1Cr18Ni9Ti (UNS S32100 / ASTM 321) Stainless Steel Coil Tube — Technical Specification
1. Product Overview
The 1Cr18Ni9Ti Stainless Steel Coil Tube (also designated as UNS S32100, ASTM A268 Type 321, or EN 1.4541 X6CrNiTi18-10) is a titanium-stabilized austenitic stainless steel coil tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is supplied in continuous coil form (Coil Tube), enabling efficient downstream processing including straightening, cutting, forming, and welding without the need for individual length handling.
1Cr18Ni9Ti is specifically engineered to address the well-documented intergranular corrosion (IGC) susceptibility of standard 304 (0Cr18Ni9) austenitic stainless steels. The addition of titanium (Ti) as a carbide stabilizer ensures that carbon preferentially forms titanium carbide (TiC) rather than chromium carbide (Cr₂₃C₆), thereby preventing chromium depletion at grain boundaries during sensitization temperatures (450°C–850°C). This makes the material particularly suitable for high-temperature service environments where corrosion resistance must be maintained after welding or thermal exposure.
2. Material & Properties
2.1 Chemical Composition (GB/T 12771 / ASTM A268)
| Element | Specification (wt%) | Remarks |
|---|---|---|
| Carbon (C) | ≤ 0.08 | Low carbon content limits free carbon available for chromium carbide precipitation |
| Chromium (Cr) | 17.00 – 19.00 | Primary corrosion-resistant element; forms passive Cr₂O₃ film |
| Nickel (Ni) | 8.00 – 10.00 | Stabilizes austenitic structure; enhances ductility and toughness |
| Titanium (Ti) | 5 × (C – 0.02) – 0.70 | Carbide stabilizer; forms TiC to prevent sensitization |
| Manganese (Mn) | ≤ 2.00 | — |
| Silicon (Si) | ≤ 0.60 | — |
| Sulfur (S) | ≤ 0.020 | Low sulfur for improved weldability and surface finish |
| Phosphorus (P) | ≤ 0.030 | — |
| Iron (Fe) | Balance | — |
2.2 Mechanical Properties (Annealed Condition)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 520 MPa (75,400 psi) | ASTM A268 / GB/T 228 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (29,730 psi) | ASTM A268 / GB/T 228 |
| Elongation (at Break) | ≥ 35% | ASTM A268 / GB/T 228 |
| Density | 7.93 g/cm³ | — |
| Thermal Conductivity (at 100°C) | 16.3 W/(m·K) | — |
| Thermal Expansion (20–100°C) | 17.2 × 10⁻⁶ /°C | — |
| Specific Heat | 0.50 J/(g·K) | — |
| Maximum Service Temperature | 870°C (1600°F) | Intergranular corrosion resistance limit |
2.3 Corrosion Resistance Characteristics
- Intergranular Corrosion Resistance: Superior to Type 304 (0Cr18Ni9) due to titanium stabilization; passes ASTM A262 Practice E intergranular corrosion test at sensitization temperatures of 450°C–850°C.
- Oxidation Resistance: Maintains excellent surface integrity in continuous service up to 870°C in oxidizing atmospheres.
- Pitting and Crevice Corrosion: Moderate resistance in chloride-containing environments; not recommended for aggressive marine or high-chloride applications (consider Super Austenitic grades instead).
- Acid Resistance: Good resistance to dilute sulfuric, phosphoric, and acetic acids; limited resistance to hydrochloric acid.
3. Specifications
3.1 Dimensions (Coil Tube Form)
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 32.0 mm (custom available) | GB/T 12771 / ASTM A268 |
| Wall Thickness | 0.3 mm – 4.0 mm | GB/T 12771 / ASTM A268 |
| Coil Length | Typically 500 m – 2,000 m per coil | Manufacturer specification |
| Coil Weight | Up to 3,000 kg per coil | — |
| OD Tolerance | ± 0.05 mm – ± 0.10 mm | GB/T 12771 |
| Wall Thickness Tolerance | ± 10% (or ± 0.03 mm, whichever is greater) | GB/T 12771 |
| Roundness | ≤ 1% of nominal OD | — |
| Surface Finish | BA (Bright Annealed) / No. 4 Brushed / Mirror (upon request) | ASTM A480 |
3.2 Applicable Standards
| Standard | Description |
|---|---|
| GB/T 12771 | Chinese National Standard — Seamless and Welded Stainless Steel Tubes for General Service |
| GB/T 14976 | Chinese National Standard — Seamless Stainless Steel Tubes for Fluid Service |
| ASTM A268 / A268M | American Standard — Seamless and Welded Austenitic Stainless Steel Tubes for Chemical and Heat-Transfer Equipment |
| ASTM A778 | American Standard — Seamless and Welded Austenitic Stainless Steel Tubes for High Temperature Service |
| EN 10217-7 | European Standard — Heat-Resistant Stainless Steel Tubes for Technical Use |
| JIS G3459 | Japanese Industrial Standard — Stainless Steel Tubes for General Use |
4. Manufacturing Process
The production of 1Cr18Ni9Ti stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorously controlled multi-stage process:
- Hot Rolling / Continuous Casting: The base steel is produced via electric arc furnace (EAF) melting with Argon Oxygen Decarburization (AOD) refining to achieve precise alloy chemistry and ultra-low sulfur/phosphorus content.
