Stainless Steel Coil Tube (Coiltube) for Fan Coil Unit Applications
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product designed primarily for heat exchange applications in HVAC (Heating, Ventilation, and Air Conditioning) systems, particularly within Fan Coil Units (FCUs). Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this product is supplied in coiled form to facilitate efficient bending, forming, and integration into complex heat exchanger geometries. The coiltube configuration eliminates the need for field welding or soldering, significantly reducing installation time, labor costs, and potential leak points.
This product line is especially relevant to the domain of fan coil unit dry-condition operation (风机盘管干工况运行), where the coil tube operates with minimal or no condensate formation, enabling simultaneous dehumidification and temperature control without the waterlogging issues associated with traditional wet-coil designs. The dry-condition operational philosophy demands exceptional material integrity, thermal conductivity, and corrosion resistance—all attributes inherently provided by high-grade stainless steel.
Material & Properties
The stainless steel coil tube is fabricated from austenitic stainless steel grades that offer an optimal balance of mechanical strength, thermal performance, and resistance to corrosion and scaling in humid or chemically aggressive environments.
- Primary Grades: AISI 304 (UNS S30408), AISI 316 (UNS S31608), AISI 316L (UNS S31603)
- Carbon Content: ≤ 0.08% (for 304/316); ≤ 0.03% (for 316L, ultra-low carbon)
- Chromium Content: 18–20% minimum, providing a self-healing passive oxide layer
- Nickel Content: 8–10.5%, stabilizing the austenitic crystal structure
- Molybdenum Content: 2–3% (in 316/316L grades), enhancing resistance to pitting and crevice corrosion
- Surface Finish: 2B (cold-rolled and annealed), BA (Bright Annealed), or No. 4 brushed finish
- Thermal Conductivity: 14–16 W/(m·K) at 20°C — superior to carbon steel in wet environments due to absence of rust-induced thermal resistance
- Operating Temperature Range: −196°C to +870°C (304); −196°C to +925°C (316)
- Yield Strength: ≥ 205 MPa (0.2% proof stress)
- Tensile Strength: 515–720 MPa
- Elongation: ≥ 40% at break
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Category | Stainless Steel Coil Tube (Coiltube) | — |
| Item No. | 1124 | Wenzhou Jixing Internal Catalog |
| Outer Diameter (OD) | 6.00 mm / 8.00 mm / 9.53 mm / 12.70 mm (custom available) | ISO 3505 |
| Wall Thickness | 0.50 mm – 1.50 mm | ASTM A269 / ASTM A270 |
| Coil Inner Diameter (ID) | 500 mm – 1200 mm (adjustable per application) | Manufacturer specification |
| Coil Length (per coil) | 50 m – 500 m (continuous) | — |
| Roundness Tolerance | ≤ 0.05 mm | GB/T 14976 |
| Wall Thickness Tolerance | ± 10% of nominal | ASTM A269 |
| Surface Roughness (Ra) | ≤ 0.8 μm (internal); ≤ 1.6 μm (external) | ISO 1302 |
| End Condition | Flat-cut, deburred, or beveled (per customer requirement) | — |
| Protective Packaging | PE (Polyethylene) film wrapping, wooden pallet, or export-grade crate | ISO 11607 |
| Compliance Standards | ASTM A269, ASTM A270, GB/T 12771, GB/T 14976, EN 10217-7 | International / National |
Manufacturing Process
The production of stainless steel coil tube follows a rigorous multi-stage process ensuring dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection & Inspection: Cold-rolled stainless steel strip is procured from certified mills and subjected to spectrographic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance with ASTM or GB standards.
- Slitting & Edge Preparation: The coil strip is slit to precise width tolerances (± 0.1 mm) using high-precision slitting lines. Edges are inspected for burrs, cracks, or deformation.
- Roll Forming: The strip passes through a series of progressively reducing rollers that incrementally bend the flat strip into a tubular cross-section. Roller configurations are CAD-optimized to prevent material thinning, wrinkling, or ovalization.
- Seam Welding (if applicable):strong> Where a welded seam is required, high-frequency induction welding (HF-W) or orbital TIG (Tungsten Inert Gas) welding is employed. The weld zone undergoes 100% eddy current testing (ECT) for defect detection.
