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The Tubular Exchanger Manufacturers Association (TEMA) classifies shell and tube heat exchangers into three main designations based on service conditions, mechanical robustness, and industry requirements:

1. TEMA Class R – Refinery & Severe Service

Applications:

• Oil refineries, petrochemical plants, high-pressure/high-temperature (HPHT) services.
• Harsh environments (corrosive fluids, fouling, thermal cycling).

Key Features:
Heavy-duty construction (thicker shells, reinforced tube sheets).
Strict tolerances for leakage prevention.
Removable bundle designs (for easy cleaning/maintenance).
High-pressure ratings (ASME Div 1 or Div 2 compliance).

Common Configurations:

• AES (Front-end stationary head, single-pass shell, rear-end floating head).
• BEM (Bonnet-type front head, fixed tube sheet, single-pass shell).

2. TEMA Class C – Commercial & General Service

Applications:

• HVAC, power plants, food processing, light chemical industries.
• Moderate pressure/temperature, non-corrosive fluids.

Key Features:
Cost-effective (lighter construction than Class R).
Simpler fabrication (fewer stringent requirements).
Fixed or floating tube sheet designs.

Common Configurations:

• NEN (Channel-type front head, fixed tube sheet, single-pass shell).
• AEP (Front-end stationary head, single-pass shell, rear-end packed floating head).

3. TEMA Class B – Chemical Process Service

Applications:

• Chemical processing, pharmaceuticals, aggressive media (acids, solvents).
• High corrosion risk, frequent thermal cycling.

Key Features:
Balanced between Class R & C (better corrosion resistance than Class C).
More stringent than Class C but not as heavy as Class R.
Often uses exotic materials (titanium, Hastelloy, duplex SS).

Common Configurations:

• BKU (Bonnet-type front head, U-tube bundle, single-pass shell).
• AEW (Front-end stationary head, floating head with backing device).

Comparison Table: TEMA Classes R, C, and B

Parameter	TEMA Class R	TEMA Class C	TEMA Class B
Service Conditions	Severe (HPHT, fouling)	Moderate (general-purpose)	Corrosive/cyclic
Construction Cost	Highest	Lowest	Medium
Maintenance	Removable bundles common	Fixed tube sheets common	Depends on design
Typical Industries	Oil & gas, refineries	HVAC, power plants	Chemical, pharma
Example Configs	AES, BEM	NEN, AEP	BKU, AEW

TEMA Nomenclature Breakdown (Example: AES, BEM, NEN, etc.)

TEMA uses a 3-letter code to describe exchanger types:

1. First Letter → Front Head Type
   1. A: Channel with removable cover (most common).
   1. B: Bonnet (integral cover, lower cost).
   1. N: Channel integral with tube sheet.
2. Second Letter → Shell Type
   1. E: Single-pass shell.
   1. F: Two-pass shell.
   1. G: Split flow (for horizontal thermosiphon reboilers).
3. Third Letter → Rear Head Type
   1. S: Floating head (removable bundle).
   1. T: Fixed tube sheet.
   1. U: U-tube design.

Example:

• AES = Removable front channel (A) + single-pass shell (E) + floating head (S).
• BEM = Bonnet front head (B) + single-pass shell (E) + fixed tube sheet (M).

When to Use Which TEMA Class?

• Class R → Refineries, high-pressure steam, fouling fluids.
• Class C → Low-cost HVAC, water cooling, non-corrosive duties.

Class B → Chemical plants, corrosive/thermal cycling services.