ASTM A249 TP304L Welded Heat Exchanger Tube Guide
1. Scope of ASTM A249 / ASME SA249
ASTM A249/A249M and ASME SA249/SA249M specify welded austenitic steel boiler tubes, superheater tubes, heat exchanger tubes and condenser tubes. The specification is distinguished from ordinary welded pipe (ASTM A312) by its weld integrity requirements: each weld is examined and the finished tube must pass flattening, reverse flattening and flaring tests that prove the seam can withstand the rolling, flaring and thermal cycling of tube-sheet joints. Grade TP304L (UNS S30403) is the low-carbon 18-8 grade that resists sensitization in welded service.
2. Chemical Composition of TP304L
| Element | TP304L, % |
|---|---|
| Carbon, C | 0.030 max |
| Manganese, Mn | 2.00 max |
| Silicon, Si | 0.75 max |
| Phosphorus, P | 0.045 max |
| Sulfur, S | 0.030 max |
| Chromium, Cr | 18.0-20.0 |
| Nickel, Ni | 8.0-12.0 |
| Nitrogen, N | 0.10 max |
The low carbon limit is the reason 304L is specified for welded heat exchanger tube: during welding, carbon is kept below the level at which chromium carbides precipitate at grain boundaries, so the weld zone keeps full corrosion resistance without post-weld heat treatment.
3. Mechanical Properties
| Grade | Tensile strength, min | Yield strength (0.2%), min | Elongation, min | Hardness, max |
|---|---|---|---|---|
| TP304L (ASTM A249) | 485 MPa | 170 MPa | 35% | 90 HRB |
| EN 1.4307 comparison | 480-680 MPa | 180 MPa | 40% | 90 HRB |
Tubes are supplied in the annealed condition. Post-weld heat treatment may be required by the design code for some applications to restore optimum corrosion resistance and mechanical properties; this is normally performed by the tube maker when specified.
4. Sizes, Schedules and Supply Forms
Size range: 1/8 inch NB to 30 inch NB; welded sizes typically 1/2 inch NB to 16 inch NB
Wall thickness series: BWG 10-25 and schedules SCH 20, 30, 40, STD, 60, 80, XS, 120, 140, 160
Lengths: single random, double random and exact cut lengths
Forms: round, square and rectangular sections; hydraulic and special shapes on request
Ends: plain, beveled or threaded
Large-diameter welded tube is a specialty of many mills for condenser and feedwater heater shells
5. Weld Quality, Testing and Applications
Because the weld seam is the critical zone, A249 tube undergoes a specific test programme:
Flattening and reverse flattening tests on the weld area
Flaring or flange test to prove ductility of the seam under expansion
Hydrostatic testing or non-destructive electrical testing of every tube
Surface finish options: polished or pickled to suit the application
For heat exchange duty, the internal surface is typically pickled or bright annealed to keep the bore clean and scale-free; internal polishing to a specified Ra value is available for hygienic service.
Heat exchangers, condensers and feedwater heaters in power and process plants
Boilers and superheaters where welded tube is permitted by the design code
Food processing and pharmaceutical plants requiring clean, hygienic surfaces
Oil refining coolers and condensers handling corrosive process streams
Welded tube is the economical alternative to seamless where the duty is moderate; the weld, if properly made and tested, has properties close to the parent metal, and the cost saving is significant for large-diameter bundles.
6. FAQ
What is the difference between ASTM A249 and ASTM A312 welded pipe?
A249 is written specifically for boiler and heat exchanger tubes and requires weld bead flattening, reverse flattening and flaring tests, plus closer control of the annealed condition. A312 covers welded pipe for general pressure service with less stringent seam testing.
Why is 304L preferred over 304 for welded heat exchanger tube?
The 0.030% carbon maximum of 304L prevents chromium carbide precipitation during welding, so the seam and heat-affected zone resist intergranular corrosion without post-weld heat treatment. This is essential for tubes that are later expanded into tube sheets.
What does BWG mean in tube wall sizing?
BWG (Birmingham Wire Gauge) is a traditional wall thickness numbering system used for heat exchanger tubes; BWG 18, 20 and 22 are common choices for condenser tubes, with lower gauge numbers meaning thicker walls.
Can A249 TP304L tube be bent into U-bends?
Yes. Welded tube can be bent, but the weld seam should be positioned on the neutral axis of the bend to minimize strain on the seam. Seamless tube is often preferred for tight-radius bends.
What documents should come with A249 tube?
The mill test certificate (EN 10204 type 3.1) with chemical analysis, mechanical values, flattening, flaring and hydrostatic results, the heat number, and confirmation of the annealed condition. Third-party inspection can be arranged for project lots.
