Stainless Steel Coil Tube — HVAC Fan Coil Unit Application Grade
Product Overview
The Stainless Steel Coil Tube (Product No. 904) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tubing product specifically designed for integration into fan coil unit (FCU) systems and hydronic heat exchanger assemblies. This coil tube is formed through continuous cold-rolling and coiling processes, delivering seamless, uniform cross-sectional geometry ideal for convective heat transfer applications. The product complies with international standards for stainless steel tubing and is engineered to withstand the thermal cycling, pressure differentials, and corrosive fluid environments encountered in commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) systems.
Unlike conventional carbon steel tubing, this stainless steel coil tube offers superior resistance to pitting corrosion, intergranular corrosion, and general chemical attack, making it the preferred material for systems handling treated water, glycol-based fluids, and other potentially corrosive working media.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, primarily from the following material grades:
- AISI 304 (UNS S30408) — General-purpose grade with excellent corrosion resistance and formability, suitable for most HVAC applications.
- AISI 316L (UNS S31603) — Enhanced corrosion resistance due to molybdenum addition (2–3% Mo), recommended for aggressive or marine environments.
- AISI 321 (UNS S32100) — Stabilized grade with titanium addition, suitable for elevated-temperature applications up to 870 °C in continuous service.
| Property | Specification | Test Method |
|---|---|---|
| Material Grade | AISI 304 / 316L / 321 (customizable) | ASTM A213 / A269 |
| Outer Diameter (OD) | Φ9.52 mm – Φ25.4 mm (standard); custom available | ASTM E141 |
| Wall Thickness | 0.5 mm – 1.5 mm (±0.1 mm tolerance) | ASTM E10 |
| Tensile Strength (Rm) | ≥ 520 MPa (304); ≥ 485 MPa (316L) | ASTM E8 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ASTM E8 |
| Elongation (A50) | ≥ 30% | ASTM E8 |
| Hardness | ≤ 200 HV (annealed condition) | ASTM E92 |
| Operating Temperature Range | −196 °C to +870 °C | — |
| Maximum Working Pressure | ≤ 1.6 MPa (16 bar) at 20 °C | ASME B31.5 |
| Surface Finish | Mirror polish (Ra ≤ 0.4 μm) or matte finish (Ra ≤ 1.6 μm) | ASTM A696 |
| Coil Length per Spool | 50 m – 200 m (standard); custom lengths available | — |
| Coil Diameter | Φ150 mm – Φ500 mm (configurable) | — |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing workflow to ensure dimensional accuracy, mechanical integrity, and surface quality:
- Raw Material Selection — Certified stainless steel wire rod or strip is sourced from approved mills, with each batch accompanied by a mill test certificate (MTC) confirming chemical composition and mechanical properties.
- Wire Drawing — The raw wire is cold-drawn through precision tungsten carbide dies to achieve the target outer diameter and wall thickness with tight tolerances (±0.05 mm).
- Intermediate Annealing — Periodic solution annealing at 1050–1150 °C in a controlled atmosphere furnace eliminates work-hardening effects, restores ductility, and prevents cracking during subsequent forming operations.
- Precision Coiling — The seamless tube is wound onto a precision coiling mandrel using CNC-controlled winding heads, maintaining uniform coil pitch and consistent bend radius to avoid ovalization or wall thinning.
- Final Annealing & Pickling — The coiled tube undergoes final solution heat treatment followed by acid pickling and passivation to remove scale, contaminants, and to establish a stable chromium oxide protective layer.
- Surface Finishing — Electropolishing or mechanical polishing is applied as required to achieve the specified surface roughness (Ra value), critical for minimizing flow resistance and preventing fouling in heat exchanger applications.
- Non-Destructive Testing (NDT) — Each coil is subjected to 100% eddy current testing (ECT) and ultrasonic testing (UT) to detect internal and surface defects in accordance with ASTM E309 and ASTM E213.
- Hydrostatic Pressure Testing — Every coil is pressure-tested at 1.5× the maximum working pressure (typically 2.4 MPa) for a minimum dwell time of 30 seconds to verify leak-tightness.
- Packaging & Shipping — Coils are wrapped in moisture-proof film, secured on protective pallets, and shipped with complete documentation including MTC, test reports, and dimensional drawings.
Applications
The stainless steel coil tube (Product No. 904) is engineered for demanding heat transfer and fluid distribution applications, including but not limited to:
- Fan Coil Units (FCUs) — Primary application; the coil tube serves as the core heat exchange element in both cooling and heating modes within commercial HVAC systems.
- Air Handler Units (AHUs) — Integration into evaporator and condenser coils for large-scale air distribution systems.
- Chilled Water Systems — Use in plate-fin heat exchangers and coil assemblies where water-side corrosion resistance is critical.
- Food & Beverage Processing — Sanitary-grade applications requiring resistance to acidic and alkaline cleaning agents (CIP systems).
- Pharmaceutical & Biotechnology — Clean-room HVAC systems and process heating/cooling loops where GMP (Good Manufacturing Practice) compliance is mandated.
- Marine & Offshore Platforms — HVAC systems exposed to high-salinity, high-humidity environments where AISI 316L grade provides essential chloride resistance.
- Industrial Process Cooling — Heat exchangers in chemical processing, semiconductor manufacturing, and data center cooling loops.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and adheres to the following international standards and certifications:
| Standard / Certification | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing and supply processes |
| ISO 14001:2015 | Environmental Management System |
| ASTM A213 / A269 | Specifications for seamless austenitic stainless steel tubing |
| ASME B31.5 | Pressure Piping — Process Piping design and testing requirements |
| EN 10217-7 | European standard for stainless steel tubes for heat exchangers and condensers |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubing |
| NACE MR0175 / ISO 15156 | Sour service compatibility (for 316L grade in H₂S environments) |
| NSF/ANSI 61 | Drinking water system component safety (for potable water applications) |
Unique Selling Points
1. Precision Coiling Technology: CNC-controlled coiling ensures uniform bend radius and minimal wall thinning, guaranteeing consistent heat transfer performance across the entire coil length.
2. Full Traceability: Each coil is serialized with a unique batch number linked to mill certificates, chemical analysis, mechanical test results, and NDT reports — enabling complete supply chain traceability.
3. Custom Engineering: Flexible customization of OD, wall thickness, coil diameter, coil length, surface finish, and material grade to meet specific OEM or project requirements.
4. Superior Corrosion Resistance: The austenitic stainless steel matrix with chromium (18–20%) and nickel (8–10%) content provides long-term resistance to pitting, crevice corrosion, and stress corrosion cracking in HVAC fluid environments.
5. High Thermal Conductivity: Optimized alloy composition and smooth surface finish (Ra ≤ 0.4 μm) maximize convective and conductive heat transfer efficiency, reducing energy consumption in fan coil unit operation.
6. Low Flow Resistance: Mirror-polished internal bore minimizes frictional pressure drop, allowing smaller fan motors and lower operational energy costs in FCU systems.
7. Extended Service Life: With proper installation and maintenance, the coil tube offers a service life exceeding 25 years in standard HVAC applications — significantly outperforming carbon steel alternatives.
Technical Note
This product knowledge reference (Document No. 904) incorporates lessons learned from the technical study "Discussion on the Selection of Fan Coil Units", which emphasizes the critical role of coil tube geometry, material selection, and dimensional accuracy in determining the overall thermal performance and selection parameters of fan coil unit assemblies. The coil tube specifications detailed herein are optimized to support accurate FCU selection calculations, including total heat output, sensible heat ratio (SHR), and air/water flow rate matching.