Section 8 — Heat Transfer Equipment

Double Pipe Heat Exchangers

IPE Engineering Practice IPE-EP-8-1-5

Document number: IPE-EP-8-1-5 · Section: 8 — Heat Transfer Equipment

SCOPE

• This Engineering Practice governs the general requirements for the design, fabrication, and materials for double–pipe and multi–tube heat exchangers for use in process services.
• This Practice, in general, governs the requirements that are unique to the design of double pipe and multi–tube heat exchangers and must be used in conjunction with EP 7–1–1 which covers the requirements for pressure vessels constructed per the ASME Code, Section VI II, Division 1.
• Any deviation to this Practice or Practices referenced herein must be approved by the procedures described in EP 1–1–3.
• An asterisk (*) indicates that a decision by the Owner or Owner’s Engineer is required, or that additional information is furnished by the Purchaser.
• Supplemental requirements for double pipe and multi–tube heat exchangers are covered in EP 7–1–4.
• A revision bar indicates all changes made to this Revision.

2.0 REFERENCES

The latest edition of the following documents are referred to herein.

STANDARDS AND PUBLICATIONS

DEFINITIONS

• Aggressive Environmental Service (AES) – Process services which result in material degradation such as cracking, scaling, blistering, and severe pitting and/or corrosion. Examples of such services are hydrogen service, wet hydrogen sulfide, cyanides, caustic, amine, and hydrofluoric acid. AES process fluid are defined in EP 10–2–1.
• Contractor – Company or business that agrees to furnish materials or perform specified services at a specified price and/or rate to the Owner.
• Hydrogen Rich Service – A service defined as a combination of hydrogen partial pressure and temperature at or below the curve for carbon steel per Figure 1 of API Publication 941, latest edition, and with a hydrogen partial pressure greater than 100 psia.
• Hydrogen Service – A service defined as a combination of hydrogen partial pressure and temperature above the curve for carbon steel per Figure 1 of API Publication 941, latest edition.
• Inspector – A Inflection Point Engineering, LLC appointed engineer or inspector.
• Manufacturer – The recipient of a direct or indirect purchase order for materials and/or equipment. In this context, a direct order is one issued to a Manufacturer by a Contractor or the Owner. An indirect order is one issued to a Manufacturer by a vendor (recipient of a direct order) for materials, fabricated components, or subassemblies.
• MAWP – Maximum Allowable Working Pressure.
• Owner – Inflection Point Engineering, LLC.
• Owner’s Engineer – A Inflection Point Engineering, LLC appointed engineer.
• Purchaser – The party placing a direct purchase order. The Purchaser is the Owner’s designated representative.

DATA SHEET, DOCUMENTATION AND PURCHASING REQUIREMENTS

• Data Sheet of EP 8–1–5 DS, spare parts and documentation requirements for double pipe and multi–tube heat exchangers shall be in accordance with EP 7–1–1, EP 7–1–4, and the additional requirements of this Practice.

PROCESS REQUIREMENTS

• Water shall be on the tube side of multi–tube coolers and condensers. Design velocities shall be 4.5–8 ft/s with admiralty tubes and 5.5–10 ft/s with carbon steel tubes.
• Tube metal exposed to cooling water shall be kept below 140ºF to prevent scale deposit of inorganic compounds on the heat transfer surface.

DESIGN AND CONSTRUCTION

• General
• Design requirement for double pipe and multi–tube heat exchangers shall be in accordance with EP 7–1–1 and the additional requirements of this Practice.

