Stainless Steel Coil Tube for HVAC Fan Coil Unit Applications
Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "SST Coil Tube") manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product specifically designed for use in medium-temperature water air conditioning systems and fan coil units (FCUs). This product represents a critical component in hydronic heat exchange systems, where thermal efficiency, corrosion resistance, and mechanical durability are paramount. The SST Coil Tube is formed through advanced cold-rolling and coiling technologies, ensuring consistent dimensional accuracy and superior surface quality suitable for demanding HVAC and refrigeration applications.
Material & Properties
The SST Coil Tube is fabricated from high-grade austenitic stainless steel, primarily utilizing grades 304 (UNS S30408) and 316L (UNS S31603), selected for their exceptional balance of mechanical strength, corrosion resistance, and thermal conductivity. The following table summarizes the key material properties:
| Property | Grade 304 (UNS S30408) | Grade 316L (UNS S31603) |
|---|---|---|
| Chemical Composition (Cr%) | 18.0 – 20.0 | 16.0 – 18.0 |
| Chemical Composition (Ni%) | 8.0 – 10.5 | 10.0 – 14.0 |
| Molybdenum (Mo%) | — | 2.0 – 3.0 |
| Tensile Strength (MPa, min.) | 515 | 485 |
| Yield Strength (MPa, min.) | 205 | 170 |
| Thermal Conductivity (W/m·K, at 20°C) | 16.3 | 14.6 |
| Corrosion Resistance | Excellent (general environments) | Superior (chloride-rich environments) |
| Operating Temperature Range (°C) | −196 to +870 | −196 to +870 |
| Surface Finish | 2B / No.4 / BA (Bright Annealed) — customizable | |
Key Material Advantages
- Non-magnetic properties in annealed condition, eliminating electromagnetic interference concerns in sensitive HVAC control environments.
- Superior hygienic performance — the smooth, non-porous surface resists biofilm formation, making it ideal for potable water and clean air distribution systems.
- Outstanding fatigue resistance under cyclic thermal loading, extending service life in continuous-duty fan coil applications.
- Full recyclability — stainless steel retains 100% of its material value upon recycling, supporting sustainable manufacturing practices.
Specifications
The following table details the dimensional and performance specifications of the SST Coil Tube product line:
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 9.52 mm – 50.8 mm (3/8" – 2") |
| Wall Thickness | 0.5 mm – 2.0 mm |
| Coil Inner Diameter (ID) | 300 mm – 1200 mm (adjustable per order) |
| Coil Length per Roll | Up to 5,000 m (continuous coil) |
| Dimensional Tolerance (OD) | ±0.05 mm – ±0.15 mm (per ASTM A513) |
| Dimensional Tolerance (Wall Thickness) | ±0.03 mm – ±0.10 mm |
| Surface Roughness (Ra) | ≤ 0.4 μm (BA finish); ≤ 0.8 μm (2B finish) |
| Pressure Test Rating | Up to 2.5 MPa (363 psi) hydrostatic |
| Heat Transfer Coefficient | ≥ 2,500 W/m²·K (internal, turbulent flow) |
| Weight per Meter (typical) | 0.08 kg/m – 0.45 kg/m (varies by OD × WT) |
| Applicable Standards | ASTM A513, ASTM A269, EN 10217-7, GB/T 14976 |
Manufacturing Process
The production of the SST Coil Tube follows a rigorous, multi-stage manufacturing protocol to ensure consistent quality and performance:
- Raw Material Procurement & Inspection — Stainless steel strip or seamless pipe stock is sourced from certified mills and subjected to spectroscopic analysis (OES) and mechanical testing to verify compliance with specified grades.
- Surface Preparation — Incoming material undergoes degreasing, acid pickling, and passivation to remove mill scale, oxides, and contaminants, establishing a clean substrate for subsequent processing.
- Cold Forming & Coiling — The tube blank is fed through precision-calibrated roller forming stations, where controlled reduction ratios and die geometries produce the target OD and wall thickness. The continuous coil is wound onto spools under tension control to prevent deformation and kinking.
- Solid Solution Annealing — Formed coils are heat-treated at 1050°C – 1150°C in a controlled-atmosphere furnace (dew point ≤ −60°C) followed by rapid quenching. This restores full austenitic microstructure, eliminates residual stresses, and achieves maximum ductility and corrosion resistance.
- Precision Cutting & Coiling to Final Dimensions — Coils are slitted, cut to specified lengths, and re-coiled to final dimensions with automated edge trimming and burr removal.
- Final Inspection & Testing — Each coil lot undergoes hydrostatic pressure testing, dimensional verification via laser gauging, surface finish measurement, and visual inspection. Sampling is conducted per ASTM A269/A513 protocols.
