Stainless Steel Coil Tube — Fan Coil Unit Series (JX-CT Series)
1. Product Overview
The JX-CT Series Stainless Steel Coil Tube is a precision-engineered coiled piping solution manufactured by Wenzhou Jixing Metal Materials Co., Ltd, specifically designed for integration into Fan Coil Unit (FCU) systems and HVAC (Heating, Ventilation, and Air Conditioning) applications. This product represents the company's expertise in forming continuous stainless steel tubing into compact, high-surface-area coil geometries that maximize heat exchange efficiency within constrained installation spaces.
Unlike conventional straight-pipe heat exchangers, the coiled configuration of the JX-CT Series provides superior thermal performance per unit volume, enabling distributed model predictive control (DMPC) strategies to be effectively implemented in multi-zone building climate management systems. The coil geometry facilitates uniform fluid distribution, reduced pressure drop, and enhanced controllability of thermal output — critical parameters for advanced control algorithm implementation.
2. Material Composition & Properties
The JX-CT Series coil tubes are fabricated from austenitic stainless steels, selected for their outstanding corrosion resistance, thermal conductivity, and long-term structural integrity under cyclic thermal loading conditions.
2.1 Available Grades
- SAE 304 / AISI 304 / UNS S30400 — General-purpose grade with excellent formability and corrosion resistance in most atmospheric and aqueous environments.
- SAE 316 / AISI 316 / UNS S31600 — Enhanced chloride resistance grade suitable for coastal environments, chemical processing, and aggressive fluid media.
- SAE 316L / AISI 316L / UNS S31603 — Low-carbon variant of 316 for improved weldability and resistance to intergranular corrosion (IGC) in welded assemblies.
- SAE 321 / AISI 321 / UNS S32100 — Titanium-stabilized grade offering superior resistance to sensitization at elevated temperatures (up to 870°C).
2.2 Key Physical Properties (SAE 304 Reference)
| Property | Value | Unit |
|---|---|---|
| Density (ρ) | 8.00 | g/cm³ |
| Thermal Conductivity (λ, at 25°C) | 16.3 | W/(m·K) |
| Specific Heat Capacity (cp) | 500 | J/(kg·K) |
| Modulus of Elasticity (E) | 193 | GPa |
| Poisson's Ratio (ν) | 0.28 | — |
| Coefficient of Thermal Expansion (α, 25–100°C) | 17.3 × 10⁻⁶ | /K |
| Maximum Service Temperature | 870 | °C |
| Yield Strength (Rp0.2, annealed) | ≥ 205 | MPa |
| Tensile Strength (Rm, annealed) | 515–720 | MPa |
| Elongation (A50) | ≥ 40 | % |
2.3 Corrosion Resistance
All grades exhibit excellent resistance to atmospheric corrosion, dilute organic and inorganic acids, and alkaline solutions. The SAE 316L variant demonstrates superior pitting resistance (PREN ≥ 24) in chloride-containing environments, making it ideal for marine HVAC systems and food-grade applications where condensate may contain elevated chloride concentrations.
3. Technical Specifications
| Parameter | Specification |
|---|---|
| Product Model | JX-CT Series (Custom configurations available) |
| Outer Diameter (OD) | 6.35 mm – 25.4 mm (¼" – 1") |
| Wall Thickness (WT) | 0.40 mm – 1.60 mm |
| Coil Inner Diameter (CID) | 20 mm – 150 mm |
| Coil Height / Stack Length | 50 mm – 500 mm |
| Number of Turns | 4 – 60 (configurable) |
| Surface Finish | No. 1 (cold-rolled), 2B (bright annealed), BA (bright annealed in protective atmosphere) |
| End Forming | Plain ends, flanged, threaded (NPT/BSP), or brazed fittings |
| Operating Pressure (Design) | 0.6 MPa – 2.5 MPa (dependent on OD/WT combination) |
| Operating Temperature Range | −196°C to +450°C (SAE 304/316); up to 870°C (SAE 321) |
| Fluid Media | Water, glycol-water mixtures, refrigerants, steam, hot water, district heating/cooling fluids |
| Standards Compliance | ASTM A213/A213M, EN 10216-5, GB/T 14976, ASME B31.9 |
| Custom Length | Up to 6,000 mm continuous coil (single piece) |
4. Manufacturing Process
The production of JX-CT Series coil tubes follows a rigorous multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection & Inspection — Ingot certification verification; chemical composition analysis via OES (Optical Emission Spectroscopy) and PMS (Photon Emission Spectrometry); mechanical property testing per ASTM A370.
- Hot Rolling & Annealing — Billet reduction to seamless tube blanks via rotary piercing; solution annealing at 1050–1150°C followed by controlled cooling to achieve full austenitic microstructure.
- Cold Drawing / Cold Reduction — Multi-pass cold drawing through precision-die tooling to achieve target OD, wall thickness, and surface finish. This process introduces beneficial work hardening while maintaining ductility for subsequent forming operations.
- Coil Forming (Tubing Coiling) — Computer-controlled CNC coiling machine winds the straight tube into precise helical geometries. Forming parameters (bend radius, pitch, number of turns) are programmatically controlled to ±0.1 mm tolerance. Springback compensation algorithms ensure dimensional accuracy post-forming.
