Procurement language often treats 'floating head' and 'fixed tubesheet' as two products on the same shelf. Mechanically they are different rear-end families in TEMA. A fixed-tubesheet exchanger has both tubesheets welded to the shell (rear letters L, M, or N). A floating-head exchanger has a rear tubesheet that can move (S, T, or packed W). Ohm Engineers manufactures fixed-tubesheet shell-and-tube units — with or without a shell expansion joint — and U-tube bundles as the removable-bundle construction. This shop does not manufacture floating-head exchangers. The comparison below is so you specify the right family, not so a datasheet can be silently rewritten.
Fixed tubesheet — what you get
Both tubesheets are integral with the shell. There is no shell-side gasket at the rear tubesheet, which is why this construction is preferred for high integrity, high pressure, and services where a rear gasket leak is unacceptable. Tube-side mechanical cleaning is practical if the front head is a removable cover and the tubes are straight. Shell-side mechanical cleaning of the bundle exterior is not practical without cutting the shell; chemical circulation or a design that does not rely on shell-side mechanical cleaning is the usual path.
When a fixed tubesheet needs an expansion joint
Tubes and shell grow by different amounts when metal temperatures differ. The residual load appears as tube axial stress and tubesheet bending. If the calculated differential is beyond what the joints and tubesheet can take, a bellows (expansion joint) is fitted in the shell. That preserves fixed-tubesheet construction and shell-side tightness while allowing axial growth. The joint is a specified item: displacement, pressure, cycle life, and material must be on the order. It is not a floating head and it does not make the bundle removable.
What a floating head is (industry / TEMA, not an Ohm SKU)
TEMA S uses a split backing device and a shell cover; the bundle can be withdrawn after the cover and backing ring are removed. TEMA T is pull-through: the rear tubesheet is small enough to come out through the shell, at the cost of more bypass area. TEMA W uses a packed gland and is generally limited to modest pressure because the packing is a leak path. All three accommodate differential expansion and allow shell-side access to the bundle. They add gaskets, covers, and diameter. Refinery and dirty-shell specifications often mandate S or T. That mandate is a purchaser TEMA choice.
If your datasheet says AES, AET, or similar S/T rear letters, you have specified a floating head. Ohm does not fabricate that rear end. State the requirement so the enquiry can be scoped honestly.
U-tube: Ohm's manufactured removable-bundle option
A U-tube exchanger (TEMA U rear) has one tubesheet. U-bends take expansion. The bundle pulls for shell-side cleaning. There is no floating-head cover and no second tubesheet. Trade-offs: you cannot rod through the U; individual tube replacement in the bend region is limited; tube-side passes are even-numbered. For many chemical duties that need expansion relief and occasional bundle pull, U-tube is the construction this shop will actually build — not a floating head 'equivalent'.
Comparison for specification
| Need | Fixed tubesheet (± expansion joint) | Floating head (TEMA S/T/W) | U-tube (Ohm manufactures) |
|---|---|---|---|
| Shell-side tightness (no rear tubesheet gasket) | Yes | Gasketed rear assembly | One tubesheet; shell-side gasket at that joint as designed |
| Differential expansion | Joint required if ΔT demands it | Inherent | Inherent (U-bends) |
| Bundle removal / shell-side mechanical clean | No (without cutting shell) | Yes | Yes |
| Tube-side mechanical rod cleaning | Yes, straight tubes, Type A cover | Yes, straight tubes | No through the U |
| Ohm manufacture | Yes | No — buyer-specified TEMA option | Yes |
How to specify without painting the wrong SKU
- If shell side is clean and ΔT is modest: fixed tubesheet.
- If ΔT is large but bundle pull is not required: fixed tubesheet plus expansion joint.
- If bundle must come out and tube side can be chemically cleaned: U-tube.
- If the owner standard requires TEMA S or T: write that explicitly; do not expect a U-tube or bellows substitution without approval.
RFQ language that keeps the rear end honest
State metal-temperature difference (or enough process data to compute it), whether shell-side mechanical cleaning is required, whether tube-side rodding is required, and any frozen TEMA code. Send the pack to /rfq?product=heat-exchangers. For fixed-tubesheet construction see /products/heat-exchangers; for removable U-bundles see /products/heat-exchangers.
RELATED EQUIPMENT FROM OHM ENGINEERS