TEMA DESIGNATIONS OF HEAT EXCHANGERS
Because of the number of variations in mechanical designs for front and rear heads and shells, and for commercial reasons, TEMA has designated a system of notations that correspond to each major type of front head, shell style and rear head. The first letter identifies the front head, the second letter identifies the shell type and the third letter identifies the rear head type.
REMOVABLE BUNDLE EXCHANGERS
Removable bundle exchangers give the customer the ability to replace the tube bundle without replacing the shell or bonnets. They are generally less cost effective than non removable designs.
BEU/AEU- U Bundle Exchangers are generally the most cost effective design style of removable bundle exchanger. Tubes may be water blasted, steam or chemically cleaned.
These units must have an even number of tube passes, sometimes limiting their applicability to a service(e.g. they generally can not be used when a temperature cross occurs).
CEU- This design has the tubesheet welded to the bonnet. You can remove the bundle from the shell, however to replace the bundle, the inlet bonnet is included or you must cut off the tubesheet. Tubes may be chemically cleaned, water blasted or steam cleaned.
BEW/AEW- These are straight tube units with one floating head and one stationary head. The floating head is generally sealed with an O-Ring. These units are most often used as oil coolers or air coolers. Cleaning can be performed either by chemical, mechanical method, water blast or steam cleaning.
AEP/BEP- These are straight tube units with one inside packed floating head and one stationary head. The floating head is generally sealed with packing. These units are most often used as intercoolers and aftercoolers with the gas on the tube side. They are also the most common style for oxygen service exchangers. These units have been used in services with tube side design pressures in excess of 2000 PSIG.
AES/AET- These units are the most expensive of the removable bundle designed units. The floating head is internal to the shell. Tubes can be cleaned mechanically, chemically, water blasted or steam cleaned. The design of these units forces an even number of tube side passes therefore they suffer the same service restrictions as U bundles. Although in theory one pass unit can be designed, this is rarely done. These units are generally used in services where U bundles are not desired and the service may be too corrosive/damaging to the packing used in AEP/BEP units.
NON REMOVABLE BUNDLE EXCHANGERS
These types of units are often used in high pressure services and services where you wish to avoid leakage problems at gasketed joints. Another advantage is that they are generally more cost effective than removable bundle designs.
NEU- The most cost effective design available. The tubesheet is welded to both the shell and bonnet. There is no access to the shell. Tubes may be chemically cleaned, water blasted or steam cleaned from inside only. These units are commonly used in high pressure services (such as feedwater heaters), where process conditions allow for even pass exchangers.
NEN- Tubesheets are welded to both the Shell & Bonnets. Access to the tubes is through covers on the channels. These units are favored in very high pressure designs as their construction minimizes the tubesheet thickness and number of high pressure retaining flanges.
AEM/BEM/AEL-Shell side is completely welded up, however, the bonnets are removable. Chemical, mechanical, and water blast cleaning of the tubes is possible, however you do not have access to the shell.
You should avoid using Steam cleaning on a fixed tube sheet unit unless the unit has a shell side expansion joint. The steam will cause the tubes to expand and pull out of the Tube Sheet causing failure at startup.
Heat Transfer by Heat Exchangers - Shell & Tube
Basic construction of shell and tube Heat Exchangers
Shell and tube Heat Exchangers represent the most widely used vehicle for the transfer of heat in industrial process applications. They are frequently selected for such duties as:
- Process liquid or gas cooling
- Process or refrigerant vapor or steam condensing
- Process liquid, steam or refrigerant evaporation
- Process heat removal and preheating of feed water
- Thermal energy conservation efforts, heat recovery
- Compressor, turbine and engine cooling, oil and jacket water
- Hydraulic and lube oil cooling
- Many other industrial applications
Shell and tube Heat Exchangers have the ability to transfer large amounts of heat in relatively low cost, servicable designs. They can provide large amounts of effective tube surface while minimizing the requirements of floor space, liquid volume and weight.
Shell and tube exchangers are available in a wide range of sizes. They have been used in industry for over 150 years, so the thermal technologies and manufacturing methods are well defined and applied by modern competitive manufacturers.
