Stainless Steel Coil Tube for Low-Temperature-Differential Fan Coil Systems
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product specifically designed for integration into low-temperature-differential (low-ΔT) fan coil unit systems. This product category addresses the growing industry demand for high-efficiency thermal exchange media capable of operating under minimal temperature differentials between supply and return fluid streams—typically within the range of 2°C to 5°C. The coil tube is formed through cold-rolling and continuous bending processes, producing a seamless, spiral-wound configuration that maximizes surface area-to-volume ratio while maintaining structural integrity under sustained thermal cycling.
Unlike conventional round-section stainless steel pipes used in general industrial piping, this coil tube is engineered with tight bending radii and uniform wall thickness tolerances to facilitate compact heat exchanger geometries. The product has been validated through extensive experimental research and performance analysis, demonstrating superior thermal conductivity, corrosion resistance, and mechanical fatigue endurance under the demanding conditions of HVAC (Heating, Ventilation, and Air Conditioning) applications.
2. Material Composition & Physical Properties
The coil tube is fabricated from austenitic stainless steel grades conforming to international metallurgical standards. The primary material specifications are detailed below:
2.1 Chemical Composition (Typical)
| Element | Grade 304 (UNS S30400) | Grade 316 (UNS S31600) | Grade 316L (UNS S31603) |
|---|---|---|---|
| Carbon (C), max % | 0.08 | 0.08 | 0.03 |
| Chromium (Cr), % | 18.00–20.00 | 16.00–18.00 | 16.00–18.00 |
| Nickel (Ni), % | 8.00–10.50 | 10.00–14.00 | 10.00–14.00 |
| Molybdenum (Mo), % | — | 2.00–3.00 | 2.00–3.00 |
| Manganese (Mn), max % | 2.00 | 2.00 | 2.00 |
| Silicon (Si), max % | 1.00 | 1.00 | 1.00 |
| Phosphorus (P), max % | 0.045 | 0.045 | 0.045 |
| Sulfur (S), max % | 0.030 | 0.030 | 0.030 |
2.2 Key Physical & Mechanical Properties
| Property | Specification |
|---|---|
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) (Grade 304); 16.0 W/(m·K) (Grade 316) |
| Specific Heat Capacity (at 20°C) | 500 J/(kg·K) |
| Linear Thermal Expansion Coefficient | 17.3 × 10⁻⁶ /K (100°C–20°C) |
| Tensile Strength (Rm) | ≥ 520 MPa (annealed condition) |
| Yield Strength (Rp0.2) | ≥ 205 MPa (annealed condition) |
| Elongation (A50mm) | ≥ 40% |
| Operating Temperature Range | −196°C to +870°C (vacuum); −196°C to +425°C (atmospheric) |
| Density | 8.00 g/cm³ (Grade 304); 8.03 g/cm³ (Grade 316) |
3. Product Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) |
| Product Code / Serial No. | 648 |
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (1/4" – 1") |
| Wall Thickness (WT) | 0.30 mm – 1.50 mm |
| Coil Pitch (Center-to-Center) | 8.0 mm – 35.0 mm |
| Bending Radius (Minimum) | 1.5 × OD (hot-bent); 2.0 × OD (cold-bent) |
| Coil Length (Per Spool) | 10 m – 100 m (customizable) |
| Surface Finish | 2B (cold-rolled, annealed, pickled); No. 4 brushed; BA (Bright Annealed) |
| OD Tolerance | ±0.05 mm |
| WT Tolerance | ±10% of nominal |
| Coil Pitch Tolerance | ±0.3 mm |
| Material Grades Available | 304, 304L, 316, 316L, 321, 310S, 904L |
| Standards Compliance | ASTM A213/A213M, ASTM A269/A269M, EN 10217-7, GB/T 12771, JIS G3459 |
| End Form | Plain cut, beveled, or flanged (upon request) |
4. Manufacturing Process
The production of stainless steel coil tubes for low-ΔT fan coil applications involves a multi-stage manufacturing sequence designed to ensure dimensional precision, metallurgical uniformity, and surface quality:
- Strip Sourcing & Incoming Inspection: Cold-rolled stainless steel strip is procured from certified mill suppliers. Incoming material undergoes spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition and mechanical property certification.
- Coil Forming (Cold Bending): The flat strip is fed through a precision coil-forming machine equipped with multi-roll tooling. The bending process is performed at ambient temperature to avoid grain distortion and work-hardening effects. Continuous in-line diameter gauging ensures OD consistency throughout the coil length.
