Shell and Tube Heat Exchangers: TEMA Types, Configurations & Selection Guide

A heat exchanger marked "BEM" on the data sheet is a bonneted, single-pass shell, fixed tubesheet exchanger — the cheapest design in the TEMA catalog and the workhorse of clean-service process piping. A unit marked "AES" is a removable bonnet, single-pass shell, floating-head split-ring design — the refinery standard for fouling service that needs mechanical cleaning on both sides. The three letters of a TEMA designation tell an experienced engineer almost everything they need to know about the exchanger: how it disassembles, what fluids it suits, how it handles thermal expansion, and roughly what it costs.

For procurement engineers, EPC contractors, and project managers specifying shell and tube heat exchangers — getting the TEMA designation right is critical. A BEM in a service that needs an AES will foul up and lose performance within a year. An AES in a service that would have run fine in a BEM costs significantly more without delivering value. The selection decision happens once at specification, and it sets the operating cost, maintenance cost, and service life of the exchanger for decades.

This guide covers the complete TEMA designation system, the practical differences between the three main configuration families (fixed tubesheet, floating head, U-tube), and the selection criteria that determine which TEMA type belongs in which service. For complete background on shell and tube vs plate heat exchangers, see our Shell & Tube vs Plate Heat Exchanger comparison and the broader Heat Exchangers pillar guide.

The TEMA Designation System

The Tubular Exchanger Manufacturers Association (TEMA) created the three-letter classification system in 1941 to standardize how shell and tube heat exchangers are specified, ordered, and inspected. The system has been refined through nine editions of the TEMA Standards (most recent: TEMA 10th Edition, 2019) and is now the universal language of shell and tube heat exchanger procurement.

A complete TEMA designation looks like this:

TEMA Type [Front Head Letter][Shell Letter][Rear Head Letter]

Each letter identifies a specific design feature:

• First letter — Front-end stationary head type (channel configuration)

• Second letter — Shell type (flow pattern and baffle arrangement)

• Third letter — Rear-end head type (how the rear tubesheet handles thermal expansion)

For example, AES decodes as:

• A — Channel and removable cover (front head)

• E — Single-pass shell

• S — Floating head with backing device (rear head)

A complete specification also includes nominal shell diameter (in inches), nominal tube length (in inches), and tube bundle configuration. Example: "AES 27-240" means TEMA Type AES with 27-inch shell diameter and 240-inch tube length.

Front Head Types (First Letter)

The front head is where the tube-side fluid enters the exchanger. Different front head types offer different combinations of access, cost, and pressure rating.

A-type (channel with removable cover) is the most common front head for refinery and process service. The cover can be removed without disturbing the tube-side piping, providing access to the tube ends for cleaning, plugging defective tubes, or inspection.

B-type (bonnet) is the simplest and lowest-cost front head. The entire bonnet must be removed to access the tubes — which means disconnecting the tube-side piping. For services where tube inspection is infrequent (clean fluids, lubricating oil, condensate), the cost saving of a B-type justifies the access penalty.

Shell Types (Second Letter)

The shell type determines how the shell-side fluid flows through the exchanger.

E-type (single-pass shell) is the standard shell configuration. The shell-side fluid enters at one nozzle, flows across the tubes guided by transverse baffles, and exits at the opposite nozzle. This is what most engineers picture when they think of a shell and tube exchanger.

K-type (kettle reboiler) has an enlarged shell diameter with vapor disengagement space at the top. Liquid enters the shell, partially vaporizes on the tubes, and the vapor leaves through a top nozzle while unvaporized liquid recirculates. K-type is the standard for distillation column reboilers in refineries.

Rear Head Types (Third Letter)

The rear head is where the most consequential design decisions happen. The rear head determines:

• How the exchanger handles differential thermal expansion between shell and tubes

• Whether the tube bundle can be removed for shell-side cleaning

• The overall cost and complexity of the unit

Fixed Tubesheet Rear Heads

The rear tubesheet is welded directly to the shell, so the bundle cannot be removed.

Fixed tubesheet advantages:

• Lowest cost design

• Maximum tube count for given shell diameter (no clearances needed for bundle removal)

• Simple construction

• No internal gaskets to leak

Fixed tubesheet limitations:

• Tube bundle cannot be removed — shell side cannot be mechanically cleaned

• Differential thermal expansion between shell and tubes creates stress

• Often requires a shell expansion joint to absorb thermal expansion (adds cost and a potential failure point)

• Steam cleaning typically not recommended without expansion joint

Floating Head Rear Heads

The rear tubesheet "floats" inside the shell, free to move axially with thermal expansion. The bundle can be removed for cleaning.

