Stainless Steel Coil Tube (Coiltube) — HVAC & Thermal Management Grade
Product Overview
The Stainless Steel Coil Tube (Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered continuous coil-form tubing specifically designed for high-efficiency heat exchange applications in HVAC (Heating, Ventilation, and Air Conditioning) systems, particularly fan coil units (FCUs). Unlike discrete straight-segment piping, the coil tube is supplied in a continuous helical or spiral-coiled configuration, enabling direct integration into heat exchanger cores with minimal secondary forming, welding, or mechanical stress.
Based on empirical research findings — as documented in the study "Surface Fouling Heat Transfer Effects of Fan Coil Units on HVAC System Energy Consumption: A Measured and Simulated Investigation" — the coil tube geometry plays a critical role in governing convective heat transfer coefficients, flow distribution uniformity, and long-term fouling resistance accumulation. The continuously wound architecture promotes turbulent boundary layer development even at low Reynolds numbers, thereby enhancing convective heat transfer performance and mitigating the energy penalty associated with progressive surface fouling.
Material & Properties
The coil tube is fabricated from austenitic stainless steel grades conforming to international standards, ensuring superior corrosion resistance, thermal stability, and mechanical integrity under prolonged thermal cycling conditions.
- Primary Grades: SUS304 (UNS S30400), SUS316 (UNS S31600), and SUS321 (UNS S32100)
- Corrosion Resistance: Chromium content of 18–20% provides robust passive oxide film formation; molybdenum addition in 316 grade enhances resistance to chloride-induced pitting corrosion
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C, suitable for efficient convective heat exchange
- Operating Temperature Range: −196°C to +870°C (SUS304); −196°C to +800°C (SUS316)
- Mechanical Properties: Tensile strength ≥ 520 MPa (annealed); elongation ≥ 40%; hardness ≤ 200 HV
- Surface Finish: 2B mill finish (Ra ≤ 0.8 μm) or electropolished (Ra ≤ 0.4 μm) for reduced fouling adhesion
- Hygienic & Food-Grade Compliance: Available in sanitary finish per 3-A Sanitary Standards and FDA 21 CFR
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (1/4" – 1") | ASTM A213 / EN 10217-7 |
| Wall Thickness (WT) | 0.5 mm – 2.0 mm | ASTM A269 |
| Coil Diameter (CD) | 100 mm – 500 mm (adjustable per application) | Internal specification |
| Pitch (Turn-to-Turn Spacing) | 1.5 mm – 10.0 mm | Design-specific |
| Coil Length (Continuous) | 5 m – 200 m (single continuous coil) | — |
| Tolerance on OD | ±0.05 mm – ±0.10 mm | ASTM A213 |
| Tolerance on WT | ±10% of nominal | ASTM A213 |
| Maximum Operating Pressure | Up to 2.5 MPa (design-dependent) | ASME BPV Code Sec. I |
| Surface Roughness (Ra) | 0.4 μm – 0.8 μm | ISO 1302 |
| Available Lengths (Straight) | 1 m – 12 m (upon request) | — |
| End Condition | Plain, beveled, or threaded | ASME B1.20.1 |
| Winding Direction | Left-hand (LH) or Right-hand (RH) | Customer specification |
Manufacturing Process
The production of stainless steel coil tube at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous, multi-stage manufacturing protocol:
- Raw Material Procurement & Inspection: Hot-rolled stainless steel strip or seamless tube stock is sourced from certified mills. Incoming material undergoes spectroscopic analysis (OES), chemical composition verification, and mechanical property testing to ensure conformance with the specified grade.
- Cold Drawing & Reduction: Tube blanks are cold-drawn through precision tungsten carbide dies to achieve the target outer diameter and wall thickness with tight dimensional tolerances. This process enhances grain alignment and surface quality.
- Intermediate Annealing: Periodic solution annealing at 1050–1150°C in a protective atmosphere (argon or hydrogen) relieves cold-work hardening, restores ductility, and ensures full austenitic microstructure.
- Precision Coiling (Winding): The formed tube is wound onto a CNC-controlled coil former to produce the helical geometry with exact pitch, coil diameter, and turn-to-turn spacing. The winding process maintains consistent tension to prevent ovalization or deformation of the tube cross-section.
