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

Various heat exchanger design codes are also available for shell and tube heat exchangers and are used worldwide for different industries. The shell and tube heat exchanger is by far the most commonly used type of heat-transfer equipment used in the chemical and allied industries. The advantages of this type are:

  1. The configuration gives a large surface area in a small volume
  2. Good mechanical layout: a good shape for pressure operation
  3. Uses well-established fabrication techniques
  4. Can be constructed from a wide range of materials
  5. Easily cleaned
  6. Well-established design procedures.

Shell-and-tube heat exchanger types

Essentially, a shell and tube exchanger consists of a bundle of tubes enclosed in a cylindrical shell. The ends of the tubes are fitted into tube sheets, which separate the shell-side and tube-side fluids. Baffles are provided in the shell to direct the fluid flow and support the tubes. The assembly of baffles and tubes is held together by support rods and spacers.

The principal types of shell and tube heat exchanger are:

  • U-tube heat exchanger
    The U-tube heat exchange (U-bundle) requires only one tube sheet and is cheaper than the floating-head types; but is limited in use to relatively clean fluids as the tubes and bundle are difficult to clean. It is also more difficult to replace a tube in this type.
  • Fixed tube heat exchanger
    This is the simplest and cheapest type of shell and tube heat exchanger. The main disadvantages of this type are that the tube bundle cannot be removed for cleaning and there is no provision for differential expansion of the shell and tubes. As the shell and tubes will be at different temperatures, and may be of different materials, the differential expansion can be considerable and the use of this type is limited to temperature differences. Some provision for expansion can be made by use including a Flexible Shell Element Expansion Joint.
  • Floating heat exchanger
    These exchangers contain an internal floating head and are more versatile than fixed head and U-tube exchangers. They are suitable for high-temperature differential and, as the tubes can be rodded from end to end and the bundle removed, are easier to clean and can be used for fouling fluids. A disadvantage of the pull through floating head design (TEMA Type S & T), is that the clearance between the outermost tubes in the bundle and the shell must be made greater than in the fixed and U-tube designs to accommodate the floating-head flange, allowing fluid to bypass the tubes. The clamp ring (split flange design), is used to reduce the clearance needed. There will always be a danger of leakage occurring from the internal flanges in these floating head designs.
    In the outside packed floating head designs (TEMA Type P), the floating-head joint is located outside the shell, and the shell sealed with a sliding gland joint employing a stuffing box. Because of the danger of leaks through the gland, the shell-side pressure in this type is usually limited to about 20 bar, and flammable or toxic fluids should not be used on the shell side.

Shell-and-tube heat exchanger design codes

The most commonly used codes and standards are summarised in the table below. It contains the most important distinguishing features of the individual codes.

EN 13445 serieASME BPVC Section VIII Div. 1TEMA® StandardAPI Standard 660
Scope and LimitsNo LimitsNo limitsInner Dia ≤ 2540 mm = 100 in.;
Design Pressure (P) ≤ 3000 psi = 20,7 MPa;
Product: Dia·P ≤ 100000 psi·in = 17,5 ·106 MPa·mm;
Shell wall thickn. ≤ 3 in = 76 mm;
Stud dia ≤ 102 mm = 4 in.;

