Stainless Steel Coil Tube — HVAC Fan Coil & Fresh Air System Application
Product Overview
The Stainless Steel Coil Tube (Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered tubular product designed specifically for integration into Fan Coil Units (FCU) and fresh air supply systems used in modern building HVAC (Heating, Ventilation, and Air Conditioning) installations. This coil tube serves as the core heat exchange and fluid distribution element within indoor micro-circulation thermal comfort systems, enabling efficient transfer of thermal energy between working media (water, refrigerant, or air) and the surrounding indoor environment.
The product is engineered to meet the stringent performance, durability, and hygiene requirements of contemporary building comfort systems, where indoor air quality (IAQ) and thermal comfort are paramount. The coil tube's geometry and material properties are optimized to maximize heat transfer efficiency while minimizing pressure drop, ensuring that the fan coil and fresh air system achieves optimal micro-circulation thermal comfort as studied in academic literature on indoor environmental quality.
Material & Properties
The Stainless Steel Coil Tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional corrosion resistance, mechanical strength, and hygienic surface characteristics.
Material Grades Available
- SAE 304 (UNS S30400) — The most widely used grade, offering excellent general-purpose corrosion resistance, formability, and weldability. Suitable for most HVAC applications involving potable water, glycol solutions, and ambient air.
- SAE 316 (UNS S31600) — Enhanced resistance to chlorides and aggressive chemical environments. Recommended for coastal installations, chemical processing facilities, and applications involving high-chloride water.
- SAE 321 (UNS S32100) — Stabilized with titanium to prevent intergranular corrosion during welding and high-temperature service. Suitable for high-temperature hot water systems.
- SAE 316L (UNS S31603) — Low-carbon variant of 316 for superior weldability and resistance to sensitization. Ideal for critical hygienic applications.
Key Material Properties
| Property | SAE 304 | SAE 316 | SAE 321 |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 | ≥ 515 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 |
| Density (g/cm³) | 8.00 | 8.03 | 7.93 |
| Thermal Conductivity (W/m·K, 20°C) | 16.3 | 16.3 | 16.3 |
| Maximum Service Temperature (°C) | 870 (oxidation) | 870 (oxidation) | 900 (oxidation) |
| Chloride Pitting Resistance (PREN) | 19 | 24 | 19 |
| Surface Finish (Ra) | ≤ 0.5 μm (polished) | ≤ 0.5 μm (polished) | ≤ 0.5 μm (polished) |
Specifications
| Parameter | Specification |
|---|---|
| Product Type | Stainless Steel Coil Tube (盘管 / Coiltube) |
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (1/4" – 1") |
| Wall Thickness | 0.5 mm – 1.5 mm |
| Coil Diameter | 100 mm – 500 mm (configurable) |
| Coil Pitch (Spacing) | 15 mm – 50 mm |
| Number of Rows | 1 – 6 rows |
| Tube Length (per coil) | 1.5 m – 12 m |
| End Connection | Flanged, Threaded (NPT/BSP), Soldered, or Brazed |
| Surface Treatment | Pickled & Passivated, Polished (Ra ≤ 0.5 μm), or Electropolished |
| Operating Pressure (Design) | ≤ 1.6 MPa (232 psi) |
| Operating Temperature Range | −40 °C to +250 °C |
| Working Media | Water, Glycol Solutions, Refrigerant, Air, Steam |
| Manufacturing Standard | ASTM A269 / ASTM A213 / GB/T 14976 / EN 10216-5 |
| Coating Option | Optional PTFE (Polytetrafluoroethylene) internal coating for enhanced anti-fouling |
| Customization | Available upon request — dimensions, geometry, and material grade |
Manufacturing Process
The production of the Stainless Steel Coil Tube follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, material integrity, and surface quality:
- Raw Material Procurement & Inspection: Cold-rolled stainless steel strip or seamless tube stock is sourced from certified mills. Incoming material undergoes spectroscopic analysis (PMI — Positive Material Identification) to verify chemical composition against the specified grade (e.g., SAE 304, 316). Mechanical test samples are subjected to tensile and hardness testing per ASTM E8 and ASTM E18, respectively.
- Cutting & Forming: The tube blank is cut to the required length using precision laser or shearing equipment. The tube is then formed into the coil geometry using CNC-controlled coiling machinery, which ensures consistent coil diameter, pitch, and row alignment. The coiling process employs controlled bending forces to prevent wall thinning, ovality distortion, or residual stress concentration.
- Heat Treatment (if required): For applications requiring solution annealing, the coiled tube is heated to 1010–1150 °C and rapidly quenched to restore full solution-tempered condition, ensuring optimal corrosion resistance and mechanical properties.
- Pickling & Passivation: The formed coil tube is subjected to acid pickling (typically using a mixture of nitric and hydrofluoric acid) to remove mill scale, oxidation, and surface contaminants. Subsequent passivation treatment forms a stable chromium oxide (Cr₂O₃) protective layer on the surface, enhancing long-term corrosion resistance.
