Stainless Steel Coil Tube (Fan Coil Unit Application)
Product Overview
The Stainless Steel Coil Tube (盘管) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product formed into helical or serpentine coil configurations. These coil tubes serve as critical heat transfer elements in Fan Coil Units (FCUs), air-handling systems, and thermal management applications. The product is designed to optimize convective heat exchange efficiency while maintaining structural integrity under prolonged exposure to varying thermal loads and fluid dynamic conditions.
Based on the research study titled "The Effect of Fan Coil Unit Position on Indoor Air Flow", the coil tube geometry and material selection directly influence indoor air distribution patterns, thermal comfort zones, and system energy performance. Wenzhou Jixing Metal Materials Co., Ltd. provides coil tubes engineered to meet the stringent requirements of modern HVAC (Heating, Ventilation, and Air Conditioning) systems.
Material & Properties
The coil tube is fabricated from high-grade stainless steel alloys, selected for their superior corrosion resistance, thermal conductivity, and mechanical durability.
Primary Alloy Grades
- 304 Stainless Steel (UNS S30400 / 1.4301): Contains 18% Chromium (Cr) and 8% Nickel (Ni). Offers excellent general corrosion resistance, formability, and weldability. Suitable for most indoor HVAC applications.
- 316 Stainless Steel (UNS S31600 / 1.4401): Contains 16–18% Cr, 10–14% Ni, and 2–3% Molybdenum (Mo). Provides enhanced resistance to chlorides and acidic environments. Recommended for coastal or chemically aggressive installations.
- 321 Stainless Steel (UNS S32100 / 1.4541): Titanium-stabilized austenitic grade offering superior resistance to intergranular corrosion at elevated temperatures (up to 870°C).
Mechanical Properties (Typical — Grade 304)
- Tensile Strength (抗拉强度): 515–720 MPa
- Yield Strength (屈服强度): ≥205 MPa (0.2% offset)
- Elongation (延伸率): ≥40% (at fracture, 50mm gauge length)
- Hardness (硬度): ≤201 HB (Brinell), ≤95 HRB
- Thermal Conductivity (热导率): 16.3 W/(m·K) at 100°C
- Density (密度): 7.93 g/cm³
- Maximum Service Temperature (最高使用温度): 870°C (oxidizing atmosphere)
Corrosion Resistance
- Pitting Resistance Equivalent Number (PREN): 19–20 (Grade 304); 24–26 (Grade 316)
- Chromium Equivalent (Cr_eq): ≥17.5%
- Nickel Equivalent (Ni_eq): ≥8.0%
- Passivation potential: Stable passive film formation in neutral to mildly acidic aqueous environments (pH 4–10)
Specifications
| Parameter | Specification | Unit | Standard Reference |
|---|---|---|---|
| Outer Diameter (OD) | 6.35 – 32.00 | mm | ASTM A213 / EN 10217-7 |
| Wall Thickness (WT) | 0.50 – 2.00 | mm | ASTM A269 |
| Coil Pitch (螺距) | 10 – 50 | mm | Custom per application |
| Coil Diameter (盘管外径) | 100 – 1000 | mm | Custom per application |
| Tube Length (per coil) | 1.5 – 30.0 | m | — |
| Number of Rows (排数) | 1 – 6 | rows | ASHRAE 15 / EN 12830 |
| Surface Finish | 2B / BA / Electropolished | — | ASTM A478 |
| Roughness (Ra) | ≤0.5 (electropolished); ≤1.6 (2B) | μm | ISO 1302 |
| End Forming | Plain / Flared / Welded headers | — | Custom |
| Operating Pressure | 0.1 – 1.6 | MPa | EN 12828 |
| Operating Temperature Range | -40 to +200 | °C | — |
| Heat Transfer Medium | Water, Glycol-water mixture, Refrigerant | — | — |
| Heat Transfer Coefficient (h) | 2500 – 5500 | W/(m²·K) | ASHRAE Handbook |
Manufacturing Process
The production of high-quality stainless steel coil tubes follows a rigorous multi-stage manufacturing protocol:
- Material Selection & Certification: Raw stainless steel strip or seamless tube stock is sourced from certified mill suppliers with full mill test certificates (MTC) in accordance with EN 10204 Type 3.1. Chemical composition is verified via Optical Emission Spectroscopy (OES) and mass spectrometry.
- Cold Rolling & Annealing: For strip-based production, the stainless steel strip undergoes cold rolling to achieve precise thickness tolerances (±0.02 mm), followed by controlled atmosphere annealing (1050–1150°C) to restore ductility and refine grain structure.
- Tube Forming (Roll Forming): Multi-roller forming stations progressively bend the flat strip into a seamless circular tube cross-section. Roller tooling is precision-ground and regularly calibrated to maintain dimensional accuracy.
- Welding (if applicable): For welded tube production, Automatic Optical Flux-Cored Arc Welding (A-FCAW) or Laser Welding is employed. Weld seams are inspected via 100% visual examination and periodic radiographic testing (RT) per ASME Section IX.
- Coil Winding & Pitch Setting: Formed tubes are wound onto precision CNC-controlled coil winding machines. Helix angle, pitch uniformity, and coil diameter are controlled to ±0.5 mm tolerance. Spring-back compensation algorithms ensure dimensional accuracy post-unloading.
