Stainless Steel Coil Tube for HVAC Fan Coil Units
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component designed for thermal exchange applications within HVAC (Heating, Ventilation, and Air Conditioning) systems. Specifically engineered for use in fan coil units (FCUs), this coil tube facilitates efficient heat transfer between the circulating refrigerant or heating medium and the airstream, playing a critical role in achieving precise terminal state point control of supply air—particularly in fresh air handling scenarios where maintaining target dry-bulb and wet-bulb temperatures is essential for indoor air quality and occupant comfort.
The coil tube is supplied in continuous coiled form (盘管/Coiltube configuration), allowing for flexible installation geometries, optimized surface area-to-volume ratios, and reduced joint density—thereby minimizing potential leak points and maximizing long-term system reliability.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its superior corrosion resistance, mechanical strength, and thermal conductivity properties. The material composition and performance characteristics are as follows:
- Base Material: Austenitic stainless steel conforming to ASTM A213/A213M or equivalent standards
- Typical Grades: SUS304 (UNS S30400), SUS316 (UNS S31600) for enhanced chloride resistance
- Corrosion Resistance: Excellent resistance to condensation water, humid environments, and chemical agents commonly encountered in HVAC systems
- Temperature Range: Operational suitability from −196 °C to +870 °C, covering all standard HVAC refrigeration and heating cycles
- Hygienic Properties: Non-toxic, non-porous surface suitable for food-grade and medical-grade air handling applications
- Mechanical Properties: Tensile strength ≥ 520 MPa; elongation ≥ 40%; hardness ≤ 200 HB
Specifications
| Parameter | Specification | Unit | Standard / Tolerance |
|---|---|---|---|
| Outer Diameter (OD) | 6.35 / 8.00 / 9.53 / 12.70 (configurable) | mm | ±0.10 mm (ASTM A213) |
| Wall Thickness | 0.50 / 0.65 / 0.80 / 1.00 | mm | ±10% of nominal |
| Coil Winding Diameter | 150 – 600 (customizable) | mm | ±5 mm |
| Coil Length (per roll) | 20 – 100 | m | ±2% |
| Surface Finish | 2B / BA (Bright Annealed) / Electropolished (Ra ≤ 0.4 μm) | — | ISO 11120 |
| Welding Method | TIG (Tungsten Inert Gas) / Orbital Auto-Welding | — | ASME B31.9 / EN 13480 |
| Pressure Rating | Up to 1.6 MPa (design) | MPa | Hydrostatic test at 1.5× design pressure |
| Fin Configuration | Aluminum or stainless steel plate fins (optional) | — | Fin density: 10 – 20 fins/inch |
| Maximum Operating Temperature | 200 | °C | — |
| Minimum Operating Temperature | −40 | °C | — |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: Certified stainless steel wire rod (SUS304/SUS316) sourced from accredited mills with full chemical and mechanical test certificates (MTC per EN 10204 3.1).
- Wire Drawing: Multi-stage cold drawing through tungsten carbide (WC) dies to achieve precise OD and wall thickness tolerances, with intermediate annealing to relieve cold work stresses.
- Tube Forming & Welding: The drawn wire is formed into a semi-circular profile and longitudinally welded using high-frequency induction welding or precision TIG welding with argon shielding to produce a seamless-quality weld seam.
- Coil Winding: The continuous tube is wound onto precision-machined mandrels using computer-controlled winding equipment to maintain uniform coil diameter and pitch, ensuring consistent hydraulic flow characteristics.
- Post-Weld Annealing: Solution annealing at 1050–1100 °C followed by controlled cooling to restore full austenitic microstructure, eliminate residual welding stresses, and maximize corrosion resistance.
- Pickling & Passivation: Acid pickling to remove oxide scale, followed by passivation treatment to form a stable chromium oxide protective layer.
- Surface Finishing: Optional electropolishing or mechanical polishing to achieve specified surface roughness (Ra ≤ 0.4 μm), critical for hygienic applications and reduced fouling resistance.
- Fin Attachment (if applicable): Plate fins are mechanically crimped or brazed onto the coil tube to increase heat transfer surface area by up to 400%.
- Quality Inspection: 100% visual inspection, dimensional verification via ultrasonic thickness gauging, hydrostatic pressure testing, and optional eddy current flaw detection of weld seams.
Applications
The stainless steel coil tube is widely deployed in the following application domains:
- HVAC Fan Coil Units: Primary heat exchange element in commercial and residential FCUs, where precise control of supply air terminal state point—encompassing dry-bulb temperature, humidity ratio, and enthalpy—is paramount for achieving design indoor conditions.
