TEMA Shell & Tube Types Explained: Choosing the Right Configuration

Every TEMA-standard shell and tube exchanger is described by a three-letter code — a front-end head, a shell type and a rear-end head. Get any one of those three letters wrong at the selection stage and you inherit a unit that either can’t be cleaned, can’t handle thermal expansion, or can’t be pulled apart for a retube without a crane and a lost weekend.

What the three TEMA letters actually control

The front-end head (A, B, C, N or D) governs how the tube bundle is accessed for cleaning and inspection. The shell type (E, F, G, H, J, K or X) governs flow path and pressure drop. The rear-end head (L, M, N, P, S, T, U or W) governs whether — and how — the bundle can be removed for maintenance. A designation like "AES" tells a fabricator everything needed to start a mechanical design before a single thermal calculation is run.

• Front-end head — removable channel and cover (A), bonnet (B), or channel integral with tubesheet (C, N)
• Shell type — one-pass (E), two-pass longitudinal baffle (F), split flow (G, H), or kettle reboiler (K)
• Rear-end head — fixed tubesheet (L, M, N), U-tube (U), or floating head (P, S, T, W)

Fixed tubesheet: simplest, cheapest, least forgiving

A fixed tubesheet design (typically AEL, BEM or NEN) welds both tubesheets directly to the shell. There is no floating head and no removable bundle — the shell side can only be cleaned chemically, not mechanically. It is the lowest-cost configuration to fabricate and the most thermally efficient per unit of shell diameter, which is why it dominates clean, non-fouling services: closed-loop cooling water, refrigerant condensers, and light hydrocarbon services with a shell-side fluid that never needs a brush.

“A fixed tubesheet exchanger with a fouling shell-side fluid isn’t a design mistake you fix in the field — it’s a design mistake you fix by cutting the shell open.”

Dolphin Group thermal design team

The trade-off is thermal expansion. Because both tubesheets are rigidly fixed, any differential expansion between the tubes and the shell — common when tube-side and shell-side operating temperatures diverge sharply — loads the tubesheet joints directly. Past a certain ΔT, TEMA requires an expansion joint in the shell, which adds cost and a maintenance item that partially erodes the configuration’s core advantage.

U-tube: handles expansion, limits tube-side cleaning

A U-tube bundle (BEU, AEU) bends the tube bank back on itself at one end, so only one tubesheet exists and the bundle is free to expand independently of the shell. That solves the thermal-cycling problem fixed tubesheets struggle with — U-tube units are the default choice for high-ΔT services like steam generators and thermal cycling duty in petrochemical plants.

The cost is on the tube side: mechanical cleaning of the U-bend itself is difficult or impossible with a straight rod, so U-tube exchangers are usually reserved for clean tube-side fluids — treated boiler feedwater, closed-loop glycol, refrigerants — never a fouling process stream on the tube side.

Floating head: full mechanical access, at a cost

A floating-head design (AES, BEP, AET) uses a second tubesheet that is not welded to the shell — it "floats," free to move axially as the bundle expands, while a floating head cover on the outside lets the entire bundle be withdrawn for mechanical cleaning on both the tube side and shell side. This is the configuration TEMA and API 660 specify by default for fouling, high-pressure, or hazardous services in oil & gas, where shutdown-window bundle pulls are routine and shell-side mechanical access is non-negotiable.