304H Austenitic Stainless Steel Coil Tube — High-Temperature Creep-Resistant Coiltube
Product Overview
The 304H Austenitic Stainless Steel Coil Tube is a specialized high-temperature alloy coil tube engineered for demanding thermal applications where conventional 304 and 304L grades fall short. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product is classified under Materials & Metallurgy with a secondary designation of Material Grade and a tertiary classification of Austenitic — General Purpose. The elevated carbon content of the 304H grade (minimum 0.04% C) provides significantly enhanced high-temperature creep strength and oxidation resistance compared to its lower-carbon counterparts (304/304L), making it the preferred choice for sustained operation in aggressive thermal environments.
Unlike seamless or welded straight pipes, coil tubes are wound into continuous coils, enabling efficient fabrication of complex geometries such as U-bends, serpentine heat exchangers, and spiral superheater elements without the need for extensive welding — thereby reducing thermal stress concentrations and improving overall system reliability.
Material & Properties
Chemical Composition (ASTM A213 / ASME SA-213 Grade TP304H)
| Element | Specification Range (%) | Role in Microstructure |
|---|---|---|
| Carbon (C) | ≥ 0.04 (max 0.10) | Enhances creep strength at elevated temperatures |
| Chromium (Cr) | 18.00 – 20.00 | Primary oxide-scale former; provides corrosion resistance |
| Nickel (Ni) | 8.00 – 10.50 | Stabilizes austenitic structure; improves ductility |
| Manganese (Mn) | ≤ 2.00 | Aid in deoxidization during smelting |
| Silicon (Si) | ≤ 1.00 | Deoxidizer; contributes to high-temperature strength |
| Sulfur (S) | ≤ 0.03 | Limited to prevent sulfide inclusions |
| Phosphorus (P) | ≤ 0.045 | Limited to avoid grain-boundary embrittlement |
| Iron (Fe) | Balance | Matrix constituent |
Mechanical Properties
| Property | Typical Value | Test Temperature |
|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa (75 ksi) | Room Temperature |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (30 ksi) | Room Temperature |
| Elongation | ≥ 40% | Room Temperature |
| Creep Strength (1% strain) | ≈ 45–50 MPa | 1100 °C (2012 °F) |
| Creep Strength (1% strain) | ≈ 100–120 MPa | 1000 °C (1832 °F) |
| Thermal Conductivity | 16.3 W/(m·K) | 100 °C |
| Specific Heat | 500 J/(kg·K) | 100 °C |
| Thermal Expansion Coefficient | 17.2 µm/(m·K) | 100 °C |
Key Performance Advantages Over 304/304L
- Superior Creep Resistance: The elevated carbon content (≥ 0.04%) promotes the formation of fine carbide precipitates that impede dislocation motion at elevated temperatures, resulting in creep strength approximately 20–30% higher than 304L at temperatures above 800 °C.
- Enhanced Hot Tensile Strength: Retains meaningful load-bearing capacity at temperatures up to 1150 °C, where 304L exhibits rapid strength degradation.
- Comparable Oxidation Resistance: Maintains the same Cr-Ni oxide scale stability as standard 304 grade, providing reliable performance in oxidizing and moderately reducing atmospheres.
- Good Fabricability: Despite higher carbon, retains sufficient ductility for cold forming of coil geometries including U-bends and spiral configurations.
