Stainless Steel Coil Tube (Coiltube) — HVAC Fan Coil Unit Application Grade
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed primarily for heat exchange and fluid distribution applications within HVAC (Heating, Ventilation, and Air Conditioning) systems, with particular emphasis on fan coil unit (FCU) installations in commercial and hospitality environments. The coil tube is supplied in continuous coil form to facilitate efficient downstream forming, bending, and installation processes.
This product represents a specialized segment within the stainless steel pipe industry, optimized for thermal transfer efficiency, long-term corrosion resistance, and dimensional consistency. It serves as a critical component in hydronic heating and cooling circuits, where reliability and hygienic performance are paramount—especially in five-star hotel environments where indoor air quality and energy efficiency standards are exceptionally stringent.
2. Material & Properties
2.1 Base Material
- Standard Grades: SUS304 (ASTM 304), SUS316 (ASTM 316), SUS316L (ASTM 316L), and SUS321 (ASTM 321)
- Composition (SUS304 typical): Carbon (C) ≤ 0.08%, Manganese (Mn) ≤ 2.0%, Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Silicon (Si) ≤ 0.75%, Phosphorus (P) ≤ 0.045%, Sulfur (S) ≤ 0.030%
- Composition (SUS316 typical): Carbon (C) ≤ 0.08%, Chromium (Cr) 16.0–18.0%, Nickel (Ni) 10.0–14.0%, Molybdenum (Mo) 2.0–3.0%
2.2 Key Physical & Mechanical Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (SUS304)
- Density: 7.93 g/cm³ (SUS304), 8.00 g/cm³ (SUS316)
- Tensile Strength: ≥ 520 MPa (SUS304), ≥ 515 MPa (SUS316)
- Yield Strength: ≥ 205 MPa (SUS304), ≥ 170 MPa (SUS316)
- Operating Temperature Range: -196°C to +870°C (SUS304); -196°C to +870°C (SUS316)
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, organic acids, and dilute inorganic acids; SUS316 grade offers superior resistance to chlorides and pitting corrosion
- Surface Finish Options: No. 2B, BA (Bright Annealed), 2B Polished, Mirror (8K), and Custom finishes
2.3 Performance Advantages
- Non-magnetic (austenitic structure) ensuring compatibility with sensitive electronic control systems
- Smooth internal surface (Ra ≤ 0.8 μm) minimizes flow resistance and prevents biofilm accumulation
- Outstanding weldability enables seamless fabrication of coil assemblies without post-weld pickling in most configurations
- High strength-to-weight ratio reduces structural support requirements in suspended installations
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (1/4" – 1") | ASTM A213 / GB/T 12771 |
| Wall Thickness | 0.30 mm – 1.50 mm | ASTM A269 / GB/T 14976 |
| OD Tolerance | ±0.05 mm (precision grade); ±0.10 mm (standard grade) | ASTM A213 |
| Wall Thickness Tolerance | ±10% of nominal | GB/T 14976 |
| Coil Inner Diameter (ID) | 500 mm – 1000 mm | Manufacturer specification |
| Coil Weight | 200 kg – 500 kg (per coil) | Manufacturer specification |
| Length per Coil | Custom (typically 200 m – 500 m) | Customer requirement |
| Surface Roughness (Internal) | Ra ≤ 0.8 μm | ISO 1302 |
| Surface Roughness (External) | Ra ≤ 1.6 μm (2B finish); Ra ≤ 0.4 μm (BA finish) | ISO 1302 |
| Pressure Rating (Test) | Hydrostatic test at 1.5× working pressure | ASTM A213 |
| End Condition | Seamless (ERW / Cold Drawn); cut ends deburred | ASME B31.9 |
| Packaging | Wooden crate / steel frame with moisture-proof wrapping | ISO 4126 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: Ingot or strip procurement from certified mills; spectrographic verification of chemical composition (C, Cr, Ni, Mo content confirmation)
- Hot Rolling / Cold Rolling: Strip production to target thickness with controlled rolling schedules to achieve desired grain structure and mechanical properties
- Acid Washing & Pickling: Removal of oxide scale using mixed acid baths (HNO₃/HF) to restore passive chromium oxide layer
- Tube Forming: Cold drawing or ERW (Electric Resistance Welding) process; for seamless coil tube, cold-drawn seamless process ensures superior pressure integrity
- Precision Sizing & Cold Drawing: Multi-pass cold drawing through calibrated dies to achieve final OD and wall thickness within tight tolerances
- Heat Treatment (Annealing): Solution annealing at 1050–1100°C followed by controlled cooling to achieve fully austenitic microstructure; stress relief to eliminate residual deformation stresses
- Surface Finishing: Mechanical polishing, electropolishing, or passivation treatment depending on specified finish grade
- Coiling: Precision coiling on mandrels to maintain dimensional stability and prevent ovality deformation
- Quality Inspection: 100% hydrostatic pressure testing, dimensional gauging, visual inspection, and sampling for chemical/microstructural analysis
- Packaging & Shipping: Protection against mechanical damage and moisture ingress during transit
4.2 Process Control Highlights
- In-line eddy current testing (ECT) for detection of wall thickness variation and surface defects
- Computer Numerical Control (CNC) coiling equipment ensuring uniform coil geometry
- Full traceability from heat number to final coil identification
5. Applications
5.1 Primary Application: HVAC Fan Coil Units
The coil tube is specifically engineered for use in hydronic fan coil unit (FCU) assemblies found in commercial buildings, five-star hotels, hospitals, and institutional facilities. In these systems, the coil tube forms the heat exchange matrix through which chilled water or hot water circulates, transferring thermal energy to or from the airstream.
