1Cr18Ni9Ti Stainless Steel Coil Tube (Coiltube) — Technical Specification
1. Product Overview
The 1Cr18Ni9Ti Stainless Steel Coil Tube (also designated as Coiltube in industry practice) is a cold-rolled, austenitic stainless steel tube supplied in continuous coil form, manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product falls under the Chinese national standard designation 1Cr18Ni9Ti (GB/T 20878), which is the Chinese counterpart to the international grade UNS S32100 / ASTM TP321 / EN 1.4541 (X6CrNiTi18-10). The "Ti" (Titanium) stabilization element distinguishes this grade from the more common 1Cr18Ni9 (304) stainless steel, providing superior resistance to intergranular corrosion (IGC) — a phenomenon extensively studied and documented in the metallurgical literature under the title "Analysis of Leakage Causes in 1Cr18Ni9Ti Stainless Steel Coil Tubes."
Coiltube form factor refers to the continuous, non-cut coil configuration in which the seamless or welded stainless steel tube is wound onto a spool, enabling high-efficiency downstream processing, roll-forming, and fabrication without the material loss associated with straight-length cutting.
2. Material & Properties
2.1 Chemical Composition
The 1Cr18Ni9Ti grade is an austenitic stainless steel stabilized by the addition of titanium (Ti), which preferentially forms titanium carbides (TiC) rather than chromium carbides (Cr₂₃C₆) during welding or high-temperature exposure. This prevents chromium depletion at grain boundaries and thereby inhibits sensitization.
| Element | C (Carbon) | Si (Silicon) | Mn (Manganese) | P (Phosphorus) | S (Sulfur) | Cr (Chromium) | Ni (Nickel) | Ti (Titanium) |
|---|---|---|---|---|---|---|---|---|
| Max / Range | ≤ 0.08 | ≤ 0.80 | ≤ 0.80 | ≤ 0.035 | ≤ 0.030 | 17.00 – 19.00 | 8.00 – 11.00 | 5 × C – 0.50 |
2.2 Mechanical Properties
| Property | Specification Value |
|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa (75.4 ksi) |
| Yield Strength (Rp0.2) | ≥ 205 MPa (29.7 ksi) |
| Elongation (A) | ≥ 35% |
| Hardness | ≤ 220 HV (Hardness Vickers) |
| Density | 7.93 g/cm³ |
| Thermal Conductivity (at 100°C) | 16.3 W/(m·K) |
| Modulus of Elasticity | 193 GPa |
| Maximum Service Temperature | 870°C (1598°F) |
2.3 Key Metallurgical Characteristics
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and mild industrial corrosive environments due to the high chromium (17–19%) and nickel (8–11%) content forming a stable passive chromium oxide (Cr₂O₃) film.
- Intergranular Corrosion Resistance: Titanium stabilization eliminates the risk of sensitization-induced grain boundary attack, a critical failure mechanism identified in the referenced leakage analysis study.
- Weldability: Superior welding performance with minimal pre/post-weld heat treatment requirements compared to unstabilized grades.
- Non-Magnetic (Annealed): Austenitic microstructure ensures non-magnetic properties in the fully annealed condition.
- Cryogenic Performance: Retains ductility and toughness down to liquid helium temperatures (4 K).
3. Specifications
| Parameter | Specification |
|---|---|
| Product Name | 1Cr18Ni9Ti Stainless Steel Coil Tube (Coiltube) |
| Equivalent Grades | UNS S32100 / ASTM TP321 / EN 1.4541 / JIS SUS321 / GB 1Cr18Ni9Ti |
| Product Form | Continuous Coil (Spooled) |
| Manufacturing Method | Seamless (Pierced & Pilgered) or ERW / Laser Welded |
| Outer Diameter (OD) | 6.0 mm – 219.1 mm (¼" – 8⅝") |
| Wall Thickness | 0.5 mm – 12.7 mm (0.020" – 0.500") |
| Coil Length | Custom (typically 200 m – 2000 m per coil) |
| Surface Finish | 2B, BA (Bright Annealed), No.4 Brushed, Mirror (8K) |
| Dimensional Tolerance | Per GB/T 14976, ASTM A213/A269, or EN 10216 |
| Packaging | Wooden pallet / export-grade coil packaging with moisture-proof wrapping |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd |
| Reference Document | Analysis of Leakage Causes in 1Cr18Ni9Ti Stainless Steel Coil Tubes (Internal Technical Study) |
4. Manufacturing Process
The production of 1Cr18Ni9Ti stainless steel coil tubes follows a rigorously controlled multi-stage metallurgical and forming process:
- Raw Material Preparation: High-purity stainless steel billets or slabs are produced via Basic Oxygen Furnace (BOF) or Electric Arc Furnace (EAF) melting, followed by Vacuum Arc Remelting (VAR) or Argon Oxygen Decarburization (AOD) to achieve precise alloy composition and minimize inclusions.
- Hot Rolling & Annealing: Billets are hot-rolled into perforated tubes or strip stock, then solution-annealed at 1010–1150°C in a protective atmosphere to establish a uniform austenitic microstructure.