Applications: heaters, condensers, coolers, and reboiler for the petroleum, petrochemical, and natural gas industry;
The minimum outside diameter of the
tubes shall be 19,05 mm (0.75 in.);
Nomenclature/TerminologyEN 13445-3, Clause 13.2Par. UHX-3Section 1Section 3
Loading casesFor fixed tube sheet heat exchangers
Annex I.1;
Par. UHX-12.4: U-Tube Tubesheets HE;
Par. UHX-13.4: Fixed Tubesheet HE;
Par. UHX-14.4: Floating Tubesheet HE;
Design of heat exchangers (HE)EN 13445-3/ Clause 13.4: U-tube HE
EN 13445-3/ Clause 13.5: Fixed tube HE
EN 13445-3/ Clause 13..6: Floating HE
Par. UHX:
U-Tube Tubesheets HE;
Fixed Tubesheet HE; Floating Tubesheet HE;
Section 5 (with references to the construction code ASME BPVC Section VIII Div. 1):
U-Tube HE;
Fixed Tube HE;
Floating Tube HE;
Comply to used Design Pressure Vessel Code;
TEMA Class R;
TEMA types “P” (Outside packed
floating head) and “W” (Externally
sealed floating tubesheet) are not
allowed.
Tube sheet designEN 13445-3/
Annex J: Alternative Design for tube sheets
Par. UHX-12: (U-Tube Tubesheet HE);
Par.UHX-13 (Fixed Tubesheet HE);
Par. UHX-14 (Floating Tubesheet HE);

App. 20 (hub);
ASME BPVC Section VIII Div. 1
or alternatively TEMA Appendix A
Par. 7.5.2
Flexible Shell Element Expansion JointEN 13445-3/ Clause 14Par. UHX-17;
Appendix 5;
Appendix 26 (for light gauge bellows with wall thickness t ≤ 5mm);
Section RCB-8:
for bellows with wall thickness t > 5mm;

if required EJMA Rules for light gauge bellows with wall thickness t ≤ 5mm
Specific requirements for expansion joints such as life cycle, liner requirement;

EJMA for light gauge bellows with wall thickness t ≤ 5mm
Thermal RelationSection 7
Flow induced vibrationSection 6Annex A A.3.2;
Installation, Operations and MaintenanceEN 13445-5/Clause 5
Technical documents & Operating instructions
Section 4
Preparation for ShipmentSection 3/G-6;Par. 11
MarkingEN 13445-5/Clause 11
Name plate incl. CE-Marking
UHX-19
Name plate incl.
ASME Certification stamp with U-designation
Data SheetEN 13445-5/Clause 5
Technical documents
UHX-19.3
Manufacturer’s Data Report
Section 3Par. 5/Annex C;

EN 13445 serie

This is the European standard for unfired pressure vessels and is harmonised as a standard under the European Pressure Equipment Directive (PED) and meets the essential safety requirements (ESR) (Annex I of the PED). In acc. to PED, all heat exchangers are classified as unfired pressure vessels according to diagrams 1 to 4 of PED. The highest category of the two pressure chambers is decisive for the classification of the heat exchanger. As a rule, a notified body (Third party) is involved in the certification process.

The EN 13445 series contains comprehensive regulations on materials, design, fabrication, testing, marking and documentation of shell-and-tube heat exchangers.

ASME BPVC Section VIII Div. 1

ASME BPVC Section VIII Div. 1 is a is an American Society of Mechanical Engineers (ASME) standard provide the single largest source of technical data used in the manufacturing, construction, and operation of boilers and unfired pressure vessels including shell-and-tube heat exchangers. Section VIII Div. 1 provides requirements applicable to the design, fabrication, inspection, testing, and certification of pressure vessels operating at either internal or external pressures exceeding 15 psig.
The manufacturer must provide an ASME certified Quality Assurance system and be authorised to affix the ASME certification symbol together with the U-Designator.

TEMA® standard

The TEMA® Standard is published by the TEMA® an association of manufacturers of shell and tube heat exchangers. The First Edition was published in 1941. Many shell and tube exchangers ordered by the process industries and for other high-severity applications throughout the world are built to TEMA® standard. TEMA would be used in conjunction with the design code for pressure vessels.

API Standard 660

This standard specifies requirements and gives recommendations for the mechanical design, material selection, fabrication, inspection, testing, and preparation for shipment of shell-and-tube heat exchangers for the petroleum, petrochemical, and natural gas industries and is applicable to the following types of shell-and-tube heat exchangers: heaters, condensers, coolers, and reboilers. API Standard 660 would be used in conjunction with the design code for pressure vessels.

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The EN 13445 series comprises European standard for unfired pressure vessel

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