Tube surfaces from standard to exotic metals with plain or enhanced surface characteristics are widely available. They can help provide the least costly mechanical design for the flows, liquids and temperatures involved.
Fixed Tube Sheet, 2-Pass Heat Exchanger
There are two distinct types of shell and tube Heat Exchangers, based in part on shell diameter. Designs from 2" to around 12" in shell diameter are available that feature shell constructions of low cost welded steel, brazed pipe with hub forgings, cast end Bonnets and copper tubing rolled or brazed to the tube sheet. Models of this type generally use1/4" and 3/8" tubing and are frequently 2 or 4 pass for general industrial use.
The other major type of shell and tube Heat Exchanger generally is seen in shell diameters from 10" to over 100". Commonly available steel pipe is generally used up to 24" in diameter.
Above 24", manufactures use rolled and welded steel plate, which is more costly and roundness can become an issue.
Heat Exchangers of this type are commonly manufactured to the standards set forth by TEMA, the Tubular Exchangers Manufacturers Association. TEMA, in cooperation with users and manufacturers, establishes a common set of guidelines for the construction methods, tolerances and practices to be employed. This allows industrial consumers to obtain more than one manufacturers offerings and know that they are generally of similar design and construction. Additionally, it allows manufactures to establish industry approved designs and offer state of the art equipment that help to assure competitiveness and overall product reliability.
Although there exists a wide variety of designs and materials available, there are components common to all designs. Tubes are mechanically attached to tube sheets, which are contained inside a shell with ports for inlet and outlet fluid or gas.
They are designed to prevent liquid flowing inside the tubes to mix with the fluid outside the tubes. Tube sheets can be fixed to the shell or allowed to expand and contract with thermal stresses by have one tube sheet float inside the shell or by using an expansion bellows in the shell. This design can also allow pulling the entire tube bundle assembly from the shell to clean the shell circuit of the exchanger.
Heat Transfer by Heat Exchangers - Tubes & Tubesheet
Heat Exchanger tubes
Tubing that is generally used in TEMA sizes is made from low carbon steel, copper, Admiralty, Copper-Nickel, stainless steel, Hastalloy, Inconel, titanium and a few others. It is common to use tubing from 5/8" to 1-1/2" in these designs.
Tubes are either generally drawn and seamless or welded. High quality ERW (electro-resistance welded) tubes exhibit superior grain structure at the weld.
Extruded tube with low fins and interior rifling is specified for certain applications. Surface enhancements are used to increase the available metal surface or aid in fluid turbulence, thereby increasing the effective Heat Transfer rate. Finned tubing is recommended when the shell side fluid has a substantially lower Heat Transfer coefficient than the tube side fluid. Finned tubing has an outside diameter in the finned area slightly under the unfinned, or landing area for the tube sheets. This is to allow assembly by sliding the tubes through the baffles and tube supports while minimizing fluid bypass.
U-tube designs are specified when the thermal difference of the fluids and flows would result in excessive thermal expansion of the tubes. U-tube bundles do not have as much tube surface as straight tube bundles, due to the bending radius, and the curved ends cannot be easily cleaned. Additionally, interior tubes are difficult to replace, many times requiring the removal of outer layers, or simply plugging the tube. Because of the ease in manufacturing and service, it is common to use a removable tube bundle design when specifying U-tubes.
TYPICAL U-TUBE BUNDLE
Tubesheets of Heat Exchangers
Tubesheets are usually made from a round flat piece of metal with holes drilled for the tube ends in a precise location and pattern relative to one another. Tube sheet materials range as tube materials. Tubes are attached to the tube sheet by pneumatic or hydraulic pressure or by roller expansion. Tube holes can be drilled and reamed and can be machined with one or more grooves. This greatly increases the strength of the tube joint.
The tubesheet is in contact with both fluids and so must have corrosion resistance allowances and have metalurgical and electrochemical properties appropriate for the fluids and velocities. Low carbon steel tube sheets can include a layer of a higher alloy metal bonded to the surface to provide more effective corrosion resistance without the expense of using the solid alloy.
