Stainless Steel Coil Tube (Coiltube) — HVAC Fan Coil Unit Application
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled piping product designed primarily for integration into HVAC (Heating, Ventilation, and Air Conditioning) systems, with a particular focus on fan coil units (FCUs) such as the FWY-600 type positive-pressure ceiling-mounted fan coil unit that was successfully appraised in Shaoxing, Zhejiang Province, China. These coil tubes serve as the core heat exchange medium, facilitating efficient thermal transfer between refrigerant/circulating fluid and the surrounding air within HVAC assemblies.
Product Reference No.: 1612
As a specialized coiltube component, this product is engineered to meet the rigorous demands of commercial and residential air conditioning systems, ensuring long-term durability, corrosion resistance, and optimal thermal performance in demanding indoor environments.
2. Material & Properties
2.1 Base Material Composition
- Primary Alloy: Austenitic stainless steel conforming to standards such as ASTM A269 (Standard Specification for Seamless Austenitic Stainless Steel Tubing for Chemical and Fertilizer Plant Service) or GB/T 12771 (Chinese National Standard for welded stainless steel tubes for fluid transport).
- Common Grades: SUS304 (18/8), SUS316 (with molybdenum), or SUS321 (with titanium stabilization), selected based on service environment requirements.
- Carbon Equivalent (CE): ≤ 0.03% (low-carbon variant) to minimize intergranular corrosion susceptibility during welding operations.
2.2 Key Mechanical Properties
- Tensile Strength (UTS): ≥ 520 MPa (for 304 grade in annealed condition)
- Yield Strength (0.2% offset): ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness (Rockwell B): 80–95 HRB
- Impact Toughness (Charpy V-Notch at −40°C): ≥ 47 J
2.3 Corrosion & Thermal Properties
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, weak acids, alkalis, and chlorinated solutions; 316 grade offers superior resistance to pitting and crevice corrosion in chloride-rich environments.
- Thermal Conductivity: 14–16 W/(m·K) at 25°C
- Operating Temperature Range: −196°C to +870°C (continuous service)
- Surface Finish: Pickled and passivated (2B finish) or electropolished for hygienic applications
3. Specifications
| Parameter | Specification |
|---|---|
| Product Category | Coiled Tube (Coiltube) — HVAC Application |
| Reference No. | 1612 |
| Outer Diameter (OD) | φ9.52 mm, φ12.70 mm, φ15.88 mm, φ19.05 mm (customizable) |
| Wall Thickness (WT) | 0.50 mm – 1.20 mm (standard); up to 2.00 mm upon request |
| Coil Inner Diameter (CID) | φ150 mm – φ600 mm (tailored to FCU frame dimensions) |
| Coil Length | Continuous coil, typically 50–200 meters per coil |
| Material Grade | SUS304 / SUS316 / SUS321 (austenitic stainless steel) |
| Manufacturing Method | Seamless (cold-drawn) or ERW (Electric Resistance Welded) with precision coiling |
| Surface Treatment | Pickled & Passivated; optional electropolishing (Ra ≤ 0.4 μm) |
| Pressure Rating | ≥ 1.6 MPa (working pressure at 25°C); burst pressure ≥ 6.4 MPa |
| Dimensional Tolerance | OD: ±0.05 mm; WT: ±0.02 mm; conforming to ASTM A213 / GB/T 14976 |
| Applicable Standard | ASTM A269, ASTM A213, GB/T 12771, GB/T 14976, EN 10216-5 |
| Packaging | Wooden coil stand with moisture-proof wrapping and rust-preventive coating |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: High-purity stainless steel billet or coil stock (from certified mills) undergoes incoming inspection for chemical composition (spectroscopic analysis) and mechanical properties.
- Tubing Forming: Either seamless cold-drawing (CD) from precision billets or ERW welding of cold-rolled strip followed by heat treatment and pickling. The seamless route is preferred for high-pressure and critical HVAC applications.
- Heat Treatment: Solution annealing at 1050–1150°C followed by controlled air or water quenching to achieve full austenitic microstructure, ensuring maximum ductility and corrosion resistance.
- Precision Coiling: The formed tube is coiled using CNC-controlled coiling machines to achieve exact coil diameter, pitch, and turn-to-turn alignment. This step is critical for seamless integration into fan coil unit heat exchanger frames.
- Pickling & Passivation: Acid pickling (HNO₃/HF blend) removes scale and oxide; subsequent passivation treatment forms a protective Cr₂O₃ passive film on the surface.
