Stainless Steel Coil Tube for Low-Temperature Fan Coil Unit Applications
Product Overview
The Stainless Steel Coil Tube (also referred to as a Coil Tube or Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product specifically designed for integration into Fan Coil Units (FCUs) operating under low-temperature conditions. This product represents a critical heat exchange component within HVAC (Heating, Ventilation, and Air Conditioning) systems, where thermal performance, mechanical integrity, and corrosion resistance are paramount.
The coil tube is fabricated from high-grade austenitic stainless steel and formed into a serpentine or helical configuration to maximize surface area and enhance convective heat transfer efficiency. Its design enables reliable operation across a wide range of thermal loads, including extreme low-temperature environments where conventional carbon steel components would suffer from frost damage, thermal stress cracking, or accelerated corrosion.
This product has been extensively evaluated through rigorous low-temperature thermal performance testing, which validates its suitability for demanding industrial and commercial HVAC applications requiring consistent heat exchange performance under sub-ambient operating conditions.
Material & Properties
The coil tube is primarily constructed from Stainless Steel (Austenitic Grade), with the following material composition and mechanical properties:
- Base Material: Austenitic stainless steel, typically conforming to AISI 304 or AISI 316L (UNS S30400 / UNS S31603), selected for superior corrosion resistance and cryogenic ductility.
- Chromium (Cr) Content: ≥18% — provides essential passivation layer formation and oxidation resistance.
- Nickel (Ni) Content: ≥8% (304) or ≥10–14% (316L) — ensures austenitic microstructure stability and low-temperature toughness.
- Molybdenum (Mo) Content: 2.0–3.0% (316L grade) — enhances resistance to pitting and crevice corrosion in aggressive environments.
- Yield Strength (Rp0.2): 205–310 MPa (annealed condition), providing adequate structural rigidity under thermal cycling loads.
- Tensile Strength (Rm): 515–720 MPa — ensures resistance to mechanical deformation during installation and operation.
- Elongation (A50mm): ≥35% — guarantees sufficient ductility to withstand low-temperature thermal contraction without brittle fracture.
- Thermal Conductivity (λ): 14.5–16.5 W/(m·K) at 20°C — optimized for efficient heat transfer between the refrigerant/fluid medium and the surrounding airstream.
- Coefficient of Thermal Expansion (α): 16–17 × 10⁻⁶ /K — compatible with expansion joints and mounting hardware in thermal cycling applications.
- Operating Temperature Range: −40°C to +120°C — validated through low-temperature thermal performance testing for cryogenic and moderate-temperature service.
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) |
| Product Code | 619 |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
| Material Grade | AISI 304 / AISI 316L (Austenitic Stainless Steel) |
| Tube Outer Diameter (OD) | 6.35 mm / 7.94 mm / 9.53 mm / 12.7 mm (customizable) |
| Tube Wall Thickness | 0.40 mm – 0.80 mm |
| Coil Pitch (Center-to-Center Spacing) | 15 mm – 30 mm (adjustable per thermal load requirements) |
| Number of Rows | 1 – 6 rows (configurable for capacity scaling) |
| Fins per Inch (FPI) | 10 – 14 (aluminum or stainless steel fins) |
| Fin Material | Anodized Aluminum 1100-H14 / Stainless Steel 304 |
| Surface Treatment | Electropolished / Pickled & Passivated / Anodized (fin surface) |
| Welding Method | TIG (Tungsten Inert Gas) Welding / Brazing (Phosphor-Copper or Silver Brazing) |
| Standard Conformity | ASTM A269 / ASTM A213 / EN 10217-7 / GB/T 12771 |
| Pressure Rating | Up to 1.6 MPa (working pressure) / 2.4 MPa (hydrostatic test) |
| Thermal Performance | Validated via low-temperature FCU thermal performance testing (ASHRAE Standard 22) |
| Application Environment | Low-temperature HVAC systems, commercial refrigeration, process cooling |
Manufacturing Process
The production of the stainless steel coil tube follows a multi-stage precision manufacturing workflow to ensure dimensional accuracy, metallurgical integrity, and optimal thermal performance:
- Material Selection & Inspection: Raw stainless steel strip or seamless tube stock is procured in compliance with ASTM A269 / ASTM A213 specifications. Incoming material undergoes spectroscopic analysis (Optical Emission Spectrometry, OES) to verify chemical composition, along with tensile testing and hardness verification.