The tube hole pattern or "pitch" varies the distance from one tube to the other and angle of the tubes relative to each other and to the direction of flow. This allows the manipulation of fluid velocities and pressure drop, and provides the maximum amount of turbulance and tube surface contact for effective Heat Transfer.
TYPICAL TUBE SHEET
Where the tube and tube sheet materials are joinable, weldable metals, the tube joint can be further strengthened by applying a seal weld or strength weld to the joint.
A strength weld has a tube slightly reccessed inside the tube hole or slightly extended beyond the tube sheet. The weld adds metal to the resulting lip.
A seal weld is specified to help prevent the shell and tube liquids from intermixing. In this treatment, the tube is flush with the tube sheet surface. The weld does not add metal, but rather fuses the two materials.
In cases where it is critical to avoid fluid intermixing, a double tube sheet can be provided. In this design, the outer tube sheet is outside the shell circuit, virtually eliminating the chance of fluid intermixing. The inner tube sheet is vented to atmosphere so any fluid leak is easily detected.
To use the data, Preliminary Exchanger Design data must be known, and the Exchanger must be rated.
The following must be known:
(a) Tube Side Pressure - Temperature Rating
(b) The Diameter of the Exchanger
(c) Type of Exchanger, AES, AET, AEM, BEU, etc.
(d) Shell Length and Pressure - Temperature Rating
(e) Number of Couplings and Nozzles
(f) Number of Straight or U-Tubes, the Square Feet of Surface Heating Area, Material Type and Bundle Length
(g) Number and Type of Baffles and Support Plates
(h) Number of Support Saddles if Exchanger is Horizontal, number of Brackets if Exchanger is Vertical and number of Lifting Lugs
(i) ASME Code Stamp and Data Sheet requirements
The data on the following taps is arranged in the above manner.
1. The data in these tables, except for Tubes and Bolting, is based on Carbon Steel Construction using A-53, A-105, A-234, A-285, A-515 and A-516 materials. The prices do not apply to Exchangers fabricated from Alloys or Stainless Steel.
Tube and shell HEAT EXCHANGERS TEMA R (Removable bundle)
- AES Exchanger
- AET Exchanger
- AEM Exchanger
- BEU Exchanger
TEMA DESIGNATIONS OF HEAT EXCHANGERS
Because of the number of variations in mechanical designs for front and rear heads and shells, and for commercial reasons, TEMA has designated a system of notations that correspond to each major type of front head, shell style and rear head.
The first letter identifies the front head, the second letter identifies the shell type and the third letter identifies the rear head type.
The BEU heat exchanger is the ideal choice for heating or cooling low-fouling fluids.
Typical process fluids include water, CIP solutions, milk and beverages.
The U-Tube bundle is attached to a single tubesheet, allowing the tubes to expand and contract freely under the influence of temperature variations. The BEU exchanger is the preferred design when the temperature difference between tube-side and shell-side fluids is high (for instance when the steam is the heating medium).
The tube bundle is removable and allows cleaning of the outside surfaces of the tubes. In the case of tube failure, a replacement bundle that is easily installed into the existing shell assembly can be suppled. The BEU exchanger is generally an economical design as only one tubesheet and waterbox are required. BEU exchangers are manufactured in a wide range of sizes. Each standard BEU meets the latest 3-A Standard and Practice requirements.
Step #1 ESTABLISH DESIGN RATING - using Tube Side Maximum Temperature and Pressure for Process Application, select Design Rating indicated at the top of appropriate column in Step 1.1. Next, determine Base Price of Exchanger from Step 1.2.
Step 1.1 Tube Side Pressure/Temperature Design Rating Chart.
Step 1.2 Base Price for all Types of TEMA Class R Exchangers.
Step 1.3 For Base Price of a Tank Suction Heater, deduct 20% from table above.
