Stainless Steel Coil Tube — Fan Coil System Application (Model No. 283)
1. Product Overview
The Stainless Steel Coil Tube (Product No. 283) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered coiled tubing product designed primarily for integration into Fan Coil Systems (FCS) used in high-rise building ventilation and air conditioning (HVAC) installations. This product represents a specialized segment within the coil tube family, combining the inherent corrosion resistance and hygienic properties of austenitic stainless steel with the geometric flexibility of continuously formed coil configurations.
The coil tube is engineered to serve as the heat exchange medium within fan coil units, where it facilitates efficient thermal transfer between circulating water (or refrigerant) and ambient air. Its coiled geometry maximizes surface area within compact envelope dimensions, making it particularly advantageous for space-constrained high-rise architectural environments.
Key Distinction: Unlike standard straight-length stainless steel tubing, this coil tube product is supplied in continuous helical or spiral coil configurations, enabling reduced installation labor, minimized joint leakage points, and superior hydraulic performance in closed-loop HVAC systems.
2. Material & Properties
2.1 Base Material Composition
The coil tube is fabricated from high-grade austenitic stainless steel, with the following typical material options available:
- AISI 304 (UNS S30408 / 1.4301): General-purpose grade with excellent corrosion resistance and formability. Contains 18–20% Chromium (Cr) and 8–10% Nickel (Ni).
- AISI 316L (UNS S31603 / 1.4404): Low-carbon variant with 2–3% Molybdenum (Mo) addition for enhanced resistance to pitting and crevice corrosion, particularly in chlorinated environments.
- AISI 321 (UNS S32100 / 1.4541): Titanium-stabilized grade offering superior resistance to intergranular corrosion at elevated temperatures (up to 870°C).
2.2 Mechanical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa | ASTM A213 / EN 10216-5 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ASTM A213 |
| Elongation (A50) | ≥ 35% | ASTM A213 |
| Hardness (HV) | ≤ 220 HV | ISO 6507 |
| Impact Energy (Charpy V-Notch, −40°C) | ≥ 47 J | ASTM A370 |
2.3 Physical & Thermal Properties
- Density: 8.00 g/cm³
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (20–100°C)
- Maximum Operating Temperature: 870°C (continuous)
- Corrosion Resistance: Excellent against atmospheric, aqueous, and mild chemical media; superior resistance to condensation water and dehumidification byproducts in HVAC environments.
3. Specifications
| Parameter | Specification | Notes |
|---|---|---|
| Product Designation | Coil Tube — Fan Coil Application | Product No. 283 |
| Outer Diameter (OD) | 6.0 mm – 25.0 mm | Custom diameters available upon request |
| Wall Thickness (WT) | 0.5 mm – 2.0 mm | ±0.1 mm tolerance |
| Coil Diameter | 500 mm – 2,000 mm | Adjustable based on installation requirements |
| Coil Length | 10 m – 200 m per coil | Continuous seamless coil |
| Surface Finish | No. 4 Brushed / BA (Bright Annealed) / Mirror (Ra ≤ 0.2 μm) | BA finish preferred for hygienic HVAC applications |
| Surface Roughness (Ra) | ≤ 0.8 μm (standard); ≤ 0.2 μm (electropolished) | ISO 1302 |
| End Preparation | Plain end / Beveled (37.5° ± 1°) / Flanged | Beveled ends recommended for welding |
| Operating Pressure | Up to 1.6 MPa (design); 2.4 MPa (burst) | Based on 6.0 mm OD × 0.8 mm WT configuration |
| Operating Temperature Range | −40°C to +250°C | Standard HVAC range: 5°C to +95°C |
| Coil Straightness | ≤ 1.5 mm/m | Measured per ASTM A213 |
| Dimensional Tolerance | OD: ±0.05 mm; WT: ±0.05 mm | Per EN 10216-5 Class T1 |
| Packaging | Wooden pallet / Steel drum with moisture barrier | Export-grade packaging available |
4. Manufacturing Process
The production of this stainless steel coil tube follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection & Ingot Casting: High-purity stainless steel billets are sourced from certified mills, with chemical composition verified via Optical Emission Spectroscopy (OES) to ensure compliance with ASTM A213 or EN 10216-5 specifications.
- Hot Rolling & Piercing: Billets are heated to 1,200–1,250°C and hot-rolled into seamless tube blanks with controlled wall thickness.
- Pilot Tube Drawing / Cross Rolling: The tube blanks are drawn through precision dies to achieve the target outer diameter and wall thickness with tight tolerances (±0.05 mm).
- Cold Drawing & Sizing: Further cold work is applied to refine dimensional accuracy and induce beneficial work-hardening, improving mechanical properties while maintaining ductility.