- Post-Coiling Annealing (Optional): For applications requiring maximum ductility or specific mechanical properties, the coiled product may undergo a final stress-relief anneal at 400–600°C.
- Surface Treatment & Cleaning: Acid pickling and passivation (per ASTM A967) remove scale and contaminants, establishing a stable chromium oxide passive layer. Electropolishing is available for hygienic or low-fouling applications.
- Final Quality Inspection: Dimensional verification (OD, WT, coil diameter, pitch), surface roughness measurement, hydrostatic pressure testing, and visual inspection are performed on every batch.
Applications
The stainless steel coil tube is a critical component in a wide range of thermal management and fluid transport systems:
- Fan Coil Units (FCUs): Serves as the core heat exchange element in commercial and residential HVAC fan coil units. The coiled geometry maximizes heat transfer surface area within a compact envelope. Research has demonstrated that coil tube surface fouling significantly impacts overall system energy efficiency; the smooth surface finish and corrosion-resistant material of this product minimize fouling accumulation and maintain heat transfer performance over extended service life.
- Air Source Heat Pumps (ASHP): Used in evaporator and condenser coils where resistance to deicing cycle corrosion and thermal cycling fatigue is essential.
- Chilled Water & Hot Water Distribution: Ideal for low-pressure hydronic systems where long-term corrosion resistance and dimensional stability are paramount.
- Refrigeration & Cryogenic Systems: SUS316 grade coil tubes are employed in ammonia-based and refrigerant circuit heat exchangers requiring high corrosion resistance.
- Process Cooling & Industrial Heat Exchangers: Utilized in shell-and-tube heat exchangers, plate-fin coils, and custom thermal management assemblies in food processing, pharmaceutical, and chemical industries.
- Geothermal Heat Exchange Loops: Continuous coil configurations are advantageous for closed-loop geothermal systems where long unbroken runs minimize connection points and potential leak paths.
- Automotive & HVAC Aftermarket: Replacement coil tubes for vehicle HVAC condensers and evaporators.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System
- ASTM A213 / A269 — Compliance for wrought austenitic stainless steel tubing
- EN 10217-7 — European standard for heat exchanger tubes
- GB/T 14976 — Chinese national standard for seamless stainless steel tubes
- ASME BPV Code Section I — Power boiler components compliance (where applicable)
- 3-A Sanitary Standards — Available for food-grade coil tube configurations
- Mill Test Certificates (MTC): Provided with every shipment, including chemical composition, mechanical test results, and traceability documentation
Unique Selling Points
1. Fouling-Resistant Design Philosophy: Drawing upon validated research into fan coil unit surface fouling effects on HVAC energy consumption, this coil tube product is engineered with surface finishes and material selections that actively resist fouling deposition. The electropolished option (Ra ≤ 0.4 μm) reduces biofilm adhesion and mineral scale nucleation, directly translating to lower energy consumption over the system lifecycle.
2. Continuous Coil Integrity: The single-continuous-coil manufacturing approach eliminates inter-turn weld seams, which are common failure initiation points in discrete-segment coil assemblies. This provides superior pressure containment and eliminates potential leakage pathways.
3. Precision Dimensional Control: CNC-controlled coiling ensures consistent pitch and coil diameter across the entire coil length, promoting uniform flow distribution and balanced heat transfer performance in the installed heat exchanger.
4. Grade Flexibility: Multiple stainless steel grades (304, 316, 321) are available to match specific service environments — from standard HVAC to aggressive chemical or cryogenic applications.
5. Customization Capability: Outer diameter, wall thickness, coil diameter, pitch, and total coil length can be customized to meet specific OEM heat exchanger designs and system engineering requirements.
Conclusion
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. represents a technologically advanced solution for heat exchange applications where energy efficiency, corrosion resistance, and long-term reliability are non-negotiable. Backed by empirical research into fouling-induced energy penalties in HVAC systems, this product is engineered to minimize total cost of ownership through superior thermal performance maintenance, extended service intervals, and reduced maintenance requirements throughout the operational lifecycle.