundle rigid during handling.
Impingement protection. An impingement plate or Dummy tube arrangement is provided where shell-side entrance conditions exceed TEMA limits, or where the fluid is erosive or two-phase.
Tube layout and pitch. Triangular 30° layouts pack more area into a given shell; square 90° layouts open cleaning lanes of at least 6 mm for mechanical cleaning of the shell side. The choice is fixed by the fouling tendency of the shell-side fluid.
The joint is where bundles fail, and TEMA/API 660 treat it accordingly. Three connection levels exist, often combined:
Hydraulic expansion is preferred for thin-wall and non-ferrous tubes: it avoids the work hardening and residual stress that mechanical rolling introduces, which matters in chloride and wet H2S service. Welding procedures are qualified to ASME Section IX.
| Component | Common materials |
|---|---|
| Tubes | SA179 / SA192 / SA210 Gr.A1 · SA213 TP304/TP316L · SA249 · duplex S31803 · titanium SB338 Gr.2 |
| Tubesheets | SA266 Gr.2 · SA182 F304L / F316L · carbon steel with 316L or Alloy 625 overlay |
| Baffles / support plates | SA285 Gr.C · SA516 Gr.70 · SA240 304/316L |
| Tie rods / spacers | Matched to baffle material per TEMA |
| Impingement plates | Matched to shell-side fluid compatibility |
Material selection follows the process side: chloride concentration drives duplex or titanium, wet H2S calls for NACE MR0175 / ISO 15156 compliance, and caustic or seawater service shifts the overlay decision. The bundle is the component most exposed to the fluid — material shortcuts here surface as tube leaks within the first turnaround cycle.
| Parameter | Range |
|---|---|
| Bundle diameter (shell ID) | DN150 – DN2000 |
| Tube outer diameter | Ø19.05 mm, Ø25.4 mm standard; others on request |
| Tube length | 1500 – 12000 mm |
| Tube pitch | 30° triangular · 90° square · 45° / 60° on request |
| Heat transfer area, per bundle | 1 – 2000 m² |
| TEMA class | R · C · B |
The table describes normal fabrication capability, not the specification of any single bundle. A replacement bundle's geometry is fixed by the shell it must enter — final dimensions come from the original tube layout drawing or field measurement, not from the range table.
Where the shell remains sound but the bundle is fouled, corroded or thermally underperforming, a replacement bundle restores the unit without replacing the pressure boundary. Two supply routes exist:
For retubed bundles reusing existing tubesheets, tube hole condition and joint type must be verified before new tubes are rolled or welded into them.
Geometry-only replacement quotes can be answered from items 1–5. Where the buyer expects the replacement to correct a thermal shortfall, item 6 is required — a bundle that matches the old one dimensionally will also match its performance limits.
Removable bundles (U-tube, S and T types) allow mechanical cleaning of the shell side; square-pitch layouts keep the cleaning lanes open. Fixed tubesheet bundles restrict cleaning to chemical methods on the shell side. After each withdrawal, tube-to-tubesheet joints should be leak-checked before reload — a joint that passed hydrostatic test on the bench can relax in service as the shell and bundle cycle thermally.
