AISI 347 Austenitic Stainless Steel Coil Tube — Nb/Ta Stabilized Heat-Resistant Grade
1. Product Overview
AISI 347 is a niobium (Nb) and tantalum (Ta) stabilized austenitic stainless steel coil tube specifically engineered for prolonged service at elevated temperatures. Developed by Wenzhou Jixing Metal Materials Co., Ltd. under the classification of austenitic heat-resistant grades (奥氏体-耐热型), this material represents a significant advancement over the conventional AISI 321 grade, offering superior high-temperature creep resistance and oxidation resistance. The coil tube form factor provides manufacturing flexibility, enabling downstream processing into precision-formed components for demanding industrial applications including gas turbine parts and high-temperature catalytic cracking units.
The primary metallurgical advantage of AISI 347 lies in its dual stabilization mechanism through niobium and tantalum additions, which effectively suppresses chromium carbide precipitation (intergranular corrosion) during heat treatment or welding cycles. This stabilization ensures consistent mechanical integrity and corrosion resistance even under thermal cycling conditions that would compromise unstabilized austenitic grades.
2. Material & Properties
The chemical composition and physical properties of AISI 347 stainless steel coil tube conform to recognized international standards including ASTM A269/A269M, ASME SA-213, and EN 10216-5.
Chemical Composition (Weight Percent)
| Element | Minimum | Maximum | Remarks |
|---|---|---|---|
| Carbon (C) | — | 0.08% | Low carbon for stabilization synergy |
| Chromium (Cr) | 18.0% | 21.0% | Oxidation and corrosion resistance |
| Nickel (Ni) | 9.0% | 13.0% | Austenite stabilizer |
| Niobium (Nb) | 10 × C | 1.00% | Primary stabilizer; minimum 10× carbon content |
| Tantalum (Ta) | — | 1.00% | Secondary stabilizer; enhances creep resistance |
| Manganese (Mn) | — | 2.00% | — |
| Silicon (Si) | — | 1.00% | — |
| Phosphorus (P) | — | 0.045% | Impurity limit |
| Sulfur (S) | — | 0.030% | Impurity limit |
Mechanical Properties (Annealed Condition)
| Property | Specification | Standard Reference |
|---|---|---|
| Tensile Strength (Rm) | ≥ 485 MPa (70 ksi) | ASTM A269 |
| Yield Strength (Rp0.2) | ≥ 205 MPa (30 ksi) | ASTM A269 |
| Elongation (A50) | ≥ 35% | ASTM A269 |
| Density | 8.00 g/cm³ | — |
| Thermal Conductivity (20°C) | 16.3 W/(m·K) | — |
| Modulus of Elasticity | 193 GPa | — |
| Maximum Service Temperature | 900°C (1652°F) | ASME SA-213 |
| Creep Strength (800°C, 1000 h) | Significantly exceeds AISI 321 | ISO 12108 |
Key Performance Advantages Over AISI 321
- Superior Creep Resistance: The combined Nb/Ta stabilization provides enhanced resistance to time-dependent deformation at temperatures exceeding 700°C, extending component service life in sustained high-temperature environments.
- Enhanced Oxidation Resistance: The modified carbide precipitation behavior and higher niobium content promote a more stable and adherent chromium oxide scale, reducing spallation rates at temperatures up to 900°C.
- Intergranular Corrosion Resistance: The dual stabilizer system ensures near-complete suppression of chromium carbide precipitation during sensitization at 450–850°C, maintaining excellent resistance in corrosive high-temperature environments.
- Weldability: Maintains excellent weldability characteristics with minimal risk of sensitization in the heat-affected zone (HAZ), requiring no pre- or post-weld heat treatment in most applications.
3. Specifications
| Parameter | Specification |
|---|---|
| Product Form | Stainless Steel Coil Tube (盘管) |
| Grade Designation | AISI 347 / UNS S34700 / 1.4550 (EN) |
| Applicable Standards | ASTM A269/A269M, ASME SA-213, EN 10216-5, GB/T 14976 |
| Outer Diameter Range | 6.0 mm – 323.9 mm (0.236" – 12.75") |
| Wall Thickness Range | 0.50 mm – 12.70 mm (0.020" – 0.500") |
| Surface Finish | 2B, BA (Bright Annealed), Pickled & Passivated, Polished |
| Coil Length | Customizable; typically 5000 mm – 12000 mm per coil |
| Hardness (Annealed) | ≤ 200 HB (Brinell) |
| Crystal Structure | FCC (Face-Centered Cubic) — Fully Austenitic |
| Magnetic Properties | Non-magnetic (annealed condition) |
| Corrosion Resistance | Excellent in oxidizing acids, atmospheric, and aqueous environments |
| Temperature Range | Cryogenic (−196°C) to 900°C continuous service |
| Packaging | Export-standard wooden crates or seaworthy packaging |
4. Manufacturing Process
The production of AISI 347 stainless steel coil tube at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous multi-stage manufacturing sequence designed to ensure consistent metallurgical quality and dimensional accuracy:
- Raw Material Selection: High-purity stainless steel billets or slabs are sourced from certified mills with controlled niobium and tantalum content to ensure proper stabilization chemistry.
