Stainless Steel Coil Tube — Fan Coil Unit (FCU) Application Grade
Product Overview
The Stainless Steel Coil Tube (SSCT) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed specifically for integration into Fan Coil Unit (FCU) systems, hydronic heating and cooling circuits, and industrial heat exchange assemblies. The coil tube is supplied in continuous coil form, enabling seamless roll-forming, bending, and fabrication into serpentine, spiral, and double-return configurations commonly employed in air handling units (AHUs), chiller terminal units, and distributed HVAC (Heating, Ventilation, and Air Conditioning) systems.
This product line is engineered with particular attention to acoustic performance — addressing the critical challenge of operational noise generation in fan coil units, which arises from fluid turbulence, vibration transmission through tube walls, and aerodynamic interaction between airflow and coil geometry. The material composition, wall thickness uniformity, and surface finish specifications are optimized to minimize flow-induced noise and structural resonance during continuous service.
Material & Properties
The coil tube is fabricated from austenitic stainless steel grades selected for their corrosion resistance, thermal conductivity, and mechanical stability across the operating temperature range typical of HVAC applications (−20 °C to +120 °C).
- Primary Grades: AISI 304 (UNS S30400), AISI 316 (UNS S31600), and AISI 321 (UNS S32100) in accordance with ASTM A213 / ASME SA-213 standards for seamless austenitic stainless steel tubing.
- Alloy Composition (AISI 304): Carbon (C) ≤ 0.08%, Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Manganese (Mn) ≤ 2.0%, Silicon (Si) ≤ 1.0%, Sulfur (S) ≤ 0.030%.
- Alloy Composition (AISI 316): Carbon (C) ≤ 0.08%, Chromium (Cr) 16.0–18.0%, Nickel (Ni) 10.0–14.0%, Molybdenum (Mo) 2.0–3.0%, ensuring enhanced resistance to chloride-induced pitting corrosion.
- Thermal Conductivity: 14.9 W/(m·K) at 20 °C (AISI 304), providing efficient heat transfer between the circulating refrigerant or heating medium and the surrounding air stream.
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100 °C), requiring proper expansion joint design in long-run installations.
- Corrosion Resistance: Superior resistance to atmospheric corrosion, condensate water, and mild chemical exposure inherent to HVAC environments; pitting resistance equivalent number (PREN) ≥ 19 for AISI 316 grade.
- Surface Finish: Available in No. 1 finish (annealed, rough), 2B finish (cold-rolled, bright), and electropolished finish (Ra ≤ 0.4 μm) for applications demanding minimal flow resistance and reduced noise generation.
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outside Diameter (OD) | 6.35 mm (¼") to 50.8 mm (2") | ASTM A213 / EN 10217-7 |
| Wall Thickness (WT) | 0.5 mm to 3.0 mm | ASTM A213 / GB/T 14976 |
| Coil Inner Diameter (CID) | 300 mm to 800 mm | Manufacturer's specification |
| Coil Length (Continuous) | 50 m to 500 m (customizable) | — |
| Material Grade | AISI 304 / 304L / 316 / 316L / 321 | ASTM A213 / ASME SA-213 |
| Manufacturing Method | Seamless (hot/cold drawn) or Welded (ERW/IGAW) | ASTM A213 / EN 10217-7 |
| Surface Finish | No. 1 / 2B / BA / Electropolished (Ra ≤ 0.4 μm) | ASTM A478 |
| Pressure Rating | Up to 1.6 MPa (16 bar) at 20 °C (grade-dependent) | ASME B31.5 |
| Operating Temperature | −20 °C to +120 °C (standard); up to +450 °C (AISI 321) | — |
| Tolerance (OD) | ±0.05 mm (precision grade); ±0.10 mm (standard grade) | ASTM A213 |
| Tolerance (WT) | ±10% of nominal | ASTM A213 |
| Hydrostatic Test Pressure | 2× working pressure (minimum 2.0 MPa) | ASTM A213 / EN 10217-7 |
| Acoustic Performance | Flow-induced noise ≤ 35 dB(A) at design flow velocity (2.5 m/s) | ISO 3744 / EN ISO 5135 |
| Coating / Passivation | Nickel passivation (ASTM A967); optional PTFE internal coating | ASTM A967 |
| Packaging | Wooden coil cradle + moisture-proof wrapping + stretch film | ISO 4180 |
Manufacturing Process
The production of stainless steel coil tube follows a rigorous multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and acoustic performance:
- Raw Material Selection and Inspection: Billet or strip material is procured from certified mills and subjected to spectrographic analysis (OES) to verify chemical composition, ultrasonic testing (UT) for internal defects, and visual inspection of surface quality.
- Piercing and Hot Rolling (Seamless Route): Solid billets are heated to 1150–1250 °C and pierced to produce hollow slabs, which are then hot-rolled to near-final dimensions.
- Cold Drawing / Cold Pilgering: The hot-rolled tube is cold-drawn through precision dies to achieve tight dimensional tolerances (±0.05 mm OD), improved surface finish, and enhanced mechanical properties through work hardening.
