Stainless Steel 347 / 347H Pipe Fittings manufactured by Amardeep Steel Center to ASTM A403 / ASME SA403 are columbium-stabilised austenitic fittings engineered for sustained service in the sensitisation range of 427°C to 816°C. Available as UNS S34700 (SS 347) and UNS S34709 (SS 347H) also designated EN 1.4550 and EN 1.4961 — our fittings eliminate intergranular corrosion risk in petroleum refineries, power generation plant, and high-temperature chemical process lines. We produce the full fitting geometry range: SS 347 elbows, tees, reducers, caps, stub ends, and pipe bends, all supplied with MTC EN 10204 3.1.
Niobium vs Titanium Stabilization: Both SS 321 (Ti-stabilized) and SS 347 (Nb-stabilized) prevent sensitization. However, niobium has a higher melting point and forms more stable carbides, giving SS 347 better retention of properties after welding and slightly superior performance in strongly oxidizing, high-temperature environments. SS 347 is often preferred in nuclear and refinery applications for this reason.
What Are Stainless Steel 347 and 347H Pipe Fittings? (UNS S34700 / S34709)
Stainless Steel 347 / 347H Pipe Fittings are specialized components used to connect, control, and branch piping systems that operate at high temperatures. Their key feature is the addition of columbium (Nb) and tantalum (Ta) as stabilizing elements, with a combined Nb+Ta content ≥ 10× the carbon content. Much like titanium in Grade 321, these elements prevent chromium carbide precipitation at grain boundaries when the steel is exposed to temperatures in the sensitization range (427°C to 816°C), making these fittings immune to intergranular corrosion — a common failure mode in high-heat applications.
The two variants in this family are tailored for specific high-temperature roles:
- Stainless Steel 347 Pipe Fittings (SS 347 Pipe Fittings): The standard stabilized grade — designated UNS S34700 / EN 1.4550, specified under ASTM A403 WP347. Offers excellent corrosion resistance after exposure to high temperatures and is a reliable choice for a wide range of heat-intensive applications.
- Stainless Steel 347H Pipe Fittings (SS 347H Pipe Fittings): The ‘H’ indicates higher carbon content — UNS S34709 / EN 1.4961, ASTM A403 WP347H. Minimum carbon 0.04% ensures superior creep resistance above 538°C (1000°F). Ideal for structural and pressure applications at elevated temperatures.
SS 347 / 347H vs SS 321 — Stabilized Grade Comparison
- Stabilizer: Niobium + Tantalum (Nb+Ta ≥ 10×C)
- Higher melting point carbides — better oxidation resistance
- Preferred for nuclear, aerospace & strongly oxidizing environments
- Slightly better weld zone stability vs 321
- Stabilizer: Titanium (Ti ≥ 5×C)
- Excellent for cyclic temperature service up to 900°C
- More economical than 347 in most cases
- Preferred for refinery furnace tubes & superheaters
Also see: SS 321/321H Pipe Fittings | SS 347 Buttweld Fittings | SS 347H Buttweld Fittings
Stainless Steel 347 / 347H Pipe Fittings Specifications
Every SS 347 / 347H Pipe Fitting is produced to precise specifications ensuring full compliance with global engineering standards.
Parameter | Details |
|---|---|
Material Standard | ASTM A403 / ASME SA403 |
Grades | WP347 (UNS S34700) | WP347H (UNS S34709) |
Dimensional Standard | ASME B16.9, ASME B16.28, MSS-SP-43, MSS SP-75 |
Buttweld Size Range | ½″ NB to 48″ NB (Seamless & Welded/Fabricated) |
Forged Fittings Size | ¼″ to 4″ NB |
Wall Thickness / Schedule | Sch 5s, 10s, 40s, STD, 80s, XS, 120, 160, XXS |
Pressure Class (Forged) | 2000 LBS, 3000 LBS, 6000 LBS, 9000 LBS |
Bending Radius | R = 1D, 2D, 3D, 5D, 6D, 8D, 10D or Custom |
Heat Treatment | Solution Annealed 1040–1121°C; 347H may require stabilization anneal 870–900°C |
Forms Available | Elbow, Tee, Reducer, Cap, Stub End, Bend, Cross, Nipple, Coupling, Socket Weld, Threaded |
End Finish | Bevelled End (BE), Plain End (PE), Threaded End (TE) |
EN / DIN Equivalent | EN 1.4550 (Grade 347), EN 1.4961 (Grade 347H) — DIN 1.4550 |
Test / Documentation | EN 10204 / 3.1 Mill TC, PMI, IGC (ASTM A262), Hydro, UT, Radiography; ASME Sect. III docs on request |
For current SS 347 / 347H Pipe Fittings pricing and lead times, contact our sales team. Standard stock items typically ship within 3–5 working days.