- Surface Finishing: Depending on the application, the tube surface is polished to a mirror finish (Ra ≤ 0.5 μm) or electropolished for maximum smoothness and hygienic performance. Electropolishing removes the top 10–50 μm of surface material, eliminating micro-cracks and embedded contaminants.
- End Preparation & Connection Fabrication: Tube ends are prepared for the specified connection type — flanged ends are machined and welded with stainless steel flanges; threaded ends are rolled or cut to NPT/BSP standards; brazed joints are pre-tinned for subsequent assembly.
- Quality Inspection & Testing: Each coil tube undergoes comprehensive quality control including:
- Dimensional verification using calipers, micrometers, and CMM (Coordinate Measuring Machine)
- Pressure testing at 1.5× design pressure with visual leak inspection
- Helium leak detection for critical-seal applications
- Visual surface inspection for weld quality, scratches, and discoloration
- Chemical spot testing to confirm passivation layer integrity
- Packaging & Dispatch: The finished coil tube is individually wrapped in protective film, placed in wooden crates with desiccant packs to prevent moisture ingress, and labeled with traceability documentation including heat number, material certificate, and inspection report.
Applications
The Stainless Steel Coil Tube is specifically engineered for use in the following HVAC and building services applications:
1. Fan Coil Units (FCU) — Indoor Micro-Circulation Thermal Comfort Systems
As studied in the academic literature on Indoor Micro-Circulation Thermal Comfort in Fan Coil Plus Fresh Air Systems, the coil tube serves as the primary heat exchanger element within fan coil units. The micro-circulation design ensures that conditioned air is distributed in a controlled, localized manner around the occupant zone, achieving superior thermal comfort with reduced energy consumption. The stainless steel coil tube's high thermal conductivity and corrosion resistance ensure long-term performance stability in these precision-controlled environments.
2. Fresh Air Supply Systems
Integrated into dedicated outdoor air systems (DOAS) and fresh air handling units, the coil tube pre-cools or pre-heats incoming outdoor air to reduce the cooling or heating load on the main HVAC plant. The hygienic surface finish prevents microbial growth and biofilm formation, maintaining indoor air quality standards.
3. Commercial & Institutional Buildings
- Hospital and laboratory HVAC systems requiring high hygiene standards
- Data center precision cooling systems
- Office building perimeter cooling and heating zones
- Hotel and hospitality air conditioning systems
- School and educational facility ventilation systems
4. Residential HVAC Systems
- Multi-split air conditioning systems
- Hydronic radiant heating systems
- Whole-house fresh air ventilation with heat recovery
5. Industrial & Special Applications
- Pharmaceutical cleanroom HVAC systems (GMP-compliant)
- Food processing facility temperature control systems
- Marine and offshore HVAC installations (SAE 316 grade)
- High-humidity environments requiring corrosion-resistant heat exchangers
Quality Certifications & Standards Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — ensuring consistent product quality and customer satisfaction |
| ISO 14001:2015 | Environmental Management System — sustainable manufacturing practices |
| ASTM A269 | Standard Specification for Stainless Steel Tubing, Seamless, Cold-Finished, for Chemical and Other Severely Corrosive Services |
| ASTM A213 | Standard Specification for Seamless Austenitic Stainless Steel Tubing for High-temperature Service |
| GB/T 14976 | Chinese National Standard — Stainless Steel Tubes for Fluid Transport |
| EN 10216-5 | European Standard — Non-alloy and Alloy Steel Tubes for Technical Uses |
| CE Marking | European Conformity — compliance with EU safety, health, and environmental protection requirements |
| 3.1 / 3.2 Material Certificate (EN 10204) | Mill test certificates providing full traceability of material composition and mechanical properties |
| NSF/ANSI 61 | Drinking Water System Components — Health Effects (applicable for potable water applications) |
Unique Selling Points
- Superior Corrosion Resistance: The austenitic stainless steel construction provides exceptional resistance to corrosion from water, glycol solutions, and humid air, ensuring a service life exceeding 25 years without degradation of heat transfer performance.
- Hygienic Surface Finish: The electropolished surface (Ra ≤ 0.5 μm) prevents bacterial adhesion and biofilm accumulation, making the coil tube ideal for hospital, pharmaceutical, and food-grade HVAC applications.
- Optimized Micro-Circulation Performance: The coil geometry is designed to promote uniform air distribution and minimize dead zones, directly supporting the indoor micro-circulation thermal comfort principles established in HVAC research literature.
- Full Traceability: Every coil tube is accompanied by a complete material traceability package including mill test certificates, chemical analysis reports, and dimensional inspection records, ensuring compliance with international quality standards.
- Customization Capability: Wenzhou Jixing Metal Materials Co., Ltd. offers full customization of dimensions, material grade, connection type, and surface finish to meet specific project requirements, from standard commercial HVAC installations to specialized industrial applications.
- Sustainability: Stainless steel is 100% recyclable with no loss of material properties. The coil tube's long service life and minimal maintenance requirements contribute to the overall energy efficiency