Stainless Steel Coil Tube for Fan Coil Unit (FCU) Applications
Product Overview
The Stainless Steel Coil Tube (SST Coil) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered coiled tubing product designed primarily for the heat exchanger cores of Fan Coil Units (FCU) and related HVAC (Heating, Ventilation, and Air Conditioning) systems. This product is categorized under the technical literature and research domain, reflecting its integral role in the cooling capacity conversion and unit selection optimization of fan coil assemblies. The coil tube serves as the primary working medium circuit within FCU systems, facilitating efficient thermal energy transfer between the refrigerant or hot/cold water loop and the ambient air stream.
As a critical component in commercial and residential HVAC systems, the SST Coil Tube must meet stringent requirements for thermal conductivity, corrosion resistance, mechanical integrity, and dimensional precision. Wenzhou Jixing Metal Materials Co., Ltd leverages advanced cold-drawing and coiling technologies to produce coil tubes that optimize the cooling capacity performance of fan coil units while ensuring long-term operational reliability.
Material & Properties
The coil tube is fabricated from high-grade stainless steel, with the following material specifications:
- Primary Alloy Grade: SUS304 / ASTM A269 TP304 (18% Chromium, 8% Nickel austenitic stainless steel)
- Alternative Grade: SUS316L / ASTM A269 TP316L (for enhanced chlorides and corrosion resistance in aggressive environments)
- Surface Finish: Mirror-polished (Ra < 0.4 μm) or matte passivated finish to minimize internal friction and fouling
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (SUS304), ensuring efficient heat transfer across the coil surface
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, condensation water, and mild chemical exposure; pitting resistance equivalent number (PREN) ≥ 19 for 304 grade
- Mechanical Properties: Yield strength ≥ 205 MPa; tensile strength ≥ 515 MPa; elongation ≥ 40%
- Operating Temperature Range: −196°C to +870°C (SUS304), comfortably accommodating all HVAC refrigerant and hydronic circuit temperatures
- Hygienic Compliance: Smooth internal bore prevents bacterial adhesion and supports easy sanitization, meeting food-grade and pharmaceutical-grade cleanliness standards
Specifications
| Parameter | Specification | Unit | Standard / Reference |
|---|---|---|---|
| Outer Diameter (OD) | 6.35 / 8.00 / 9.53 / 12.70 | mm | ASTM A269 / GB/T 12771 |
| Wall Thickness (WT) | 0.50 / 0.60 / 0.80 / 1.00 | mm | ±10% tolerance |
| Inner Diameter (ID) | 5.35 / 6.80 / 7.93 / 10.70 | mm | Derived from OD − 2×WT |
| Coil Pitch (Turn-to-Turn Spacing) | 1.5 – 4.0 | mm | Customizable per FCU design |
| Coil Diameter (Mean) | 150 – 600 | mm | Application-dependent |
| Coil Length (Total Tube Length) | 5.0 – 50.0 | m | Per heat exchanger core requirement |
| Coil Turns | 15 – 200 | turns | Determined by thermal load |
| End Connection Type | Flared / Butt-welded / Brazed / Crimped | — | Per OEM specification |
| Surface Roughness (Internal) | ≤ 0.8 | μm Ra | ISO 1101 |
| Surface Roughness (External) | ≤ 1.6 | μm Ra | ISO 1101 |
| Pressure Rating | ≥ 1.6 | MPa | HVAC standard operating pressure |
| Hydrostatic Test Pressure | 2.4 – 3.2 | MPa | 1.5× operating pressure |
| Coating (Optional) | Anti-corrosion passivation / PTFE lining | — | Per application requirement |
| Applicable Refrigerants | R-134a, R-410A, R-22, R-32, Water/Glycol | — | ASHRAE Standard 34 |
Manufacturing Process
The production of the Stainless Steel Coil Tube at Wenzhou Jixing Metal Materials Co., Ltd follows a rigorous multi-stage manufacturing workflow to ensure dimensional accuracy, metallurgical integrity, and functional performance:
- Raw Material Procurement: Stainless steel strip or seamless tube stock sourced from certified mills (e.g., Outokumpu, POSCO, Taiyuan Stainless Steel) with full mill test certificates (MTC) conforming to EN 10204 Type 3.1.
- Coil Annealing: Incoming material is subjected to solution annealing at 1050°C – 1150°C followed by rapid quenching to dissolve carbide precipitates and restore full austenitic ductility.