Chemical Composition of Stainless Steel 347 / 347H Pipe Fittings
The addition of Columbium (Niobium) + Tantalum is the key to this alloy’s high-temperature stability. Nb+Ta = Niobium + Tantalum combined; tantalum is often present as a trace element but is counted together with Nb for specification purposes.
Grade |
C |
Mn |
Si |
P |
S |
Cr |
Ni |
Nb+Ta |
Fe |
|---|---|---|---|---|---|---|---|---|---|
SS 347 (WP347) |
0.08 max |
2.00 max |
0.75 max |
0.045 max |
0.030 max |
17.0–19.0 |
9.0–13.0 |
10×C min |
Balance |
SS 347H (WP347H) |
0.04–0.10 |
2.00 max |
0.75 max |
0.045 max |
0.030 max |
17.0–19.0 |
9.0–13.0 |
8×C min |
Balance |
Mechanical Properties of Stainless Steel 347 / 347H Pipe Fittings
Room-temperature mechanical properties per ASTM A403:
Property |
WP347 / WP347H |
|---|---|
Tensile Strength (min) | 515 MPa (75 ksi) |
Yield Strength 0.2% (min) | 205 MPa (30 ksi) |
Elongation in 2″ (min) | 40% |
Hardness, Rockwell B (max) | 95 HRB |
For elevated temperature allowable stresses (>538°C), refer to ASME BPVC Section II Part D, Table 1A for WP347H — 347H provides higher creep and stress rupture values than 347 above this threshold.
Physical Properties of SS 347 / 347H
Property |
Value |
|---|---|
Density | 7.96 g/cm³ |
Melting Range | 1398°C – 1454°C |
Modulus of Elasticity | 193 GPa |
Thermal Conductivity (at 100°C) | 16.3 W/m·K |
Mean Coeff. of Thermal Expansion (20–100°C) | 17.2 × 10²&sup6;/°C |
Electrical Resistivity | 0.73 μΩ·m |
Heat Treatment of SS 347 / 347H Pipe Fittings
All our SS 347 / 347H Pipe Fittings are supplied in a stabilized annealed condition. Heat treatment involves heating the fittings to 1010°C to 1120°C (1850°F to 2050°F) followed by rapid quenching. This process relieves manufacturing stresses and ensures columbium carbide is properly distributed — essential for maximum resistance to intergranular corrosion during high-temperature service.
For SS 347H in the most demanding elevated-temperature applications, a stabilizing anneal at 870–900°C may be specified after welding to re-precipitate niobium carbides in the weld heat-affected zone. No PWHT is required for general corrosion resistance purposes.
Dimensional Tolerances of SS 347 / 347H Pipe Fittings
All fittings are manufactured to the governing dimensional tolerance standards below:
Fitting Type |
Governing Standard |
OD Tolerance |
Wall Thickness Tolerance |
End-to-End (ETE) Tolerance |
|---|---|---|---|---|
Buttweld Fittings |
ASME B16.9 |
±1.6 mm (up to NPS 10) |
±12.5% of nominal |
±3.2 mm (NPS ≤2), ±4.8 mm (NPS >2) |
Forged SW / Threaded |
ASME B16.11 |
As per standard table |
±12.5% |
±1.6 mm |
Special Fittings |
MSS SP-43 |
Per schedule |
Per schedule |
Per schedule |
Note: Tolerances for sizes NPS 12 and above are per ASME B16.9 Table 4 — available on request.
Dimensional Reference — SS 347 / 347H 90° LR Elbow (ASME B16.9)
NPS |
OD (mm) |
Centre-to-End A (mm) |
Wall Sch 40S (mm) |
Approx. Wt (kg) |
|---|---|---|---|---|
½″ | 21.3 | 38 | 2.77 | 0.06 |
1″ | 33.4 | 57 | 3.38 | 0.18 |
2″ | 60.3 | 76 | 3.91 | 0.49 |
4″ | 114.3 | 152 | 6.02 | 2.82 |
6″ | 168.3 | 203 | 7.11 | 8.43 |
8″ | 219.1 | 254 | 8.18 | 17.4 |
How SS 347 / 347H Compares to Other Stainless Grades
Property |
SS 347 / 347H |
SS 321 |
SS 316L |
|---|---|---|---|
Stabilising Element | Columbium (Nb) + Tantalum (Ta) | Titanium (Ti) | Molybdenum (Mo) |
Max Service Temp | 816°C (347) / >816°C (347H) | 816°C | 870°C (oxidising only) |
Intergranular Corrosion Resistance | Excellent | Excellent | None (not stabilised) |
Chloride Resistance | Moderate | Moderate | Good |
Creep Strength (>538°C) | Higher (347H superior) | Good | Lower |
Polythionic Acid SCC | Excellent | Good | Poor |
Typical Standard | ASTM A403 WP347/WP347H | ASTM A403 WP321 | ASTM A403 WP316L |
Types of Stainless Steel 347 / 347H Pipe Fittings
Amardeep Steel Center manufactures a comprehensive range of SS 347 / 347H fittings to meet any project specification:
- SS 347 Elbows (45°, 90°, 180°) — Long Radius (LR) and Short Radius (SR), ASME B16.9
- SS 347 Tees (Equal & Reducing) — straight and reducing branch tees for 90° connections
- SS 347 Reducers (Concentric & Eccentric) — for connecting pipes of different diameters
- SS 347 Caps — permanent pressure-rated end closures
- SS 347 Stub Ends (Long & Short Pattern) — for use with lap joint flanges
- SS 347 Pipe Bends — 1D to 10D bending radius, custom angles
- SS 347 Socket Weld Fittings — couplings, elbows, tees to ASME B16.11 (Class 3000 / 6000)
- SS 347 Threaded (Screwed) Fittings — NPT and BSP threads to ASME B16.11
- SS 347 Cross Fittings — equal and reducing, for four-way junction piping
- SS 347 Piggable Bends — full bore, for pipeline inspection gauge (PIG) access
Applications of Stainless Steel 347 / 347H Pipe Fittings
The unique high-temperature, intergranular corrosion-resistant properties of SS 347 / 347H Pipe Fittings make them essential across critical industries:
- Nuclear Power Plants: Reactor auxiliary piping, spent fuel storage circuits, radioactive waste handling & coolant system headers. ASME Section III documentation available.
