Stainless Steel Coil Tube (Coiltube) — Fan Coil Unit & HVAC Grade
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) produced by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component designed primarily for use in fan coil units (FCU), air handling systems, and hydronic heating/cooling circuits. The coil tube is manufactured in continuous coil form to facilitate downstream forming, bending, and coil-winding operations without the need for additional joining or welding at intermediate stages. This product represents a critical component in the thermal exchange architecture of modern HVAC (Heating, Ventilation, and Air Conditioning) systems, where reliability, thermal conductivity, and long-term corrosion resistance are paramount.
The design philosophy behind this coil tube product incorporates lessons learned from reliability improvement studies on fan coil unit motors and hydraulic circuits — emphasizing reduced failure rates, minimized thermal cycling degradation, and extended service life under continuous operational conditions.
2. Material & Properties
2.1 Base Material Grades
- AISI 304 / SUS 304 — Austenitic stainless steel (18% Cr, 8% Ni); general-purpose grade offering excellent corrosion resistance and formability.
- AISI 316 / SUS 316 — Austenitic stainless steel with 2–3% Mo addition; enhanced resistance to chloride-induced pitting and crevice corrosion.
- AISI 321 / SUS 321 — Stabilized austenitic grade with Ti addition; superior resistance to intergranular corrosion at elevated temperatures.
- AISI 316L / SUS 316L — Low-carbon variant of 316; optimized for welding applications and reduced sensitization risk.
2.2 Key Mechanical & Physical Properties
- Tensile Strength (UTS): ≥ 520 MPa (for 304 grade, annealed condition)
- Yield Strength: ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Thermal Conductivity: 14.9 – 16.3 W/(m·K) at 20°C
- Maximum Service Temperature: 870°C (oxidation limit in continuous air)
- Density: 8.0 g/cm³
- Surface Finish: Bright annealed (BA) or 2B; Ra ≤ 0.4 μm available upon request
2.3 Corrosion Resistance Performance
- Pitting Resistance Equivalent Number (PREN) ≥ 19 for 316 grade
- Compliant with ASTM A968 for corrosion testing methodology
- Withstands up to 5% NaCl solution without measurable pitting at 23°C over 72-hour exposure
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 25.0 mm (custom sizes available) | ISO 6507 / ASTM A213 |
| Wall Thickness | 0.4 mm – 2.0 mm | ISO 6507 | Coil Length | 50 m – 500 m per coil (standard); up to 1000 m upon request | Manufacturer specification |
| Coil Inner Diameter (ID) | 150 mm – 300 mm | — |
| OD Tolerance | ±0.10 mm | ISO 6507 |
| Wall Thickness Tolerance | ±10% of nominal | ASTM A213 |
| Straightness | ≤ 1.5 mm/m | — |
| Roundness | ≤ 0.5% of OD | — |
| Surface Condition | Bright Annealed (BA) / Pickled & Passivated | ASTM A967 |
| End Condition | Plain cut / Beveled / Flanged (upon request) | — |
| Heat Treatment | Solution Annealed (1050°C – 1150°C, water or air quenched) | ASTM A213 |
| Pressure Test | Hydrostatic test at 1.5× working pressure, minimum 30 s dwell | ASME B31.5 |
| Minimum Order Quantity | 500 kg per grade | — |
| Delivery Form | Coil on wooden reel with protective wrapping | — |
4. Manufacturing Process
4.1 Process Flow Overview
- Raw Material Selection & Incoming Inspection: Stainless steel strip or seamless tube blanks are sourced from certified mills (e.g., Outokumpu, POSCO, Tsingshan). Each batch undergoes spectroscopic verification (PMI — Positive Material Identification) to confirm grade compliance.
- Slitting & Leveling: Wide strip is precision-slitted to target width and leveled to achieve flatness within ±0.2% of width.
- Forming / Roll Forming: Multi-stand roll forming machines progressively shape the strip into a seamless tube profile with precise OD and wall thickness control. For welded coil tube, a high-frequency induction welding (HFW) process is employed at 200 – 600 meters per minute.
- Inline Annealing (if applicable): For welded tube, an inline annealing furnace restores ductility and eliminates weld-zone hardness. Annealing atmosphere is controlled to prevent oxidation (dew point ≤ −60°C).
- Sizing & Cutting: The formed tube passes through a final sizing roll train to achieve dimensional tolerances, followed by cut-to-length or continuous coil winding.
- Pickling & Passivation: Chemical treatment removes mill scale and surface contaminants; a passivation layer (chromium oxide film) is established per ASTM A967 to maximize corrosion resistance.
- Coil Winding & Packaging: Finished tube is wound onto steel or wooden cores with controlled layer tension to prevent kinking. Each coil is wrapped in moisture-barrier film and secured with steel strapping.
- Quality Assurance & Final Inspection: Every coil undergoes dimensional verification, visual surface inspection, hydrostatic pressure testing, and — where specified — ultrasonic testing (UT) for internal defect detection.