- Stress Relief Annealing: Tubes are annealed at 1050–1100 °C followed by controlled air cooling to relieve residual stresses, restore full austenitic microstructure, and prevent stress corrosion cracking (SCC).
- Precision Coiling: The straight tube is coiled onto a precision coil winder at controlled tension to prevent ovality, kinking, or surface damage. Coil diameter and pitch are calibrated to the target application geometry.
- Surface Treatment: Pickling and passivation (ASTM A967) remove oxide scale and form a protective chromium oxide layer. Electropolishing is available for high-purity applications requiring surface roughness below Ra 0.4 μm, which directly reduces turbulent flow noise.
- Quality Inspection: Every coil undergoes 100% hydrostatic pressure testing, eddy current testing (ECT) for wall thickness and surface defect detection, dimensional verification via laser micrometry, and spectrographic re-verification.
- Acoustic Performance Validation: Sample coils are tested in a flow loop rig to measure flow-induced noise levels, vibration transmission coefficients, and resonant frequency characteristics, ensuring compliance with noise control requirements for fan coil unit integration.
Applications
Primary Application: Fan Coil Unit (FCU) Systems
The coil tube is the core heat exchange element in fan coil units, where it transfers thermal energy between the circulating water (heating or cooling) and the air stream forced across the coil by an integrated fan. The acoustic performance of the coil tube directly influences the overall noise level of the FCU unit. Key considerations include:
- Flow Velocity Optimization: Tube internal diameter and wall thickness are selected to maintain water flow velocity between 1.5–3.0 m/s, balancing heat transfer efficiency against turbulent noise generation.
- Structural Damping: Wall thickness uniformity and material homogeneity reduce vibration transmission from the water circuit to the fan housing and building structure.
- Surface Smoothness: Electropolished internal surfaces minimize turbulence intensity, reducing hydrodynamic noise by up to 5–8 dB(A) compared to standard finish tubes.
Additional Applications
- HVAC (Heating, Ventilation, and Air Conditioning) chiller terminal units and air handling units (AHUs)
- Industrial process heating and cooling circuits
- Refrigeration evaporator and condenser coils
- Domestic and commercial water heating systems
- Food and pharmaceutical process piping (AISI 316L, electropolished)
- Marine and offshore HVAC systems (AISI 316 with chloride resistance)
- Renewable energy thermal systems (solar thermal collectors)
Quality Certifications & Compliance
| Certification / Standard | Scope | Validity |
|---|---|---|
| ISO 9001:2015 | Quality Management System | Active |
| ISO 14001:2015 | Environmental Management System | Active |
| ISO 45001:2018 | Occupational Health & Safety Management | Active |
| CE Marking (EU) | Pressure Equipment Directive (PED 2014/68/EU) compliance | Active |
| EN 10204 3.1 | Inspection Certificate — material and dimensional verification | Per batch |
| ASTM A213 / ASME SA-213 | Standard specification for seamless austenitic stainless steel tubing | Applicable |
| EN 10217-7 | Heat-resistant, creep-resistant, and high-strength stainless steels — tubes and pipes | Applicable |
| GB/T 14976 | Chinese national standard for cold-rolled stainless steel seamless tubes | Applicable |
| NSF/ANSI 61 | Drinking water system components — health effects (for potable water applications) | Available on request |
| Mill Test Reports (MTR) | Chemical analysis, mechanical properties, and heat treatment records | Per lot |
Unique Selling Points
- Acoustic-Optimized Design: The coil tube is engineered with surface finish and dimensional tolerances specifically calibrated to minimize flow-induced noise in fan coil unit applications, addressing a critical pain point in commercial HVAC installations where noise levels below 35 dB(A) are required for occupied spaces.
- Dimensional Precision: Outside diameter tolerance of ±0.05 mm ensures seamless integration into stamped fin coils and brazed plate heat exchangers without secondary machining.
- Material Traceability: Full heat-lot traceability from raw material mill to finished coil, supported by EN 10204 3.1 inspection certificates and digital material passports.
- Custom Coil Configuration: Coil inner diameter, length, and pitch are customizable to match specific coil-forming machinery and application geometries, reducing fabrication waste and installation time.
- Multi-Grade Availability: Seamless supply of AISI 304, 304L, 316, 316L, and 321 grades from a single source, simplifying procurement and ensuring consistent quality across product lines.
- Corrosion Durability: Nickel passivation and optional PTFE internal coating extend service life beyond 25 years in standard HVAC duty cycles, minimizing maintenance frequency and lifecycle cost.
- Environmental Compliance: ISO 14001-certified manufacturing processes with zero-chloride pickling alternatives, recyclable packaging, and full compliance with RoHS and REACH regulations.
Technical Notes
Installation Guidance: When fabricating coil assemblies for fan coil units, it is recommended to maintain a minimum bend radius of 3× the tube outside diameter to prevent wall thinning and ovality. Brazing joints should use silver-based filler alloys (AWS BAg-7, 45% Ag) with maximum joint temperature not exceeding 950 °C to avoid intergranular corrosion in the heat-affected zone. All installations should incorporate expansion loops or flexible connectors to accommodate thermal expansion differential between