S-type floating head (split-ring) is the most common design for refinery and petrochemical service where thermal expansion must be accommodated and shell-side cleaning is required. The tube bundle can be removed; the shell side can be cleaned mechanically or chemically.

T-type floating head (pull-through) has the simplest maintenance — the entire bundle can be pulled out through the shell as a single unit. Higher cost than S-type because the floating head diameter is smaller than the shell (creating dead annulus space and reducing tube count).

P-type and W-type use packing or gasket seals on the floating tubesheet. These are limited to non-toxic, non-volatile fluids because the packing/gasket can leak.

U-Tube Rear Head

A single tubesheet at the front; the tubes themselves are bent into U-shapes that turn around and return to the same tubesheet.

U-tube advantages:

• Allows unlimited differential thermal expansion (U-bend can flex)

• Removable bundle (slides out the front)

• No floating head gasket or packing — no internal leakage path

• Lower cost than floating head designs

• Tight tube-to-shell clearances possible

U-tube limitations:

• Tube-side cleaning is difficult (mechanical cleaning tools cannot pass through U-bends)

• Suitable only for clean tube-side fluids

• Replacement of individual tubes is complicated (must access through tubesheet)

• Tube count slightly lower than fixed tubesheet (U-bend takes space)

The Most Common TEMA Configurations

Although TEMA allows hundreds of combinations, only a handful are commonly used in industry. These are the ones you'll see most often:

BEM — The Workhorse

Decoded: Bonnet front + single-pass shell + fixed tubesheet rear (bonneted)

Configuration: Both front and rear heads are bonnets. Single-pass shell. Tubesheets welded to shell (fixed).

Pros:

• Lowest cost in the TEMA catalog

• Maximum tube count for given shell diameter

• Simple construction

• No floating gasket — no internal leakage

Cons:

• Shell side cannot be mechanically cleaned (bundle is fixed)

• Differential thermal expansion limited (may need shell expansion joint)

• Tube-side cleaning requires disconnecting both ends of piping

Best for: Clean fluid services with moderate temperature differential. Common in HVAC, lube oil cooling, refinery utility systems, and any application where the shell-side fluid is clean and the tube-side fluid is clean.

AES — The Refinery Standard

Decoded: Channel with removable cover front + single-pass shell + floating head with backing device

Configuration: A-type front head (channel cover removable without disturbing piping). E-type shell (single pass). S-type rear (split-ring floating head — bundle removable for cleaning).

Pros:

• Both tube-side and shell-side can be mechanically cleaned

• Floating head accommodates differential thermal expansion

• Standard refinery configuration — widely manufactured, parts available

• Suitable for fouling fluids

• Suitable for hazardous fluids (no packing or external gaskets)

Cons:

• Higher cost than BEM (typically 25-40% premium for carbon steel construction)

• Larger physical size for given duty

• Internal split-ring requires careful assembly

Best for: Refinery process service (crude preheat, distillation column overheads, hydrocarbon coolers), petrochemical plants, any application with fouling service that requires shell-side cleaning. The default specification for refinery process duties.

BEU — The Thermal Cycling Specialist

Decoded: Bonnet front + single-pass shell + U-tube bundle rear

Configuration: B-type front head (bonnet). E-type shell. U-tube bundle (only one tubesheet at the front; tubes bend around and return).

Pros:

• Handles unlimited differential thermal expansion (U-bend flexes)

• Lower cost than floating head designs

• Removable bundle (slides out front)

• No floating head gasket

• Tight bundle-to-shell clearances

Cons:

• Tube-side cleaning is difficult (mechanical cleaning cannot pass through U-bends)

• Suitable only for clean tube-side fluid

• Individual tube replacement is complicated

• Tube count slightly lower than fixed tubesheet

Best for: Steam reboilers, hot oil heaters, applications with high thermal cycling (steam coming on and off, batch processes), and any service where the tube-side fluid is clean enough not to require mechanical cleaning. Common in power plant feedwater heaters and refinery hot oil systems.

AEL — The Fixed Tubesheet with Tube Access

Decoded: Channel with removable cover front + single-pass shell + fixed tubesheet rear (with channel cover)

Configuration: A-type front (channel cover removable). E-type shell. L-type rear (channel cover with fixed tubesheet — allows tube-side access from both ends).