- Intermediate Annealing (if required) — For complex multi-turn geometries requiring additional ductility, an intermediate solution anneal (1050°C, 1–2 hours) may be performed between forming operations.
- End Processing & Fitting Installation — Precision cutting, deburring, end-flanging, threading, or brazing of inlet/outlet fittings as specified by the customer's system design.
- Pickling & Passivation — Chemical treatment to remove surface oxides and form a protective chromium oxide passive film, enhancing long-term corrosion resistance.
- Final Inspection & Testing — Dimensional verification (CMM), hydrostatic pressure testing (1.5× design pressure, 30-second hold), visual surface inspection, and optional eddy current testing for wall thickness uniformity.
- Protective Packaging — Individual protective wrapping with desiccant packaging for moisture-sensitive applications; bulk packaging with wooden pallets for shipment.
5. Applications
5.1 HVAC Fan Coil Unit Systems
Primary application domain. The coil tube serves as the heat exchange element within fan coil units, transferring thermal energy between the circulating fluid (hot water or chilled water) and the air stream. The compact coil geometry maximizes heat transfer surface area within the FCU housing envelope while maintaining acceptable air-side pressure drop.
5.2 Distributed Building Climate Control
As referenced in distributed model predictive control (DMPC) research for fan coil systems, the JX-CT Series coil tubes enable precise thermal modulation at the zone level. Their consistent thermal response characteristics and low thermal mass facilitate rapid transient response, which is essential for advanced control algorithms that coordinate multiple FCU zones across large commercial buildings.
5.3 Additional Application Domains
- Industrial Process Cooling/Heating — Heat exchangers in chemical processing, pharmaceutical manufacturing, and food processing plants.
- Marine HVAC Systems — SAE 316L grade coil tubes resist chloride-induced pitting in marine environments.
- Medical & Cleanroom Systems — BA-finish coil tubes for laminar flow systems and hospital HVAC where hygienic surface requirements are critical.
- Food & Beverage Industry — Sanitary-grade coil tubes for beverage cooling, dairy processing, and food storage temperature control.
- Automotive HVAC Prototyping — Compact coil heat exchangers for vehicle thermal management system development.
- Refrigeration & Cold Storage — Evaporator coil assemblies for commercial refrigeration units.
- District Heating & Cooling Networks — Terminal heat exchanger elements in building energy distribution systems.
6. Quality Certifications & Standards
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — Certified for all manufacturing operations |
| ISO 14001:2015 | Environmental Management System |
| EN 10204 3.1 | Inspection Certificate — Full material traceability documentation |
| CE Marking | Compliance with EU Machinery Directive and Pressure Equipment Directive (PED 2014/68/EU) |
| ASTM A213/A213M | Standard Specification for Seamless Austenitic Chromium-Nickel Steel Tubing for High-Temperature Service |
| GB/T 14976 | Chinese National Standard for Seamless Stainless Steel Tubes for Fluid Transport |
| NSF/ANSI 61 | Drinking Water System Components — Health Effects (available upon request for potable water applications) |
| ASME B31.9 | Pressure Piping — Building Services (design and fabrication compliance) |
7. Unique Selling Points
Engineered for Advanced Control Integration: The JX-CT Series coil tubes are specifically characterized for compatibility with distributed model predictive control (DMPC) architectures. Consistent thermal response time constants, predictable heat transfer coefficients, and low thermal inertia enable accurate first-order-plus-dead-time (FOPDT) modeling of each FCU zone — a prerequisite for effective DMPC implementation in multi-zone commercial buildings.
- Precision CNC Coiling — ±0.1 mm dimensional tolerance ensures uniform heat transfer performance across all production units, eliminating batch-to-batch variability.
- Multi-Grade Material Flexibility — Four austenitic stainless steel grades available, allowing customers to optimize the cost-performance-corrosion resistance triangle for their specific application environment.
- Compact Thermal Performance — Coil geometry provides 3–5× greater heat exchange surface area per unit volume compared to equivalent straight-pipe designs, enabling smaller, lighter FCU assemblies.
- Full Traceability — Each coil tube is traceable to the original mill heat number, with complete chemical and mechanical property documentation provided per EN 10204 Type 3.1.
- Custom Engineering Support — Wenzhou Jixing Metal Materials provides custom coil configurations (OD, wall thickness, turn count, pitch, end fittings) tailored to specific FCU OEM designs and system requirements.
- Extended Service Life — Austenitic stainless steel construction provides a design life exceeding 25 years in standard HVAC service conditions, with no degradation of thermal performance over time due to scaling or corrosion.
8. Technical Support & Ordering Information
Wenzhou Jixing Metal Materials Co., Ltd offers comprehensive technical support including thermal performance calculations, system integration guidance, and custom engineering consultation. Customers are encouraged to provide their specific FCU system parameters (flow rate, inlet/outlet temperatures, air-side design conditions, and control architecture requirements) to receive a tailored coil tube specification and performance prediction.
For detailed material certificates, dimensional drawings, or sample requests, please contact the technical sales department with reference to the JX-CT Series product line (Catalog No. 371).