310S (25Cr-20Ni) Austenitic Heat-Resistant Stainless Steel Coil Tube
Product Overview
The 310S (UNS S31008) Austenitic Heat-Resistant Stainless Steel Coil Tube is a premium-grade, high-temperature alloy tubing product supplied by Wenzhou Jixing Metal Materials Co., Ltd. Engineered for extreme thermal environments, this coil tube is the industry benchmark for applications demanding sustained service temperatures up to 1050°C (1922°F). The coil configuration enables efficient downstream forming, bending, and fabrication into complex geometries including furnace internals, radiant tubes, and waste heat recovery systems.
Material Composition & Metallurgical Properties
The 310S grade is a modified version of the standard 310 austenitic stainless steel, with a reduced carbon content (≤0.08% C) to improve resistance to intergranular corrosion and sensitization during welding. Its unique 25% Chromium (Cr) – 20% Nickel (Ni) alloy system provides exceptional oxidation resistance, thermal stability, and mechanical strength at elevated temperatures.
Chemical Composition (Typical)
| Element | Specification (%) | Remark |
|---|---|---|
| Carbon (C) | ≤ 0.08 | Low-carbon modification for weldability |
| Chromium (Cr) | 24.0 – 26.0 | Primary oxidation-resistant alloying element |
| Nickel (Ni) | 19.0 – 22.0 | Stabilizes austenitic structure at high temperatures |
| Manganese (Mn) | ≤ 2.0 | — |
| Silicon (Si) | ≤ 1.0 | Contributes to high-temperature strength |
| Sulfur (S) | ≤ 0.03 | — |
| Phosphorus (P) | ≤ 0.035 | — |
| Iron (Fe) | Balance | — |
Mechanical Properties (Annealed Condition)
| Property | Value | Test Condition |
|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa | Room temperature |
| Yield Strength (0.2% offset) | ≥ 205 MPa | Room temperature |
| Elongation | ≥ 40% | 50 mm gauge length |
| Continuous Service Temperature | Up to 1050°C | Oxidizing atmosphere |
| Intermittent Service Temperature | Up to 1150°C | Short-duration excursions |
| Cyclic Oxidation Resistance | Up to 1150°C | Repeated heating/cooling cycles |
| Coefficient of Thermal Expansion | 17.0 × 10⁻⁶ /°C | 25–1000°C |
| Thermal Conductivity | 21.5 W/(m·K) | 100°C |
| Density | 8.0 g/cm³ | 20°C |
Technical Specifications
| Parameter | Specification |
|---|---|
| Material Grade | 310S / UNS S31008 / ASTM A213 TP310S |
| Product Form | Coil Tube (盘管 / Coiltube) |
| Alloy System | 25Cr-20Ni Austenitic Heat-Resistant |
| Outer Diameter (OD) | Customizable (typically 6.0 mm – 159.0 mm) |
| Wall Thickness (WT) | Customizable (typically 0.5 mm – 12.0 mm) |
| Coil Length | Up to 100 m per coil (configurable) |
| Surface Finish | 2B / BA / Pickled & Passivated |
| Tolerance (OD) | ±0.1 mm – ±0.5 mm (per ASTM A213) |
| Tolerance (WT) | ±10% nominal |
| Heat Treatment | Solution Annealed at 1040–1120°C, followed by air or water quench |
Manufacturing Process
The production of 310S coil tube at Wenzhou Jixing Metal Materials Co., Ltd follows a rigorous, multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and superior surface quality:
- Raw Material Selection & Ingot Casting: High-purity chromium and nickel are alloyed with iron via vacuum arc or electro-slag remelting (ESR) to produce homogeneous billets with minimal inclusions.
- Hot Rolling & Homogenization: Billets are reheated to 1200–1250°C and hot-rolled into seamless tube blanks with controlled grain structure.
- Piercing & Pilgering: The hot blanks are pierced to form hollow tubes, followed by pilger rolling to achieve preliminary dimensional specifications.