Pros:

• Lower cost than floating head

• Mechanical cleaning possible on tube side from both ends

• Maximum tube count

Cons:

• Shell side cannot be mechanically cleaned

• Thermal expansion limited

• Requires expansion joint for significant temperature differentials

Best for: Tube-side fouling fluids with clean shell-side fluids. Common in cooling water applications where the tube-side cooling water is the fouling fluid and the shell-side is clean process fluid.

NEN — The High-Pressure Specialist

Decoded: Integral front head + single-pass shell + integral rear head

Configuration: Both tubesheets welded to the shell. Channel access through bolted covers on each end.

Pros:

• Suitable for very high pressures (Class 1500, 2500 and above)

• Minimum tubesheet thickness (no large gasket faces)

• Fewer high-pressure flanges to leak

Cons:

• Shell side cannot be cleaned

• Tube cleaning requires removing channel covers on both ends

• Higher manufacturing complexity

Best for: High-pressure hydrogen service, high-pressure gas processing, reactor effluent coolers in refineries, any service at Class 1500+ pressure ratings.

AET — Pull-Through Floating Head

Decoded: Channel with removable cover front + single-pass shell + pull-through floating head

Configuration: A-type front. E-type shell. T-type rear (pull-through floating head — bundle pulls out as one piece).

Pros:

• Easiest maintenance among floating head designs

• Bundle pulls out without disassembling rear head

• Excellent for frequent cleaning

Cons:

• Higher cost than S-type

• Reduced tube count (floating head diameter smaller than shell)

• Larger physical size

Best for: Critical service requiring frequent shell-side cleaning, applications where minimizing maintenance downtime matters.

TEMA Configuration Selection Matrix

Fixed Tubesheet vs Floating Head vs U-Tube: The Big Decision

Among all the TEMA configurations, the most consequential decision is the rear head family. Here's a head-to-head comparison:

The Selection Logic

Choose fixed tubesheet (BEM/AEM/AEL/NEN) when:

• Both fluids are clean (no shell-side cleaning needed)

• Temperature differential between shell and tubes is moderate

• Budget is the priority

• Maximum tube count for given shell diameter is needed

• High pressure (NEN especially) is the priority

Choose floating head (AES/AET/BES/BET) when:

• Shell-side fluid is fouling and requires mechanical cleaning

• Significant thermal expansion expected

• Refinery or petrochemical service standard

• Both sides may need cleaning

Choose U-tube (BEU/AEU) when:

• High thermal cycling (steam systems, hot oil heaters)

• Tube-side fluid is clean

• Cost is a concern (cheaper than floating head)

• Shell-side cleaning preferred but no internal gaskets desired

Materials of Construction

The TEMA designation specifies the configuration, but materials must be specified separately. Common combinations:

Shell-Side Materials

For complete coverage of stainless plate materials, see Stainless Steel Plate: Grades 304, 316, 321. For carbon steel plate options, see Carbon Steel Plate: ASTM A516 & A36.

Tube Materials

Tube-to-Tubesheet Joint

The tube-to-tubesheet joint is critical for leak prevention. Options:

• Expanded — tube mechanically expanded into tubesheet hole; simple, lower cost

• Welded — tube welded to tubesheet face; higher integrity, leak-proof

• Expanded + welded — both methods combined; maximum reliability for high-pressure or critical service

• Hydroexpansion — high-pressure hydraulic expansion; produces uniform contact

For high-pressure and critical service, expanded + welded is standard.

Expansion Joints in Shell and Tube Heat Exchangers

For fixed tubesheet designs (BEM, AEM, AEL, NEN), differential thermal expansion between shell and tubes can generate significant stress. When the temperature differential exceeds approximately 50°C for typical carbon steel construction, a shell expansion joint is often required.

The expansion joint is a bellows-type element welded into the shell, allowing axial movement to absorb thermal expansion. For complete coverage, see Expansion Joints: Types, Materials & Applications.

Trade-off: Fixed tubesheet with expansion joint is still typically cheaper than floating head, but the expansion joint adds:

• Material and fabrication cost

• A potential failure point (bellows can crack from fatigue)

• Additional inspection requirements during shutdowns

For services with high thermal cycling, U-tube (BEU) often outperforms fixed tubesheet with expansion joint — the U-bend handles unlimited expansion with no added components.

TEMA Service Classes

In addition to the three-letter type, TEMA specifies three service classes that determine construction quality:

TEMA R (refinery class) has the most stringent requirements — heaviest construction, tightest tolerances, most rigorous inspection. Required for refinery process piping.

