A shell-and-tube exchanger can meet the specified heat duty while leaving a practical question unresolved: can the plant clean and maintain the surfaces that will need attention?
Choose the design by matching cleaning access, differential-expansion requirements and maintenance space. A fixed-tubesheet arrangement can provide straight-tube cleaning access but restricts access outside the tubes. A removable floating-head arrangement provides another maintenance route; U-tubes require a suitable bend-cleaning method. Confirm the actual construction and mechanical assessment before selecting the complete exchanger.
The comparison below separates those decisions and explains where kettle and pull-through arrangements fit. The aim is a configuration the project can justify from its operating requirements and maintenance plan.
Start with the Configuration, Not Just the Design Name
Fixed tubesheet, U-tube and floating head describe different arrangements of the tubes and their end restraints. Kettle and pull-through describe other aspects of the equipment, so they should not be treated as five mutually exclusive choices.
TEMA nomenclature separates the front head, shell and rear end. This lets a specification describe the assembly more precisely than a general product name. TEMA nomenclature chart
| Design name | What it describes | What to establish before selection |
|---|---|---|
| Fixed tubesheet | Straight tubes between tubesheets restrained by the shell in the common welded construction | Tube-end access and the acceptability of a non-removable bundle |
| U-tube | Tubes return through U-bends to one tubesheet | Bend cleaning and whether the specified assembly is removable |
| Floating head | One tubesheet can move relative to the shell | The particular floating-head closure and maintenance arrangement |
| Pull-through floating head | A floating-head arrangement that can pass through the shell with the bundle | Withdrawal route and the clearance needed by that assembly |
| Kettle | A shell arrangement associated with boiling service | Reboiler duty, shell geometry and the separately selected bundle/end construction |
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The first four distinctions are visible in the manufacturer’s construction drawings; the word “removable” should still be confirmed on the offered design. API Basco brochure, configuration drawings
Keep kettle reboilers in the comparison when the process needs reboiling. They are not the automatic answer to every phase-change duty: thermosiphon reboilers are another established arrangement. Alfa Laval, shell-and-tube reboilers
Compare Tube-Side and Shell-Side Cleaning Access
For a fixed tubesheet vs floating head heat exchanger comparison, identify the fouling side first. A conventional fixed-tubesheet exchanger with accessible straight-tube ends can be mechanically cleaned inside the tubes. Its principal access limitation is outside the tubes, within the shell. The fixed bundle cannot simply be withdrawn to expose those surfaces. SPE, exchanger types and fluid allocation
| Construction under consideration | Tube-side access | Shell-side access | Procurement check |
|---|---|---|---|
| Fixed tubesheet, straight tubes, removable end closures | Tube interiors accessible after opening the appropriate closures | No routine bundle withdrawal for external tube cleaning | Show the end-opening arrangement and proposed shell-side maintenance method |
| Removable U-tube bundle | Straight legs accessible; the return bend prevents straight-through rigid rodding | Tube exteriors exposed after withdrawal, subject to bundle geometry | Confirm a method that reaches the bends and the required outer surfaces |
| Removable straight-tube floating-head bundle | Straight-tube interiors accessible after the required disassembly | Tube exteriors exposed after withdrawal, subject to bundle geometry | Identify the exact closure, disassembly route and cleaning lanes |
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These are access descriptions, not guarantees of deposit removal. Manufacturer drawings distinguish fixed, U-tube and floating-head assemblies. API Basco configuration drawings
Specify the required result separately from the method. For example, ask whether a proposed method can remove the expected deposit from the required surfaces and how the contractor will verify the result. A statement that an exchanger can be chemically cleaned does not answer whether a mechanical tool can reach its tube exteriors. Chemical compatibility and deposit response also need project-specific confirmation.
Avoid ranking designs by “fouling resistance” when the intended comparison is cleanability. Easier access describes maintenance capability; it does not establish how quickly deposits will form in the proposed service.
