Stainless Steel Coil Tube (Coiltube) — Fan Coil Unit Water Circuit System
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Code: 1647
Category: Stainless Steel Coil Tubes for HVAC Fan Coil Unit (FCU) Water Circuit Systems
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component specifically designed for the water circuit systems of Fan Coil Units (FCU) in commercial and residential HVAC (Heating, Ventilation, and Air Conditioning) applications. This product represents an advanced alternative to traditional copper or aluminum coil tubes, offering superior corrosion resistance, extended service life, and enhanced thermal performance under demanding operating conditions.
Wenzhou Jixing Metal Materials Co., Ltd. specializes in the manufacture of high-grade stainless steel coil tubes that serve as the core heat exchange elements within fan coil unit water circuit systems. The coil tube functions as the primary medium through which thermal energy is transferred between the circulating water (hot or chilled) and the ambient air, thereby achieving precise temperature regulation in enclosed spaces.
Unlike conventional materials susceptible to galvanic corrosion and scale buildup, the stainless steel coil tube maintains structural integrity and thermal efficiency over prolonged operational cycles, particularly in environments with aggressive water chemistry, high humidity, or elevated chloride ion concentrations.
2. Material & Properties
2.1 Base Material Composition
The coil tube is fabricated from austenitic stainless steel grades conforming to international standards. The primary grades utilized include:
- AISI 304 (UNS S30408): General-purpose grade with excellent formability and moderate corrosion resistance; suitable for standard HVAC water circuit applications.
- AISI 316L (UNS S31603): Enhanced grade with added molybdenum (Mo) content, providing superior resistance to pitting and crevice corrosion in chloride-rich environments.
- AISI 321 (UNS S32100): Titanium-stabilized grade offering improved resistance to intergranular corrosion at elevated temperatures.
2.2 Mechanical Properties
| Property | Grade 304 | Grade 316L | Test Standard |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 | ASTM A270 / GB/T 12771 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ASTM A270 / GB/T 12771 |
| Elongation (%) | ≥ 40 | ≥ 40 | ASTM A270 / GB/T 12771 |
| Hardness (HBW) | ≤ 217 | ≤ 217 | ASTM A270 |
| Thermal Conductivity (W/m·K) | 16.3 | 14.6 | — |
2.3 Corrosion Resistance
- Resistance to atmospheric corrosion in industrial and marine environments
- Immunity to dezincification and general acid attack typical of circulating water systems
- Pitting Resistance Equivalent Number (PREN) ≥ 19 for Grade 316L, ensuring durability in high-chloride water circuits
- Non-magnetic in annealed condition, eliminating electromagnetic interference concerns
2.4 Surface Finish
The coil tube is supplied with a polished or electropolished interior surface (Ra ≤ 0.8 μm) to minimize hydraulic resistance and prevent biofilm accumulation. The exterior surface may be brushed or matte finished to facilitate fin attachment during heat exchanger assembly.
3. Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Outer Diameter (OD) | 6.0 / 7.0 / 8.0 / 9.52 / 10.0 | mm |
| Wall Thickness (WT) | 0.30 / 0.35 / 0.40 / 0.50 / 0.60 | mm |
| Bundling Pitch | 12.7 / 15.88 / 19.05 / 25.4 | mm |
| Coil Length | 2,000 – 15,000 (customizable) | mm |
| Coil Diameter | 150 – 500 | mm |
| Row Configuration | 1 / 2 / 3 / 4 rows | — |
| Operating Pressure | ≤ 1.6 | MPa |
| Operating Temperature Range | -40 to +200 | °C |
| Tolerance on OD | ±0.05 | mm |
| Tolerance on Wall Thickness | ±0.02 | mm |
| Material Grade | SUS 304 / SUS 316L / SUS 321 | — |
| Surface Treatment | Pickled & Passivated / Electropolished | — |
| Delivery Form | Coiled (spooled) / Cut-to-length | — |
4. Manufacturing Process
The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical quality, and surface integrity:
- Coil Uncoiling & Straightening: The cold-rolled stainless steel strip is uncoiled from the master coil and fed through a precision straightener to eliminate residual curvature and ensure flatness within ±0.1 mm/m.
- Edge Trimming & Cleaning: The strip edges are trimmed to the exact width required for the target tube OD. Surface contaminants (oils, oxides, handling residues) are removed via alkaline degreasing and acid pickling.
