Stainless Steel Coil Tube (Coiltube) for HVAC Fan Coil Applications
Product Overview
The Stainless Steel Coil Tube (Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered continuous stainless steel tubing product supplied in coil form for efficient downstream processing and fabrication. This product is specifically designed and optimized for integration into heating-type fan coil unit (FCU) systems, where thermal efficiency, corrosion resistance, and long-term structural integrity are paramount. The coil tube configuration enables seamless feeding into automated forming, bending, and welding lines, significantly reducing material waste and manufacturing cycle time.
As a critical component in hydronic heating and cooling systems, the coil tube serves as the primary heat exchange conduit, facilitating the transfer of thermal energy between circulating fluid media (water or glycol-based solutions) and ambient air. The continuous coil form factor eliminates the need for butt-welding individual tube segments, thereby minimizing potential failure points and enhancing system reliability.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, typically conforming to the following material specifications:
- Grade 304 (UNS S30400): Chromium-Nickel austenitic stainless steel offering excellent general corrosion resistance, formability, and weldability. Suitable for standard heating applications with non-aggressive fluid media.
- Grade 316 (UNS S31600): Molybdenum-enhanced austenitic stainless steel providing superior resistance to pitting and crevice corrosion. Recommended for applications involving chlorinated water, coastal environments, or chemically aggressive fluids.
- Grade 316L (UNS S31603): Low-carbon variant of Grade 316, optimized for welding applications where sensitization and intergranular corrosion resistance are critical.
Mechanical Properties (Typical Values for Grade 304)
- Tensile Strength: ≥ 520 MPa (75,400 psi)
- Yield Strength (0.2% Proof): ≥ 205 MPa (29,730 psi)
- Elongation at Break: ≥ 40%
- Hardness (HB): ≤ 187
- Thermal Conductivity: 16.3 W/(m·K) at 25°C
- Specific Heat Capacity: 500 J/(kg·K) at 25°C
- Maximum Service Temperature: 870°C (in continuous air service)
- Cold Bending Radius: ≥ 2.5 × Tube Outer Diameter (without crack initiation)
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
| Product Category | Seamless / Welded Stainless Steel Tubing in Coil Form |
| Available Grades | SUS 304, SUS 316, SUS 316L, SUS 321, SUS 310S |
| Outer Diameter (OD) | 3.0 mm – 32.0 mm (customizable upon request) |
| Wall Thickness | 0.3 mm – 2.0 mm (±10% tolerance) |
| Coil Inner Diameter | 150 mm – 600 mm (configurable per customer requirement) |
| Coil Length | 20 m – 500 m per coil (continuous) |
| Coil Weight | Up to 1,500 kg per coil |
| Surface Finish | Bright Annealed (BA), No. 4 Satin, No. 8 Mirror, Pickled & Passivated |
| End Condition | Plain Cut, Formed Ends, or Custom Profile |
| Dimensional Tolerance (OD) | ±0.05 mm (precision grade); ±0.10 mm (standard grade) |
| Dimensional Tolerance (Wall) | ±10% of nominal |
| Straightness | ≤ 0.5 mm/m |
| Hydrostatic Test Pressure | 1.5 × Maximum Operating Pressure (minimum 5.0 MPa) |
| Operating Temperature Range | -196°C to +870°C |
| Maximum Operating Pressure | Up to 16.0 MPa (subject to wall thickness and OD) |
| Standards Compliance | ASTM A269/A270, EN 10216-5, GB/T 12771, JIS G3459 |
Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing sequence to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection & Inspection: High-purity stainless steel wire rod or strip is procured from certified mills. Incoming material undergoes spectroscopic analysis (OES) to verify chemical composition compliance with the specified grade.
- Wire Rod Annealing & Acid Pickling: The raw wire rod is subjected to controlled annealing at 1,050°C – 1,150°C followed by rapid water quenching to achieve a fully austenitic microstructure with optimal ductility. Subsequent pickling in a mixed acid bath (HNO₃/HF) removes scale and impurities from the surface.
- Piercing & Forming: For seamless tubing, the annealed billet is hot-pierced to form a hollow shell, which is then cold-drawn through a series of reducing dies to achieve the target OD and wall thickness. For welded tubing, continuous strip is precision-formed into a tubular profile and longitudinally welded via TIG (Tungsten Inert Gas) or laser welding processes.
- Cold Drawing & Sizing: The tube blank is cold-drawn through calibrated dies and mandrels to achieve precise dimensional tolerances. This process induces beneficial work hardening while maintaining the required elongation properties.
- Intermediate Annealing: Where multiple cold-drawing passes are required, intermediate annealing cycles restore ductility and prevent cracking during subsequent forming operations.
- Coil Winding & Straightening: The finished tube is coiled onto a precision winding machine with controlled tension to prevent deformation. Prior to coiling, the tube passes through a straightening unit to ensure dimensional straightness within specification.
- Final Heat Treatment & Passivation: A final solution annealing treatment (1,040°C – 1,120°C with rapid quench) ensures a uniform, fully austenitic microstructure. Chemical passivation treatment (HNO₃-based solution) establishes a protective chromium oxide film on the surface, enhancing corrosion resistance.
- Quality Inspection & Testing: Each coil undergoes comprehensive non-destructive testing (NDT) including eddy current inspection (ECI) for wall thickness and surface defect detection, hydrostatic pressure testing, and dimensional verification via laser measurement systems.