- Coil Forming / Tube Bending: The stainless steel tube is cold-formed into the desired serpentine or helical coil geometry using CNC-controlled bending machinery. Bending radii are optimized to prevent wall thinning, ovalization, and micro-cracking in the bend regions. The minimum bend radius is maintained at ≥3× the tube OD to preserve structural integrity.
- Fin Attachment: Aluminum or stainless steel fins are attached to the formed coil tubes via a roll-bonding process or stamping-and-welding method. The fin-to-tube interface is mechanically locked and, where required, brazed to ensure low thermal contact resistance (<0.5 m²·K/W).
- Welding & Brazing: Header connections and end fittings are joined using TIG welding (for tube-to-header joints) or phosphor-copper brazing (for fin-to-tube and header connections). Weld joints are inspected via visual examination and, where applicable, dye penetrant testing (DPT) per ASTM E709.
- Surface Treatment: The completed coil tube assembly undergoes electropolishing or pickling and passivation to remove surface contaminants, restore the chromium oxide passive film, and achieve a surface roughness (Ra) of ≤0.4 μm. This treatment enhances corrosion resistance and reduces fouling potential.
- Quality Control & Testing: Each coil tube unit is subjected to hydrostatic pressure testing (at 1.5× working pressure for a minimum of 30 seconds) to verify leak-tightness. Dimensional inspection is performed using coordinate measuring machines (CMM) and laser micrometers to confirm coil pitch, row alignment, and overall assembly dimensions.
- Thermal Performance Verification: Representative coil tube samples are installed in a calibrated test chamber and evaluated under low-temperature conditions per ASHRAE Standard 22 (Method of Testing Air-Cooled and Water-Condensing Heat Pumps and Air Conditioners). Key performance metrics include total cooling capacity (W), sensible heat ratio (SHR), air-side pressure drop (Pa), and overall heat transfer coefficient (U-value, W/m²·K).
Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. is engineered for a broad spectrum of low-temperature and high-performance HVAC applications:
- Commercial Fan Coil Units (FCUs): Primary heat exchange element in ceiling-mounted, concealed, and ducted fan coil units used in office buildings, hotels, hospitals, and retail facilities. The coil tube's low-temperature thermal performance ensures efficient dehumidification and cooling even when supply air temperatures drop below 10°C.
- Industrial Process Cooling: Integration into process cooling loops for semiconductor manufacturing, pharmaceutical production, and food processing facilities where precise temperature control and corrosion resistance are critical.
- Low-Temperature Refrigeration Systems: Application in cold storage facilities, walk-in coolers, and blast freezers where operating temperatures may reach −20°C to −40°C. The austenitic stainless steel composition prevents low-temperature brittleness and maintains mechanical strength.
- Marine & Offshore HVAC: Suitable for marine air conditioning systems where exposure to saltwater-laden air demands exceptional chloride resistance (particularly with AISI 316L grade).
- Medical & Laboratory HVAC: Deployment in cleanroom environments, operating theaters, and laboratory ventilation systems where hygienic surface conditions and reliable thermal performance are non-negotiable.
- Energy Recovery Ventilators (ERV/HRV): Use in heat recovery coils within energy recovery systems to maximize thermal efficiency in both heating and cooling modes.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that every coil tube product meets international standards and regulatory requirements:
- ISO 9001:2015 — Quality Management Systems certification, demonstrating a commitment to consistent product quality and continuous improvement.
- ISO 14001:2015 — Environmental Management Systems certification, ensuring environmentally responsible manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management Systems certification.
