Stainless Steel Coil Tube — FP-102WAZD Fan Coil Unit Integration Series
Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coil Tube") is a precision-engineered heat exchange component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Designed for seamless integration into HVAC (Heating, Ventilation, and Air Conditioning) systems — specifically the FP-102WAZD Fan Coil Unit (FCU) assembly — this product represents the convergence of metallurgical excellence and thermal engineering. The coil tube serves as the primary heat transfer medium, facilitating efficient thermal exchange between the refrigerant or hot water circuit and the ambient air stream within the fan coil unit envelope.
Unlike conventional carbon steel or copper tube alternatives, the stainless steel coil tube offers superior corrosion resistance, extended service life, and hygienic performance characteristics, making it particularly suitable for demanding environments including medical facilities, pharmaceutical cleanrooms, food processing plants, and coastal industrial installations.
Material Composition and Properties
The coil tube is fabricated from austenitic stainless steel grades conforming to international metallurgical standards. The primary material specification is as follows:
- Grade 304 (UNS S30408 / 1.4301): The standard-grade austenitic stainless steel containing 18% Chromium (Cr) and 8% Nickel (Ni), providing excellent general-purpose corrosion resistance and formability.
- Grade 316 (UNS S31603 / 1.4401): Enhanced-grade austenitic stainless steel with 2–3% Molybdenum (Mo) addition, offering superior resistance to pitting and crevice corrosion in chloride-rich environments.
- Grade 316L (UNS S31603L / 1.4404): Low-carbon variant of 316 with Carbon (C) content ≤ 0.03%, optimized for welding applications requiring resistance to intergranular corrosion (IGC).
Mechanical Properties (Typical Values for Grade 304)
- Tensile Strength (UTS): ≥ 515 MPa (74,700 psi)
- Yield Strength (0.2% Proof Stress): ≥ 205 MPa (29,700 psi)
- Elongation at Break: ≥ 40%
- Hardness (Brinell): ≤ 217 HB
- Thermal Conductivity (at 100°C): 16.3 W/(m·K)
- Coefficient of Thermal Expansion (20–100°C): 17.3 × 10⁻⁶ /K
- Density: 8.0 g/cm³
Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 6.35 mm (1/4"), 9.53 mm (3/8"), 12.70 mm (1/2") | ASTM A213 / ASME SA-213 |
| Wall Thickness | 0.50 mm – 1.20 mm | ASTM A269 |
| Coil Pitch (Helix Pitch) | 12.7 mm – 25.4 mm (adjustable per thermal load) | ISO 14692 |
| Coil Outer Diameter | 150 mm – 600 mm | Manufacturer's Design Specification |
| Tube Length per Coil | 3.0 m – 15.0 m (continuous) | — |
| Surface Finish | Ba ≤ 0.4 μm (Electropolished) or Ra ≤ 1.6 μm (Pickled & Passivated) | ASTM A967 |
| Operating Temperature Range | −196°C to +870°C | ASME BPVC Section VIII |
| Maximum Operating Pressure | 1.6 MPa (232 psi) — Design Pressure | ASME BPVC Section VIII, Div. 1 |
| Refrigerant / Fluid Compatibility | R-22, R-407C, R-410A, R-134a, Hot Water, Glycol Solutions | ASHRAE Standard 34 |
| Corrosion Resistance (Pitting) | PEN ≥ 18 (Grade 316L) | ASTM G48 Practice A |
| Welding Method | TIG (GTAW) — Tungsten Inert Gas Welding, Argon Shielded | ASME Section IX, Qualification Group PW-8 |
| Applicable FCU Model | FP-102WAZD (and derivative configurations) | Manufacturer's Product Manual |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous, multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and thermal performance:
- Raw Material Procurement and Inspection: Cold-rolled stainless steel strip is sourced from certified mills and subjected to spectrographic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance with ASTM specifications. Heat number traceability is maintained throughout the supply chain.
- Tube Forming (Cold-Forming / Seamless Drawing): The flat strip is precision-formed into a seamless tubular configuration using either a rotary-drawing process or a cold-forging die system. This ensures a homogeneous microstructure without weld seams that could compromise corrosion resistance or structural integrity.
- Coil Winding (Helical Forming): The formed tube is helically wound around a precision mandrel to achieve the specified coil pitch and outer diameter. The winding process is performed under controlled tension to prevent ovality distortion (ovality tolerance: ≤ 2% of OD) and kinking.
- Heat Treatment (Annealing): Where required, the coiled tube undergoes solution annealing at 1050°C ± 15°C followed by controlled cooling in an inert atmosphere (Argon or Nitrogen). This process relieves residual stresses, restores full austenitic grain structure, and ensures maximum corrosion resistance.