- Heat Treatment / Solution Annealing: The formed tube is solution-annealed at 1050–1100°C followed by rapid water quenching to dissolve carbide precipitates, restore full austenitic structure, and maximize corrosion resistance.
- Pickling & Passivation: The tube surface is immersed in a citric acid or nitric acid bath to remove oxide scale, followed by passivation to re-establish a uniform chromium oxide protective film.
- Coiling & Dimensional Verification: The finished tube is wound into coils of specified diameter. Each coil is verified for OD, wall thickness, roundness, and length using ultrasonic thickness gauges and laser micrometers.
- Final Packaging: Coils are wrapped in moisture-barrier PE film, secured with steel strapping, and palletized for shipment.
Applications
The stainless steel coil tube finds extensive application across multiple industries, with particular relevance to HVAC thermal management:
- Fan Coil Units (FCUs) — Dry Condition Operation: The primary application domain. In dry-condition FCU design, the coil tube operates with air-side heat exchange only (no refrigerant-side condensate accumulation), enabling precise humidity control. Stainless steel's corrosion resistance ensures long-term performance even in high-humidity environments where carbon steel coils would degrade.
- Chilled Water / Heating Water Heat Exchangers: Coiltube is used to fabricate serpentine heat exchangers for commercial HVAC systems, providing high surface-area-to-volume ratios for efficient thermal transfer.
- Refrigeration & Air Conditioning Systems: Used as evaporator and condenser tubes in split-system and packaged HVAC units.
- Food & Beverage Processing: Sanitary-grade 316L coiltube is employed in pasteurization heat exchangers, brewing systems, and dairy processing equipment where hygienic standards are mandatory.
- Pharmaceutical & Biotechnology: Used in CIP (Clean-in-Place) systems, bioreactor cooling jackets, and sterile fluid transfer lines.
- Chemical Processing: Resistant to acidic and alkaline media; suitable for heat exchangers handling corrosive process fluids.
- Marine & Offshore: 316L grade provides excellent resistance to chloride-induced pitting in marine environments.
- Building Services & District Energy: Used in secondary loop distribution coils, radiator assemblies, and thermal energy storage systems.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework to ensure product conformity and traceability:
- ISO 9001:2015 — Quality Management System certification, ensuring consistent product quality and process control.
- ISO 14001:2015 — Environmental Management System, demonstrating commitment to sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health & Safety Management System.
- CE Marking — Conformity with European Union directives for product safety.
- Mill Test Certificates (MTC) — En 10204 Type 3.1 certificates issued for every production batch, documenting chemical composition, mechanical properties, and heat treatment records.
- NACE MR0175 / ISO 15156 — Compliance for sour service applications (316L grade).
- 3-A Sanitary Standards — Available for food-grade applications (electropolished 316L).
Unique Selling Points
1. Continuous Coiled Supply — Zero-Waste Fabrication: Unlike straight-length tubes, coiltube enables seamless, continuous fabrication of heat exchanger coils without butt joints. This eliminates potential leak points, reduces material waste by up to 15%, and accelerates production throughput.
2. Superior Corrosion Resistance in Dry-Condition FCU Environments: Stainless steel coil tubes maintain structural integrity and thermal performance over service lives exceeding 25 years, compared to 8–12 years for carbon steel equivalents in similar applications. This is particularly critical in dry-condition FCU operation where fluctuating humidity levels can accelerate corrosion in inferior materials.
3. Enhanced Thermal Efficiency: The absence of internal rust scale ensures consistent thermal conductivity throughout the product lifecycle. Internal surface roughness of ≤ 0.8 μm minimizes flow resistance and fouling, maintaining optimal heat transfer coefficients.
4. Full Traceability & Customization: Every coil is traceable to its heat number and production batch. Custom OD, wall thickness, coil diameter, and surface finish configurations are available to meet specific OEM (Original Equipment Manufacturer) requirements.
5. Integrated Supply Chain: Wenzhou Jixing Metal Materials Co., Ltd provides end-to-end solutions from raw material sourcing through finished coil delivery, ensuring consistent quality and competitive lead times.