Stainless Steel Coil Tube (Coiltube) — Annealed Continuous Coiled Tubing
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a continuously coiled seamless or welded tubing product designed for high-volume, high-efficiency downstream processing. This product category represents a significant advancement in stainless steel tube manufacturing, where tubing is produced in continuous coil form rather than discrete straight lengths, thereby minimizing material waste, reducing cutting losses, and enabling seamless integration with automated forming and fabrication lines.
The coil tube product line is distinguished by its post-forming annealing treatment conducted in a Fully Refractory Fiber Lined Roll Bottom Copper Coil Tube Annealing Furnace (全耐火纤维炉衬辊底式铜盘管退火炉). This specialized thermal processing equipment ensures uniform temperature distribution, precise cooling rate control, and consistent mechanical property development across the entire coil length, resulting in superior grain structure homogeneity and dimensional stability.
Material & Properties
Material Grades
- AISI 304 / ASTM 304 (UNS S30400) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability
- AISI 304L / ASTM 304L (UNS S30403) — Low-carbon variant suitable for post-welding applications without sensitization concerns
- AISI 316 / ASTM 316 (UNS S31600) — Molybdenum-enhanced grade offering superior resistance to pitting and crevice corrosion
- AISI 316L / ASTM 316L (UNS S31603) — Low-carbon molybdenum-bearing grade for aggressive chemical and marine environments
- AISI 321 / ASTM 321 (UNS S32100) — Titanium-stabilized grade with enhanced resistance to intergranular corrosion at elevated temperatures
- AISI 310S / ASTM 310S (UNS S31008) — High-temperature grade suitable for sustained service above 1000°C
Mechanical Properties (Annealed Condition)
| Property | 304 / 304L | 316 / 316L | 321 | 310S |
|---|---|---|---|---|
| Tensile Strength (Rm) | ≥ 515 MPa | ≥ 515 MPa | ≥ 515 MPa | ≥ 515 MPa |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 205 MPa | ≥ 205 MPa | ≥ 205 MPa |
| Elongation (A50) | ≥ 40% | ≥ 40% | ≥ 40% | ≥ 40% |
| Hardness (HBW) | ≤ 217 | ≤ 217 | ≤ 217 | ≤ 217 |
| Density (g/cm³) | 8.00 | 8.03 | 8.00 | 8.03 |
| Thermal Conductivity @ 100°C (W/m·K) | 16.3 | 14.6 | 16.3 | 14.6 |
| Maximum Service Temperature (°C) | 870 | 870 | 900 | 1150 |
Specifications
| Parameter | Specification Range |
|---|---|
| Outer Diameter (OD) | 6.0 mm – 168.3 mm (¼" – 6½") |
| Wall Thickness (WT) | 0.5 mm – 12.7 mm (0.020" – ½") |
| Coil Length | 50 m – 200 m per coil (continuous) |
| Coil Inner Diameter | 400 mm – 600 mm |
| Coil Weight | 500 kg – 3,000 kg per coil |
| Surface Finish | No.1 Hot Rolled, 2B Cold Rolled, No.4 Brushed, No.8 Mirror, BA (Bright Annealed) |
| Dimensional Tolerance (OD) | ±0.05 mm – ±0.30 mm (per ASTM A213 / A269) |
| Dimensional Tolerance (WT) | ±10% nominal wall thickness |
| Straightness | ≤ 1.0 mm/m (for straightened sections) |
| End Condition | Plain end, beveled end, or threaded (upon request) |
| Heat Treatment | Solution Annealed (1010°C – 1150°C) with controlled air cooling |
| Applicable Standards | ASTM A213, ASTM A269, ASTM A554, EN 10216-5, GB/T 14976, GB/T 12771 |
Manufacturing Process
1. Raw Material Selection and Incoming Inspection
High-purity stainless steel slabs or billet materials are procured from certified mills with full traceability documentation. Incoming materials undergo spectrographic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance with the specified grade requirements. Physical property verification includes hardness testing and grain size assessment.
2. Hot Rolling / Extrusion
For seamless coil tube production, the material is subjected to hot rolling or hot extrusion processes to achieve the desired initial tube dimensions. The hot working temperature is maintained within the austenitic phase field (typically 1100°C – 1250°C) to ensure complete recrystallization and elimination of processing defects.
3. Cold Drawing / Cold Sizing
The hot-rolled tube is cold-drawn through precision tooling to achieve final dimensional tolerances and surface finish. This process introduces controlled work hardening that enhances mechanical strength while maintaining the material's formability characteristics.