Assess Differential Expansion Across the Operating Cases
Fixed-tubesheet suitability requires a mechanical assessment of the shell and tube system. It cannot be decided from material names or a single difference between fluid inlet temperatures.
A floating end permits axial movement relative to the shell, while U-bends accommodate tube expansion through their geometry. Fixed tubesheets restrain that relative movement, so the resulting loads need evaluation. API Basco construction drawings
The relevant temperatures include the metal temperatures of the tubes and shell. Chemstations’ technical manual explicitly identifies these as inputs for mechanical stress analysis of fixed-tubesheet exchangers. Matching materials does not establish matching metal temperatures or equal thermal growth. Fluid temperatures alone do not supply the complete mechanical input. Chemstations CC-THERM manual, shell-side and tube-side data
Ask the design team to document:
- Temperatures and materials: the basis for shell and tube metal temperatures and the material properties used in the calculation.
- Geometry and restraint: the specified assembly, dimensions and any proposed expansion provision.
- Operating cases: normal duty and the relevant startup, shutdown, upset or cleaning conditions, with their associated pressures.
- Acceptance basis: the project design code, edition and purchaser requirements used to judge the result.
Codeware’s design documentation illustrates why multiple conditions matter: exchanger assessment may include upset, shutdown and steam-out cases, not just the normal rating point. Its modeling scope also includes the tubesheets, shell, tubes, expansion joint and connected pressure-containing parts. Codeware design conditions, Codeware modeling
An expansion joint is a design option to evaluate, not an automatic approval for a fixed-tubesheet proposal. IOGP’s 2018 S-614 guidance directs consideration of floating-head or U-tube construction when the differential-temperature stress limits cannot be met with fixed tubesheets. Its project-specific restrictions should not be converted into universal selection thresholds. IOGP S-614, Annex D.5.2.3
Accordingly, request the calculation basis before accepting “the materials match” or “the temperature difference is small” as a selection justification.
Check How the Bundle Will Be Removed and Serviced
A removable bundle is useful only if the installed layout supports its removal and subsequent work. Require a maintenance arrangement drawing alongside the equipment outline.
Floating-head designs differ here. A pull-through head can travel through the shell with the bundle; a split-ring arrangement requires additional rear-end disassembly. API Basco’s BET and AES drawings show this distinction. Neither description means that the exchanger can be opened without releasing the applicable connections. API Basco brochure, BET and AES arrangements
For the proposed installation, ask the supplier and maintenance team to mark:
- Opening space: where covers and heads move, and which connected items must be disturbed.
- Withdrawal space: the extraction direction, required clear length and any obstructions.
- Handling arrangements: assembly weights, lifting access and the intended laydown area.
- Work space: where cleaning, inspection and approved repairs can actually take place.
Do not stop the review at the shell opening. Tube layout and supports can restrict access between tubes after removal. IOGP S-614 specifically addresses keeping cleaning lanes clear of tie rods and spacers in square or rotated-square layouts. This is a useful drawing-review question even when that specification is not the project’s contractual basis. IOGP S-614, 7.5.3.6
Also request a proposed repair approach. For example, establish what access would be needed to inspect or replace damaged tubes and what disassembly would precede that work. “Removable bundle” alone is not a complete maintenance specification.
Compare Complete-Equipment Proposals on the Same Basis
Use the access and expansion reviews to narrow the candidates, then compare complete exchangers against one common duty and maintenance brief. A design label is not enough to establish the best purchase.
The following is a screening framework, not a final engineering selection:
| Project requirement | Candidate to investigate | Evidence to request before acceptance |
|---|---|---|
| Straight-tube cleaning is required, but shell-side mechanical access is unnecessary | Fixed tubesheet | Acceptable expansion assessment and a credible shell-side maintenance plan |
| Shell-side access is required and the proposed tube-side method can handle bends | Removable U-tube arrangement | Confirmed removability and bend-cleaning capability |
| Straight-tube access and bundle removal are both required | Removable floating-head arrangement | Exact head construction, extraction drawing and sealing details |
| The duty requires reboiling | Kettle or another suitable reboiler arrangement | Thermal basis and a separately justified bundle/maintenance configuration |
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These questions follow the access distinctions above; they are not claims that one configuration is suitable for every fluid in a category.