- Chilled Water Coils: Cooling capacity 2.0–15.0 kW per unit; supply temperature 6–12°C
- Hot Water Coils: Heating capacity 2.5–20.0 kW per unit; supply temperature 45–70°C
- Two-Pipe Systems: Single coil tube circuit serving both heating and cooling via valve switching
- Four-Pipe Systems: Dual coil tube circuits providing simultaneous heating and cooling zones
5.2 Additional Applications
- Refrigeration and air conditioning condenser/evaporator coils
- Industrial heat exchangers and process piping
- Food and beverage processing (hygienic-grade SUS316L)
- Pharmaceutical equipment fluid lines
- Marine and coastal environment heat exchange systems
- Solar thermal energy collection systems
5.3 Technical Considerations for Hotel FCU Installations
In five-star hotel environments, the selection and positioning of temperature control panels (thermostatic control units) directly influence coil tube performance. Optimal panel placement—typically 1.4–1.6 m above finished floor level, away from direct solar radiation and heat-generating equipment—ensures accurate ambient temperature sensing and minimizes unnecessary cycling of the coil tube heat exchange circuit. The stainless steel coil tube's thermal inertia characteristics complement electronic control strategies including proportional-integral-derivative (PID) modulation and VAV (Variable Air Volume) control, achieving energy savings of 15–25% compared to conventional on/off control schemes.
6. Quality Certifications & Compliance
6.1 Product Certifications
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System certification
- CE Marking — Conformity with European directives for construction products
- EN 10216-5 — European standard for seamless and welded stainless steel tubes for heat exchangers
- ASME B31.9 — Compliance with piping code for refrigeration and air-conditioning systems
6.2 Testing & Inspection Protocols
- Chemical Analysis: Spectroscopic verification per ASTM E415
- Mechanical Testing: Tensile testing per ASTM A370; hardness testing per ASTM E18 (Rockwell B)
- Hydrostatic Testing: 100% inline testing per ASTM A213
- Intergranular Corrosion Testing: Per ASTM A240 Clause 9 (Acid Test) for stabilization verification
- Pitting Corrosion Testing: Per ASTM G48 (Ferric Chloride Method) for SUS316 grades
- Dimensional Inspection: CMM (Coordinate Measuring Machine) verification of OD, wall thickness, and straightness
- Surface Quality: Visual inspection under controlled illumination; surface roughness measurement per ISO 4287
6.3 Traceability
Each coil tube lot is accompanied by a Mill Test Certificate (MTC) conforming to EN 10204 Type 3.1, providing complete traceability from raw material heat number through all manufacturing stages to final product identification. Digital traceability codes (QR/barcode) enable real-time quality data retrieval.
7. Unique Selling Points
- Precision Dimensional Control: OD tolerance as tight as ±0.05 mm ensures optimal fit in heat exchanger tube sheets, reducing assembly time and improving thermal contact resistance
- Extended Service Life: 25–30 year design life in HVAC applications with no cathodic protection or liner requirements
- Hygienic Design: Smooth internal surface (Ra ≤ 0.8 μm) eliminates dead zones for microbial growth, critical for hospital and food-grade applications
- Energy Efficiency: Superior thermal conductivity relative to carbon steel alternatives reduces pumping energy by 8–12% through lower flow resistance
- Custom Coil Configuration: Flexible coil inner diameter and weight options accommodate diverse downstream forming equipment requirements
- Full Material Traceability: End-to-end quality documentation enabling compliance with stringent hospitality and healthcare industry auditing standards