2.8 Type L - Rear End Heads - Add to Base Price of Exchanger at cost shown for Type A Front End Head.
2.9 Type M - Rear End Heads - Allowance for Type M Rear End Head included in Base Price of Exchanger.
2.10 Type N - Rear End Heads - Add to Base Price of Exchanger at cost shown for Type C Front End Head.
2.11 Type U - Rear End Heads - (Elliptical Head for U-Tube Exchanger). Allowance for Type U Rear End Head included in base Price of Exchanger.
Step #3 SHELLS - For Types E, F, G, H, J, and X
Step 3.1 Use Shell Side Pressure Rating as basis for selection.
Multiply required Bundle Length x Cost per Lineal Foot and add to Base Price as follows:
Shell Cost Per Lineal Foot of Tube Bundle When Shell Rating Is
Step 3.2 FOR TYPE K SHELLS - (Kettle Type Reboiler) - Refer to Pressure Vessels, and add to Base Price of Exchanger cost for the required Diameter, Thickness, and Length of Transition Section, at 1.5 times the Cost shown for two SE Heads. Do not add for Shop Handling. Continue Estimate from Step #4, below. If Baffles are required in Type K Shells, add from section blow.
Step 3.3 EXPANSION JOINTS - Costs for Expansion Joints (as may be required for Fixed Tube Sheet Exchangers) may be estimated at the cost of 5 Lineal Feet of Shell as shown above.
The prices do not apply to Exchangers fabricated from Alloys or Stainless Steel.
BAFFLES, DRAW-OFF BOXES AND VORTEX BREAKERS
Determine the Square Feet of Plate required and price on a Square Foot basis as follows:
Step #4 ADD COUPLINGS, NOZZLES, AND FLANGES
Step #4.1 COUPLINGS (Screwed) - Forged Steel, in Shell or Heads.
Step #4.2 NOZZLES (Buttweld Flange Type) - in Shell or Heads.
Step #4.3 BLIND FLANGES. For Carbon Steel Blind Flange, Alloy Studs and Gaskets on Nozzles above, add to Base Price of Exchanger as follows:
Step #5 TUBES (For purposes of this Estimation, Disregard Tube Pitch)
All Tube Costs based on Tubes of Domestic Manufacture.
Step 5.1 Straight Tube Exchangers. To Estimate Cost of Tubes for Straight Tube Exchangers:
(a) Multiply required Number of tubes by the figure corresponding to the Tube Diameter and Tube
(b) Calculate Square Feet of Heating Surface of Tubes by multiplying Tube length by Square Feet
per Lineal Foot factor; then multiply by figure under selected Material of Construction.
(c) Take sum of (a) plus (b) and add to Base Price of Exchanger.
Step 5.2 U-Tube Exchangers. To Estimate Cost of Tubes for U-Tube Exchangers:
(a) Multiply required Number of tubes by the figure corresponding to the Tube Diameter and Tube Side Rating:
(b) Calculate Square Feet of Heating Surface of Tubes and multiply by figure under selected Material of Construction.
To Estimate the Square Feet of Heating Surface of U-Tubes, first consider the Bundle Length x 2 (two legs of the "U"). Multiply this product by the Square Feet per Lineal Foot factor for
U-Tubes from following page (Step 5.2 continued), then multiply by the number of Bundles required.
To allow for Bends in U-Tubes, multiply Diameter of Tube x 2.5 (Radius of Bend) x 2; multiply this product by the Square Feet per Lineal Foot factor. Multiply this product by the number of bundles
required, and add this number to the Square Feet of the two legs of the "U".
Example: 3/4" U-Tubes, 10' Bundle Length, 269 Bundles, Square Feet per Lineal Foot factor 0.1963 10' Bundle length x 2 = 20'; 20' x 0.1963 Square Feet per Lineal Foot factor = 3.926 Square Feet per Tube; 3.296 Square Feet x 269 Bundles = 1,056.09 Square Feet Heating surface of Tubes.
0.75" Diameter of Tube x 2.5 = 1.875 (Radius of Bend); 1.875 x 2 = 3.75; 3.75 x 0.1963 = 0.736 Square Feet; 0.736 Square Feet x 269 Bundles = 197.98 Square Feet allowance for Bends.