- Packaging & Dispatch: Coils are wrapped in moisture-proof protective film, secured with steel strapping, and palletized for transport. Each coil is accompanied by a mill test certificate (MTC) documenting chemical composition, mechanical properties, and dimensional data.
Applications
The stainless steel coil tube finds extensive application across multiple industrial sectors, with particular emphasis on HVAC and hydronic heating systems:
Primary Applications
- Heating-Type Fan Coil Units (FCUs): The coil tube serves as the core heat exchange element in fan coil units deployed in commercial buildings, hospitals, hotels, and residential complexes. The continuous coil form enables efficient serpentine tube layouts within compact FCU housings, maximizing surface area-to-volume ratios for optimal heat transfer.
- Chilled Water & Hot Water Distribution Systems: Utilized as distribution piping in central HVAC systems where corrosion resistance and long service life are essential requirements.
- Underfloor Heating Systems: The coil tube's flexibility and corrosion resistance make it ideal for radiant floor heating circuits, where it remains permanently embedded in concrete or screed layers.
- Condensing Boilers & Heat Exchangers: Employed in high-efficiency condensing boilers where the tube withstands aggressive acidic condensate formed during flue gas condensation.
Secondary Applications
- Food & Beverage Processing: Sanitary-grade tubing for dairy, brewing, and pharmaceutical processing equipment where CIP (Clean-In-Place) compatibility and hygienic surface finish are mandated.
- Chemical & Petrochemical Industry: Process piping for corrosive fluid handling, reactor coil assemblies, and heat exchanger bundles.
- Marine & Offshore Engineering: Seawater-cooled heat exchangers, ballast water systems, and desalination plant components.
- Automotive Industry: Radiator tubes, turbocharger coolant circuits, and fuel delivery systems.
- Medical Equipment: Autoclave piping, dialysis machine fluid circuits, and sterilization equipment.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring product conformity to international standards:
- ISO 9001:2015: Quality Management System certification demonstrating systematic quality control across all production stages.
- ISO 14001:2015: Environmental Management System certification reflecting commitment to sustainable manufacturing practices.
- ISO 45001:2018: Occupational Health & Safety Management System certification.
- CE Marking (EU): Conformity with European Health, Safety, and Environmental Protection standards for products marketed within the European Economic Area.
- EN 10204 3.1: Inspection Certificate Type 3.1, providing independent third-party verification of material conformity.
- ASME Stamp (where applicable): For pressure-containing applications requiring ASME Section VIII compliance.
- PED (Pressure Equipment Directive 2014/68/EU): Compliance for equipment subject to pressure regulations in the European market.
- NACE MR0175 / ISO 15156: Materials resistance to sulfide stress cracking for oil and gas applications (Grade 316 variants).
- NSF/ANSI 61: Drinking water system components certification (for potable water applications).
Unique Selling Points
1. Continuous Coil Form Factor: The seamless coil configuration eliminates longitudinal joints, reducing potential leak points by up to 90% compared to field-assembled pipe segments. This translates directly to enhanced system reliability and reduced maintenance costs over the service life.
2. Precision Dimensional Control: Advanced cold-drawing and laser measurement systems ensure OD tolerance within ±0.05 mm and wall thickness tolerance within ±10%, guaranteeing consistent heat transfer performance and compatibility with automated forming equipment.
3. Optimized for Fan Coil Integration: The coil tube's cold-workability and controlled springback characteristics enable precise serpentine bending with minimal dimensional deviation, ensuring optimal fit within compact FCU cabinets and maximizing effective heat exchange area.
4. Comprehensive Material Traceability: Each production coil is assigned a unique heat number with full traceability from raw steel mill certificate through final inspection, enabling complete supply chain accountability and facilitating warranty claims or failure analysis.
5. Surface Quality Excellence: Multi-stage pickling, passivation, and finishing processes produce surfaces with Ra ≤ 0.4 μm (BA finish), minimizing scale formation and fouling within heat exchange circuits, thereby maintaining thermal efficiency over extended service periods.
6. Customization Capability: Flexible manufacturing infrastructure supports custom OD, wall thickness, coil diameter, surface finish, and end-forming configurations to meet specific customer engineering requirements, reducing downstream processing costs and accelerating time-to-market.
Technical Notes & Recommendations
- Storage: Coils should be stored indoors in a dry environment with ambient temperature maintained between 5°C and 40°C. Avoid direct contact with carbon steel surfaces to prevent galvanic contamination.
- Handling: Use dedicated coil handling equipment (C-frame hoists or coil cars) to prevent deformation. Avoid dragging coils on abrasive surfaces.
- Welding: When welding coil tube into assemblies, use matching filler metals (e.g., ER308 for Grade 304, ER316L for Grade 316L) with TIG or MIG processes. Apply pre-heating at 100°C – 150°C for wall thicknesses exceeding 3.0 mm to minimize distortion.
- Post-Weld Passivation: Following welding operations, perform post-weld passivation treatment to restore the protective chromium oxide film and ensure long-term corrosion resistance at weld zones.
- Design Considerations for FCU Applications: Ensure minimum bend radius of 2.5 × OD to prevent wall thinning and cracking. Incorporate flow straighteners upstream of coil tube entries to minimize vibration-induced fatigue.