Stainless Steel Coil Tube – HVAC & Heat Pump Application Series
Product Overview
Wenzhou Jixing Metal Materials Co., Ltd. presents its premium-grade Stainless Steel Coil Tube (Coiltube), engineered specifically for high-performance air-source heat pump and fan coil unit (FCU) heating and cooling systems. This product series is designed to meet the rigorous demands of variable water temperature control (VWT) applications, where thermal efficiency, corrosion resistance, and long-term structural integrity are paramount. The coil tube serves as a critical heat exchange component, facilitating efficient thermal transfer between the refrigerant circuit and the conditioned air stream within commercial and residential HVAC systems.
The coil tube architecture is optimized for integration into air-source heat pump (ASHP) systems that employ variable water temperature (VWT) control strategies. These systems require coil tubes that maintain consistent thermal conductivity across a wide operating temperature range, typically from -10°C to 80°C, while resisting scaling, fouling, and galvanic corrosion under continuous operation.
Material & Properties
Base Material Composition
- Primary Alloy: Austenitic stainless steel conforming to ASTM A213 / A269 standards, with options including Type 304 (UNS S30400), Type 316 (UNS S31600), and Type 316L (UNS S31603) for enhanced chlorided environments.
- Chemical Composition (Type 316L): Carbon ≤ 0.030%, Chromium 16.5–18.5%, Nickel 10.0–14.0%, Molybdenum 2.0–3.0%, Manganese ≤ 2.0%, Silicon ≤ 1.0%, Phosphorus ≤ 0.045%, Sulfur ≤ 0.030%.
- Surface Treatment: Passivated finish with optional electropolishing to achieve a surface roughness (Ra) of ≤ 0.4 μm, minimizing fouling and biofilm adhesion.
Mechanical & Thermal Properties
- Tensile Strength: ≥ 515 MPa (Type 316L)
- Yield Strength: ≥ 205 MPa
- Elongation: ≥ 40%
- Thermal Conductivity: 14.9 W/(m·K) at 25°C
- Linear Expansion Coefficient: 16.0 × 10⁻⁶ /°C
- Operating Pressure Rating: Up to 1.6 MPa (PN16) for standard configurations; up to 2.5 MPa for reinforced variants
- Corrosion Resistance: Excellent resistance to pitting and crevice corrosion (PREN ≥ 24 for 316L)
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ6.0 mm – Φ19.0 mm (customizable) | ASTM A269 / EN 10217 |
| Wall Thickness | 0.5 mm – 2.0 mm | ASTM A213 |
| Coil Diameter | Φ150 mm – Φ600 mm | Manufacturer specification |
| Tube Length (per coil) | Up to 50 m continuous | — |
| Material Grade | 304 / 316 / 316L / 321 | ASTM A269 |
| Surface Finish | 2B / BA / Electropolished (Ra ≤ 0.4 μm) | ASTM A478 |
| Operating Temperature Range | -196°C to 800°C | — |
| Maximum Working Pressure | 1.6 MPa (standard) / 2.5 MPa (reinforced) | EN 10217-7 |
| Bending Radius | ≥ 3× OD (cold forming) | — |
| Welding Method | TIG (GTAW) / Orbital / Laser welding | ASME B31.3 |
| Coil Pitch | 10 mm – 25 mm (adjustable) | — |
| Number of Circuits | 1 – 4 circuits per coil assembly | — |
| Connection Type | Flanged / Threaded / Soldered / Brazed | ASME B31.3 |
Manufacturing Process
- Raw Material Selection & Inspection: Cold-rolled stainless steel strip is sourced from certified mills (e.g., Outokumpu, POSCO, Tsingshan) and subjected to spectrographic analysis (OES) to verify alloy composition within specified tolerance bands.
- Slitting & Edge Preparation: The strip is slit to precise widths using high-precision slitting lines, with edge quality verified to prevent roll-in defects during tube forming.
- Tube Forming (Cold Roll Forming): Multi-stand roll forming machines progressively shape the strip into seamless circular tubes. The forming process maintains metallurgical integrity without requiring subsequent welding, ensuring uniform wall thickness and mechanical properties throughout the tube length.
- Coiling & Pitch Control: The formed tube is wound into a precise spiral coil using CNC-controlled coiling equipment. Coil diameter and pitch are maintained within ±0.5 mm tolerance to ensure uniform heat transfer characteristics and airflow distribution.
