Stainless Steel Coil Tube (Coiltube) — Model JX-CT Series
Product Overview
The Stainless Steel Coil Tube (Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered tubular product delivered in continuous coiled form. Unlike traditional straight-length seamless or welded pipes, coil tubes are produced through continuous forming and welding processes, enabling extended lengths without butt joints and significantly reducing downstream cutting and welding operations. This product line is particularly distinguished by its application in novel microalgae cultivation systems, where the coil geometry facilitates high surface-area-to-volume ratios, optimized light penetration, and efficient thermal exchange within bioreactor configurations.
Coil tubes are classified under UNS (Unified Numbering System) 304, 316, and 316L austenitic stainless steel grades, selected for their superior corrosion resistance, biocompatibility, and long-term structural integrity in aqueous and biochemically aggressive environments.
Material & Properties
Alloy Composition (Typical — AISI 316L)
- Chromium (Cr): 16.0–18.0% — provides primary passive film formation and general corrosion resistance
- Nickel (Ni): 10.0–14.0% — stabilizes the austenitic crystal structure
- Molybdenum (Mo): 2.0–3.0% — enhances pitting and crevice corrosion resistance, critical for chloride-containing media
- Carbon (C): ≤ 0.03% — low-carbon designation ("L" suffix) to prevent intergranular sensitization during welding or high-temperature exposure
- Iron (Fe): Balance
Mechanical Properties (Cold-Wrought Condition)
- Tensile Strength (UTS): ≥ 515 MPa (75 ksi)
- Yield Strength (0.2% offset): ≥ 205 MPa (30 ksi)
- Elongation: ≥ 40% (in 50 mm gauge length)
- Hardness (Rockwell B): ≤ 95 HRB
- Impact Energy (Charpy V-Notch, −196 °C): ≥ 200 J — excellent cryogenic toughness
Corrosion Resistance Characteristics
- Pitting Resistance Equivalent Number (PREN): 24–26 (Cr + 3.3 × Mo + 16 × N)
- Passive Film Stability: Self-healing chromium oxide layer in aerated and deaerated aqueous environments
- Resistance to: Chloride pitting, acid rain, microalgae metabolic byproducts (organic acids, hydrogen sulfide traces), and seawater exposure
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) | — |
| Model Designation | JX-CT Series | Wenzhou Jixing proprietary |
| Material Grades | AISI 304 / 316 / 316L / 321 | ASTM A213 / A269 |
| Outer Diameter (OD) | 6.0 mm – 159.0 mm | Customizable |
| Wall Thickness | 0.5 mm – 6.0 mm | Customizable |
| Tolerance (OD) | ±0.15 mm (standard); ±0.05 mm (precision) | ASTM A213, Class 1 |
| Tolerance (Wall) | ±10% of nominal | ASTM A269 |
| Surface Finish | 2B (No. 4 Brushed), Electropolished (Ra ≤ 0.4 μm), or Mirror (Ra ≤ 0.2 μm) | ASTM A269, Type 2 / Type 3 |
| Coil Length per Spool | Up to 500 m (continuous, joint-free) | Manufacturer specification |
| Coil Inner Diameter | 300 mm – 1200 mm (configurable) | Manufacturer specification |
| Weld Type | Longitudinal TIG (GTAW) or orbital welded; seamless available for smaller OD | ASME B31.3 |
| Operating Temperature Range | −196 °C to +425 °C (316L); up to +870 °C (321) | ASME Section IX |
| Maximum Operating Pressure | Dependent on OD, wall thickness, and grade (per Barlow formula) | ASME B31.3 |
| End Treatment | Cut square (±0.5 mm), beveled per ASME B31.3, or threaded | ASME B31.3 |
| Packaging | Wooden spool with moisture-proof wrapping; export-grade palletized | ISO 4180 |
Manufacturing Process
1. Raw Material Procurement and Heat Treatment
High-purity stainless steel strip or round bar stock is procured from certified mills (e.g., Outokumpu, Nippon Steel, Sandvik). Each incoming lot undergoes spectroscopic verification (OES — Optical Emission Spectroscopy) and mechanical property testing to confirm conformance to the specified grade composition and mechanical requirements.
2. Coil Forming and Welding
Flat strip is fed through a series of progressively reducing roll-forming stations (typically 8–12 passes) to achieve the target circular cross-section. For welded coil tubes, the longitudinal seam is joined via Gas Tungsten Arc Welding (GTAW / TIG) under inert gas shielding (argon or argon-helium mixtures). Orbital welding systems ensure uniform heat input and consistent weld bead geometry along the entire coil length.
3. Cold Drawing and Sizing
The formed coil is passed through a multi-die cold drawing system to achieve precise dimensional tolerances, enhance mechanical properties through strain hardening, and improve surface finish. This step is critical for achieving the tight OD and wall thickness tolerances required in microalgae bioreactor applications.