TEMA B (chemical process class) is the most common modern specification. Construction is robust but not as conservative as R.

TEMA C (commercial class) allows lighter construction and is suitable for general commercial applications.

Most industrial heat exchangers in modern specifications use TEMA Class R or TEMA Class B.

Sizing Information for Specification

When specifying a shell and tube heat exchanger, the following information is needed:

Process Information

• Hot fluid: name, flow rate, inlet temperature, outlet temperature, properties (viscosity, density, specific heat, thermal conductivity)

• Cold fluid: same parameters

• Operating pressure (shell side and tube side)

• Design pressure (shell side and tube side)

• Maximum operating temperature

Mechanical Specification

• TEMA type (e.g., AES)

• TEMA class (R, C, or B)

• Shell diameter (nominal, e.g., 24")

• Tube length (nominal, e.g., 240")

• Tube outside diameter and wall thickness (e.g., 25.4mm × 2.11mm)

• Tube pitch and pattern (triangular, square)

• Baffle type (segmental, helical) and spacing

• Number of tube passes (1, 2, 4, 6, 8)

Materials

• Shell material

• Tube material

• Tubesheet material

• Bolting material

• Gasket material

Other Requirements

• Code compliance (ASME Section VIII Div 1, etc.)

• Hydrostatic test pressure

• Insulation requirements

• Connection types (flanged with size and rating)

• Inspection requirements (NACE, customer-specific)

Common Specification Mistakes

After 15+ years supplying shell and tube heat exchangers to refinery, petrochemical, and process projects:

Mistake 1: Specifying BEM Where AES Is Needed

A buyer specifies a BEM for cost reasons, but the shell-side fluid is fouling. Within 1–2 years, shell-side fouling reduces heat transfer to 60% of design. The exchanger must be removed from service and chemically cleaned (limited effectiveness) or replaced. Total cost over service life: 2–3× the original AES cost.

Prevention: If shell-side fluid causes fouling, specify AES or AET regardless of initial cost.

Mistake 2: Specifying Floating Head for Clean Service

A buyer specifies AES because "it's the refinery standard," but both fluids are clean. The result: 25–40% higher capital cost than equivalent BEM with no operational benefit.

Prevention: For clean services (both sides), specify BEM or AEM. Save the AES specification for fouling service.

Mistake 3: BEU in Fouling Tube-Side Service

A buyer specifies BEU for thermal cycling but the tube-side fluid fouls. Within 18 months, tube-side fouling reduces heat transfer. Mechanical cleaning is impossible (U-bends block cleaning tools). Chemical cleaning is the only option, with limited effectiveness.

Prevention: BEU requires clean tube-side fluid. If tube side fouls, specify AES or AET instead.

Mistake 4: Missing Expansion Joint

A buyer specifies BEM for high-temperature service but omits the shell expansion joint. Within months, differential thermal expansion cracks the tubesheet weld or pulls tubes out of the tubesheet.

Prevention: For BEM/AEM with shell-tube temperature differential >50°C in carbon steel construction, specify shell expansion joint.

Mistake 5: Wrong TEMA Class

A buyer specifies TEMA Class C (commercial) for refinery service. The lighter construction is inadequate for hydrocarbon service. The unit fails inspection or operates with reduced safety margin.

Prevention: Match TEMA class to service. Refinery → R. Chemical → B. General → C.

Supply from Kasko Makine

Kasko Makine supplies shell and tube heat exchangers for refinery, petrochemical, power generation, oil and gas, chemical processing, and industrial applications:

TEMA configurations:

• All standard configurations: BEM, AEM, AEL, AES, AET, BEU, AEU, NEN, AKU, BKU, AXM

• Custom configurations per customer specification

• TEMA Class R, B, or C as specified

Sizing range:

• Shell diameter: 150mm to 2,500mm

• Tube length: 1m to 12m

• Heat duty: 50 kW to 50+ MW

Materials:

• Shell: A516 Gr 70 carbon steel, A387 alloy steel, A240 stainless steel, A240 duplex

• Tubes: A179/A192 carbon steel, A213 stainless steel, B111 Cu-Ni alloys, B338 titanium, A789 duplex

• Tubesheets: Carbon steel, stainless, clad, or full-alloy as required

Code compliance:

• ASME Section VIII Div 1 (with U-stamp where required)

• TEMA Standards 10th Edition (2019)

• PED (Pressure Equipment Directive) for European projects

• Other codes as required (e.g., GOST for Russia/CIS)

Documentation per shipment:

• ASME U-1A data sheets (for code-stamped units)

