321 Austenitic Heat-Resistant Stainless Steel Coil Tube
Product Overview
The 321 austenitic heat-resistant stainless steel coil tube is a premium-grade continuous coil tubing product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This specialized alloy is engineered for exceptional resistance to intergranular corrosion within the temperature range of 450°C to 900°C, making it an indispensable material for high-temperature industrial applications. The coil tube format provides seamless continuity, minimal joint vulnerability, and superior formability, ideal for complex fabrication processes requiring extended lengths without weld interruptions.
Material & Properties
Grade 321 stainless steel is classified under the austenitic-heat-resistant category within the materials and metallurgy classification system. Its defining metallurgical characteristic is the deliberate addition of titanium (Ti) at a ratio of Ti/C ≥ 5×%C. This titanium stabilization mechanism preferentially binds with carbon to form titanium carbide (TiC) precipitates, thereby preventing chromium carbide (Cr₂₃C₆) formation at grain boundaries. This precipitation control is the fundamental mechanism by which Grade 321 achieves outstanding resistance to intergranular corrosion (IGC) during sensitization temperature exposures.
Key Mechanical and Physical Properties:
- Crystal Structure: Face-Centered Cubic (FCC) austenitic
- Maximum Service Temperature: 900°C (1,652°F)
- Sensitization Resistance Range: 450°C – 900°C (842°F – 1,652°F)
- Titanium Stabilization Ratio: Ti/C ≥ 5×%C (molar)
- Corrosion Resistance: Superior resistance to intergranular corrosion, atmospheric corrosion, and dilute acid environments
- Weldability: Excellent — does not require post-weld stabilization heat treatment
- Formability: High ductility retained at elevated temperatures
Specifications
| Parameter | Specification |
|---|---|
| Material Grade | SAE/AISI 321 (UNS S32100) |
| Classification | Austenitic – Heat-Resistant Type |
| Titanium Content | 0.10% – 0.80% (Ti/C ≥ 5×%C) |
| Carbon Content | ≤ 0.15% (max) |
| Chromium Content | 17.0% – 19.0% |
| Nickel Content | 9.0% – 12.0% |
| Operating Temperature Range | –196°C to +900°C (–321°F to +1,652°F) |
| Intergranular Corrosion Resistance | Effective at 450°C – 900°C |
| Product Form | Continuous Coil Tube (盘管) |
| Surface Finish | Mill finish, pickled & passivated, or custom |
| Standard References | ASTM A269, ASTM A778, ASME SA-269, EN 10217 |
Manufacturing Process
The production of 321 stainless steel coil tubes follows a rigorous multi-stage manufacturing protocol:
- Raw Material Preparation: High-purity 321-grade stainless steel slabs are sourced with verified chemical composition meeting the Ti/C ≥ 5×%C stabilization requirement.
- Hot Rolling: Slabs are reheated and hot-rolled into semi-finished coil stock with controlled grain size and dimensional tolerances.
- Heat Treatment: Solution annealing is performed at 1010°C – 1150°C followed by rapid water quenching to dissolve carbides and restore full austenitic microstructure.
- Piercing & Tube Forming: The coil stock is pierced and drawn through calibrated dies to form the desired tube geometry with precise wall thickness and outer diameter control.
- Pickling & Passivation: Tubes undergo acid pickling to remove oxide scales, followed by passivation treatment to establish a protective chromium oxide surface layer.
- Coil Winding: The continuous tube is wound into coils with controlled tension to prevent deformation, ensuring dimensional stability during storage and transport.
- Quality Inspection: Each coil undergoes non-destructive testing (EDDY current testing), dimensional verification, and chemical composition analysis.
Applications
321 stainless steel coil tubes are deployed across demanding high-temperature industrial sectors:
- Aerospace Industry: Aircraft exhaust pipe systems, turbine housing components, and thermal management conduits requiring sustained performance at elevated exhaust temperatures.
- Power Generation: Boiler headers (集箱), superheater tubes, and economizer sections in coal-fired and oil-fired boilers operating within the sensitization temperature window.
- Heat Exchangers: Shell-and-tube heat exchangers, process condensers, and evaporators in chemical, petrochemical, and pharmaceutical processing facilities.
- Automotive Industry: Catalytic converter substrates, exhaust manifold systems, and turbocharger heat shields.
- Industrial Furnaces: Burner tubes, radiant tubes, and furnace structural components exposed to cyclic thermal loading.
- Pulp & Paper Industry: Chemical recovery boilers and high-temperature process piping.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality assurance systems to ensure product conformity:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001 — Environmental Management System Certification
- ASTM/ASME Compliance — Materials certified per ASTM A269/A778 and ASME SA-269 standards
- Mill Test Reports (MTR) — Comprehensive chemical analysis, mechanical test data, and traceability documentation provided with each shipment
- Non-Destructive Testing (NDT) — 100% eddy current inspection for wall thickness uniformity and defect detection
- Intergranular Corrosion Testing — Verified per ASTM A262 Practice No. 1E (48-hour 6% oxalic acid test) and Practice No. 4E (intergranular corrosion test)
- Third-Party Inspection — Available upon request from SGS, Bureau Veritas, or Lloyd's Register
Unique Selling Points
Titanium Stabilization Advantage: The Ti/C ≥ 5×%C ratio provides permanent intergranular corrosion resistance without requiring costly post-weld stabilization heat treatment, reducing fabrication costs and delivery timelines.
Coil Tube Format: Continuous coil delivery eliminates butt welds, maximizes material utilization, and enables automated forming operations for high-volume production environments.
Wide Temperature Capability: Maintains mechanical integrity and corrosion resistance from cryogenic temperatures up to 900°C, offering unmatched versatility across diverse operating conditions.
Superior Weldability: Can be welded using all standard fusion welding methods (TIG, MIG, resistance) without preheating or post-weld heat treatment requirements.