- Cold Drawing / Forming: Precision cold-drawing through tungsten carbide (WC) dies reduces the tube to the target OD and WT with controlled work hardening. Multi-pass drawing ensures uniform wall thickness within ±5%.
- Precision Coiling: The formed tube is wound onto a CNC-controlled coiling machine with programmable pitch, diameter, and turn count. Real-time tension control prevents kinking, ovality, or springback.
- End Forming & Connection Preparation: Tube ends are flared, crimped, or prepared for brazing/butt-welding per the FCU OEM assembly specification.
- Surface Passivation: Chemical passivation treatment (nitric acid or citric acid immersion) removes free iron contamination and establishes a stable chromium oxide passive film (Cr₂O₃) on the surface.
- Non-Destructive Testing (NDT): 100% eddy current testing (ECT) for wall thickness verification; dye penetrant testing (PT) for surface defect detection; optional ultrasonic testing (UT) for internal flaw detection.
- Hydrostatic Pressure Testing: Each coil assembly is pressure-tested at 1.5× the rated working pressure to verify leak-tightness and structural integrity.
- Final Inspection & Packaging: Dimensional verification via coordinate measuring machine (CMM); visual inspection for surface quality; protective packaging with desiccants and moisture barrier wrapping.
Applications
The Stainless Steel Coil Tube is engineered for integration into the following HVAC and thermal management systems:
- Fan Coil Units (FCU): Primary application — serves as the refrigerant or hydronic heat transfer circuit within ceiling-mounted, wall-mounted, or ducted FCU assemblies. The coil tube geometry directly influences the cooling capacity conversion efficiency and the selection parameters (airflow rate, ΔT, COP) of the FCU.
- Chiller Heat Exchangers: Used in shell-and-tube and plate-and-frame heat exchangers within central chiller plants for large commercial buildings.
- Condensers & Evaporators: Integral component of split-type and packaged air conditioning systems.
- Heat Recovery Units (HRU): Enables energy-efficient heat exchange in ventilation systems with heat recovery functionality.
- Refrigerated Display Cabinets: Commercial refrigeration equipment requiring corrosion-resistant heat exchange tubes.
- Process Cooling Systems: Industrial applications including pharmaceutical manufacturing, food processing, and electronics cooling where hygiene and corrosion resistance are critical.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system ensuring that every coil tube product meets international standards and regulatory requirements:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- ISO 45001:2018 — Occupational Health and Safety Management System
- ASTM A269 / A270 — Standard specification for austenitic stainless steel seamless, welded, and heavily cold-worked tubing
- EN 10217-7 — European standard for seamless stainless steel tubes for pressure purposes
- GB/T 12771 — Chinese national standard for welded stainless steel tubes
- JIS G3446 — Japanese Industrial Standard for seamless stainless steel tubes
- ASME B31.5 — Process piping design compliance for refrigeration and air conditioning systems
- RoHS 2.0 (EU Directive 2011/65/EU) — Restriction of hazardous substances compliance
- REACH (EC No 1907/2006) — Registration, Evaluation, Authorisation and Restriction of Chemicals compliance
- SGS / BV / TUV Third-Party Inspection — Independent quality verification available upon request
Unique Selling Points
1. Superior Thermal Performance: The precision-controlled coil geometry and high-purity austenitic stainless steel material deliver optimized cooling capacity conversion, directly contributing to the energy efficiency (COP/EER) of the host Fan Coil Unit. The smooth internal bore minimizes flow resistance, reducing pumping power and fan energy consumption.
2. Exceptional Corrosion Durability: Unlike copper or aluminum coil tubes, the stainless steel construction provides outstanding resistance to condensate corrosion, chloride-induced pitting, and chemical degradation — significantly extending service life in coastal, industrial, and high-humidity environments.
3. Precision Manufacturing for Optimal FCU Selection: Each coil tube is manufactured to exact dimensional tolerances that enable accurate cooling capacity calculations and proper FCU unit selection. The controlled pitch, diameter, and turn count ensure predictable thermal performance characteristics essential for HVAC system design.
4. Full Traceability & Certification: Every production batch is accompanied by mill test certificates, dimensional inspection reports, and NDT documentation, providing complete material traceability and quality assurance for end-user verification.
5. Customization Capability: Wenzhou Jixing Metal Materials Co., Ltd offers flexible customization of OD, WT, coil diameter, pitch, and end connection types to match specific FCU OEM designs and thermal load requirements.