Stainless Steel Coil Tube for Fan Coil Unit Heat Exchange Systems
Product Overview
The Stainless Steel Coil Tube (Product No. 728) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered coiled tubing product designed for integration into fan coil unit (FCU) heat exchange assemblies. This product serves as a critical component in hydronic air-conditioning systems, where it functions as the primary heat transfer medium within evaporator and condenser coils. The coil tube is specifically engineered to withstand elevated operating temperatures and sustained thermal cycling, making it suitable for both standard and high-temperature operating conditions commonly encountered in commercial HVAC (Heating, Ventilation, and Air Conditioning) installations.
Unlike conventional copper or aluminum tubing alternatives, the stainless steel coil tube offers superior resistance to corrosion, chemical degradation, and mechanical fatigue, extending the operational service life of the complete fan coil unit assembly significantly.
Material & Properties
The coil tube is fabricated from high-purity austenitic stainless steel, conforming to recognized international material standards. The following table summarizes the key material properties:
| Property | Specification | Standard Reference |
|---|---|---|
| Base Material | Austenitic Stainless Steel (304 / 316 Grade) | ASTM A269 / ASME SA-269 |
| Chemical Composition (304) | C ≤ 0.08%, Si ≤ 1.00%, Mn ≤ 2.00%, Cr 18.0–20.0%, Ni 8.0–10.5% | ASTM A240 |
| Chemical Composition (316) | C ≤ 0.08%, Si ≤ 1.00%, Mn ≤ 2.00%, Cr 16.0–18.0%, Ni 10.0–14.0%, Mo 2.0–3.0% | ASTM A240 |
| Tensile Strength | ≥ 520 MPa (75,000 psi) | ASTM A269 |
| Yield Strength | ≥ 205 MPa (29,700 psi) | ASTM A269 |
| Elongation | ≥ 40% | ASTM A269 |
| Thermal Conductivity | 14.9–16.3 W/(m·K) at 100°C | — |
| Maximum Operating Temperature | 870°C (1,598°F) in non-oxidizing atmosphere | — |
| Corrosion Resistance | Excellent resistance to oxidizing acids, atmospheric corrosion, and chloride-induced pitting (316 grade) | ASTM G48 |
| Surface Finish | Bright Annealed (BA) / Pickled and Passivated | — |
| Hardness | ≤ 92 HRB (Annealed Condition) | ASTM A269 |
Specifications
| Parameter | Specification |
|---|---|
| Product Designation | Stainless Steel Coil Tube (盘管 / Coiltube), Item No. 728 |
| Tube Outer Diameter (OD) | 7.94 mm (⅜") / 9.53 mm (⅜" nominal) / 12.70 mm (½") |
| Wall Thickness | 0.50 mm – 1.50 mm (customizable) |
| Coil Length per Spool | 50 m – 500 m (configurable based on order requirements) |
| Bend Radius | ≥ 3× tube OD (minimum cold-form bend radius) |
| Fins (if finned variant) | Aluminum or Stainless Steel plate fins; 8–14 fins per inch (FPI) |
| Operating Pressure | Up to 1.6 MPa (232 psi) at rated temperature |
| Operating Temperature Range | −40°C to +200°C (−40°F to +392°F) continuous service |
| Heat Transfer Medium | Water, glycol-water mixture, or refrigerant (R-410A, R-134a compatible) |
| Flux Coating | Available with anti-flux coating for brazed assemblies |
| Packaging | Reeled on galvanized steel spools; moisture-proof wrapping; export-grade wooden crates |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Coil Uncoiling & Straightening: Cold-rolled stainless steel strip is uncoiled from the master coil and passed through a precision straightening line to eliminate residual curvature and set up uniform tension.
- Forming & Welding: The flat strip is mechanically formed into a tubular geometry using roll-forming dies. A continuous TIG (Tungsten Inert Gas) welding process is employed along the longitudinal seam to produce a full-penetration weld joint with minimal heat-affected zone (HAZ).