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Material Grade | 304H (UNS S30409 / 1.4309) | ASTM A213 / ASME SA-213 |
| Product Form | Coil Tube (Continuous Coil) | — |
| Outer Diameter (OD) | 6.35 mm – 50.8 mm (¼" – 2") | ASTM A213 |
| Wall Thickness | 0.50 mm – 3.00 mm | ASTM A213 |
| Coil Inner Diameter | 150 mm – 600 mm (customizable) | — |
| Coil Length | 50 m – 500 m (continuous) | — |
| Surface Finish | Pickled & Passivated (2B) / Mill Finish | ASTM A478 |
| Heat Treatment | Solution Annealed (1050–1100 °C, water/quench cooled) | ASTM A213 |
| Tolerance — OD | ±10% (per ASTM A213) | ASTM A213 |
| Tolerance — Wall | ±10% (per ASTM A213) | ASTM A213 |
| Maximum Service Temperature | 1150 °C (2094 °F) | — |
| Minimum Service Temperature | −196 °C (−320 °F) | — |
Manufacturing Process
- Raw Material Selection: High-purity 304H stainless steel slabs are sourced from certified electric arc furnace (EAF) or vacuum arc remelting (VAR) producers, with chemical composition verified to meet the minimum 0.04% carbon requirement.
- Hot Rolling: Slabs are reheated to 1200–1250 °C and hot-rolled into a semi-finished coil of the desired OD and wall thickness, followed by controlled cooling to prevent excessive grain growth.
- Pickling & Passivation: The hot-rolled coil is subjected to acid pickling (HNO₃/HF mixture) to remove mill scale, followed by passivation to establish a stable chromium oxide surface layer.
- Cold Drawing / Expansion: The coil is drawn through precision dies to achieve final dimensional tolerances, ensuring uniform wall thickness and roundness throughout the coil length.
- Solution Annealing: The cold-worked coil is heated to 1050–1100 °C in a protective atmosphere (H₂/N₂) and rapidly quenched to dissolve any intermetallic precipitates and restore full austenitic structure.
- Final Pickling & Passivation: Post-annealing pickling removes any oxidation formed during heat treatment, restoring the passive surface.
- Non-Destructive Testing (NDT): Eddy current testing (ECT) and hydrostatic pressure testing are performed to verify internal and external integrity.
- Coiling & Packaging: The finished tube is wound onto a spool, wrapped in protective film, and packaged for shipment with full traceability documentation.
Applications
The 304H Coil Tube is specifically designed for high-temperature thermal applications where sustained mechanical integrity is critical. Primary applications include:
- Boiler Superheaters: The primary application — 304H coil tubes are formed into U-bends and serpentine configurations for steam superheater tubes in utility boilers, recovering boilers, and waste-to-energy (WtE) plants operating at steam temperatures of 450–600 °C.
- High-Temperature Steam Pipelines: Used in main steam lines, reheat steam piping, and steam distribution networks in power generation facilities where creep resistance at sustained high temperatures is essential.
- Industrial Furnace Elements: Coil tubes employed as heating elements or structural components in industrial furnaces operating up to 1000 °C in oxidizing atmospheres.
- Heat Exchanger Coils: Serpentine coil configurations for air preheaters, economizers, and process heat exchangers in petrochemical and power generation industries.
- Aerospace Heat Shielding: Secondary application in thermal protection systems where oxidation resistance and elevated-temperature strength are required.
- Concentration Solar Power (CSP): Receiver tubes in solar thermal power plants exposed to concentrated solar radiation temperatures exceeding 500 °C.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality assurance programs to ensure compliance with international standards:
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System
- ASTM A213 / ASME SA-213 — Full compliance for austenitic stainless steel tube specifications
- EN 10216-5 — European standard for stainless steel tubes (where applicable)
- JIS G3459 — Japanese Industrial Standard for stainless steel tubes
- MTC (Mill Test Certificate) EN 10204 3.1 — Third-party verified chemical and mechanical test reports for each heat
- NDT Certification: Eddy current and hydrostatic testing performed per ASTM E309 and ASTM A530
- Traceability: Full heat-to-heat traceability from raw material to finished product, with each coil batch linked to its production records
Unique Selling Point: The 304H Coil Tube from Wenzhou Jixing Metal Materials offers a critical performance advantage over standard 304/304L coil tubes — approximately 20–30% improvement in high-temperature creep strength at operating temperatures above 800 °C — while maintaining full corrosion resistance and fabricability. This makes it the optimal material selection for boiler superheater and high-temperature steam pipeline applications where equipment longevity and operational safety are paramount.