- Pilot Mill Finishing: Tubes pass through a pilot mill for final sizing and surface refinement to meet target OD and WT tolerances.
- Solution Annealing (固溶处理): Tubes are heated to 1040–1120°C in a controlled atmosphere furnace, held for uniform carbide dissolution, and rapidly quenched to lock in the austenitic microstructure.
- Pickling & Passivation: Tubes are pickled in a mixed acid bath (HNO₃/HF) to remove oxide scales, followed by passivation to form a protective chromium oxide layer.
- Coiling & Inspection: Finished tubes are coiled to specified lengths, with each coil subjected to ultrasonic testing (UT), hydrostatic testing, and spectrographic verification.
Applications & Industry Sectors
The exceptional combination of high-temperature strength, oxidation resistance, and thermal fatigue endurance makes 310S coil tube indispensable in the following critical applications:
- Furnace Internal Components (炉膛内构件): Burner tubes, support structures, hangers, and refractory anchoring systems operating in continuous high-temperature environments up to 1050°C.
- Radiant Tubes (辐射管): Direct-fired heating elements in petroleum refineries, chemical processors, and steel rolling mills where radiant heat transfer is required at sustained temperatures exceeding 900°C.
- High-Temperature Flue Gas Waste Heat Recovery (高温烟气余热回收): Heat exchanger tubes, economizer elements, and superheater components that recover thermal energy from exhaust gases in power generation, cement, and glass manufacturing industries.
- Additional Applications:
- Gas turbine exhaust ducts and thermal barrier substrates
- Industrial kiln mesh supports and conveyor systems
- Pyrometric cones and thermocouple sheaths
- Heat treatment furnace fixtures and tooling
- Aluminum smelting pot lids and heat shields
Unique Selling Points
- Industry-Leading Thermal Endurance: Continuous service capability at 1050°C — among the highest temperatures achievable with commercial stainless steels — with intermittent tolerance up to 1150°C.
- Coil Format Flexibility: The coiled configuration eliminates butt-weld joints inherent in straight-length tubing, reducing failure points and enabling seamless forming into complex geometries.
- Superior Oxidation & Scaling Resistance: The 25% Cr content forms a stable, self-healing Cr₂O₃ protective oxide layer, significantly extending service life in oxidizing and sulfur-containing atmospheres.
- Low-Carbon Advantage: The ≤0.08% C specification of 310S (vs. 310) provides enhanced resistance to sensitization and intergranular corrosion, critical for welded assemblies.
- Excellent Thermal Fatigue Performance: Maintains mechanical integrity through repeated thermal cycling, making it ideal for applications with fluctuating temperature profiles.
- Full Traceability: Each coil is accompanied by mill test certificates (MTC) with full chemical and mechanical data, ensuring complete supply chain traceability.
Quality Certifications & Compliance
All 310S coil tube products manufactured by Wenzhou Jixing Metal Materials Co., Ltd comply with the following international standards and quality assurance frameworks:
- ASTM A213 / A213M: Standard Specification for Seamless Austenitic Stainless Steel Tubing for High-Temperature Service
- ASTM A778: Standard Specification for Wrought Chromium-Nickel Iron-Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for High-Temperature Service
- ISO 3506: Stainless Steel Fasteners — General Technical Delivery Conditions
- EN 10216-2: Non-alloy and Alloy Steel Tubes for Mechanical, Technical, and General Purposes
- GB/T 12770: Chinese National Standard for Seamless Stainless Steel Tubes for High-Temperature Service
- ISO 9001:2015: Quality Management System Certification
- ISO 14001:2015: Environmental Management System Certification
Technical Advisory Note: While 310S offers outstanding performance in oxidizing environments, it is not recommended for reducing atmospheres or direct contact with molten metals, where carbide precipitation and sulfidation may compromise structural integrity. For applications involving hydrogen or carburizing environments, consider alternative grades such as 310 (higher carbon) or specialized superalloys. Always consult with qualified metallurgical engineers for application-specific suitability assessment.