- Cold Coiling: The formed tube is cold-coiled around a precision mandrel to achieve the target coil diameter and pitch. The coiling process is controlled to prevent ovality and maintain uniform cross-sectional geometry throughout the entire spool length.
- Pickling & Passivation: The coiled tube undergoes acid pickling (typically using a hydrofluoric/nitric acid blend) to remove weld oxide and surface contamination. A subsequent passivation treatment using nitric acid or citric acid establishes a stable chromium oxide passive film, enhancing long-term corrosion resistance.
- Non-Destructive Testing (NDT):strong> Each spool is subjected to 100% hydrostatic pressure testing to verify weld integrity and dimensional conformance. Ultrasonic testing (UT) may be applied to critical weld joints for subsurface defect detection.
- Final Inspection & Packaging: Dimensional verification (OD, wall thickness, coil diameter, straightness) is performed using calibrated instruments. Conforming product is coiled, wrapped, and crated for shipment.
Applications
The stainless steel coil tube is deployed across a broad spectrum of thermal management and heat exchange applications, including but not limited to:
- Fan Coil Units (FCUs): Primary heat exchange coils in commercial and residential HVAC systems, particularly in high-temperature operating scenarios where conventional copper tubing may suffer accelerated corrosion or thermal fatigue.
- Chilled Water & Hot Water Distribution Systems: Coil assemblies for air handling units (AHUs), variable air volume (VAV) systems, and radiant cooling panels.
- Industrial Process Heating & Cooling: Heat exchangers in food processing, pharmaceutical manufacturing, chemical plants, and semiconductor fabrication facilities requiring hygienic-grade or corrosion-resistant tubing.
- Marine & Offshore HVAC: Heat exchange coils in marine air-conditioning systems where resistance to saltwater-induced corrosion is paramount.
- Refrigeration & Condensing Systems: Condenser and evaporator coils in commercial refrigeration units operating with ammonia or HFC-based refrigerants.
- Solar Thermal Systems: Heat collection coils in solar water heating installations requiring long-term durability under cyclic thermal loading.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework ensuring that all coil tube products meet or exceed international standards:
- ISO 9001:2015 — Quality Management System certification covering design, manufacturing, and delivery processes.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- ASTM A269 / ASME SA-269 — Conformance to the standard specification for seamless and welded austenitic stainless steel tubing.
- EN 10216-5 — European standard for welded stainless steel tubes for heat exchangers and similar purposes.
- GB/T 14976 — Chinese national standard for seamless stainless steel tubes for fluid transport.
- NSF/ANSI 61 — Drinking water system components certification (where applicable for potable water heat exchange applications).
- Mill Test Reports (MTRs): Each production batch is accompanied by a comprehensive mill test report documenting chemical composition, mechanical properties, and heat treatment condition.
Unique Selling Points
- Exceptional High-Temperature Performance: Engineered to maintain mechanical integrity and dimensional stability under sustained high-temperature operating conditions, addressing a critical limitation of conventional copper and aluminum coil tubes in demanding FCU applications.
- Superior Corrosion Resistance: The austenitic stainless steel matrix provides outstanding resistance to atmospheric, chemical, and chloride-induced corrosion, dramatically reducing maintenance frequency and extending service life to 25+ years.
- Full Traceability: Every coil spool is serialized with batch traceability codes, enabling complete supply chain accountability from raw material mill to end installation.
- Custom Engineering Capability: Flexible customization of tube OD, wall thickness, coil pitch, fin configuration, and surface finish to meet project-specific thermal performance requirements.
- Reduced Total Cost of Ownership (TCO): Although the initial material cost may be higher than copper alternatives, the extended service life, reduced maintenance requirements, and lower replacement frequency result in a significantly lower total cost of ownership over the asset lifecycle.
Technical Note: For high-temperature fan coil unit applications exceeding 150°C continuous operating temperature, 316-grade stainless steel coil tube with a minimum wall thickness of 1.00 mm is recommended. For applications involving chloride-containing fluids (e.g., brine solutions, coastal environment condensate), 316L (low-carbon 316) grade is advised to minimize intergranular corrosion risk.