ASME SA213 TP347H / UNS S34709 Stainless Steel Seamless Tube EN 1.4961 Heat Exchanger Tube
ASME SA213 UNS S34709 / TP347H Stainless Steel Seamless Tube Pickled Annealed Heat Exchanger Tube
ASME SA213 TP347H / UNS S34709 is a Nb-stabilized austenitic stainless steel seamless tube with high-temperature creep strength and sensitization resistance. This material is very common used in heat exchangers. EN 1.4961 is a related European grade, but it has different Cr/Ni chemistry. They can be dual-certified only with tight chemistry control. For ASME work, order and certify to ASME SA213 TP347H UNS S34709 — do not accept EN 1.4961 alone as a substitute.
SCC limits: TP347H resists polythionic acid SCC if properly solution-annealed, but it is not immune to chloride SCC.
When engineers choose TP347H?
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High-temperature creep service
Above about 550–600°C, 304H and 316H allowable stresses drop rapidly. TP347H has higher allowable stress in the 500–700°C range, so it can allow thinner walls, higher pressure, or longer life. -
Polythionic acid SCC risk
In refinery hydroprocessing, catalytic cracking, and similar units, polythionic acid can form during shutdown. Sensitized 304H/316H can crack. TP347H is stabilized with Nb, so it resists sensitization and is a standard choice. -
Welded construction without PWHT
TP347H is often used where post-weld heat treatment is impractical. The Nb stabilization reduces chromium carbide precipitation in the HAZ, lowering sensitization risk. -
Long-term exposure to 425–815°C
In this sensitization range, unstabilized grades can form chromium carbides at grain boundaries. TP347H ties up carbon as NbC, maintaining corrosion resistance. -
Power plant superheaters/reheaters
For steam temperatures around 540–620°C, TP347H is a common upgrade from 304H/316H when creep strength is limiting. -
Cost-effective step below 310H or nickel alloys
If 310H or Alloy 800H is over-specified, TP347H can be a lower-cost alternative — provided chlorides and sulfidation are not severe.
Equivalent Grade OF ASME SA213 TP347H / UNS S34709 Stainless Steel Seamless Tube
| JIS | GB | STANDARD | WERKSTOFF NR. | UNS |
|---|---|---|---|---|
| SUS347H | 07Cr18Ni11Nb | SS 347H | 1.4961 | S34709 |
Chemistry Composition% of ASME SA213 TP347H / UNS S34709 Stainless Steel Seamless Tube
| C | Si | Mn | P | S | Cr | Ni | Nb |
| 0.04-0.10 | 1.00 max | 2.00 max | 0.045 max | 0.030 max | 17.0-19.0 | 9.0-13.0 | 8*C-1.1 |
| Tensile Strength , MPa | Yield Strength, MPa | Elongation, % | Hardness, Rockwell B |
| 515 min | 205 min | 40 min | 92 |
Do not substitute one for the other without a thorough engineering review.
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Using standard 347 where 347H is specified could lead to premature creep failure and rupture under high stress at temperature.
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Using 347H where standard 347 is specified is often overkill, may be more expensive, and the coarse grain structure offers slightly lower yield strength at room temperature, which could be a design consideration for fabrication.
The "H" is a specific pedigree for the most demanding high-temperature, high-stress environments in the energy and process industries.
Application
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Refinery heat exchangers and furnace tubes
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Power plant superheaters and reheaters
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Petrochemical steam/gas heat exchangers
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High-temperature steam service
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Applications needing resistance to polythionic acid SCC
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