- Header & Connection Welding: Coil ends are joined to inlet/outlet headers via TIG (Tungsten Inert Gas) welding with argon (Ar) back protection to prevent internal oxidation. Weld quality is verified by helium leak testing (detection limit: 1×10⁻⁹ Pa·m³/s).
- Surface Treatment & Passivation: Final coils undergo acid pickling (HNO₃ + HF blend) and passivation to remove welding scale and establish a stable chromium oxide passive film. Surface roughness is verified via contact profilometry.
- Pressure Testing & Hydrostatic Proof: Each coil assembly is subjected to hydrostatic pressure testing at 1.5× the maximum working pressure, held for a minimum of 60 seconds with zero pressure drop tolerance.
- Final Inspection & Packaging: Products undergo dimensional verification (OD, wall thickness, coil geometry), surface inspection, and are packaged in moisture-barrier wrapping with desiccant for export shipping.
Applications
Wenzhou Jixing Metal Materials Co., Ltd. stainless steel coil tubes find extensive application across multiple industries:
- HVAC Systems (Heating, Ventilation, and Air Conditioning): Primary application in Fan Coil Units (FCUs), Chilled Water Coils, and Heating Coils. The coil tube geometry directly influences indoor air flow distribution, thermal stratification, and occupant comfort — as demonstrated in the referenced study on fan coil unit positioning effects on indoor air movement patterns.
- Air Conditioning Heat Exchangers: Evaporator and condenser coils in commercial and residential air conditioning systems, providing efficient refrigerant-to-air heat transfer.
- Industrial Process Cooling: Heat exchange coils in chemical processing, pharmaceutical manufacturing, and food processing plants requiring hygienic-grade materials.
- Marine & Offshore Systems: Grade 316 coil tubes for marine HVAC systems and offshore platform thermal management, leveraging superior chloride resistance.
- Commercial Building Systems: Underfloor heating coils, radiating floor systems, and perimeter heating coils in institutional and commercial architecture.
- Medical & Laboratory Facilities: Precision temperature control coils in cleanroom environments, laboratory fume hoods, and medical equipment cooling systems.
- Food & Beverage Industry: Hygienic-grade coil tubes for pasteurization systems, beverage cooling, and food processing thermal management (FDA-compliant, 3-A Sanitary Standards).
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring traceability, consistency, and compliance with international standards:
Management System Certifications
- ISO 9001:2015 — Quality Management Systems (质量管理体系)
- ISO 14001:2015 — Environmental Management Systems (环境管理体系)
- ISO 45001:2018 — Occupational Health and Safety Management Systems (职业健康安全管理体系)
Product & Material Standards
- ASTM A213/A213M — Standard Specification for Seamless Austenitic Stainless Steel Tubing for High-Temperature Service
- ASTM A269/A269M — Standard Specification for Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service
- ASTM A478 — Standard Specification for Stainless Steel Tubular Products (General Requirements)
- EN 10217-7 — Technical Delivery Conditions for Seamless Stainless Steel Tubes for Heat Exchangers and Heat Transfer
- GB/T 17705 (Chinese National Standard) — Technical Delivery Conditions for Stainless Steel Tubes
- JIS G 4805 — Hot-Rolled Stainless Steel Sheets and Strips (for raw material verification)
Testing & Inspection Protocols
- 100% Hydrostatic Pressure Testing per ASTM A530
- Dimensional verification per ASME B1.20.1 thread gauges and ISO 1 series calipers
- Chemical composition analysis via OES and ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy)
- Heat treatment verification via hardness testing (Rockwell/Brinell) and grain size assessment per ASTM E112
- Corrosion testing: Salt spray testing (ASTM B117), Pitting resistance testing (ASTM G48), and Crevice corrosion testing
- Weld quality: Visual inspection per AWS D1.6, radiographic testing (RT) per ASME Section V Article 2
- Leak testing: Helium mass spectrometry leak detection (detection limit ≤1×10⁻⁹ Pa·m³/s)
Unique Selling Points
- Precision Coil Geometry: CNC-controlled winding ensures uniform pitch and helix angle, directly improving heat transfer efficiency and reducing pressure drop compared to conventionally wound coils.
- Material Traceability: Full batch traceability from mill certificate through final inspection, enabling complete supply chain transparency for regulated industries.
- Custom Engineering Capability: Customizable coil configurations (pitch, diameter, number of rows, header design) tailored to specific HVAC load calculations and airflow distribution requirements.
- Research-Informed Design: Product design incorporates findings from thermal fluid dynamics research, including the validated understanding that fan coil unit positioning significantly affects indoor air velocity profiles, temperature stratification, and thermal comfort indices (PMV/PPD — Predicted Mean Vote / Predicted Percentage of Dissatisfied).
- Hygienic Surface Finish: Electropolished surfaces (Ra ≤0.5 μm) minimize biofilm formation and facilitate cleaning in pharmaceutical and food-grade applications.
- Extended Service Life: Stainless steel construction eliminates the corrosion and scaling issues associated with carbon steel coils, extending system lifespan by 3–5× while maintaining stable thermal performance over time.
Note: All specifications listed are typical values for reference purposes. Actual product specifications may vary based on customer requirements, application conditions, and applicable regional codes. Wenzhou Jixing Metal Materials Co., Ltd. provides detailed engineering datasheets and Mill Test Certificates (MTC) upon request for each production lot.