- Roll Forming (Cold Forming): The flat strip is progressively formed into a tubular geometry through a series of precision-rolled rolls. This cold working process imparts beneficial strain hardening while maintaining dimensional tolerances. The forming angle is controlled to prevent material thinning beyond acceptable limits.
- Seam Welding (TIG Welding): The longitudinal seam is closed using Tungsten Inert Gas (TIG) welding with a backing gas (argon) shield to prevent internal oxidation. Weld parameters (voltage, current, travel speed) are precisely controlled to produce a uniform, penetration-free weld bead.
- Coil Winding (Coiling): The formed and welded tube is wound onto a mandrel or drum to produce the final coil geometry. The winding tension is controlled to maintain consistent bundling pitch and prevent tube deformation.
- Heat Treatment (Annealing): Where required, the coil tube undergoes solution annealing at 1050–1100°C followed by rapid water quenching to restore full austenitic microstructure, relieve residual stresses, and maximize ductility.
- Pickling & Passivation: The tube surface is treated with a mixed acid bath (HNO₃ + HF) to remove heat scale and welding discoloration, followed by passivation with nitric acid to restore the chromium oxide passive film for maximum corrosion protection.
- Final Inspection & Packaging: Each coil is inspected for dimensional accuracy, surface defects, and weld integrity. Approved coils are packaged with protective end caps, moisture-absorbing desiccants, and wooden or steel crates for transport.
5. Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. is applicable across a broad spectrum of HVAC and industrial thermal management systems:
- Commercial HVAC Fan Coil Units: Primary application in air handling units (AHU), ceiling-mounted FCUs, and ducted systems for office buildings, shopping malls, and hotels.
- Residential HVAC Systems: Concealed and exposed fan coil units in high-end residential buildings requiring low-maintenance water circuit components.
- Marine HVAC Systems: Fan coil units aboard vessels where saltwater exposure and high humidity demand superior corrosion resistance from Grade 316L stainless steel.
- Process Cooling Systems: Chilled water coil tubes in pharmaceutical, food and beverage, and semiconductor manufacturing facilities requiring hygienic-grade surfaces.
- Geothermal Heat Exchange Systems: Coil tubes in ground-source heat pump systems where long-term durability in subterranean environments is critical.
- Industrial Drying & Heating: Steam-heated coil tubes in industrial ovens, drying chambers, and process heating applications.
6. Quality Certifications & Standards Compliance
| Certification / Standard | Scope | Relevance |
|---|---|---|
| ISO 9001:2015 | Quality Management System | Ensures consistent manufacturing quality and process control |
| ISO 14001:2015 | Environmental Management System | Environmental sustainability in production processes |
| GB/T 12771 | Chinese National Standard | Stainless steel welded tubes for general fluid conveyance |
| ASTM A270 | American Standard | General requirements for austenitic stainless steel welded tubes |
| EN 10217-7 | European Standard | Heat exchanger tubes — austenitic stainless steel |
| SGS Material Testing | Third-party verification | Chemical composition, mechanical properties, and dimensional verification |
| Mill Test Certificate (MTC) | Per-batch documentation | Traceability of material grade, heat number, and test results |
7. Unique Selling Points
- Superior Corrosion Resistance: Austenitic stainless steel construction eliminates the risk of internal scaling, dezincification, and pitting corrosion that plagues copper and carbon steel alternatives — extending service life by 3–5× in aggressive water circuit environments.
- Hygienic Interior Surface: Electropolished interior (Ra ≤ 0.8 μm) prevents microbial growth and biofilm formation, meeting sanitary requirements for food-grade and pharmaceutical applications.
- Customizable Geometry: Full range of OD, wall thickness, bundling pitch, and coil length configurations to match specific FCU design requirements, from compact residential units to large commercial air handlers.
- Thermal Efficiency Retention: Unlike copper tubes that develop oxide layers reducing heat transfer coefficients over time, stainless steel maintains near-constant thermal conductivity throughout the operational lifecycle.
- Non-Magnetic & Non-Toxic: Suitable for environments with electromagnetic sensitivity requirements and safe for potable water contact applications.
- Weldability & Fabrication Compatibility: Excellent TIG and orbital welding compatibility for seamless integration into heat exchanger assemblies with aluminum fins.
- Environmental Sustainability: Stainless steel is 100% recyclable, aligning with green building certification requirements (LEED, BREEAM, GREEN STAR).
Wenzhou Jixing Metal Materials Co., Ltd. — Committed to delivering precision-engineered stainless steel coil tube solutions that redefine reliability and performance in HVAC water circuit systems worldwide.