- Hot Extrusion or Piercing: Billet material is heated to 1,150°C–1,200°C and extruded through calibrated dies to produce seamless tube blanks at the desired outer diameter and wall thickness.
- Cold Drawing / Cold Rolling: The hot-finished tubes are cold-worked to achieve final dimensional tolerances, surface quality, and enhanced mechanical properties (up to 30% strength improvement over annealed condition).
- Intermediate Annealing: Periodic solution annealing at 1,050°C–1,100°C in protective atmosphere (argon or endothermic gas) is performed to relieve cold work stresses and restore ductility, preventing cracking during subsequent forming operations.
- Pickling and Passivation: Surface scale is removed via citric acid or mixed acid pickling; a protective chromium oxide passive film is then formed to enhance corrosion resistance.
- Final Annealing and Coiling: The finished tube is solution-annealed at 1,050°C with rapid water quenching (or controlled cooling) to achieve a fully austenitic microstructure with maximum TiC precipitation. The tube is then wound into coils on precision mandrels.
- Quality Inspection: Each coil undergoes 100% ultrasonic testing (UT) for internal defects, eddy current testing (ECT) for surface/subsurface flaws, hydrostatic pressure testing, dimensional verification, and chemical composition analysis (OES/Spark Emission Spectroscopy).
5. Applications
The titanium-stabilized nature of 1Cr18Ni9Ti makes this coil tube grade uniquely suited for applications involving welding, heat treatment, or sustained high-temperature exposure:
- Heat-Exchanger Tubes: Boiler tubes, condensers, evaporators, and superheaters in power generation and petrochemical plants where weld sensitization is a concern.
- Food and Beverage Processing: Sanitary-grade tubing for dairy, brewery, and pharmaceutical equipment requiring high-temperature steam sterilization (CIP/SIP systems).
- Automotive Exhaust Systems: Catalytic converter substrates, exhaust manifolds, and muffler components operating at 400°C–900°C.
- Chemical Processing: Pipelines and heat-transfer coils for handling organic acids, nitric acid solutions, and sulfuric acid dilutions.
- Building and Construction: Architectural structural tubing, handrails, and decorative applications requiring long-term atmospheric corrosion resistance.
- Petroleum and Natural Gas: Downhole tubing, heat exchangers, and refinery process piping exposed to cyclic thermal loading.
- Nuclear Industry: Steam generator tubes and reactor coolant system components requiring resistance to radiation-induced sensitization.
- Aerospace: Engine exhaust components, structural tubing, and fuel system lines.
6. Quality Certifications & Testing
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring product conformity to international standards:
| Certification / Test | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing and supply processes |
| ISO 14001 | Environmental Management System certification |
| CE Marking | European Conformity marking per PED 2014/68/EU for pressure equipment components |
| Mill Test Certificate (MTC) | EN 10204 Type 3.1 Certificate of Conformity provided with each shipment |
| Intergranular Corrosion Test | ASTM A262 Practice E (Acid Solution Test) or Practice A (Intergranular Test in 65% Boiling HNO₃) |
| Non-Destructive Testing (NDT) | 100% Ultrasonic Testing (UT) per ASTM E1149 / E1277; Eddy Current Testing per ASTM E309 |
| Hydrostatic Pressure Test | 100% pressure testing at 3–5 MPa for minimum 3 seconds per tube length |
| Chemical Composition Verification | OES (Optical Emission Spectroscopy) or ICP-OES for each heat lot |
| Mechanical Testing | Tensile, hardness (HV30), and impact testing per ASTM A268 / GB/T 228 |
| Petrochemical Approval | API Monel/SS approval available for oil and gas industry applications |
7. Unique Selling Points
Titanium Stabilization Advantage: Unlike standard 304 coil tubes, 1Cr18Ni9Ti retains full intergranular corrosion resistance after welding and heat exposure up to 870°C, eliminating the risk of grain boundary attack in high-temperature service environments.
- Coil Form Efficiency: Supplied as continuous coil tubing, reducing cutting waste by up to 40% compared to straight-length supply; ideal for high-volume fabrication operations requiring automated tube processing.
- Weldability: Excellent weldability without preheating or post-weld annealing requirements (unlike 304 in sensitization-prone applications); supports TIG, MIG, and resistance welding.
- Formability: Superior cold-forming characteristics enable complex bending, rolling, and stamping operations without cracking or excessive work hardening.
- Custom Dimensional Capability: Wide range of OD and wall thickness options with tight tolerances, tailored to specific customer application requirements.
- Traceability: Full heat-to-coil traceability from raw material melting through final inspection, ensuring complete supply chain accountability.
- Cost-Effective Alternative: Provides 321