What Is ASTM A688 Material? Feedwater Heater Tubing Explained
Nov 10, 2025
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What Is ASTM A688 Material?
Covered dimensions: OD 15.9 to 25.4 mm (inclusive)
Wall thickness: average or minimum, 0.028 in (0.7 mm) and above
Application: tubular feedwater heaters (power plants)
A262 - intergranular corrosion susceptibility test
A480/A480M - general requirements for flat-rolled stainless steel
A941 - terminology
A1016/A1016M - general requirements for stainless tubes
E112 - average grain size determination
E527 - UNS numbering
chemical composition of ASTM A688 Material
⚠️ A688 is a product standard rather than a single material grade. It covers multiple UNS grades including TP304, TP304L, TP316 and TP316L. The chemical compositions (wt%) of the four most commonly used grades are listed below.
| Element | TP304S30400 | TP304LS30403 | TP316S31600 | TP316LS31603 |
|---|---|---|---|---|
| C max | 0.08 | 0.035 | 0.08 | 0.035 |
| Mn max | 2.00 | 2.00 | 2.00 | 2.00 |
| Si max | 0.75 | 0.75 | 0.75 | 0.75 |
| P max | 0.040 | 0.040 | 0.040 | 0.040 |
| S max | 0.030 | 0.030 | 0.030 | 0.030 |
| Cr | 18.00‑20.00 | 18.00‑20.00 | 16.00‑18.00 | 16.00‑18.00 |
| Ni | 8.00‑11.00 | 8.00‑13.00 | 10.00‑14.00 | 10.00‑15.00 |
| Mo | ‑ | ‑ | 2.00‑3.00 | 2.00‑3.00 |
Mechanical Properties(Room Temperature, Solution‑Annealed)
| Grade | UNS | Tensile Strength Min (MPa) | 0.2% Yield Strength Min (MPa) | Elongation (50 mm) Min % | Hardness Max |
|---|---|---|---|---|---|
| TP304 | S30400 | 515 | 205 | 35 | 90 HRB |
| TP304L | S30403 | 485 | 175 | 35 | 90 HRB |
| TP316 | S31600 | 515 | 205 | 35 | 90 HRB |
| TP316L | S31603 | 485 | 175 | 35 | 90 HRB |
| TP304LN | S30453 | 515 | 205 | 35 | 90 HRB |
| TP316LN | S31653 | 515 | 205 | 35 | 90 HRB |
⚠️ ASTM A688 only specifies mandatory minimum mechanical properties. Physical properties are typical reference values for the material; the standard itself does not define physical property figures.
Physical Properties (Typical Reference Values for TP316L)
| Property | Value |
|---|---|
| Density | 7.98 g/cm³ |
| Melting Range | 1370‑1400 °C |
| Specific Heat Capacity (20 °C) | 500 J/(kg·K) |
| Thermal Conductivity (20 °C) | 16.0 W/(m·K) |
| Electrical Resistivity (20 °C) | 0.74 μΩ·m |
| Coefficient of Thermal Expansion (20‑100 °C) | 15.9 ×10⁻⁶ /°C |
| Coefficient of Thermal Expansion (20‑500 °C) | 17.5 ×10⁻⁶ /°C |
| Young's Modulus | 193 GPa |
| Poisson's Ratio | 0.3 |
Note: ASTM A688 does not specify physical properties; these values depend on the material grade.
U-Bend Tube Manufacturing (Typical Capabilities)
Straight length: up to 30,000 mm
Leg length: up to 12,000 mm (points of tangency to leg end)
Bending radius: up to 1,500 mm
Manufacturing method: TIG welding, cold drawn
Finishes: annealing-pickling (AP), bright annealed (BA)
Straight length = 2 × leg length + 3.1416 × R
Heat treatment of the U-bend area plus about 150 mm of each leg beyond the tangent point, if specified
Application Scenarios of ASTM A688
1.Feedwater heaters for thermal power & nuclear power plants (Primary Application)
U‑tube bundles for high‑pressure and low‑pressure feedwater heaters. Subject to high‑temperature feedwater and cyclic thermal stress. U‑shape compensates thermal expansion. A688 requires special tests such as reverse bend test for power‑plant serviceASTM Inter.
2.Auxiliary heat‑exchange equipment in power stations
Selected condensers, closed‑loop coolers. TP316L / TP316LN grades are preferred for improved corrosion resistance.
3.Special chemical‑process U‑tube heat exchangers
Only adopted when project specification explicitly references ASTM A688. A688 shall not replace A269 / A213 for general heat‑exchanger service without specification approval.
High pressure feedwater heater
A688 U‑bent tube
Power plant heater internal tube bundle
Exporter of ASTM A688
GNEE supplies ASTM A688 / SA‑688 austenitic stainless steel tubes for feedwater heaters, including straight tubes and finished U‑bent tubes, with both seamless and welded types available. Covered grades: TP304, TP304L, TP304LN, TP316, TP316L, TP316LN, N08367 (AL‑6XN); size range OD 15.9‑25.4 mm, wall thickness ≥0.7 mm. Both minimum‑wall and average‑wall ordering modes are supported.
EN 10204‑3.1 material certificates are provided upon delivery. PMI spectroscopy and third‑party witness inspection by SGS/BV are available. Deep processing services such as cut‑to‑length and U‑bending are supported. Export protective packaging adopts VCI anti‑rust paper plus fumigated wooden cases to prevent chloride contamination. Stock covers commonly‑used power‑plant specifications. Both small and bulk orders are accepted, and we can provide professional procurement solutions for overseas power‑plant projects.
If you are looking for high‑quality ASTM A688 stainless steel products, please click below to contact us. We can offer you professional purchasing solutions.
If you are looking for high‑quality ASTM A688 stainless steel products, please click below to contact us. We can offer you professional purchasing solutions.
FAQ
1.What grades are covered under ASTM A688?
Common grades include TP304, TP304L, TP304LN, TP316, TP316L, TP316LN and N08367 (AL‑6XN). The exact UNS grade shall be clearly stated on purchase orders.
2.What is the difference between ASTM A688 and A269?
Though using the same material grades, A269 is a general‑purpose precision tube standard. ASTM A688 adds power‑plant specific tests such as reverse bend test for feedwater heater service, and has fixed size limits for feedwater heater tubing.
3.Can ASTM A688 replace A213 heat exchanger tubes?
Not for general replacement. A213 is for high‑temperature boiler tubing. A688 is dedicated to feedwater heaters with limited OD range and special test requirements. Follow project technical specifications.
4.Can ASTM A688 replace A213 heat exchanger tubes?
Not for general replacement. A213 is for high‑temperature boiler tubing. A688 is dedicated to feedwater heaters with limited OD range and special test requirements. Follow project technical specifications.
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