4. Solution Annealing in Refractory Fiber Lined Roll Bottom Furnace
The cold-worked coil tube is fed into the Fully Refractory Fiber Lined Roll Bottom Copper Coil Tube Annealing Furnace. This specialized equipment features:
- Refractory Fiber Lining — High-temperature ceramic fiber insulation providing superior thermal efficiency, reduced thermal mass, and rapid furnace ramp-up capability
- Roll Bottom Design — A series of precision-machined rollers supporting the coil tube throughout the furnace length, ensuring uniform heat transfer and preventing tube deformation under its own weight
- Atmosphere Control — Controlled protective atmosphere (nitrogen, endothermic gas, or vacuum) to prevent oxidation and scale formation during the annealing cycle
- Multi-Zone Temperature Control — Independent heating zones enabling precise temperature profiling along the furnace length for optimal phase transformation kinetics
- Controlled Cooling — Programmable cooling rates to achieve desired grain structure and mechanical properties without inducing residual stresses
The annealing cycle typically involves heating to 1010°C – 1150°C (depending on grade), holding for sufficient time for complete solution treatment and carbide dissolution, followed by controlled air or forced-air cooling. This process eliminates cold-work hardening, restores ductility, dissolves precipitated carbides (particularly in stabilized grades), and produces a uniform equiaxed austenitic microstructure.
5. Surface Finishing
Post-annealing surface treatments include pickling and passivation (acid cleaning to remove any residual oxide scale and establish a protective chromium oxide passive layer), mechanical polishing, or electropolishing depending on the specified finish grade.
6. Dimensional Inspection and Coiling
The finished tube undergoes comprehensive dimensional inspection including ultrasonic wall thickness measurement, optical OD verification, and straightness assessment. The tube is then coiled onto precision mandrels with controlled tension to prevent kinking or ovality introduction.
7. Protective Packaging
Coils are wrapped in moisture-proof polyethylene film, secured with steel strapping, and protected with corner guards for safe transport and storage. Customized packaging configurations are available for export shipments.
Applications
Primary Application Sectors
- Petrochemical and Oil & Gas Industry — Heat exchanger tubes, reactor internals, distillation column components, and process piping in refineries and chemical plants where continuous coil form enables efficient fabrication
- Food and Beverage Processing — Hygienic-grade tubing for dairy processing, beverage manufacturing, and pharmaceutical equipment requiring cleanable, corrosion-resistant surfaces
- Automotive Industry — Exhaust system components, turbocharger housings, and fuel injection lines where coil form enables automated cutting and forming operations
- Heat Exchanger Manufacturing — Continuous coil tube is the preferred form for heat exchanger tube banks, enabling high-speed U-tube bending and tube insertion operations
- Medical Device Manufacturing — Precise-diameter tubing for endoscopes, surgical instruments, and implantable device components
- Construction and Architectural Applications — Structural and decorative tubing for building facades, handrails, and structural supports
- Energy Sector — Solar thermal collector tubes, geothermal heat exchangers, and nuclear-grade instrumentation tubing
- Marine and Offshore — Seawater cooling systems, ballast water piping, and offshore platform structural components
Advantages of Coil Form
- Elimination of butt welds between straight lengths, improving structural integrity and flow characteristics
- Material utilization rates exceeding 95%, compared to 80–85% for straight-length tube
- Compatibility with automated continuous processing lines for high-volume manufacturing
- Reduced handling and inventory management complexity
- Consistent mechanical properties along the entire coil length due to uniform thermal processing
Quality Certifications and Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and process control |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health and Safety Management System certification |
| CE Marking (PED 2014/68/EU) | Compliance with European Pressure Equipment Directive for pressure-containing applications |
| ASME SB-801 / SB-814 | Material specifications for pressure-containing tubing used in boiler and pressure vessel applications |
| EN 10204 3.1 | Material test report (MTR) documentation per European standard for mill certification |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes for fluid transport |
| GB/T 12771 | Chinese national standard for welded stainless steel tubes |
| NACE MR0175 / ISO 15156 | Compliance for use in sour service (H₂S-containing) environments |
| Third-Party Inspection | Available upon request (SGS, Bureau Veritas, DNV, Lloyd's Register) |
Unique Selling Points
Specialized Refractory Fiber Annealing Technology: The use of a fully refractory fiber lined roll bottom furnace represents a significant technological advantage over conventional annealing equipment. The ceramic fiber lining provides superior thermal insulation (reducing energy consumption by up to 30%), enables rapid furnace cycling for improved throughput, and delivers exceptional temperature uniformity (±3°C across the working zone). The roll bottom design eliminates tube-to-floor contact, preventing localized overheating and surface damage while ensuring consistent dimensional stability throughout the annealing cycle.
- Full Traceability: Every coil is traceable from raw material heat number through all manufacturing stages to final delivery, with comprehensive Mill Test Reports (MTRs) documenting chemical analysis, mechanical testing, and heat treatment parameters.
- Customization Capability: Flexible production parameters accommodate custom OD, wall thickness, coil length, surface finish, and dimensional tolerance requirements beyond standard catalog specifications.
- Consistent Microstructure: The controlled annealing atmosphere and precise thermal cycling ensure uniform austenitic grain