TEMA® is a trade association of the world’s leading manufacturers of shell and tube heat exchangers. TEMA has developed standards that define the design, fabrication, tolerances, installation and maintenance of shell-and-tube type heat exchangers. The TEMA standard defines the main configuration of exchangers and the classification for usage in the industry. This standard and the ASME code are the main governance used to design and fabricate exchangers along with any customer specifications.

The TEMA® standards have achieved worldwide acceptance as the authority on shell and tube heat exchanger mechanical design.

Criteria to ensure the highest level of technical expertise, which gives TEMA® members a meaningful advantage when designing or fabricating heat exchangers.

Before a company can even become a member of TEMA®

• Must have a minimum of 5 years of continuous service in the manufacture, design, and marketing of shell and tube heat exchangers. 
• All TEMA® companies must have in-house thermal and mechanical design capabilities, thoroughly understand current code requirements, and initiate strict quality control procedures.
• All welding must be done by the company’s own personnel, and the company must have its own quality control inspectors.

TEMA® Standard

The TEMA Standard includes 10 sections, covering nomenclature through to the physical properties of fluids used in shell and tube heat exchangers.

1. Nomenclature
2. Fabrication Tolerances
3. General Fabrication and Performance Information
4. Installation, Operation, and Maintenance
5. Mechanical Standards TEMA Class RCB Heat Exchangers
6. Flow Induced Vibration
7. Thermal Relations
8. Physical Properties of Fluids
9. General Information (for example: pipe, tube, fitting and flange dimensions; pressure-temperature ratings; conversion factors)

Scope of the TEMA standard

The TEMA Mechanical Standards are applicable to shell and tube heat exchangers which do not exceed any of the following criteria:

1. inside diameter of 100 in. (2540 mm);
2. product of nominal diameter, in. (mm) and design pressure, psi (kPa): 100000 in.• psi
   (17.5• 10⁶ mm•kPa = 17,5 • 10³ mm•MPa);
3. a design pressure of 3000 psi (20684 kPa = 20,684 MPa = 206,8 bar);

The intent of these parameters is to limit the maximum shell wall thickness to approximately 3 in. (76 mm), and the maximum stud diameter to approximately 4 in. (102 mm).

Criteria contained in these TEMA Standards may be applied to units which exceed the above parameters.

Three classes of mechanical standards

Three classes of mechanical standards, C, R, and B, reflecting acceptable designs for various services are applicable:

TEMA Class	Definition	Notes
C	Specify design and fabrication of unfired shell and tube heat exchangers for the generally moderate requirements of commercial and general process applications.	This is the least restrictive, and therefore the most commonly used type of exchanger and have the lowest requirements among the TEMA classifications. These shells and tubes are typically used in such as water heating, air conditioning, and process heat transfer. They are suitable for fluids that are nonvolatile, non-toxic, and non-corrosive, and that have moderate fouling and thermal expansion.
R	Specify design and fabrication of unfired shell and tube heat exchangers for the generally severe requirements of petroleum and related processing applications
B	Specify design and fabrication of unfired shell and tube heat exchangers for chemical process service

Construction Codes

Unless otherwise specified, the individual vessels shall comply with the ASME BPVC Section VIII, Division 1.

TEMA Nomenclature

TEMA has specified not just a set of standards for heat exchanger manufacturing, but also designated a notation system. There are many mechanical design variations for front heads, rear heads and shells, so the notations identify the major varieties to create clarity.

The first letter corresponds to the front head, the second to the shell type and the third to the rear head type (see picture below):

Advantages and limits for any types of heat exchangers

Type	Design	Advantages	Limits	Applications
Removable Bundle, Internal Split Ring Floating Head AES BES	These designs are recommended when frequent tube bundle removal is necessary. They are more favourable to thermal shock than AEW or BEW designs and they are also suitable for volatile or toxic fluids;	Floating head design allows thermal expansion; Higher heat transfer surface area than pull-through designs (AET or BET Types); Available to multiple passes on tube side;	Shell cover, split ring and floating head cover must be removed to remove the tube bundle, which results in higher maintenance costs;	Chemical processing applications for toxic fluids; Special gas after coolers and intercoolers;
Straight Tube and Fixed Tube Sheet BEM AEM AEL NEN	This design is the simplest design and usually more economical. The tube sheet is welded to the shell, while heads are bolted to the tube sheet.	More economical than removable bundle designs; ‘ Capable of multiple pass designs;	Chemical solution is need to clean the shell side; No capacity to absorb thermal expansion between the outer shell and tube bundle;
Removable Bundle, Pull Through Floating Head; AET BET	These types of design are the best option for applications when frequent tube bundle removal is necessary because  the floating head is bolted directly to the floating tube sheet. This allows the bundle to be pulled at the same with the head.	Floating head design allows thermal expansion Shell side can be inspected and mechanically cleaned; Large shell side nozzle entrance area for proper distribution over the bundle; Multiple tube side passes available; Suitable for volatile or toxic fluids;	General industrial applications requiring frequent cleaning; Chemical processing applications for toxic fluids; Hydrocarbon fluid condensers;	Optimal for steam to liquid applications; Chemical, oil and water heating applications;
Removable Bundle, U-tube BEU AEU	This design is recommended for high thermal shock applications, as each tube can expand and contract independently and u-tube bundles are normally very economical. It is usually the best option for maximum thermal expansion applications	U-tube design allows differential thermal expansion between the shell and the tube bundle as well as between individual tubes; Capacity to handle high thermal shock applications; More economical design for removable bundles; Shell side can be inspected and mechanically cleaned; Bundle can be removed from one end for cleaning or replacement; Multiple tube side passes are available;		Optimal for steam to liquid applications; Chemical, oil and water heating applications
Removable bundle; externally sealed floating sheet; AEW BEW	this design allows for the removal, inspection and cleaning the shell circuit and shell interior; A special floating tube sheet prevents intermixing of fluids, a straight tube design is more economical than u-tube design;	Floating tube sheet allows differential thermal expansion between the shell and the tube sheet bundle; Shell circuit can inspected and either steam- or mechanically cleaned; The tube bundle can be repaired or replaced without disturbing the shell pipe; Less costly than TEMA types BEP or BES which have an internal floating head; Maximum surface for given shell diameter for removable bundle design; Tubes can cleaned in AEW model without removing piping;	Fluids in both the shell and tube circuits must be non-volatile and nontoxic; Tube side passes are limited to single or two-pass design; All tubes are attached to two tube sheets. Tube cannot expand independently, so large thermal shock application should be avoided; Packing materials produce limits on design pressure and temperature;	Intercoolers and after coolers, air inside the tubes; Coolers with water inside the tubes; Jacket water coolers other other high differential temperature duty; Place hot side fluid through the shell with entry nearest the front end;

Read More

Shell-and-tube heat exchangers: Applicable Codes and Standards