- Welding (Where Applicable): For welded coil tube configurations, a TIG (Tungsten Inert Gas) welding process is employed with high-purity argon shielding gas (≥ 99.99% Ar) to prevent oxidation of the weld zone. Weld bead height is controlled to ≤ 0.15 mm to minimize flow resistance in heat exchanger applications.
- Heat Treatment & Annealing: Fully welded coils undergo solution annealing at 1050°C–1150°C followed by controlled-rate water quenching to restore the fully austenitic microstructure, eliminate residual stresses from forming and welding, and achieve the required softness (HV ≤ 200) for downstream processing.
- Pickling & Passivation: The annealed coil is subjected to pickling (using a mixed acid bath of HNO₃/HF or citric acid) to remove oxide scale, followed by passivation to form a stable chromium oxide (Cr₂O₃) surface film. This step is critical for ensuring long-term corrosion resistance.
- Precision Sizing & Straightening: The coil tube passes through a multi-die sizing line to achieve final dimensional tolerances. A straightening section corrects any residual helical deviation.
- Final Inspection & Non-Destructive Testing (NDT): Each coil is inspected for surface defects, dimensional accuracy, and internal weld integrity. Hydrostatic pressure testing (to 1.5× working pressure) is performed to verify seam integrity. Eddy current testing may be applied for weld quality verification.
- Coiling, Packaging & Dispatch: Finished coils are wound onto protective cores, wrapped with VCI (Vapor Corrosion Inhibitor) film and protective cardboard, and crated for shipment.
5. Applications
The stainless steel coil tube is engineered for the following primary and secondary applications:
- Low-Temperature-Differential Fan Coil Units: The primary design application. The coil tube serves as the heat transfer medium in fan coil units operating with supply/return temperature differentials as low as 2°C, enabling precise indoor climate control in commercial buildings, hospitals, laboratories, and clean rooms.
- Air Handling Units (AHUs): Used as tube bundles in evaporator and condenser coils within centralized air handling systems.
- Chilled Water & Hot Water Distribution: Integral components of secondary loop piping in hydronic heating and cooling systems.
- Industrial Process Heat Exchangers: Plate-fin and shell-and-tube heat exchangers in food processing, pharmaceutical manufacturing, and chemical industries where corrosion resistance is paramount.
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration units, cold storage facilities, and HVAC chiller systems.
- Marine & Offshore HVAC: Corrosion-resistant coil tubes for shipboard and offshore platform climate control systems, leveraging the superior chloride resistance of Grade 316/316L stainless steel.
- Geothermal Heat Pump Systems: Ground-loop heat exchanger tubing for renewable energy heating and cooling installations.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring product conformity with global standards:
- ISO 9001:2015 — Quality Management System certification covering design, manufacturing, and post-sale service.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- CE Marking — European Conformity certification for products intended for the European Economic Area (EEA) market.
- EN 10204 3.1 — Material test certificates issued for each production lot, documenting chemical analysis, mechanical testing, and dimensional verification results.
- ASTM & ASME Standards — Product specifications aligned with American Society for Testing and Materials (ASTM) and American Society of Mechanical Engineers (ASME) requirements.
- GB/T Standards — Compliance with Chinese national standards for stainless steel tubes (GB/T 12771, GB/T 21832).
- Mill Test Reports (MTRs) — Third-party verified material certification traceable to the original steel mill.
7. Unique Selling Points
7.1 Precision Low-ΔT Optimization: The coil tube geometry is specifically engineered for low temperature-differential operation, with uniform pitch tolerance (±0.3 mm) ensuring balanced fluid distribution across all coil passes. This eliminates thermal stratification and maximizes the log-mean temperature difference (LMTD) efficiency in heat exchanger performance.
7.2 Superior Corrosion Resistance: Available in Grades 316 and 316L with Molybdenum content up to 3%, providing exceptional resistance to pitting and crevice corrosion in chlorinated environments—critical for coastal installations and humid indoor HVAC systems.
7.3 Tight Dimensional Tolerances: OD tolerance of ±0.05 mm and wall thickness tolerance of ±10% enable direct insertion into precision-machined tube sheets without reaming or fitting, reducing assembly time and labor costs in heat exchanger fabrication.
7.4 Full Traceability: Each coil is laser-marked with heat number, grade, dimensions, and production date, enabling complete supply chain traceability from raw material to finished product.
7.5 Customization Capability: Wenzhou Jixing Metal Materials Co., Ltd. offers fully customizable coil tube solutions, including non-standard diameters, pitches, lengths, surface finishes, and end configurations, supported by a dedicated engineering team for application-specific design consultation.