- Fresh Air Handling Systems: In systems where fresh air is introduced directly into the occupied zone, the coil tube enables accurate dehumidification and temperature conditioning to meet ASHRAE 62.1 ventilation standards.
- Commercial Refrigeration: Low-temperature evaporator coils for cold storage facilities and refrigerated display cases.
- Process Cooling: Heat exchangers in pharmaceutical, food and beverage, and semiconductor manufacturing facilities requiring sanitary-grade materials.
- Marine & Offshore HVAC: Corrosion-resistant coil assemblies for shipboard and offshore platform air conditioning systems exposed to high-salinity environments.
- Building Energy Efficiency Systems: High-efficiency coil configurations integrated with Variable Refrigerant Flow (VRF) and Variable Air Volume (VAV) systems for optimized energy performance.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications and complies with the following international standards:
- ISO 9001:2015 — Quality Management System certification for consistent product quality and process control
- ISO 14001:2015 — Environmental Management System certification
- ISO 45001:2018 — Occupational Health and Safety Management System
- ASME B31.9 — Compliance for pressure piping and components in refrigeration systems
- EN 10217-7 — European standard for seamless and welded stainless steel tubes
- ASTM A213/A213M — American standard for wrought austenitic stainless steel tubing
- NACE MR0175 — Resistance to sulfide stress cracking (for sour service applications)
- CE Marking — Conformity with European machinery and pressure equipment directives (PED 2014/68/EU)
- Material Test Certificate (MTC) — EN 10204 Type 3.1 for each production batch
Unique Selling Points
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. distinguishes itself in the competitive HVAC component market through the following value propositions:
- Precision Engineering for Terminal State Control: The coil tube's consistent geometry and high thermal conductivity enable precise modulation of supply air conditions, directly supporting advanced HVAC control strategies for fresh air terminal state point optimization—including accurate humidity management, sensible heat ratio control, and enthalpy-based economizer operations.
- Superior Corrosion Longevity: Austenitic stainless steel construction provides a service life exceeding 25 years under normal HVAC operating conditions—significantly outperforming carbon steel alternatives and eliminating the need for replacement due to internal corrosion.
- Reduced Fouling & Maintenance: The smooth electropolished surface (Ra ≤ 0.4 μm) minimizes scale and biofilm accumulation, reducing cleaning frequency and maintaining heat transfer efficiency over the system's lifecycle.
- Customizable Configuration: Flexible specifications in OD, wall thickness, coil diameter, and fin density allow OEMs to optimize coil performance for specific capacity, pressure drop, and footprint constraints.
- Continuous Coil Design: The continuous coiled form eliminates longitudinal weld joints across the heat exchanger, reducing leak probability and improving structural integrity under thermal cycling.
- Full Traceability: Each coil tube batch is traceable from raw material mill certificate through final inspection, ensuring complete supply chain accountability.
Technical Notes on Fresh Air Terminal State Point Applications
In HVAC system design, the terminal state point of fresh air—defined by its dry-bulb temperature (DBT), wet-bulb temperature (WBT), relative humidity (RH), and specific enthalpy—determines the thermal and hygroscopic load imposed on the occupied space. The stainless steel coil tube serves as the primary heat transfer medium through which these parameters are precisely controlled. Key engineering considerations include:
- Sensible Heat Ratio (SHR) Optimization: Coil tube geometry (OD, fin density, circuit count) is engineered to achieve target SHR values, ensuring that the proportion of sensible to latent heat removal aligns with the building's psychrometric requirements.
- Low Wet-Bulb Approach: High-efficiency coil configurations minimize the temperature approach between the coil surface and the dew point of the incoming air, enabling effective dehumidification without excessive supercooling that would require reheat energy.
- Variable Air Volume (VAV) Compatibility: The coil tube's hydraulic and thermal characteristics are designed to maintain stable performance across a wide range of airflow rates (typically 50%–120% of design), supporting energy-efficient VAV operations.
- Free Cooling / Economizer Integration: The coil tube's thermal inertia and response characteristics are optimized for rapid transition between mechanical cooling and free cooling modes, reducing annual energy consumption.
This product represents a synthesis of metallurgical excellence, precision manufacturing, and HVAC engineering expertise—delivering a coil tube solution that meets the demanding requirements of modern building climate control systems while maintaining the highest standards of quality, safety, and environmental responsibility.