- Heat Treatment (if applicable): For certain grades, solution annealing is performed at 1050–1100°C followed by rapid water quenching to achieve full austenitic structure and optimal corrosion resistance.
- Surface Treatment & Passivation: Tubes undergo nitric acid pickling and passivation to remove mill scale and form a protective chromium oxide layer. Electropolishing is available for applications requiring ultra-low surface roughness.
- Quality Inspection: Each batch undergoes hydrostatic pressure testing (at 1.5× working pressure), dimensional verification, and visual inspection. Radiographic testing (RT) or ultrasonic testing (UT) is performed on weld seams where applicable.
- Finishing & Packaging: Finished coil tubes are cut to specified lengths, ends are deburred, and products are packaged in moisture-proof wrapping with desiccant to prevent oxidation during transit.
Applications
- Air-Source Heat Pump Systems: Primary heat exchanger component in variable water temperature (VWT) control systems, enabling efficient heat recovery and delivery across diverse climate conditions.
- Fan Coil Units (FCU): Evaporator and condenser coils in commercial and residential air handling systems, providing precise temperature modulation.
- Chiller & Refrigeration Systems: Evaporator tubes in water chillers, ice machines, and cold storage units requiring corrosion-resistant heat transfer surfaces.
- Industrial Process Heating: Heat exchangers in chemical processing, pharmaceutical manufacturing, and food & beverage production where hygienic and corrosion-resistant materials are mandated.
- Marine & Coastal HVAC: HVAC systems installed in high-humidity, salt-spray environments where 316L stainless steel provides superior resistance to chloride-induced corrosion.
- Solar Thermal Systems: Coil heat exchangers in solar water heating and district heating networks.
Quality Certifications & Compliance
- ISO 9001:2015 – Quality Management System certification ensuring consistent manufacturing quality and process control.
- ISO 14001:2015 – Environmental Management System certification.
- CE Marking – Compliance with European Machinery Directive (2006/42/EC) and Pressure Equipment Directive (PED 2014/68/EU).
- EN 10217-7 – Tubes for heat exchangers and heat sinks – Technical delivery conditions for stainless steel tubes.
- ASTM A269 / A213 – Standard specifications for seamless austenitic stainless steel tubing and pipe.
- GB/T 12771 – Chinese national standard for welded stainless steel tubes for fluid transport.
- ASME B31.3 – Compliance with pressure piping code for process applications.
- Material Certificates: 3.1 Certificate (EN 10204) available for each production batch, including mill test reports (MTR) with full chemical and mechanical property documentation.
Unique Selling Points
1. Superior Thermal Performance for VWT Systems: Engineered specifically for variable water temperature control applications, the coil tube geometry and material properties ensure consistent heat transfer coefficients across the entire operating temperature range, maximizing the COP (Coefficient of Performance) of air-source heat pump systems.
2. Extended Service Life: The selection of high-grade austenitic stainless steel (316L) provides a design life exceeding 25 years under continuous operation, significantly outperforming copper and aluminum alternatives in corrosive environments.
3. Precision Manufacturing: CNC-controlled coiling ensures uniform pitch and coil diameter tolerances of ±0.5 mm, guaranteeing balanced airflow distribution and optimal heat exchange efficiency across the entire coil face.
4. Hygienic & Food-Grade Compatibility: Electropolished surfaces with Ra ≤ 0.4 μm meet FDA and EHEDG standards, making these coils suitable for pharmaceutical, dairy, and food processing applications.
5. Customizable Configurations: Full flexibility in OD, wall thickness, coil diameter, pitch, and number of circuits allows tailored solutions for specific system designs and thermal load requirements.
6. Sustainability: Stainless steel is 100% recyclable with no loss of material properties, supporting circular economy objectives and reducing lifecycle carbon footprint compared to composite heat exchanger materials.
Technical Notes
When integrating the coil tube into variable water temperature control systems, it is recommended to pair with a flow control valve and temperature sensor array to achieve the desired modulation of water supply temperature. The stainless steel coil tube's stable thermal conductivity across temperature variations (±3% over -10°C to 80°C) ensures predictable system response and efficient energy management. For systems operating in environments with chloride ion concentrations exceeding 200 ppm, Type 316L material is strongly recommended over Type 304 to prevent intergranular corrosion and pitting.