4. Solution Annealing and Pickling
After cold working, the coil is subjected to solution annealing at 1050–1100 °C followed by rapid water quenching to dissolve carbides and restore full austenitic microstructure. Subsequent acid pickling (nitric-hydrofluoric acid blend) removes the heat-affected oxide scale, and passivation further enriches the surface chromium content for optimal corrosion resistance.
5. Surface Finishing
Depending on the application, the coil tube undergoes one or more of the following finishing processes:
- Mechanical polishing: For 2B or No. 4 brushed finishes
- Electropolishing: Electrochemical removal of surface material to achieve Ra ≤ 0.4 μm; critical for hygienic and biofilm-resistant applications
- Mirror polishing: Multi-stage buffing to achieve Ra ≤ 0.2 μm
6. Quality Inspection and Testing
Every coil undergoes a comprehensive inspection regimen:
- Visual inspection: 100% inspection of weld seam and surface finish
- Dimensional verification: Caliper and micrometer measurements at intervals ≤ 10 m
- Hydrostatic pressure testing: 1.5 × working pressure, held for minimum 30 seconds per segment
- Eddy current testing (ECT): Non-destructive detection of subsurface weld defects
- Chemical analysis: OES verification of alloy composition per lot
- Intergranular corrosion testing: Per ASTM A240 (for 316L grades)
- Pitting corrosion testing: Per ASTM G48, Method A (ferric chloride solution)
7. Coiling and Packaging
The finished tube is wound onto precision steel spools with controlled tension to prevent kinking or ovality. Each spool is wrapped in moisture-barrier polyethylene film and secured with steel strapping. Export shipments are palletized and labeled per ISO 4180 (freight container loading, stowage, and securing).
Applications
Primary Application: Microalgae Cultivation Systems
The JX-CT coil tube is specifically engineered for integration into novel coiltube-based microalgae bioreactors. The continuous coil geometry provides the following technical advantages in photobioreactor design:
- Maximized Light Penetration: The tubular coil configuration ensures that every point in the culture medium is within a short radial distance from the tube wall, minimizing light attenuation in turbid algal cultures and enabling efficient photosynthesis at high cell densities
- High Surface-to-Volume Ratio: Enhanced gas-liquid mass transfer for CO₂ supply and O₂ removal, critical for maintaining optimal dissolved gas concentrations
- Thermal Regulation: The coil geometry facilitates efficient heat exchange, maintaining culture temperature within the narrow optimal range (typically 20–30 °C) for microalgae species such as Chlorella vulgaris, Spirulina platensis, and Nannochloropsis oculata
- Continuous Flow Capability: The joint-free coil length supports plug-flow or continuous stirred-tank reactor (CSTR) configurations without interruption
- Hygienic Design: Electropolished surfaces minimize biofilm attachment and facilitate CIP (Clean-In-Place) and SIP (Sterilize-In-Place) protocols
Additional Industrial Applications
- Heat Exchangers and Radiator Coils: HVAC systems, industrial process cooling, and automotive thermal management
- Food and Beverage Processing: Dairy, brewing, and pharmaceutical piping where hygienic surface integrity is mandated (FDA 21 CFR, EU 1935/2004)
- Chemical Processing: Transfer lines for corrosive media, acid storage, and chemical injection systems
- Marine and Offshore Engineering: Seawater piping, ballast systems, and desalination plant components
- Medical and Laboratory Equipment: Fluid delivery lines in analytical instruments, dialysis machines, and laboratory apparatus
- Aerospace: Fuel lines, hydraulic systems, and cabin air conditioning circuits (321 grade for high-temperature service)
Quality Certifications and Standards Compliance
| Standard / Certification | Scope |
|---|---|
| ASTM A213 | Specification for Seamless and Welded Austenitic Stainless Steel Tubing for High-Temperature Service |
| ASTM A269 | Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Heat-Transfer Applications |
| ASME B31.3 | Process Piping Code — design, materials, fabrication, and inspection requirements |
| ISO 9001:2015 | Quality Management System certification for manufacturing operations |
| EN 10216-5 | European standard for austenitic stainless steel tubes for pressure purposes |
| GB/T 12771 | Chinese national standard for stainless steel welded tubes for general application |
| NSF/ANSI 61 | Drinking water system components — health effects certification (for potable water applications) |
| 3-A Sanitary Standards | International Dairy and Food Grade certification (for food processing applications) |
| CE Marking | Conformity with European directives for machinery and pressure equipment (PED 2014/68/EU) |
Unique Selling Points
- Joint-Free Continuous Length: Coil tubes up to 500 m per spool eliminate the need for field welding, reducing installation time by up to 60% and eliminating potential leak points at butt welds
- Precision Dimensional Control: Cold-drawn sizing to ±0.05 mm tolerance ensures reliable fit-up in precision assemblies and consistent hydraulic performance in bioreactor applications
- Biocompatible Surface Integrity: Electropolished finish with Ra ≤ 0.4 μm provides a smooth, non-p