- Hot Rolling: Billets are reheated to 1200–1250°C and hot-rolled into semi-finished tube blanks with controlled wall thickness and outer diameter tolerances.
- Heat Treatment (Solution Annealing): Tubes are heated to 1010–1150°C and rapidly cooled (air or water quenched) to dissolve carbides and achieve a fully austenitic microstructure with uniform mechanical properties.
- Pickling & Passivation: Acid pickling (nitric/hydrofluoric acid blend) removes oxide scale, followed by passivation treatment to establish a protective chromium oxide film on the surface.
- Cold Drawing / Cold Rolling: For tighter dimensional tolerances and superior surface finish, tubes undergo cold working processes with intermediate annealing as required.
- Coiling: Finished tubes are coiled to specified lengths on precision coiling equipment, ensuring uniform curvature and minimal surface damage.
- Quality Inspection: Each batch undergoes chemical analysis (OES/SEM), mechanical testing, hydrostatic testing, dimensional verification, and non-destructive testing (eddy current, ultrasonic).
5. Applications
AISI 347 coil tube is specifically designed for high-temperature industrial applications where sustained performance and oxidation resistance are critical:
Primary Applications
- Gas Turbine Components: Combustion chamber liners, exhaust manifold sections, turbine casing parts, and heat exchanger tubes operating at sustained temperatures of 700–900°C. The superior creep resistance ensures dimensional stability under prolonged thermal loading.
- High-Temperature Catalytic Cracking Units: Reactor internals, transfer lines, and heat recovery systems in petroleum refining processes where temperatures routinely exceed 500°C in corrosive hydrocarbon environments.
- Furnace Components: Heat treatment furnace fixtures, conveyor systems, radiation tubes, and furnace lining supports requiring oxidation resistance at 800–1000°C.
- Automotive Exhaust Systems: Turbocharger exhaust manifolds and high-performance exhaust components operating at sustained elevated temperatures.
- Petrochemical Equipment: High-temperature heat exchangers, process piping, and reactor internals in oil and gas processing facilities.
- Aerospace Applications: Engine exhaust components and thermal barrier system substrates requiring excellent high-temperature oxidation and creep resistance.
Unique Selling Points
Why AISI 347 Over Competing Grades:
- Outperforms AISI 321 in creep resistance at temperatures above 700°C due to enhanced Nb/Ta dual stabilization, providing 15–25% longer service life in sustained high-temperature applications.
- Coil Tube Format enables efficient downstream forming, welding, and machining operations, reducing material waste and manufacturing lead times.
- Comprehensive Standards Compliance ensures seamless integration into global supply chains with ASME, ASTM, EN, and GB certification options.
- Full Traceability from mill certificate to final inspection report, meeting ISO 9001 quality management requirements.
6. Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality assurance systems ensuring that every AISI 347 coil tube product meets international standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing operations |
| ISO 14001:2015 | Environmental Management System certification |
| EN 10204 3.1 | Material Test Certificate with full inspection reports |
| ASTM A269/A269M | Standard Specification for Seamless Austenitic Stainless Steel Tube |
| ASME SA-213 | Standard for Seamless Austenitic Chromium-Nickel Steel Tubes for High Temperature Service |
| EN 10216-5 | Non-ferrous metal tubes — Technical delivery conditions — Austenitic stainless steel |
| GB/T 14976 | Chinese National Standard for seamless stainless steel tubes for fluid transport |
| Third-Party Inspection | Available via SGS, Bureau Veritas, or TÜV upon customer request |
| Mill Test Report (MTR) | Provided with every shipment including chemical composition, mechanical test results, and heat number traceability |
Testing Protocols Include:
- Chemical composition verification via Optical Emission Spectroscopy (OES)
- Tensile testing per ASTM E8/E8M at room temperature
- Charpy V-notch impact testing per ASTM E23 (where required)
- Hydrostatic pressure testing per ASTM A530
- Intergranular corrosion testing per ASTM A262 Practice E (acid solution test)
- Surface defect inspection via Eddy Current Testing (ECT)
- Dimensional verification using calibrated measurement instruments
- Visual surface inspection under controlled lighting conditions
Wenzhou Jixing Metal Materials Co., Ltd. — Delivering premium-grade austenitic stainless steel coil tube solutions with proven performance in the world's most demanding high-temperature applications.