Include the sealing arrangement in the comparison. An internal floating-head gasket is a different interface from an external closure or packing arrangement. Ask where leakage could travel, how the selected design would be inspected, and what testing is required after maintenance. Do not assign one leakage probability to every floating-head design. API Basco, floating-head construction details
For quotations, issue the same fluid data, flow rates, inlet and outlet requirements, allowable pressure drops and design cases to each bidder. Request a clear list of inclusions, exclusions and required site provisions. Then assess the quoted equipment price together with the proposed maintenance route and the plant’s own outage assumptions. Avoid unsupported cost percentages or a universal “cheapest-to-best” ranking.
For a broader purchasing checklist, see the shell-and-tube heat exchanger selection guide. Keep the final evaluation tied to the offered drawings and documented design basis.
Frequently Asked Questions
Does a removable channel cover mean the bundle is removable?
No. Opening a channel cover provides access at the tube end; it does not establish how the bundle connects to the shell. TEMA’s nomenclature distinguishes head arrangements from the rear-end construction. Check both on the equipment drawing. TEMA nomenclature chart
Can specialized equipment clean inside U-bends?
Specialized methods exist, so “U-tubes cannot be mechanically cleaned” is too broad. For example, a cleaning-equipment manufacturer describes projectiles designed to travel around U-bends. This does not prove suitability for every tube geometry or deposit: have the proposed cleaning provider confirm compatibility and the method of checking completion. Projectile Tube Cleaning, U-tube cleaning
Does a TEMA configuration designation prove code compliance?
No. The designation identifies the construction arrangement. Compliance requires assessment against the specified design rules and project requirements; it is not established by the three-letter label. Request the applicable edition and supporting design documentation with the offer. TEMA nomenclature chart, Codeware, design-code evaluation
Choose the Maintenance Route Before Finalizing the Exchanger
Select the configuration only after the proposed cleaning method, expansion assessment and installed maintenance space agree. Ask for the drawings and design basis that demonstrate that fit.
For a complete-equipment inquiry, review the shell-and-tube heat exchanger product page and send your project requirements, including both fluids, operating cases, cleaning expectations and available maintenance space.
References
- Tubular Exchanger Manufacturers Association (TEMA). Heat Exchanger Nomenclature. Public nomenclature chart; publication year not stated. Used for construction terminology, not verification of the complete TEMA Standards.
- API Heat Transfer. BASCO Engineered Shell & Tube Heat Exchangers. File revision R4; publication year not confirmed. Configuration drawings on PDF pages 8–10.
- Society of Petroleum Engineers / JPT. Static Equipment: Understanding Heat Exchangers. July 17, 2019. Sections on fluid allocation and exchanger types.
- Chemstations. CC-THERM Shell & Tube User’s Guide and Tutorial. Version 5.6, 2006. Shell-side and tube-side data discussion, printed pages 49–50.
- Codeware. Modeling Heat Exchangers in COMPRESS and Multiple Heat Exchanger Design Conditions. Pages dated May 21, 2026.
- IOGP JIP33. S-614: Supplementary Specification to API Standard 660, Shell-and-Tube Heat Exchangers. Version 1.0, December 2018. Section 7.5.3.6 and informative Annex D.5.2.3. Cited as published guidance, not as a declaration of project compliance.
- Alfa Laval. A Reboiler for the Space Age. Reprinted from Hydrocarbon Engineering, November 2003; PPI00056EN 0311. Shell-and-tube reboiler discussion.
- Projectile Tube Cleaning, Inc. Cleaning UTube Heat Exchangers. Publication year not confirmed. Cited only for the existence of a specialized U-bend cleaning method.
