Stainless Steel Coil Tube (Coiltube) — Dry Coil Unit for HVAC Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled stainless steel tubing product designed primarily for use in dry coil tube air conditioning systems, pre-cooling heat pump solution humidification fresh air units, and related HVAC (Heating, Ventilation, and Air Conditioning) applications. The coil tube serves as the core heat exchange element, facilitating efficient thermal transfer between refrigerant or water circuits and the surrounding air stream while minimizing moisture transfer — a critical requirement in dehumidification and humidity control scenarios.
This product line represents a specialized segment of the stainless steel pipe and tubing industry, where corrosion resistance, thermal conductivity, and dimensional precision converge to deliver reliable performance in demanding environmental control systems. The coil tube configuration maximizes surface area within a compact envelope, enabling high-efficiency heat exchange in space-constrained installations.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of corrosion resistance, mechanical integrity, and thermal performance characteristics. The primary material grades include:
- ASTM A269 / A270 Type 304 (UNS S30400): The most widely specified grade, offering excellent general corrosion resistance, good weldability, and adequate cryogenic toughness. Contains 18–20% Chromium (Cr) and 8–10.5% Nickel (Ni).
- ASTM A269 / A270 Type 316 (UNS S31600): Enhanced corrosion resistance through the addition of 2–3% Molybdenum (Mo), making it ideal for applications involving chlorides, acidic environments, or coastal conditions.
- ASTM A269 / A270 Type 321 (UNS S32100): Titanium-stabilized grade providing superior resistance to intergranular corrosion during welding and high-temperature service.
Key Material Properties:
- Corrosion Resistance: Superior resistance to atmospheric, chemical, and aqueous corrosion due to the passive chromium oxide film that forms spontaneously on the surface.
- Thermal Conductivity: Approximately 16–17 W/(m·K) for Type 304, providing adequate heat transfer capability for HVAC coil applications.
- Operating Temperature Range: −196°C to +870°C (depending on grade and application conditions).
- Mechanical Strength: Minimum tensile strength of 515 MPa (Type 304), with elongation of ≥40% in the annealed condition.
- Non-Magnetic (Annealed): Austenitic grades remain non-magnetic after solution annealing, ensuring compatibility with sensitive instrumentation.
- Hygienic Surface: Low surface roughness (Ra ≤ 0.5 μm achievable) prevents bacterial colonization and facilitates cleaning.
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) | — |
| Material Grade | 304, 316, 321 (ASTM A269 / A270) | ASTM A269, ASTM A270 |
| Tube Outer Diameter (OD) | 3.0 mm – 25.4 mm (adjustable per order) | ASTM A269 |
| Wall Thickness | 0.3 mm – 2.0 mm | ASTM A269 |
| Coil Inner Diameter (Coil ID) | 200 mm – 800 mm | Custom specification |
| Coil Length (Uncoiled) | 5 m – 100 m (or as required) | Custom specification |
| Surface Finish | Pickled & Passivated (2B), Electropolished, or Brushed | ASTM A240 |
| Surface Roughness | Ra ≤ 0.5 μm (electropolished); Ra ≤ 1.6 μm (2B finish) | ISO 1302 |
| Tolerance on OD | ±0.05 mm (precision rolled) | ASTM A269 |
| Tolerance on Wall Thickness | ±10% of nominal | ASTM A269 |
| Heat Treatment | Solution Annealed at 1040–1120°C followed by water quench | ASTM A269 |
| Maximum Operating Pressure | Up to 1.6 MPa (design dependent) | ASME B31.3 |
| Coil Pitch / Fin Spacing | Variable — optimized for heat transfer coefficient | Project-specific |
| End Treatment | Plain end, Beveled, or Flanged connection | Custom specification |
| Packaging | Wooden crate with moisture-proof wrapping; coil secured on pallet | ISO 4180 |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: Cold-rolled stainless steel strip or seamless tubing conforming to ASTM A269/A270 specifications is procured from certified mills. Incoming material undergoes spectroscopic verification (OES — Optical Emission Spectroscopy) to confirm chemical composition.
- Precision Forming & Coiling: The tubing is cold-formed into the desired coil geometry using CNC-controlled coiling equipment. The forming process maintains uniform wall thickness and prevents work hardening that could compromise subsequent performance.
- Solution Annealing: Coiled tubes are subjected to solution annealing at temperatures between 1040°C and 1120°C, followed by rapid water quenching. This process eliminates residual stresses, restores full ductility, and ensures a uniform austenitic microstructure.