- Oil & Gas Refining: Catalytic cracker (FCC) units, hydroprocessing units, reformer furnace piping & polythionic acid service — where PASCC resistance is mandatory.
- Aerospace & Defence: Aircraft exhaust collector rings, jet engine exhaust manifolds, thrust reverser components & rocket engine manifolds requiring resistance to thermal fatigue under cyclic high-temperature loading.
- Boilers & Pressure Vessels: Superheater tubes, steam headers & pressure vessel nozzle fittings to ASME Section VIII standards.
- Chemical Processing: High-temperature reaction systems, pyrolysis units, furnace tube connections & equipment operating within the carbide precipitation range in petrochemical plants.
- Power Generation: Gas turbine exhaust manifolds, heat recovery steam generators (HRSG) & high-temperature steam circuits.
- Heat Exchangers: High-temperature shell and tube exchangers where sustained service in the sensitisation range demands a stabilised grade.
- Industrial Furnaces: Radiant superheaters, furnace parts and other high-heat components requiring long-term oxidation resistance.
- Food Processing & Pharma: Equipment operating at sustained elevated temperatures where both product purity and high-temperature corrosion resistance are required.
- Pulp & Paper: Digesters and bleach plant piping exposed to corrosive chemicals at elevated temperatures — where intergranular corrosion immunity is critical.
Export Packing & Documentation
All SS 347 / 347H Pipe Fittings are packed in wooden cases or on pallets with end protectors and moisture-resistant wrapping. Each shipment is supplied with: Mill Test Certificate (EN 10204 3.1) | Commercial Invoice | Packing List | Certificate of Origin | Bill of Lading | Third-Party Inspection Report (on request).
Technical content reviewed by Amardeep Steel Centre’s in-house metallurgical and quality assurance team, Mumbai, India.
Related Products
- Stainless Steel 347 Butt weld Fittings
- Stainless Steel 347H Butt weld Fittings
- Stainless Steel 347 Forged Fittings
- Stainless Steel 347H Forged Fittings
Frequently Asked Questions
What stabilizing element is added to SS 347 stainless steel?
SS 347 uses Niobium (Columbium) + Tantalum as stabilizing elements, with Nb+Ta ≥ 10×carbon content. This prevents chromium carbide precipitation at grain boundaries during high-temperature service — the key mechanism behind sensitization and intergranular corrosion.
Why is SS 347 preferred over SS 321 for nuclear applications?
Niobium carbides are more thermodynamically stable (higher melting point) than titanium carbides and show better resistance in strongly oxidizing environments typical in nuclear auxiliary systems. SS 347 weld zones have historically shown more consistent stabilization performance — critical in nuclear safety-class piping.
Do SS 347 / 347H fittings require post-weld heat treatment?
No PWHT is required for corrosion resistance purposes — niobium stabilization prevents sensitization at weld heat-affected zones. A stabilizing anneal (870–900°C) may be specified for the most demanding applications to re-precipitate niobium carbides after welding.
What is the difference between SS 347 and SS 316 pipe fittings?
SS 316 uses molybdenum for chloride corrosion resistance at moderate temperatures. SS 347 uses columbium stabilisation for immunity to intergranular corrosion at elevated temperatures (427°C–816°C). For high-temperature service, SS 347 is the correct choice; for marine or chloride-rich environments, SS 316/316L is preferred.
What is the price of SS 347 / 347H pipe fittings?
Pricing depends on fitting type, size (NPS), wall schedule, and order quantity. Contact Amardeep Steel Center for a current price list and no-obligation quote.