- Solution Annealing: Tubes are heated to 1,050–1,150°C and rapidly quenched in air or water to dissolve carbide precipitates, restore full austenitic microstructure, and relieve cold-work stresses. This ensures optimal corrosion resistance and toughness.
- Surface Finishing: Depending on the specified grade, tubes undergo Pickling & Passivation (acid immersion to remove oxide scale), Brushing (No. 4 finish), or Electropolishing (mirror finish with Ra ≤ 0.2 μm) for hygienic HVAC applications.
- Coil Forming: The straight tubes are fed through precision bending stations equipped with hydraulic servo-control systems to form continuous coils of the specified diameter. The forming process is carefully controlled to prevent ovalization, kinking, or micro-cracking at the bend radius.
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Quality Inspection & Testing: Each coil undergoes comprehensive inspection including:
- Dimensional verification (OD, WT, coil diameter) via ultrasonic and caliper measurement
- Hydrostatic pressure testing (1.5× working pressure, held for minimum 10 seconds)
- Surface inspection (visual + magnetic particle or eddy current for surface defects)
- Chemical composition verification (OES or spark spectrometry)
- Corrosion testing (salt spray per ASTM B117, minimum 24 hours without red rust)
- Packaging & Dispatch: Qualified coils are wrapped with protective film, placed on wooden pallets or steel drums, and labeled with full traceability documentation including heat number, mill certificate, and test reports.
5. Applications
5.1 Primary Application — Fan Coil Systems in High-Rise Buildings
The principal application domain for this product is within Fan Coil Systems (FCS) installed in high-rise commercial and residential buildings. In such systems, the stainless steel coil tube serves as the core heat exchange element, performing the following functions:
- Heating & Cooling: Transfers thermal energy between circulating water (from a central chiller or boiler plant) and the indoor air stream drawn by the fan unit. The coiled geometry provides high surface-area-to-volume ratio, achieving thermal efficiency (COP) improvements of 15–25% over flat-plate alternatives.
- Dehumidification: During cooling mode, moisture condenses on the cold coil surface. The stainless steel material's inherent resistance to condensation water corrosion eliminates the need for additional coatings, ensuring long service life in humid indoor environments.
- Hygienic Air Quality: The smooth, non-porous surface of BA-finish stainless steel prevents microbial colonization (bacteria, mold, Legionella), complying with indoor air quality (IAQ) standards such as ASHRAE 62.1 and ISO 16890.
5.2 Performance Optimization in High-Rise Ventilation
Research into the application of fan coil systems in high-rise buildings has identified several performance challenges that this product addresses:
- Pressure Drop Optimization: The precise inner diameter tolerance (±0.05 mm) of this coil tube minimizes turbulent flow losses, reducing the pumping energy requirement by 8–12% compared to tubes with wider tolerances.
- Thermal Stress Management: The austenitic microstructure provides excellent thermal shock resistance, accommodating the rapid temperature cycling common in high-rise HVAC systems with varying floor-zone loads.
- Corrosion-Free Longevity: In high-rise buildings where recirculated air may contain trace chlorides from coastal locations or cleaning agents, the Mo-bearing 316L grade provides a design life exceeding 25 years without degradation.
- Maintenance Reduction: The seamless coil construction eliminates brazed joints that are common failure points in copper-tube alternatives, reducing maintenance intervals and lifecycle costs.
5.3 Secondary Applications
- Chilled water distribution loops in commercial HVAC systems
- Underfloor radiant heating and cooling systems
- Pharmaceutical and food-grade cleanroom HVAC installations (316L electropolished grade)
- Marine HVAC systems for offshore platforms and luxury vessels
- Industrial process cooling circuits requiring corrosion-resistant heat exchange
6. Quality Certifications & Standards Compliance
This product is manufactured under a certified Quality Management System (QMS) and complies with the following international standards and certifications:
| Certification / Standard | Description | Relevance |
|---|---|---|
| ISO 9001:2015 | Quality Management Systems | Ensures consistent product quality and process control |
| ISO 14001:2015 | Environmental Management Systems | Demonstrates environmentally responsible manufacturing |
| ISO 45001:2018 | Occupational Health & Safety | Worker safety in production processes |
| ASTM A213 | Standard Specification for Seamless Austenitic Stainless Steel Tubing | Material and product specification compliance |
| EN 10216-5 | Seamless and Welded Stainless Steel Tubes for Heat Exchangers | European standard for HVAC heat exchange applications |
| GB/T 14976 (Chinese National Standard) | Stainless Steel Seamless Tubes for Fluid Transport | Mandatory compliance for domestic Chinese market |
| NORSOK M-001 | Requirements for Materials in Offshore Applications | For marine and offshore HVAC applications |
| NSF/ANSI 61 | Drinking Water System Components — Health Effects | For potable water contact applications |
| CE Marking (EU) | European Conformity |