• The Manufacturer shall be responsible for the mechanical and thermal design.
• The shell–to–tube closure and the tube side closure shall not have a common flange or common bolting. A separated head type of design shall be used.
• All flange joints shall be through–bolted.
• The effective tube wall and fin metal resistance shall be considered in calculating the heat transfer coefficient.
• Bolts between connecting nozzles of stacked exchangers shall be supplied and shall be removable without moving the exchangers.
• Fouling factors given on the Data Sheet of EP 8–1–5 DS are net. Tube side values shall be increased by the ratio of the outside to the inside surface areas when sizing the heat exchanger.
• Materials
• Materials requirements for primary pressure boundary components shall be per EP 7–1–1. Additional material requirements for Aggressive Environmental Services are stipulated in EP 10–2–1.
• (*) Fins shall be essentially the same material as the tube element. Approval from the Owner’s Engineer is required to use unlike materials (e.g., aluminum or steel fins on brass tubes).
• Tubes
• Tube design, material and selection requirements shall be in accordance with EP 8–1–9 and the additional requirements of this Practice.
• Multi–tube bundles or the inner pipe of double pipe units shall be removable without cutting the shell or connecting piping and without disconnecting the shell piping.
• Fins shall be longitudinal and may be attached either by welding, high–temperature brazing, or mechanical bonding. The minimum thickness of the fins shall be 0.035 inch for carbon steel and 0.02 inch for non–ferrous materials.
• (*) The maximum tube length shall be 20 feet, unless otherwise approved by the Owner’s Engineer.
• (*) “Cores” or turbulence promoters inside tubes are acceptable only with approval by the Owner’s Engineer and only in services with a tubeside fouling factor of 0.001 hr–ft2–ºF/Btu or less.
• Multi–tube units using straight tubes with packed joints may be used in non–flammable services up to 150 psig or 300ºF.
• When the fouling service is on the shellside, the tube layout must be on a square pitch with a minimum of 1/4 inch cleaning lanes.
• Nozzles and Other Connections
• The requirements for nozzle and nozzle flanges and all other connections for double–pipe and multi–tube heat exchangers shall be in accordance with EP 7–1–1, unless otherwise specified by this Practice.

• Selection rating, facing, and gasketing requirements for flanges on nozzles shall be in accordance with EP 5–2–2. The design pressure and temperature used to establish the flange rating shall be the design conditions stipulated in EP 7–1–1.

• One NPS 1 inch instrument connection shall be provided in each nozzle, and shall be in accordance with EP 7–1–1.
• (*) Chemical cleaning connections shall be provided at the inlet and outlet of exchangers in cooling water service, or when specified by the Owner’s Engineer. For exchanger nozzles less than NPS 4 inch, chemical cleaning connections shall be installed in the connecting piping in accordance with EP 5–1–2.
• Chemical cleaning connections, when specified, shall be NPS 1–1/2 inch connections for nozzles NPS 4 inch or NPS 6 inch, and NPS 2 inch connection shall be provided on NPS 8 inch or larger nozzles.
• Nozzle minimum thickness requirements are as given in EP 7–1–1.
• 90º long radius ells with flanges shall be welded to the tube side stub ends on each exchanger bank inlet and outlet.
• Connections Between Sections
• The Manufacturer shall provide all required manifolds.
• Stub ends, connectors, and adapters shall be of the same material as the mating part. Wall thicknesses shall be in accordance with EP 7–1–1.
• Gaskets
• Gasket materials shall be in accordance with EP 5–2–2.
• Return bend housing closures shall have confined gasketed joints (e.g. tongue and groove type) when the shell size is NPS 4 inch or larger and the MAWP is over 300 psig. Confined gasketed joints are required on all shell sizes for shell side MAWP’s over 500 psig. Solid metal or soft steel double jacketed, graphite filled gaskets shall be used.
• Two spare sets of gaskets shall be furnished with each section.

FABRICATION

• General

Fabrication requirements for multi–tube and double pipe heat exchangers shall be in accordance with EP 7–1–1 and the additional requirements of this Practice.

• Subcontracted Work
• (*) Written approval shall be obtained from the Owner’s Engineer before any welding, preparation for welded fabrication, or forming is subcontracted to others.
• The Owner’s Engineer’s approval will cover the extent of the work to be subcontracted and the qualifications of the subcontractor under consideration.
• Tube Installation

Tube installation, tube–to–tubesheet joint design, and fabrication requirements shall be in accordance with EP 8–1–8.

• Welding

Welding shall be in accordance with EP 7–1–1.

• Heat Treatment (Stress Relieving)
• Heat treatment shall be in accordance with EP 7–1–1.

• Heat treatment requirements for tube joint welds and the tube U-bends shall be in accordance with EP 8–1–8 and EP 8–1–9, respectively.

INSPECTION AND TESTING

• General

Inspection and testing requirements shall be in accordance with EP 7–1–1, EP 8–1–8, and the additional requirements of this Practice.

• Hydrostatic Test
• Hydrostatic testing shall be in accordance with EP 7–1–1 and the additional requirements of this Practice.
• (*) When multiple sections are furnished, the Manufacturer shall assemble and hydrostatically test the entire unit (including any required manifolds). The entire unit shall be shipped assembled unless approved by the Owner’s Engineer.

© 2026 Inflection Point Engineering, LLC. All rights reserved.