Heat Exchanger Tube Selection Guide: Material, ASTM Standard, Wall Thickness and Inspection

Choose heat exchanger tubes by checking four things together: the operating environment, the approved tube specification, the ordered wall basis and the tube-to-tube sheet interface. A familiar grade and an outside diameter are not enough to compare quotations. Before releasing an order, reconcile the design drawing, the supplier offer and the inspection plan against the same requirements.

This guide covers tubing for shell-and-tube exchangers and condensers. It helps buyers prepare and review a purchase specification; equipment sizing and pressure-boundary approval remain with the responsible designer. It uses the public technical sources listed at the end, and the contract edition and approved engineering documents govern each order.

Where are you in the selection process?

Tube selection is rarely one decision. Start with the question that is still open, then work through the numbered stages that follow.

For replacement work, use the existing heat exchanger retubing specification guide to collect the equipment records. A worn sample alone cannot reliably establish the original ordered wall or material condition.

1. Collect service data before choosing a tube material

Material selection for heat exchanger tubes starts with the environments on both sides of the tube wall. Record both tube-side and shell-side fluids, normal and design temperatures, pressures, differential-pressure cases, contaminants, deposits and cleaning methods. Include shutdown and upset conditions: a material acceptable during normal circulation may face a different environment when stagnant or chemically cleaned.

For water service, record chloride content, treatment chemicals and the location of deposits rather than writing only “cooling water.” For process service, identify the actual chemical composition and concentration range. Give the materials reviewer the failure history when one exists.

Figure 1. Shell and tube exchanger components and the tube wall separating the two fluids. Schematic, not to scale.

Alleima’s published exchanger examples show why material selection needs the specific environment: its hydrochloric-acid service discussion compares corrosion performance for defined alloys and conditions, rather than treating all stainless steels as equivalent (Alleima material selection article).

Tube material families to review: carbon steel, stainless steel, duplex and specialist alloys

Use the following shortlist as a review sequence, not an automatic alloy selector.

Do not attach one universal chloride limit or maximum operating temperature to a whole material family. For example, Alleima’s SAF 2707 HD data discusses a particular grade, test environment and tube-to-tube sheet arrangement. Those results do not approve every duplex tube for every seawater duty.

2. Match the ASTM tube standard to the approved manufacturing route

For a heat exchanger tube inquiry, identify the product standard and manufacturing route before requesting availability. A product standard defines a tube category. It does not approve the complete exchanger, establish the heat duty or make a different manufacturing route an acceptable substitution.

ASTM A179, A214, A213, A249 and A789 compared

Scope references: ASTM A179, ASTM A214, ASTM A213, ASTM A249 and ASTM A789.

Read the scopes together. A179 and A214 address carbon steel tubes by manufacturing route (seamless cold-drawn and electric-resistance-welded). A213 covers seamless alloy and stainless grades, and A249 covers the welded austenitic route. A789 applies to ferritic/austenitic (duplex) stainless tubing. The choice between standards is therefore a choice of material family and manufacturing route, and neither is better in general.

Read the applicable general requirements and purchase-order options with the product standard. Do not substitute general-service pipe or tubing solely because the alloy name matches. Our A213 versus A249 comparison addresses the seamless-versus-welded decision in more detail.

For exchanger construction, state the governing equipment requirements and edition separately. TEMA’s current standards page describes its 2026 edition and updated exchanger specification sheet. A new edition on a website is a reason to check the contract, not to silently change an existing project’s requirements.

3. Specify tube wall thickness: BWG, minimum wall and average wall

Order tube outside diameter, wall thickness, wall basis, length and tolerances explicitly. Pipe NPS and schedule are not a substitute for exchanger-tube dimensions.

What a BWG number means for a tube order

BWG (Birmingham Wire Gauge) numbers are a common way to talk about exchanger tube wall. The gauge is a label for a thickness, so the order should also state the corresponding thickness and units. The nominal values below are for orientation only; the tolerance and acceptance basis come from the ordered product standard.

Source for gauge values:ProjectMaterials tube gauge reference.

Minimum wall versus average wall

Figure 2. Tube dimensions and the distinction between local minimum wall and average wall assessment. Schematic, not to scale.

Minimum-wall ordering controls a lower wall acceptance limit under the applicable specification; average-wall ordering uses a different dimensional acceptance basis. The order must name the intended basis rather than leaving the supplier to infer it. ASTM A213/A213M allows minimum wall or, when specified in the order, average wall. ASTM A789/A789M describes average wall thickness or, if specified in the order, minimum wall thickness. The default wording therefore differs from A213; copying only the grade and thickness can leave the intended acceptance basis unclear. Confirm the actual tolerance rules for the selected product and dimensions instead of applying one percentage to all tubes.

Worked example: why the wall basis changes a quotation

Assume, solely for this example, that an approved requirement calls for at least 1.50 mm wall at acceptance and that a proposed average-wall offer permits a 10% negative variation. The assumed percentage is not an ASTM tolerance quoted by this article.

• An offer of 1.50 mm average wall could permit 1.50 × 0.90 = 1.35 mm.

• Under that assumed tolerance, the nominal wall would need to be at least 1.50 ÷ 0.90 = 1.667 mm to preserve a 1.50 mm lower limit.

• Selecting a suitable ordered thickness still requires confirmation of the actual standard, rounding, available size and approved drawing.

This arithmetic only compares an assumed purchase tolerance with an acceptance threshold. It is not a pressure-design calculation. It shows why two offers reading “1.50 mm tube” may be commercially incomparable.

Keep corrosion allowance and manufacturing tolerance as separate entries in the design review. A buyer cannot resolve an inadequate design wall by relabelling an average-wall order as minimum wall.