4.2 Process Control Highlights
- Real-time OD and wall thickness monitoring via laser sensors at 100 Hz sampling rate
- Statistical Process Control (SPC) applied to critical dimensions with CpK ≥ 1.33
- Full traceability from raw material mill certificate to finished coil heat number
5. Applications
5.1 Primary Applications
- Fan Coil Units (FCU): Coil tubes form the core heat exchange element in FCUs used in commercial buildings, hotels, hospitals, and data centers. The stainless steel construction eliminates the risk of internal corrosion that plagues carbon steel alternatives, particularly in systems utilizing treated water or glycol-based heat transfer fluids.
- Chilled Water & Hot Water Circuits: Used in secondary loop piping and coil assemblies for VRF (Variable Refrigerant Flow) systems and central hydronic systems.
- Air Handling Units (AHU): Integrated into heating and cooling coils within rooftop and packaged AHUs.
- Condenser & Evaporator Coils: Employed in refrigeration and process cooling applications where corrosion resistance is critical.
5.2 Secondary Applications
- Marine HVAC systems (316/316L grades for saltwater proximity)
- Food and pharmaceutical processing equipment (hygienic-grade BA finish)
- Automotive thermal management components
- Industrial heat exchangers and process piping
6. Quality Certifications & Standards Compliance
6.1 Applicable International Standards
- ASTM A213 / A213M — Standard Specification for Seamless Ferritic, Austenitic, and Ferritic-Austenitic Stainless Steel Tubing for High-Temperature Service
- ASTM A554 / A554M — Standard Specification for Seamless Austenitic Stainless Steel Electric-Resistance-Welded Tubing for High-Temperature Service
- ASTM A967 — Standard Practice for Chemical Cleaning and Passivation of Stainless Steel Parts
- ISO 6507 — Tubes and Fittings — Dimensions and Tolerances
- EN 10217-7 — Tubes for Heat Exchangers and Heat Transfer Equipment
- JIS G3459 — Cold-Drawn Stainless Steel Tubing for General Purposes
6.2 Factory Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health & Safety Management System
- CE Marking — Compliance with EU Pressure Equipment Directive (PED 2014/68/EU) where applicable
- TÜV / SGS Third-Party Inspection — Available upon customer request
6.3 Testing & Inspection Protocol
| Test Type | Standard | Frequency |
|---|---|---|
| Chemical Composition (Spectrometry) | ASTM E415 | Every heat / batch |
| Mechanical Properties (Tensile Test) | ASTM A370 | Every heat / batch |
| Hydrostatic Pressure Test | ASME B31.5 | 100% of coils |
| Ultrasonic Testing (UT) | ASTM E309 | As specified / 100% |
| Surface Quality Inspection | Visual + Ra gauge | 100% of coils |
| Pitting Corrosion Test | ASTM G48 | Periodic / on request |
| Intergranular Corrosion Test | ASTM A262 Practice E | Periodic / on request |
7. Unique Selling Points
Engineered for Reliability: The product development process incorporates findings from systematic reliability improvement studies on fan coil unit motors and hydraulic circuits. Key design decisions — including wall thickness optimization, surface finish refinement, and material selection — are guided by failure-mode analysis (FMEA) data from real-world FCU deployments, resulting in a coil tube product with demonstrably lower field failure rates.
- Superior Corrosion Longevity: Stainless steel construction provides a service life exceeding 25 years in typical HVAC water circuits — compared to 8–12 years for carbon steel with internal coatings — eliminating the need for costly coil replacement and system downtime.
- Continuous Coil Form: Delivered in continuous coil format, enabling seamless integration into automated coil-winding and forming lines, reducing labor costs and eliminating weld joints that are common failure points in cut-and-welded alternatives.
- Precision Dimensional Control: Advanced inline monitoring ensures OD and wall thickness tolerances within ±0.10 mm, guaranteeing optimal fin-to-tube contact resistance and maximum heat transfer efficiency in downstream coil assembly.
- Full Traceability: Every coil is traceable to its raw material mill heat number, enabling complete supply chain transparency for regulated industries (pharmaceutical, food, aerospace).
- Customization Capability: Wenzhou Jixing Metal Materials offers tailored solutions including non-standard OD/wall combinations, custom coil lengths, specialized surface finishes (electropolished, pickled & passivated), and bespoke end treatments to meet specific OEM requirements.
- Environmental Responsibility: Stainless steel is 100% recyclable with no loss of material properties. The manufacturing process adheres to ISO 14001 environmental management standards, minimizing waste and energy consumption.
8. Technical Data Summary
Wenzhou Jixing Metal Materials Co., Ltd. — Product No. 787 | Stainless Steel Coil Tube (Coiltube) | Available in AISI 304, 316, 321, 316L grades | OD: 6–25 mm | Wall: 0.4–2.0 mm | Coil lengths up to 1000 m | Compliant with ASTM A213, A554, ISO 6507, EN 10217-7 | ISO 9001:2015 Certified Manufacturer