Stainless Steel Coil Tube for HVAC Fan Coil Unit Applications
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed primarily for use in Fan Coil Units (FCUs) and peripheral zone air conditioning systems. These coil tubes serve as the critical heat exchange medium within chiller and boiler systems, facilitating efficient thermal transfer in commercial, industrial, and residential building management systems (BMS). The product is delivered in continuous coil form, enabling seamless integration into automated coil winding and brazing production lines.
Reference Document: "Automatic Control Method of Air Conditioning in Peripheral Zone Fan Coil Unit" — This study highlights the critical role of coil tube geometry, material integrity, and hydraulic performance in achieving precise temperature regulation, energy efficiency, and zoning control in modern HVAC systems.
Material & Properties
Material Grades
- 304 Stainless Steel (UNS S30400) — Austenitic grade with excellent general corrosion resistance; suitable for potable water and standard HVAC applications.
- 316L Stainless Steel (UNS S31603) — Low-carbon variant with added molybdenum (Mo 2–3%); superior resistance to chloride-induced pitting and crevice corrosion; recommended for marine environments and aggressive chemical service.
- 321 Stainless Steel (UNS S32100) — Titanium-stabilized austenitic grade; excellent resistance to intergranular corrosion; suitable for high-temperature coil applications up to 870 °C.
Key Mechanical & Physical Properties
| Property | 304 Grade | 316L Grade | 321 Grade |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 | ≥ 515 |
| Yield Strength (MPa) | ≥ 205 | ≥ 170 | ≥ 170 |
| Elongation at Break (%) | ≥ 40 | ≥ 40 | ≥ 40 |
| Thermal Conductivity (W/m·K, 20 °C) | 16.3 | 14.6 | 16.3 |
| Density (g/cm³) | 8.00 | 8.03 | 8.00 |
| Operating Temperature Range (°C) | −196 to +870 | −196 to +870 | −196 to +900 |
| Corrosion Resistance | Excellent (general) | Superior (chloride) | Excellent (intergranular) |
Chemical Composition (wt%, typical)
| Element | 304 | 316L | 321 |
|---|---|---|---|
| C (Carbon) | ≤ 0.08 | ≤ 0.03 | ≤ 0.08 |
| Cr (Chromium) | 18.0–20.0 | 16.0–18.0 | 17.0–19.0 |
| Ni (Nickel) | 8.0–10.5 | 10.0–14.0 | 9.0–13.0 |
| Mo (Molybdenum) | — | 2.0–3.0 | — |
| Ti (Titanium) | — | — | 5 × (C − 0.02) min |
| S (Sulfur) | ≤ 0.03 | ≤ 0.03 | ≤ 0.03 |
Specifications
| Parameter | Specification |
|---|---|
| Product Form | Continuous Coil Tube (盘管) |
| Outer Diameter (OD) | Φ 6.0 mm – Φ 25.0 mm (customizable) |
| Wall Thickness | 0.5 mm – 2.0 mm |
| Coil Inner Diameter (ID) | Φ 200 mm – Φ 600 mm |
| Coil Length per Spool | 500 m – 3,000 m (adjustable) |
| Surface Finish | 2B / BA (Bright Annealed) / Pickled |
| Surface Roughness (Ra) | ≤ 0.8 μm (BA finish) |
| Tolerance on OD | ± 0.1 mm |
| Tolerance on Wall Thickness | ± 0.05 mm |
| Standards Compliance | ASTM A269 / A270; GB/T 12771; EN 10216-5 |
| Maximum Operating Pressure | ≤ 2.5 MPa (design dependent) |
| Refrigerant Compatibility | R-134a, R-410A, R-407C, water/brine |
| Coil Winding Pitch | 15 mm – 50 mm (application-specific) |
Manufacturing Process
- Raw Material Selection: Cold-rolled stainless steel strip (CRSS) conforming to ASTM A240/A480 is selected with certified mill test reports (MTR) verifying chemical composition and mechanical properties.
- Slitting & Edge Trimming: The strip is slit to precise width using high-speed slitting lines, ensuring edge squareness and dimensional accuracy within ± 0.1 mm tolerance.
- Tube Forming (Seam Welding): The strip is fed through a high-precision tube mill equipped with a TIG (Tungsten Inert Gas) or MIG (Metal Inert Gas) welding head. Welding is performed under argon shielding gas to prevent oxidation. Seam weld quality is verified by ultrasonic testing (UT) and dye penetrant inspection (DTI).
- Heat Treatment / Solution Annealing: Tubes are annealed at 1050 °C ± 20 °C followed by controlled cooling to restore full austenitic microstructure, relieve residual stresses, and maximize corrosion resistance.
- Pickling & Passivation: Surface scale and welding discoloration are removed via hydrofluoric-nitric acid pickling, followed by citric acid passivation to restore the chromium oxide passive film (≥ 5 μm thickness).
- Coil Winding: Annealed tubes are wound into coils using CNC-controlled winding machines, maintaining uniform tension (50–200 N) to prevent kinking, ovality, or permanent deformation. Winding pitch and layer-to-layer contact are monitored by in-line laser sensors.