- Cold Drawing / Cold Rolling: Tubes are cold-drawn through precision dies or strip is cold-rolled and longitudinally welded (ERW or Laser Weld) to achieve final OD and wall thickness dimensions with tight tolerances.
- Pickle & Passivate (P&P): The formed tube is pickled in a mixed acid solution (HNO₃ + HF) to remove oxide scale, followed by passivation to restore the protective chromium oxide layer.
- Final Annealing (Bright Anneal): Tubes are annealed in a controlled hydrogen or vacuum atmosphere to relieve cold-work stresses and achieve the required mechanical properties and surface finish (BA surface).
- Coiling: The continuous tube is wound onto a precision steel spool with controlled tension to prevent deformation, marking, or surface damage during storage and transport.
- Non-Destructive Testing (NDT): Each coil undergoes 100% ultrasonic testing (UT) and eddy current testing (ECT) for internal and surface defect detection, supplemented by hydrostatic pressure testing per ASTM A269.
4.1 Critical Failure Analysis — Leakage Prevention
The referenced technical study "Analysis of Leakage Causes in 1Cr18Ni9Ti Stainless Steel Coil Tubes" identifies the following root causes of tube leakage in service:
- Intergranular Corrosion (Sensitization): Exposure to temperatures in the 450–850°C range without adequate titanium stabilization can lead to chromium carbide precipitation at grain boundaries, causing localized thinning and perforation. The Ti addition in 1Cr18Ni9Ti specifically mitigates this mechanism.
- Stress Corrosion Cracking (SCC): Chloride-induced SCC in austenitic stainless steels under tensile stress, particularly in the coil form where residual stresses may be elevated.
- Manufacturing Defects: Inclusion-induced cracks, seam weld defects, and cold-work-induced micro-cracking during the coiling process.
- Corrosion Under Insulation (CUI): Moisture ingress beneath thermal insulation layers, creating localized corrosive environments.
- Improper Welding Practices: Excessive heat input during downstream fabrication leading to sensitization in the Heat-Affected Zone (HAZ).
Wenzhou Jixing Metal Materials Co., Ltd incorporates these findings into its quality assurance protocols, implementing enhanced NDT coverage, controlled residual stress management during coiling, and rigorous material traceability.
5. Applications
The 1Cr18Ni9Ti Stainless Steel Coiltube is widely deployed across industries requiring high corrosion resistance, thermal stability, and continuous-length processing efficiency:
- Petrochemical & Oil Refining: Heat exchanger tubes, furnace tubes, condensers, and process piping operating in oxidizing environments at elevated temperatures.
- Power Generation: Boiler tubes, superheater tubes, and steam lines in coal-fired and nuclear power plants.
- Food & Beverage Processing: Hygienic-grade process tubing for dairy, brewing, and pharmaceutical production lines (BA/Mirror finish).
- Automotive Industry: Exhaust system components, turbocharger piping, and catalytic converter substrates.
- Chemical Processing: Reactor internals, distillation columns, and corrosive fluid transfer lines.
- Heating Systems: Radiator coils, underfloor heating loops, and solar thermal collector tubing (leveraging the coil form for continuous installation).
- Construction & Architecture: Structural elements, handrails, and decorative tubing with corrosion-resistant exterior finish.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains comprehensive quality management systems and product certifications to ensure the 1Cr18Ni9Ti Coiltube meets international standards:
- ISO 9001:2015 — Quality Management System (QMS) Certification
- ISO 14001:2015 — Environmental Management System (EMS) Certification
- ISO 45001:2018 — Occupational Health & Safety Management System (OHSMS)
- EN 10204 — Type 3.1 Mill Test Certificates (MTC) with third-party inspection available
- Product Standards Compliance:
- GB/T 14976 (Chinese National Standard for Seamless Stainless Steel Tubes)
- GB/T 20878 (Stainless Steel Chemical Composition Designations)
- ASTM A213 / A269 / A778 (American Standards for Stainless Steel Tubes)
- EN 10216-5 (European Standard for Non-Alloy and Alloy Steel Tubes)
- JIS G3459 (Japanese Industrial Standard for Austenitic Stainless Steel Tubes)
- Third-Party Inspection: Available through SGS, BV (Bureau Veritas), TUV, and DNV upon customer request
- Material Traceability: Full heat-number traceability from raw material melt through final coil dispatch
7. Unique Selling Points
- Titanium-Stabilized Corrosion Protection: The Ti addition provides inherent resistance to intergranular sensitization — the primary failure mode identified in the referenced leakage analysis — eliminating the need for post-fabrication stabilization heat treatment.
- Continuous Coil Form Factor: Eliminates butt-weld joints in downstream applications, reducing potential leak paths and improving process flow efficiency. Ideal for roll-forming, tube bending, and continuous installation applications.
- Enhanced Quality Assurance Informed by Failure Analysis: The manufacturer's technical study on leakage causes has been directly integrated into production protocols, resulting in enhanced NDT coverage, residual stress control during coiling, and superior defect detection rates.
- Wenzhou Industry Cluster Advantage: Located in Wenzhou, Zhejiang Province — one of China's leading hubs for stainless