1,056.09 Square Feet heating Surface of Legs + 197.98 Square Feet Heating Surface of Bends = 1,254.07, say 1,254 Square Feet Total Heating Surface of Tubes.
(c) Take sum of (a) plus (b) and add to Base Price of Exchanger.
Step 5.3 Tubes Welded to Tube Sheet
If Tubes are welded to Tube Sheet, add per Tube as follows:
ADD PER TUBE.
Step 5.4 Tubes - Minimum Wall Gauges
Minimum Wall Gauge Used In All Cost Data Above
Step #6 BAFFLES AND SUPPORT PLATES
Step #6.1 (a) Transverse Baffles and Support Plates
Costs above include Tie Rods and Spacers.
(b) Longitudinal Baffles - for Longitudinal Baffles add $13.50 per Square Foot of Baffle.
Step #7 SUPPORT SADDLES, SUPPORT BRACKETS, AND LIFTING LUGS
Step #8 ASME CODE
(a) For fabrication in accord with ASME Code, no Additive or Deductive.
(b) For ASME Code Stamp and Data Sheets, add $400.00.
Step #9 ESTIMATED WEIGHTS OF HEAT EXCHANGERS
The following may be used to estimate the weight of TEMA R Shell and Tube Heat Exchangers. The Exchanger weight is calculated as the number of Square Feet of Heating Surface in the Exchanger multiplied by the Pounds given below.
The table below shows Estimated Average Weight range for TEMA R Exchangers in Pounds per Square Foot of Heating Surface.
When the equipment is received at the project site, it will be necessary to unload, inspect, transport to point of installation, install, and perform the cleanup work occasioned by the foregoing.
The Direct Labor Manhours required for the work described may be estimated as follows:
How to calculate Mhs Installation:
- Estimate the Manhours for installing a Shell & Tube Heat Exchanger that weighs 5.6 Tons.
5.6 Tons (18.0) Manhours
5.6 Tons x (1.5) Manhours = (8.4) Manhours
Total for a 5.6 Ton Exchanger (26.4) Manhours
- Estimate the Manhours for installing a Shell & Tube Heat Exchanger that weighs 22 Tons.
15 Tons (41.0) Manhours
7 Tons x (1.2) Manhours = (8.4) Manhours
Total for a 22 Ton Exchanger (49.4) Manhours
The Manhours above assume the transporting distance will not be in excess of 200'0" and that site
or other obstructions do not exist.
- MANHOURS EXTENSION TO DETERMINE DIRECT LABOR COST FOR INSTALLATION
The Manhours should be extended by a Composite Crew Rate determined from the Wage Rates in effect at the project site.
28" Diameter Type BEU Exchanger, TEMA Class R; Tube Side 250 PSI @ 650°F; Shell Side 400 PSI @ 650 F; One Each 2", One Each 6" and Two Each 8", 300# RF Nozzles; 269 Each 3/4" diameter 14 Gauge A-214 U-Tubes 10'0" Bundle Length; 1,254 Square Feet Surface Heating area; Four Each Support Plates; Two Each Support Saddles; ASME Code Stamp and Data Sheets Required.
20" Diameter Type AEM Exchanger, TEMA Class R, Tube Side 250 PSI @ 150°F; Shell Side 250 PSI @ 150°F; Two Each 6" and Two Each 8" 150# RF Nozzles; 336 Each 3/4" Diameter 14 Gauge A-214 Straight Tubes 20'0" Bundle Length; 1,320 Square Feet Heating Surface Area; 19 Each 3/4 Cut Segmental baffles; Two Each Support Saddles; ASME Code Stamp and Data Sheets Required.
20" Diameter Type AET, TEMA Class R, Two Pass Exchanger; Tube Side 250 PSI @ 150°; Shell Side 250 PSI @ 150°F; Two 4" and Two 12" 150# RF Nozzles; 188 Each 3/4" 14 Gauge A-214 Straight Tubes 30'0" Bundle Length; 1,108 Square Feet Heating Surface Area; 29 Each 3/4 Cut Baffles; Two each Support Saddles; ASME Code Stamp and Data Sheets Required.