4. Check the tube as part of the bundle: tubesheet fit and U-bends

Review the tube drawing with the tubesheet and fabrication drawing before approving a substitution. Confirm straight or U-bent configuration, straight length or developed length, bend geometry, end projection, hole fit and the specified expanded, welded or combined joint.

Changes in tube outside diameter or wall alter the bore. They can affect fluid velocity, pressure drop, cleaning access and the tube-to-tubesheet procedure. A thicker tube is therefore not an automatic replacement upgrade.

For U-tubes, identify who performs bending and which dimensional checks, heat treatment and examinations are required after bending. Evidence for the original straight tube does not, by itself, demonstrate the final bent component’s condition.

The practical interface check is simple: every proposed material or geometry change needs an owner. Ask who approves corrosion compatibility, thermal performance, pressure integrity and fabrication fit. Record the approvals against a drawing revision rather than resolving them only in email descriptions.

5. Agree what each inspection result must demonstrate

Figure 3. Dimensions, traceability, specified examination and inspection records form complementary purchase evidence. Schematic, not to scale.

Nondestructive examination (NDE) and pressure testing provide different evidence. “100% tested” does not state the method, sensitivity, coverage or acceptance criteria. Specify the examinations required by the ordered standard and project inspection plan, including any additional tests that the buyer requests.

Do not assume eddy-current testing, ultrasonic testing and hydrostatic testing establish the same condition. The required test combination must follow the product specification and purchase order; a certificate saying “pass” should be traceable to that scope.

6. Compare supplier offers through a deviation register

Price comparison becomes useful after technical differences are visible. Ask each supplier to mark every requirement as compliant, excluded or proposed for approval.

What to attach to a heat exchanger tube RFQ

A usable request for quotation (RFQ) attaches the following. Require a separate deviation list; silence should not be interpreted as acceptance.

1. Equipment data sheet and tube drawing, with revision

2. Material and product specification, with editions

3. Ordered dimensions: OD, thickness with units, wall basis, tolerances and length

4. Quantity by length and, for U-tubes, bend requirements

5. Fabrication scope and tube-to-tubesheet joint details

6. Inspection plan and documentation requirements

7. Delivery basis

For a supply enquiry, send Forever Steel the approved specifications and quantity schedule. Availability, manufacturing route, inspection scope and delivery are confirmed against the inquiry.

Heat exchanger tube selection FAQ

What is the difference between ASTM A179 and ASTM A213 tubes?

ASTM A179 covers seamless cold-drawn low-carbon steel exchanger and condenser tubes, while ASTM A213 covers seamless ferritic and austenitic alloy-steel boiler, superheater and exchanger tubes [3][5]. The decision depends on the approved material family and route, so check the ordered grade and edition against the design specification.

Is seamless tubing always the better selection?

The approved service, grade, manufacturing route and examination requirements determine acceptability. ASTM A213 covers seamless tubes and ASTM A249 covers welded austenitic tubes; a purchasing decision should not replace the designer’s approval with a general “seamless is better” rule.

Is a BWG number enough to order exchanger tubing?

No. Include the actual thickness, units, ordered wall basis and applicable tolerances, together with OD, length and product specification.

Minimum wall or average wall: which should the order specify?

The one the approved design requires. Minimum-wall and average-wall ordering use different acceptance bases, and a copied grade and thickness can leave the basis unclear. Name it in the order.

Can I replace heat exchanger tubes with a thicker wall?

Not automatically. A thicker wall changes the bore, which can affect fluid velocity, pressure drop, cleaning access and the tube-to-tubesheet procedure. Get the change approved against a drawing revision.

Can 316L solve every cooling water corrosion problem?

No. Assess the actual chemistry, temperature, deposits, cleaning and stress conditions. Retubing with a familiar grade without diagnosing the damage can repeat the original problem.

Which inspection records should come with heat exchanger tubes?

Typically a material certificate, dimensional report, nondestructive examination and hydrostatic test records where required, final fabrication records for U-tubes, and packing and marking records. The required set follows the product specification and purchase order.

What should be checked before accepting a cheaper tube offer?

Reconcile material and route, minimum acceptable wall, dimensions, final fabrication condition, tests, traceability and delivery scope. Record exclusions before treating the prices as equivalent.

Conclusion

Heat exchanger tube selection is complete only when service suitability, product route, accepted wall, bundle fit and inspection evidence describe the same item. Compare quotations against that approved specification and record every deviation. Changing an alloy or buying a thicker tube requires review of the consequences for corrosion, performance and fabrication.

Related Articles

1. ASTM A213 vs A249 for Stainless Steel Heat Exchanger Tubes

2. Heat Exchanger Retubing Specification: How to Replace Tubes Without Repeating the Original Failure

3. ASTM A192 vs A210 vs A213 Boiler Tubes: Material Selection and RFQ Requirements

References & Sources

Public scope pages support the standard descriptions below. They do not reproduce the complete standards or replace the edition specified by the contract. Manufacturer guidance applies within its stated material or service conditions. Sources checked 27 October 2026.

[1] Choosing the right material can advance the life of your heat exchanger

[2] SAF® 2707 HD Tube and pipe, seamless

[3] ASTM A179/A179M-24: Seamless Cold-Drawn Low-Carbon Steel Heat-Exchanger and Condenser Tubes

[4] ASTM A214/A214M-25: Electric-Resistance-Welded Carbon Steel Heat-Exchanger and Condenser Tubes

[5] ASTM A213/A213M-25: Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes

[6] ASTM A249/A249M-24aε1: Welded Austenitic Steel Boiler, Superheater, Heat-Exchanger, and Condenser Tubes

[7] ASTM A789/A789M-24: Seamless and Welded Ferritic/Austenitic Stainless Steel Tubing for General Service

[8] The 2026 Edition introduces numerous changes to the TEMA® Standards