- Hydrostatic Testing: Each coil undergoes hydrostatic pressure testing at 1.5× working pressure (minimum 2.4 MPa) for a dwell time of ≥ 30 seconds to verify weld integrity and structural soundness.
- Dimensional & Surface Inspection: Final inspection includes laser micrometry for OD/WT verification, surface roughness profiling, and visual examination for defects.
- Packaging & Dispatch: Coils are placed on wooden pallets or stands, wrapped in VCI (Vapor Corrosion Inhibitor) film, and labeled with batch traceability documentation.
4.2 Quality Control Milestones
- Incoming material certification (Mill Test Certificate — MTC) verification
- In-process dimensional checks at coiling station (statistical process control — SPC)
- Post-pickling surface quality audit (visual + magnetic particle inspection for subsurface defects)
- Final hydrostatic test with documented pressure–time records
5. Applications
5.1 Primary Application: HVAC Fan Coil Units
The coil tubes are specifically designed for integration into ceiling-mounted fan coil units (such as the FWY-600 series), where they function as the refrigerant or hydronic circuit heat exchange coil. The coiled geometry maximizes surface area within a compact envelope, enabling efficient sensible and latent heat transfer for space conditioning.
5.2 Secondary Applications
- Commercial Air Conditioning: Chilled water coils in VAV (Variable Air Volume) systems for office buildings, hotels, and hospitals.
- Industrial Process Cooling: Condenser and evaporator coils in chemical processing, food & beverage, and pharmaceutical cleanroom environments.
- Refrigeration Systems: Evaporator coils in cold storage and commercial refrigeration units requiring hygienic-grade materials.
- Heat Recovery Systems: Run-around coils in energy recovery ventilation (ERV) installations.
- Domestic HVAC: Ducted and ductless mini-split air conditioning systems for residential applications.
6. Quality Certifications & Compliance
6.1 Certifications Held
- ISO 9001:2015 — Quality Management System (QMS)
- ISO 14001:2015 — Environmental Management System (EMS)
- CE Marking — Conformity with EU Pressure Equipment Directive (PED 2014/68/EU) for pressure-bearing components
- GB/T 19001-2016 — Chinese national equivalent of ISO 9001
- National Product Appraisal — Successfully passed technical appraisal in Shaoxing, Zhejiang Province (for associated fan coil unit systems incorporating these coil tubes)
6.2 Material Traceability
Every coil tube batch is accompanied by a Mill Test Certificate (MTC) in accordance with EN 10204 Type 3.1, providing full traceability of chemical composition, mechanical test results, and heat treatment parameters. Batch numbering ensures end-to-end traceability from raw material to finished product.
6.3 Testing & Verification
- Chemical Analysis: Optical emission spectrometry (OES) or wet chemical analysis for full alloy composition verification
- Mechanical Testing: Tensile testing (ASTM E8), impact testing (ASTM E23), and hardness testing (ASTM E18)
- Corrosion Testing: Salt spray test (ASTM B117, 1000 hours minimum for 304 grade; 2000 hours for 316 grade), intergranular corrosion test (ASTM A269, Section 9)
- Non-Destructive Testing (NDT): Eddy current testing for surface/subsurface defect detection; magnetic particle inspection where applicable
7. Unique Selling Points
- Superior Corrosion Resistance: Austenitic stainless steel construction eliminates the risk of internal/external corrosion that plagues carbon steel alternatives, extending service life to 20+ years without replacement.
- Precision Coiling Geometry: CNC-controlled coiling ensures consistent pitch and alignment, enabling drop-in compatibility with standard fan coil unit frames and reducing assembly time.
- Hygienic Surface Finish: Electropolished surfaces (Ra ≤ 0.4 μm) prevent microbial growth and facilitate cleaning, making the product suitable for pharmaceutical and food-grade applications.
- Full Traceability: End-to-end batch tracking with EN 10204 3.1 certification provides complete material provenance documentation.
- Customization Capability: Wenzhou Jixing Metal Materials Co., Ltd. offers tailored OD, wall thickness, coil diameter, and length configurations to meet specific OEM requirements.
- Appraised System Integration: The coil tubes are validated as integral components of the nationally appraised FWY-600 fan coil unit system, providing proven performance in real-world HVAC installations.
Technical Note: When specifying coil tubes for fan coil unit integration, ensure that the coil inner diameter, tube OD, and wall thickness are matched to the heat exchanger frame geometry and refrigerant circuit design. Consult Wenzhou Jixing Metal Materials Co., Ltd. for application-specific engineering support and custom configuration.