Stainless Steel Coil Tube — HVAC Fan Coil Application Series
Product Overview
The Stainless Steel Coil Tube (盘管 Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered tubular product designed specifically for heating, ventilation, and air conditioning (HVAC) applications, with particular emphasis on fan coil unit (FCU) systems used in commercial and hospitality environments. This product combines the corrosion resistance and hygienic properties of stainless steel with the thermal efficiency required for effective air-side heat exchange in terminal air handling systems.
Unlike conventional carbon steel coil tubes, the stainless steel variant offers extended service life, resistance to condensation-induced corrosion, and compliance with stringent indoor air quality (IAQ) standards — making it an ideal selection for hotel, hospital, and cleanroom environments where both thermal performance and sanitary integrity are paramount.
Material & Properties
Material Grades
- Austenitic Stainless Steel 304 (UNS S30400 / 08Cr19Ni10): The standard grade offering excellent general corrosion resistance, weldability, and formability. Suitable for most HVAC applications with moderate chemical exposure.
- Austenitic Stainless Steel 316 (UNS S31600 / 06Cr17Ni12Mo2): Enhanced grade with molybdenum addition providing superior resistance to chlorides, de-icing salts, and aggressive condensate environments. Recommended for coastal installations and high-moisture fan coil applications.
- Austenitic Stainless Steel 316L (UNS S31603 / 03Cr17Ni12Mo2): Low-carbon variant of 316 offering improved weldability and resistance to intergranular corrosion, ideal for post-welding service without sensitization risk.
Key Mechanical & Physical Properties
| Property | 304 Grade | 316 Grade | 316L Grade |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 | ≥ 485 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 170 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 45 |
| Density (g/cm³) | 7.93 | 8.00 | 8.00 |
| Thermal Conductivity at 100°C (W/m·K) | 16.3 | 16.3 | 16.3 |
| Thermal Expansion Coefficient (10⁻⁶/K) | 17.3 | 17.5 | 17.5 |
| Maximum Service Temperature (°C) | 870 | 870 | 870 |
Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.53 mm (3/8"), 12.70 mm (1/2"), 15.88 mm (5/8"), 19.05 mm (3/4") |
| Wall Thickness | 0.5 mm – 1.5 mm (customizable) |
| Coil Length | 3 m – 50 m per continuous coil (standard); up to 100 m (special order) |
| Coil Inner Diameter | 100 mm – 600 mm (adjustable based on coil bundle configuration) |
| Surface Finish | Mirror polished (Ra ≤ 0.1 μm), electropolished, or standard 2B finish |
| Bend Radius | ≥ 1.5 × OD (minimum); up to 5 × OD for low-stress applications |
| Tolerance on OD | ±0.05 mm (precision); ±0.10 mm (standard) |
| Tolerance on Wall Thickness | ±10% of nominal |
| Applicable Standards | ASTM A269, ASTM A312, EN 10217-7, GB/T 12771 |
| End Preparation | Plain cut, beveled (37.5°), or threaded (NPT/BSP) |
Manufacturing Process
- Raw Material Selection & Incoming Inspection: Stainless steel strip or seamless tubing stock is sourced from certified mills and subjected to spectrographic analysis (OES), confirming chemical composition within ASTM/EN specification limits.
- Coil Forming & Bending: Precision CNC-controlled coil winding machines form straight tubes into the required helical or serpentine coil geometry. Bend radii are maintained at or above 1.5×OD to prevent wall thinning and ovality distortion.
- Welding & Joining: Where continuous coil length exceeds single-tube supply, orbital TIG (Tungsten Inert Gas) welding or laser welding is employed to achieve full-penetration, leak-tight joints with minimal heat-affected zone (HAZ).
- Surface Treatment: Tubes undergo pickling and passivation (HNO₃/HF mixed acid bath) to remove scale and restore the protective chromium oxide layer. Electropolishing is applied for hygiene-critical applications, achieving a mirror finish with sub-0.1 μm surface roughness.
- Pressure Testing & Leak Detection: Each coil assembly is hydrostatically tested at 1.5× the maximum working pressure (typically 1.0–1.6 MPa) and held for a minimum of 30 minutes. Helium leak detection is performed on critical applications with sensitivity ≤ 10⁻⁹ mbar·L/s.
- Final Inspection & Packaging: Dimensional verification, surface quality assessment, and material traceability documentation are completed before protective packaging in moisture-resistant wraps with desiccant.
Applications
Primary Application: Hotel Fan Coil Unit Systems
The stainless steel coil tube serves as the core heat exchange element in fan coil units deployed within hotel HVAC systems. In the context of fresh air treatment terminal state selection (as analyzed in industry literature on hotel ventilation system design), the coil tube directly influences:
- Dehumidification Efficiency: The low thermal conductivity of stainless steel can be optimized through thin-wall designs (0.5–0.8 mm) to achieve effective coil surface temperatures below the dew point, enabling precise latent heat removal.
- Terminal State Control: The material's dimensional stability across thermal cycling ensures consistent coil geometry, maintaining predictable airflow-coil interaction and accurate supply air state point delivery.
- Condensate Management: The corrosion-resistant surface prevents pitting and micro-roughness accumulation, reducing biofilm formation and maintaining long-term thermal performance in high-humidity environments typical of hotel guest rooms and public areas.
Additional Applications
- Commercial and institutional HVAC systems (hospitals, laboratories, cleanrooms)
- Chilled water distribution loops and terminal air handling units
- Process heating and cooling in food and pharmaceutical industries
- Marine and coastal HVAC installations requiring chloride resistance
- Domestic and commercial hot water recirculation coils
Quality Certifications
- ISO 9001:2015 — Quality Management System certification covering all manufacturing and testing processes
- ISO 14001:2015 — Environmental Management System ensuring sustainable production practices
- EN 10204 3.1 — Material Test Certificates (MTC) issued per batch with full chemical and mechanical test data
- CE Marking — Compliance with European Pressure Equipment Directive (PED 2014/68/EU) where applicable
- ASME B31.9 — Compliance for refrigeration and air-conditioning piping systems
- NSF/ANSI 61 — Drinking water system component certification (for potable water coil applications)
Unique Selling Points
1. Superior Hygienic Performance: The electropolished stainless steel surface eliminates micro-pitting and crevice corrosion, preventing microbial colonization and ensuring compliance with HACCP and FDA sanitation requirements — a critical advantage over carbon steel coils in hospitality applications.
2. Extended Service Life: With a design life exceeding 25 years in aggressive condensate environments (compared to 8–12 years for galvanized carbon steel), the stainless steel coil tube delivers significant total cost of ownership (TCO) reduction through reduced maintenance and replacement frequency.
3. Precision Coil Geometry: CNC-controlled forming ensures consistent coil pitch, bend radius, and dimensional accuracy, enabling optimized air-side heat transfer coefficients and predictable system performance across the terminal state range.
4. Design Flexibility: Available in multiple grades (304, 316, 316L), wall thicknesses, and coil configurations to match specific fan coil unit design parameters, including supply air temperature, humidity ratio, and volumetric flow rate requirements.
Technical Reference
This product specification references industry knowledge on hotel fan coil system fresh air terminal state selection analysis (《旅馆风机盘管系统新风处理终状态选择分析》), incorporating considerations of coil performance, latent and sensible heat ratios, and the impact of material properties on system-level HVAC design optimization.