Stainless Steel Coil Tube — HVAC Fan Coil Unit (Dry Condition) Application Grade
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Catalog No.: 1169 | Product Category: Stainless Steel Coil Tube (Coiltube) for HVAC Systems
1. Product Overview
The Wenzhou Jixing Stainless Steel Coil Tube is a precision-engineered, cold-rolled stainless steel tubing product specifically designed for use in Fan Coil Unit (FCU) systems operating under dry-condition configurations integrated with Fresh Air (FA) Conditioning methods. This coil tube serves as the core heat-exchange medium in air distribution systems where latent heat removal is managed externally via dedicated fresh air handling, thereby maintaining the coil surface temperature above the dew point and eliminating condensation risk.
Unlike conventional copper or carbon steel coil tubes, the stainless steel construction provides superior resistance to corrosion, scaling, and microbial growth — attributes critical for maintaining indoor air quality (IAQ) and extending service life in demanding commercial and industrial environments. The coil tube is supplied in continuous coil form, enabling seamless coil winding processes without the need for brazing or welding at intermediate joints, which minimizes leak points and ensures uniform hydraulic performance.
2. Material & Properties
2.1 Grade Composition
The primary material grade utilized is AISI 304 (UNS S30400) austenitic stainless steel, with optional availability in AISI 316L (UNS S31603) for enhanced chloride resistance in coastal or chemically aggressive environments.
- Carbon (C): ≤ 0.08% (304) / ≤ 0.03% (316L)
- Chromium (Cr): 18.0% – 20.0%
- Nickel (Ni): 8.0% – 10.5%
- Molybdenum (Mo): — (304) / 2.0% – 3.0% (316L)
- Manganese (Mn): ≤ 2.0%
- Sulfur (S): ≤ 0.030%
2.2 Mechanical & Thermal Properties
- Tensile Strength: ≥ 515 MPa (75,000 psi)
- Yield Strength: ≥ 205 MPa (30,000 psi)
- Elongation: ≥ 40% (at 50 mm gauge length)
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C
- Density: 8.0 g/cm³
- Operating Temperature Range: −196°C to +870°C
2.3 Surface Finish
The coil tube is available in Bright Annealed and Pickled (BAP), No. 4 Brushed, or Mirror (8K) finishes. The inner surface is maintained at a roughness of Ra ≤ 0.8 μm to minimize flow resistance and prevent biofilm accumulation, which is particularly important in HVAC applications where water quality directly impacts indoor air quality.
3. Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (¼"), 9.52 mm (⅜"), 12.70 mm (½"), 15.88 mm (⅝"), 19.05 mm (¾") | ASTM A778 / GB/T 12771 |
| Wall Thickness | 0.50 mm – 1.50 mm (standard); 0.30 mm – 0.50 mm (thin-wall option) | ASME B36.19M |
| Coil Diameter | 500 mm – 1,200 mm (adjustable per customer requirement) | Manufacturer Specification |
| Coil Length | Up to 500 m per coil (continuous, seamless) | — |
| Surface Roughness (Inner) | Ra ≤ 0.8 μm | ISO 4287 |
| Surface Roughness (Outer) | Ra ≤ 1.6 μm (BAP); Ra ≤ 0.4 μm (Mirror) | ISO 4287 |
| Pressure Rating | Up to 1.6 MPa (232 psi) at 25°C | EN 12729 |
| Dimensional Tolerance (OD) | ±0.05 mm (precision grade) | ASTM A778 |
| Dimensional Tolerance (Wall) | ±0.03 mm | ASTM A778 |
| Strut Size (for Fin-Coil Assembly) | Standard: 2.0 mm × 2.0 mm; Custom: 1.5 mm – 3.0 mm | ASHRAE Standard 15 |
| Fin Pitch (Recommended) | 10 – 14 fins per inch (FPI) | — |
| Maximum Working Pressure | 1.6 MPa (gauge) | EN 12729 / GB/T 12771 |
| Hydrostatic Test Pressure | 2.5 × Working Pressure (minimum 3.0 MPa) | ASME B31.9 |
4. Manufacturing Process
The production of the Wenzhou Jixing Stainless Steel Coil Tube follows a rigorous multi-stage manufacturing workflow adhering to international quality standards:
- Raw Material Selection & Ingot Casting: High-purity nickel and chromium feedstocks are melted in vacuum arc furnaces (VAR) or electron beam melting (EBM) to produce ultra-clean ingots with minimized impurity content.
- Hot Rolling & Annealing: Ingot slabs are hot-rolled into strip stock and subsequently annealed at 1,050°C – 1,100°C to achieve a fully austenitic microstructure with uniform grain size.
- Cold Rolling & Cold Drawing: The strip is cold-rolled to the target wall thickness with controlled reduction ratios (≤ 80% per pass) to ensure dimensional accuracy and mechanical property consistency.