- Surface Treatment (Pickling and Passivation): The coil tube is treated with a nitric acid/hydrofluoric acid (HNO₃/HF) pickling solution to remove oxide scale, followed by passivation to establish a chromium-rich passive film (Cr₂O₃) thickness of 2–5 nm. This critical step ensures long-term corrosion immunity.
- Hydrostatic Pressure Testing: Each coil assembly is subjected to hydrostatic testing at 1.5× the design pressure (2.4 MPa) for a minimum of 30 seconds to verify weld integrity and dimensional soundness.
- Final Quality Inspection: Non-Destructive Testing (NDT) methods including eddy current inspection (ASTM E309) and visual examination (VT) are employed. Dimensional verification is performed using laser scanning and coordinate measuring machines (CMM).
Applications
The stainless steel coil tube is engineered for deployment in a wide spectrum of HVAC and thermal management applications:
- HVAC Fan Coil Units: Primary application in the FP-102WAZD series and equivalent commercial/industrial FCU systems for space heating, cooling, and dehumidification in office buildings, hotels, hospitals, and retail environments.
- Medical and Pharmaceutical Facilities: The hygienic surface finish and corrosion resistance make the coil tube suitable for cleanroom HVAC systems (ISO 14644 Class 5–8), operating theater ventilation, and pharmaceutical manufacturing facilities requiring CIP (Clean-in-Place) compatibility.
- Food and Beverage Processing: Compliance with FDA 21 CFR Part 178 and EU Regulation 1935/2004 ensures suitability for food-grade thermal exchange in breweries, dairies, and processing plants.
- Marine and Coastal Environments: Grade 316L coil tubes provide exceptional resistance to chloride-induced pitting corrosion in marine HVAC systems, offshore platforms, and coastal commercial installations.
- Industrial Process Cooling: Integration into industrial chiller systems, heat recovery units, and process water cooling loops where chemical resistance and thermal efficiency are paramount.
- Commercial Refrigeration: Use in evaporator coils for walk-in coolers, display cases, and refrigerated distribution centers.
Quality Certifications and Compliance
The manufacturing facility and product line hold the following certifications and comply with international standards:
- ISO 9001:2015 — Quality Management Systems
- ISO 14001:2015 — Environmental Management Systems
- ISO 45001:2018 — Occupational Health and Safety Management
- CE Marking (EU Directive 2014/68/EU — PED) — Pressure Equipment Directive compliance for pressure-bearing components
- ASME "S" Stamp / "U" Stamp — Section VIII, Division 1 certification for pressure vessels and components
- EN 10204 3.1 Material Test Certificate — Third-party verified material conformity
- NSF/ANSI 61 — Drinking Water System Components (where applicable to hydronic systems)
- UL 484 / UL 1995 — Safety certification for HVAC equipment integration
Unique Selling Points
1. Superior Corrosion Longevity: The austenitic stainless steel construction provides a service life exceeding 25 years in aggressive environments — significantly outperforming copper (10–15 years in chloride exposure) and carbon steel alternatives.
2. Hygienic Surface Integrity: Electropolished surfaces with Ra ≤ 0.4 μm prevent microbial adhesion and biofilm formation, meeting pharmaceutical GMP (Good Manufacturing Practice) requirements.
3. Thermal Efficiency Optimization: Precision-controlled coil pitch geometry maximizes the heat transfer surface area-to-volume ratio, achieving a heat transfer coefficient (U-value) of 250–350 W/(m²·K) depending on flow configuration.
4. Zero-Leak Guarantee: Seamless tube construction eliminates longitudinal weld seams, the primary failure point in conventional welded coil tubes, ensuring zero-leak integrity over the product lifecycle.
5. Full Traceability: Each production batch is accompanied by a complete material passport including mill certificate, heat number, chemical analysis, mechanical test data, and NDT reports — enabling full supply chain traceability per ISO 10007.
Integration Notes for FP-102WAZD Fan Coil Unit
When integrated into the FP-102WAZD Fan Coil Unit, the stainless steel coil tube is configured in a multi-row serpentine arrangement with aluminum fin tubes (fin spacing: 2.1 mm, fin thickness: 0.15 mm) to maximize air-side heat transfer. The coil tube connects to the unit's header manifold via brazed or welded joints (Type A brazing per AWS A5.8) with a nitrogen-purged joint to prevent copper oxide contamination. The overall unit achieves a cooling capacity of 2.0–5.5 kW and a heating capacity of 2.5–6.0 kW depending on the specific coil tube configuration and flow rate parameters.
The seamless integration of this stainless steel coil tube with the FP-102WAZD platform represents a significant advancement in HVAC component engineering, combining metallurgical durability with thermal performance optimization to deliver reliable, long-lasting climate control solutions.