- CE Marking — Conformity with European Union directives for machinery and pressure equipment safety.
- EN 10204 3.1 Certification — Mill Test Certificates (MTC) issued for each batch of raw material and finished product, providing traceability of chemical composition and mechanical properties.
- ASTM Compliance — Products conform to ASTM A269 (Seamless and Welded Austenitic Stainless Steel Tubing for General Applications) and ASTM A213 (Seamless Austenitic Stainless Steel Tubing for High-Service Boilers, Heaters, Exchangers, and Similar Applications).
- GB/T 12771 — Conformity with Chinese national standards for stainless steel welded tubes and pipes for general applications.
- Third-Party Testing Reports — Independent thermal performance and mechanical property verification conducted by accredited laboratories (CNAS-accredited in China / ISO 17025-accredited internationally).
Unique Selling Points
- Validated Low-Temperature Performance: Unlike generic coil tubes, this product has been specifically evaluated through rigorous low-temperature thermal performance testing, providing quantifiable data on cooling capacity, heat transfer coefficient, and frost resistance under extreme conditions. This eliminates design uncertainty for engineers specifying HVAC systems for cold-climate or low-temperature applications.
- Corrosion-Resistant Construction: The use of austenitic stainless steel (304/316L) ensures long-term resistance to corrosion from condensate, refrigerants, and ambient moisture — a common failure mode for carbon steel coil tubes that leads to reduced efficiency and premature replacement.
- Superior Ductility at Cryogenic Temperatures: The austenitic microstructure retains its toughness and ductility down to −40°C, preventing catastrophic brittle fracture that can occur with ferritic or martensitic stainless steels at low temperatures.
- Hygienic Surface Finish: The electropolished surface (Ra ≤ 0.4 μm) minimizes microbial adhesion and fouling, making the coil tube suitable for pharmaceutical, food-grade, and medical applications where sanitary standards are enforced.
- Customizable Configuration: Tube OD, wall thickness, coil pitch, row count, and fin density can be tailored to specific thermal load requirements, enabling optimized system design and reduced over-sizing costs.
- Full Traceability: Each production batch is accompanied by mill test certificates (EN 10204 3.1), providing complete traceability from raw material through to finished product — essential for regulated industries and warranty documentation.
Thermal Performance Analysis Summary
Based on the low-temperature fan coil unit thermal performance testing referenced in the product documentation, the following key performance characteristics have been established:
| Performance Metric | Typical Value | Test Condition |
|---|---|---|
| Total Cooling Capacity | 3.5 kW – 28 kW (per unit) | DB 27°C / WB 19°C, Airflow 0.35 m³/s per m² face area |
| Sensible Heat Ratio (SHR) | 0.65 – 0.75 | Low-temperature supply air (8–12°C) |
| Overall Heat Transfer Coefficient (U-value) | 85 – 120 W/(m²·K) | Water-side velocity 1.0–2.0 m/s |
| Air-Side Pressure Drop | 50 – 150 Pa | Standard fin density (10–14 FPI) |
| Water-Side Pressure Drop | 15 – 45 kPa | Flow rate 0.5–3.0 m³/h |
| Performance Retention at −20°C | ≥85% of rated capacity | Low-temperature thermal cycling test |
Note: The above performance values are representative benchmarks derived from standardized testing procedures. Actual performance will vary depending on specific coil tube configuration, operating conditions, and system design parameters. Wenzhou Jixing Metal Materials Co., Ltd. provides custom thermal performance reports upon request for specific project requirements.
Technical Standards Reference
- ASHRAE Standard 22 — Method of Testing Air-Cooled and Water-Condensing Heat Pumps and Air Conditioners
- ASHRAE Standard 90.1 — Energy Standard for Buildings Except Low-Rise Residential Buildings
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Applications
- ASTM A213 — Standard Specification for Seamless Austenitic Stainless Steel Tubing for High-Service Boilers, Heaters, Exchangers, and Similar Applications
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