- Packaging & Dispatch — Finished coils are wrapped in moisture-proof film, strapped, and palletized for secure transportation, with accompanying mill test certificates and traceability documentation.
Applications
The SST Coil Tube finds extensive application across multiple sectors, with primary focus on HVAC and related thermal management systems:
Primary Applications
- Medium-Temperature Water Air Conditioning Systems — As the core heat exchange element in fan coil units, the SST Coil Tube facilitates efficient heat transfer between circulating water (typically 35°C – 55°C for heating; 7°C – 18°C for cooling) and ambient air.
- Commercial & Residential HVAC Systems — Used in ceiling-mounted, wall-mounted, and ducted fan coil units for precise temperature and humidity control in offices, hospitals, hotels, and residential complexes.
- Industrial Process Cooling — Employed in process chillers, condensers, and evaporators where corrosion-resistant heat exchange surfaces are required.
Secondary Applications
- Refrigeration & Cryogenic Systems — Suitable for ammonia and CFC-free refrigerant circuits due to excellent chemical compatibility.
- Domestic Hot Water & Radiator Systems — Utilized in boiler feedwater coils, underfloor heating manifolds, and radiator serpentine tubes.
- Food & Beverage Processing — Hygienic-grade coils for pasteurization, sterilization, and clean-in-place (CIP) compatible heat exchange equipment.
- Pharmaceutical & Medical Equipment — Compliant with sanitary standards for use in bioreactor cooling jackets and medical air preparation systems.
Performance in Fan Coil Unit Systems
Research into medium-temperature water air conditioning system fan coil unit performance has demonstrated that the use of stainless steel coil tubes yields measurable improvements in overall system efficiency. Compared to traditional copper tube and aluminum fin (CU-AL) configurations, SST Coil Tubes offer comparable or superior heat transfer coefficients while providing significantly enhanced corrosion resistance — particularly in environments where water quality control is challenging. The thermal stability of austenitic stainless steel across wide temperature ranges minimizes thermal fatigue cracking, reducing maintenance intervals and extending the service life of fan coil units by an estimated 30% – 50%.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring full compliance with international and domestic standards:
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System — covers all manufacturing, inspection, and dispatch processes. |
| ISO 14001:2015 | Environmental Management System — governs waste, emissions, and resource utilization controls. |
| ISO 45001:2018 | Occupational Health & Safety Management System. |
| CE Marking (EU) | Compliance with European Machinery Directive and Pressure Equipment Directive (PED 2014/68/EU) for pressure-containing applications. |
| ASTM A513 / A269 | American Society for Testing and Materials — seamless and welded stainless steel tube specifications. |
| EN 10217-7 | European standard for austenitic stainless steel tubes for pressure purposes. |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes for general engineering purposes. |
| NB (National Supervision) | China's National Supervision and Inspection Bureau certification for pressure vessel and pressure piping components. |
| Mill Test Certificate (MTC) — EN 10204 3.1 | Third-party verified material certification issued with every production lot, ensuring full chemical and mechanical traceability. |
Unique Selling Points
- Enhanced Corrosion Resistance — The inherent chromium oxide passive layer provides self-healing protection, dramatically outperforming carbon steel alternatives in humid, saline, or chemically aggressive environments.
- Extended Service Life — Elimination of internal and external corrosion mechanisms translates to a projected service life exceeding 25 years in standard HVAC duty, with minimal degradation of heat transfer performance.
- Hygienic & Food-Grade Compliance — BA (Bright Annealed) finish options meet FDA and 3-A sanitary standards, enabling direct use in food, beverage, and pharmaceutical processing applications without additional surface treatment.
- Design Flexibility — Available in a wide range of OD and wall thickness combinations, with custom coil dimensions and surface finishes tailored to specific OEM requirements.
- Sustainable Manufacturing — Full recyclability and low embodied carbon relative to alternative materials align with global ESG (Environmental, Social, and Governance) and green building certification objectives (LEED, BREEAM).
- Comprehensive Documentation — Every shipment includes a full quality dossier comprising material certificates, dimensional inspection reports, and pressure test records, facilitating seamless integration into client quality assurance workflows.
Technical Notes
Users and system integrators are advised to observe the following guidelines when specifying and installing SST Coil Tubes in fan coil unit and HVAC applications:
- Ensure compatible welding methods (TIG/GTAW preferred) with filler metals matching the base alloy grade to preserve corrosion resistance at weld joints.
- Implement proper water treatment and filtration to prevent scaling and biofouling within the coil circuit, thereby maintaining optimal thermal performance over the system lifecycle.
- Adhere to manufacturer-recommended maximum operating pressures and temperatures; consult the applicable standard (ASTM A513 or EN 10217-7) for pressure rating tables specific to each OD × WT combination.
- Store coils in a dry, indoor environment away from direct contact with carbon steel to prevent galvanic corrosion and surface staining.