- Seam Welding (if applicable): For welded tube configurations, high-frequency induction welding (HFW) or orbital TIG welding is employed with full penetration and 100% radiographic inspection (RT) of weld seams.
- Coil Winding & Forming: The continuous tube is precisely wound onto mandrels of the required coil diameter using CNC-controlled winding equipment to ensure uniform spacing and absence of kinks or deformation.
- Solution Annealing & Pickling: Post-forming annealing at 1,050°C followed by acid pickling and passivation removes oxide scale and restores the protective chromium oxide layer.
- Final Inspection & Testing: Includes hydrostatic pressure testing, dimensional verification, surface inspection, and material certification.
5. Applications
The coil tube is engineered for the following primary application domains:
- HVAC Fan Coil Units (Dry-Condition Operation): Serves as the heat exchange coil in FCUs where the coil operates above the dew point, with dehumidification handled by a separate fresh air system. This configuration eliminates condensate drainage, reduces microbial growth risk, and improves overall system efficiency.
- Fresh Air Conditioning Systems: Integrated with dedicated outdoor air systems (DOAS) for precise control of ventilation air temperature and humidity.
- Commercial Air Handling Units (AHU): Used in heating, cooling, and ventilation coils for office buildings, hospitals, and laboratories requiring high IAQ standards.
- Food & Pharmaceutical Processing: Hygienic-grade stainless steel coil tubes for process cooling and heating where sanitary requirements are paramount.
- Marine & Coastal Applications: 316L grade coil tubes for HVAC systems in marine environments with high chloride exposure.
- Industrial Process Cooling: Precision temperature control in manufacturing processes requiring corrosion-resistant heat exchangers.
6. Unique Selling Points
- Elimination of Condensation Risk: In dry-condition FCU configurations, the stainless steel coil tube operates above the dew point, completely eliminating condensate formation and the associated risks of mold growth, microbial proliferation, and structural water damage.
- Superior Corrosion Resistance: The austenitic stainless steel matrix provides exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking — far surpassing copper and carbon steel alternatives in longevity.
- Seamless Continuous Coil: The coil form eliminates intermediate joints and brazing points, resulting in a virtually leak-free heat exchanger with uniform flow distribution.
- Enhanced Indoor Air Quality: The smooth inner surface (Ra ≤ 0.8 μm) and passive chromium oxide layer inhibit biofilm formation, contributing to healthier indoor environments.
- Full Customization: OD, wall thickness, coil diameter, and surface finish are all customizable to meet specific project requirements and OEM specifications.
- Extended Service Life: Expected operational lifespan exceeds 25 years under normal conditions, significantly outperforming copper coil alternatives (typically 10–15 years).
7. Quality Certifications & Compliance
All Wenzhou Jixing Stainless Steel Coil Tube products are manufactured under a certified quality management system and conform to the following international and national standards:
- ISO 9001:2015 — Quality Management Systems
- ISO 14001:2015 — Environmental Management Systems
- ISO 45001:2018 — Occupational Health & Safety Management
- ASTM A778 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing
- ASTM A270 — Standard Specification for Seamless and Wrought Stainless Steel Tubing, Hydraulic and Structural
- ASME B36.19M — Dimensions for Welded and Seamless Wrought Stainless Steel Pipe
- GB/T 12771 — Stainless Steel Seamless Tubes for General Purposes (Chinese National Standard)
- EN 10217-7 — Technical Delivery Conditions for Stainless Steel Tubes for Mechanical and Technical Purposes
- ASME B31.9 — Pressure Piping — Process Piping
- ASHRAE Standard 15 — Safety Standard for Refrigeration Systems
- EN 12729 — Stainless Steel Tubes for Pressure Purposes
8. Technical Note on Dry-Condition FCU + Fresh Air Integration
In the dry-condition Fan Coil Unit (FCU) configuration, the stainless steel coil tube operates at a surface temperature maintained above the dew point of the indoor air. Dehumidification is exclusively performed by a separate Fresh Air (FA) handling unit, which introduces precisely conditioned outdoor air. This architectural separation of sensible and latent loads offers several engineering advantages: (1) the coil tube experiences no condensate, thereby eliminating the need for drain pans and condensate pumps; (2) the absence of standing water on the coil surface prevents Legionella and other pathogenic microbial growth; (3) the coil tube can be operated at higher temperatures, improving the Coefficient of Performance (COP) of the associated chiller plant; and (4) the overall system achieves superior IAQ through dedicated filtration and conditioning of the ventilation air stream. The stainless steel coil tube material is ideally suited for this application due to its corrosion resistance, thermal conductivity, and hygienic surface properties.
For further technical inquiries, custom specifications, or bulk procurement requests, please contact Wenzhou Jixing Metal Materials Co., Ltd. directly.