347 Stainless Steel Flange Supplier: 347, 347H
347H stainless steel flange (UNS S34709) is a high-carbon version of 347 stainless steel flanges.

Chemical Composition of 347 Stainless Steel Flange (347/H)
| Élément | C | Mn | P | S | Si | Cr | Ni | Nb+Ta | Fe |
|---|---|---|---|---|---|---|---|---|---|
| 347 | ≤ 0.08 | ≤ 2.00 | ≤ 0.045 | ≤ 0.030 | ≤ 1.00 | 17.0 – 19.0 | 9.0 – 13.0 | 10 × C Min / 1.10 Max | Équilibre |
| 347H | 0.04 - 0.10 | ≤ 2.00 | ≤ 0.045 | ≤ 0.030 | ≤ 1.00 | 17.0 – 19.0 | 9.0 – 13.0 | 8 × C Min / 1.10 Max | Équilibre |
Analysis of Key Ingredients
Carbone :
The 347H grade specifies a lower minimum limit (0.04%),which ensures higher creep strength at high temperatures.
Niobium:
This is the core element of the 347 series.Niobium has a very strong affinity for carbon and preferentially forms niobium carbides,thereby preventing chromium from combining with carbon to form chromium carbides.This preserves the chromium content at the grain boundaries,preventing intergranular corrosion during welding or in high-temperature environments ranging from 427°C to 816°C.
Dual Certification (347/347H)
On the Material Test Report (MTR), this flange is designated as “347/347H,” indicating that it possesses both the general corrosion resistance of 347 and the high-temperature mechanical properties of 347H.
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Mechanical Properties of 347 Stainless Steel Flange Series
| Mesures de performance | 347 | 347H |
|---|---|---|
| Résistance à la traction | ≥ 515 MPa (75 ksi) | ≥ 485 MPa (70 ksi) |
| Limite d'élasticité 0,2% | ≥ 205 MPa (30 ksi) | ≥ 205 MPa (30 ksi) |
| Allongement en 50 mm | ≥ 30% | ≥ 30% |
| Dureté | ≤ 187 HBW | ≤ 187 HBW |
Comparison of Maximum Allowable Stress (ASME BPVC Section II, Part D)
| Température | 347 Flange (ksi) | 347H Flange (ksi) | Performance Gap |
|---|---|---|---|
| 1000°F / 538°C | 13.5 | 14.2 | 347H is ~5% stronger |
| 1100°F / 593°C | 10.1 | 13.2 | 347H is ~30% stronger |
| 1200°F / 649°C | 6.4 | 10.5 | 347H is ~64% stronger |
| 1300°F / 704°C | 3.5 | 6.5 | 347H is ~85% stronger |
| 1400°F / 760°C | 1.8 | 3.8 | 347H is ~110% stronger |
| 1500°F / 816°C | 0.9 | 1.9 | 347H is ~111% stronger |
4 Manufacturing Methods for 347 Stainless Steel Flange
Forgeage
Découpage et usinage de tôles
Moulage centrifuge
Seamless Rolled Ring Forging
Applications of 347 Stainless Steel Flange (347/H)
Bride en acier inoxydable 347
- Aerospace Exhaust Systems
- Traitement chimique
- Composants de l'énergie nucléaire
- Oil & Gas Refining (Sour Service)
- Pharmaceutical Equipment
347H Stainless Steel Flange
- Supercritical Power Boilers
- Petrochemical Hydrocracking
- Steam Reformers
- Heat Recovery Steam Generators
- Waste Incineration Plants
FAQs About 347 Stainless Steel Flange Grades
This is because it contains niobium (Nb). At high temperatures, niobium reacts with carbon first to form stable niobium carbides, thereby preventing chromium (Cr) from combining with carbon. This protects the material from intergranular corrosion caused by “chromium depletion,” which is why it is referred to as “stabilized” steel.
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