- Pickling & Passivation: Post-annealing, the tubes undergo pickling (acid cleaning) to remove oxide scale, followed by passivation treatment (typically nitric acid or citric acid solution) to re-establish the protective chromium oxide passive layer.
- Surface Finishing: Depending on application requirements, tubes may receive additional electropolishing (reducing Ra to ≤ 0.5 μm) or mechanical brushing for specific aesthetic or functional purposes.
- Quality Inspection: Each coil undergoes dimensional verification (OD, wall thickness, coil ID), visual inspection, and pressure testing. Sampling for mechanical testing (tensile, hardness) and chemical analysis is conducted per lot.
- Coil Assembly & Fin Integration (if applicable): For dry coil applications, the stainless steel tubing may be integrated with aluminum or stainless steel fins using mechanical expansion or brazing techniques to enhance the heat transfer surface area.
- Final Packaging: Completed coil tubes are secured on wooden pallets, wrapped in moisture-proof material, and packed in export-grade wooden crates with adequate cushioning to prevent deformation during transit.
Applications
The stainless steel coil tube is engineered for a diverse range of applications where corrosion resistance, thermal efficiency, and long service life are paramount:
- Dry Coil Air Conditioning Systems: Primary application in pre-cooling heat pump solution humidification fresh air units, where the coil tube acts as the sensible heat exchanger, removing heat from incoming air without condensation — essential for precise humidity control in pharmaceutical, data center, and cleanroom environments.
- HVAC (Heating, Ventilation, and Air Conditioning) Systems: Chiller coils, cooling coils, and heating coils in commercial and industrial air handling units.
- Heat Pump Systems: Evaporator and condenser coils in water-source and air-source heat pump configurations.
- Food & Beverage Industry: Pasteurization coils, cooling coils, and heat exchangers where hygienic standards (FDA, 3-A Sanitary) are required.
- Pharmaceutical Manufacturing: Cleanroom HVAC coils, GMP-compliant heat exchange systems requiring high-purity stainless steel construction.
- Marine & Offshore Applications: Seawater-cooled condensers and evaporators where chloride-induced corrosion resistance is critical (Type 316L).
- Chemical Processing: Heat exchanger coils in corrosive process streams requiring austenitic stainless steel durability.
- Solar Thermal Systems: Collector coils and storage tank internal coils for renewable energy applications.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management and certification systems to ensure product reliability and regulatory compliance:
- ISO 9001:2015 — Quality Management System certification ensuring consistent production quality and process control.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for Chemical and Heat-Transfer Service.
- ASTM A270 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Service.
- ASME B31.3 — Process Piping Code compliance for pressure-containing applications.
- EN 10217-7 — European standard for austenitic stainless steel tubes for pressure purposes (where applicable).
- Mill Test Certificates (MTC): Provided with every shipment, including chemical composition analysis, mechanical test results, and traceability documentation.
- Third-Party Inspection: Available upon request through accredited inspection bodies (e.g., SGS, Bureau Veritas, DNV).
Unique Selling Points
- Superior Corrosion Resistance: Austenitic stainless steel construction eliminates concerns about rust, pitting, and chloride-induced degradation, extending service life beyond 25 years in demanding environments.
- Precision Coiling Technology: CNC-controlled coiling ensures uniform coil geometry, consistent pitch, and minimal material waste — critical for optimal heat transfer performance in dry coil applications.
- Hygienic Design: Electropolished surfaces with Ra ≤ 0.5 μm meet the most stringent sanitary requirements for pharmaceutical and food-grade applications.
- Customization Capability: Full flexibility in tube OD, wall thickness, coil diameter, length, surface finish, and end treatment to match specific project requirements.
- Thermal Efficiency: Optimized coil geometry and material selection maximize the heat transfer coefficient (U-value), reducing energy consumption in HVAC systems by up to 15% compared to conventional carbon steel alternatives.
- Traceability & Quality Assurance: Complete batch traceability from raw material to finished product, supported by comprehensive MTC documentation and optional third-party verification.
- Cost-Effective Lifecycle: While initial material cost is higher than carbon steel, the elimination of corrosion-related maintenance, replacement cycles, and downtime results in significantly lower total cost of ownership (TCO).
Note: All specifications are subject to modification based on specific project requirements and applicable standards. Custom engineering solutions are available upon consultation with the technical team at Wenzhou Jixing Metal Materials Co., Ltd. Product performance data should be validated against the specific operating conditions of each installation.