- Final Quality Inspection: Each coil undergoes 100% visual inspection, dimensional verification (OD, wall thickness, coil ID), hydrostatic pressure testing (1.5× design pressure for 30 seconds), and random sampling for PMI (Positive Material Identification) spectroscopy.
Applications
Primary Application: HVAC Fan Coil Units
Stainless steel coil tubes are the core heat transfer element in Fan Coil Units (FCUs), which are widely deployed in:
- Commercial Buildings: Office towers, hotels, shopping malls, hospitals, and educational facilities requiring zoned temperature control.
- Peripheral Zone Conditioning: As discussed in the referenced literature on automatic control methods, coil tubes in peripheral zones must handle simultaneous heating and cooling loads, making material thermal stability and corrosion resistance paramount.
- Industrial Facilities: Clean rooms, pharmaceutical plants, food processing facilities, and data centers where hygienic and corrosion-free conditions are mandatory.
- Residential High-Rise Buildings: VRF (Variable Refrigerant Flow) and CHW (Chilled Water) systems utilizing FCUs for individual room climate control.
Secondary Applications
- Automotive radiator and intercooler tubes
- Heat exchangers in chemical and petrochemical processing
- Condensers and evaporators in refrigeration systems
- Medical and laboratory gas delivery systems
- Food and beverage industry heat exchange equipment
Unique Selling Points
- Superior Corrosion & Hygiene Performance: Stainless steel coil tubes eliminate the risk of internal corrosion, scale buildup, and biofilm formation inherent in copper or carbon steel alternatives — critical for potable water and sanitary HVAC systems.
- Precision Coil Winding: CNC-controlled winding ensures consistent pitch, minimal ovality (< 0.5%), and uniform layer contact, directly translating to improved heat transfer efficiency and reduced pressure drop in FCU coils.
- Wide Grade Availability: Multiple stainless steel grades (304, 316L, 321) are available to match specific environmental and performance requirements, from standard indoor HVAC to aggressive marine or chemical service.
- Energy Efficiency Contribution: Low surface roughness (Ra ≤ 0.8 μm) minimizes fluid friction losses, supporting the energy-saving objectives of automatic control algorithms in peripheral zone FCU systems.
- Long Service Life: With proper installation and maintenance, stainless steel coil tubes deliver a service life exceeding 25 years, significantly outperforming copper alternatives in corrosive environments.
- Recyclability: Stainless steel is 100% recyclable with no loss of material properties, supporting sustainable manufacturing and green building certifications (LEED, BREEAM).
Quality Certifications & Standards
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| ISO 45001:2018 | Occupational Health & Safety Management |
| ASTM A269 | Welded Austenitic Stainless Steel Tubing |
| ASTM A270 | Welded Austenitic Stainless Steel Pipe |
| GB/T 12771 | Chinese National Standard for Stainless Steel Tubes |
| EN 10216-5 | European Standard for Heat Exchanger Tubes |
| NSF/ANSI 61 | Drinking Water System Components (where applicable) |
| CE Marking | European Conformity for pressure equipment |
Testing & Inspection Protocols
- Hydrostatic Testing: 100% of coils tested at 1.5× maximum operating pressure for a minimum of 30 seconds; zero leakage tolerance.
- Ultrasonic Testing (UT): 100% seam weld inspection per ASTM E213 for volumetric defect detection.
- Positive Material Identification (PMI): XRF (X-Ray Fluorescence) spectroscopy performed on each heat to verify alloy grade compliance.
- Corrosion Testing: Salt spray testing per ASTM B117 (≥ 500 hours without pitting for 316L grade).
- Dimensional Verification: In-line laser measurement systems verify OD, wall thickness, and coil geometry throughout production.
- Mechanical Testing: Tensile testing and impact testing (Charpy V-Notch) per ASTM A370 on certified samples from each production heat.
Technical Notes for Integration with Automatic Control Systems
Based on the referenced study on automatic control methods for peripheral zone fan coil units, the following design considerations are recommended when specifying stainless steel coil tubes for FCU integration:
- Thermal Mass Optimization: Select wall thickness to balance thermal response speed (thin walls for rapid control) against structural integrity and pressure rating.
- Hydraulic Design: Coil tube geometry (OD, pitch, row count) must be optimized to minimize pressure drop while maximizing heat transfer area, supporting the control algorithm's ability to modulate flow rates accurately.
- Anti-Scale Surface Treatment: Consider electropolished or electropolished-and-passivated finishes to minimize fouling resistance over the coil's service life, ensuring consistent performance with control system calibration.
- Temperature Sensor Compatibility: Ensure coil tube surface finish and material allow reliable attachment of RTD (Resistance Temperature Detector) or thermistor sensors for feedback control loops.
Company: Wenzhou Jixing Metal Materials Co., Ltd.
Product Reference No.: 1394
Category: Coil Tube (盘管) for HVAC Applications