• Material test certificates (EN 10204 Type 3.1)

• Welding procedure qualifications (WPQ)

• Welder performance qualifications

• Non-destructive examination reports (RT, UT, PT, MT as applicable)

• Hydrostatic test certificates

• Final assembly drawings

• Thermal performance test reports

Engineering services:

• Thermal and mechanical design per ASME and TEMA

• Vibration analysis

• Stress analysis for high-temperature service

• Materials selection per process conditions

• Performance optimization for specific duties

Need a shell and tube heat exchanger? Send us your duty (kW), fluid types, flow rates, inlet/outlet temperatures, pressure, fouling factors, and any TEMA preference to info@kaskomakine.com or WhatsApp +90 (537) 521 1399. Our thermal design team will recommend the optimal TEMA configuration, materials, and sizing, and provide a detailed quotation within 48 hours. We deliver to projects across Africa, the Middle East, Central Asia, and beyond.

Continue Reading: Heat Exchanger Series

• Heat Exchangers: 6 Types, Working Principles & Selection Guide — The master pillar covering all heat exchanger types

• Shell & Tube vs Plate Heat Exchanger — Comparison guide for choosing between the two main types

• Expansion Joints: Types, Materials & Applications — Critical accessory for fixed tubesheet exchangers

• Stainless Steel Plate: Grades 304, 316, 321 — Materials for corrosion-resistant heat exchangers

• Carbon Steel Plate: ASTM A516 & A36 — Pressure vessel plate for standard heat exchanger construction

FAQ SCHEMA

Q: What does the TEMA designation BEM mean?
A: BEM is a TEMA Type designation for a shell and tube heat exchanger with a Bonnet front head, single-pass E-type shell, and fixed-tubesheet M-type rear head. BEM is the lowest-cost shell and tube configuration, suitable for clean fluid services with moderate thermal stress. It is widely used in HVAC, lube oil cooling, refinery utility systems, and general process applications where shell-side cleaning is not required.

Q: What is the difference between BEM, AES, and BEU heat exchangers?
A: BEM has a fixed tubesheet (no bundle removal, lowest cost, clean service). AES has a floating head with split-ring backing device (removable bundle, mechanical cleaning both sides, refinery standard for fouling service). BEU has U-tube bundle (handles unlimited thermal expansion, clean tube-side service, common in steam reboilers and hot oil heaters). The choice depends on cleaning requirements, thermal stress, and budget.

Q: When should I use a floating head heat exchanger?
A: Specify a floating head TEMA type (AES, AET, BES, BET) when the shell-side fluid is fouling and requires mechanical cleaning, when significant thermal expansion is expected, and when refinery or petrochemical service is the application. Floating head designs cost 25-40% more than fixed tubesheet for carbon steel construction but enable shell-side cleaning that fixed tubesheet designs cannot provide.

Q: What is the difference between fixed tubesheet, floating head, and U-tube?
A: Fixed tubesheet has both tubesheets welded to the shell — lowest cost, no bundle removal, limited thermal expansion. Floating head has a free-moving rear tubesheet — removable bundle, handles thermal expansion, suitable for fouling service. U-tube has only one tubesheet at the front and U-shaped tubes — removable bundle, handles unlimited thermal expansion, suitable for clean tube-side fluids only.

Q: What TEMA configuration should I use for refinery service?
A: AES is the standard refinery configuration. The A-type front head allows tube-side access without disturbing piping. The E-type shell provides standard flow. The S-type floating head with split-ring backing device handles thermal expansion and allows the bundle to be removed for shell-side cleaning. AES is suitable for fouling hydrocarbon service typical of refinery process applications.

Q: What is TEMA Class R, B, and C?
A: TEMA Class R is for refinery service — most stringent construction with heaviest materials and tightest tolerances. TEMA Class C is for commercial service — lighter construction for general applications. TEMA Class B is for chemical process service — robust construction suitable for chemical industry use. Most modern industrial specifications reference Class R or Class B. Match the class to the service severity.

Q: When do I need an expansion joint in a fixed tubesheet heat exchanger?
A: For BEM, AEM, AEL, and NEN heat exchangers, a shell expansion joint is typically required when the temperature differential between shell-side and tube-side fluids exceeds approximately 50°C in carbon steel construction. The expansion joint absorbs differential thermal expansion to prevent stress cracking. For services with high thermal cycling, U-tube (BEU) designs often outperform fixed tubesheet with expansion joint because U-bends handle unlimited expansion with no added components.