Stainless Steel Coil Tube (Coiltube) for HVAC Fan Coil Unit Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered coiled tubing product specifically designed for integration into Fan Coil Unit (FCU) air conditioning systems and broader HVAC (Heating, Ventilation, and Air Conditioning) applications. This product is engineered to meet the rigorous thermal cycling, pressure differential, and corrosion resistance demands encountered in demand-response-enabled building energy management systems. The coil tube serves as the primary heat exchange medium within fan coil units, facilitating efficient thermal transfer between the circulating refrigerant or hot water and the conditioned air stream.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, ensuring superior mechanical integrity and long-term service durability under demanding environmental conditions.
- Base Alloy Grades: AISI 304 (UNS S30400), AISI 316 (UNS S31600), and AISI 321 (UNS S32100) conforming to ASTM A213/A213M specifications.
- Corrosion Resistance: Excellent resistance to chlorides, sulfides, and condensate-induced pitting corrosion, particularly in 316-grade variants containing minimum 2.0% Ni and 2.5% Mo.
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C, optimized for efficient heat exchanger performance.
- Operating Temperature Range: −196°C to +870°C (depending on grade selection).
- Maximum Working Pressure: Up to 1.6 MPa (232 psi) for standard configurations; up to 2.5 MPa (363 psi) for reinforced variants.
- Surface Finish: Pickled and passivated interior/exterior surfaces with surface roughness Ra ≤ 0.8 μm to minimize fouling and maximize heat transfer coefficients.
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm, 9.52 mm, 12.70 mm, 15.88 mm, 19.05 mm | ASTM A213/A213M |
| Wall Thickness | 0.5 mm – 1.5 mm | EN 10216-5 |
| Coil Diameter (CD) | 100 mm – 600 mm | Manufacturer Tolerance ±5% |
| Coil Length (per spool) | 10 m – 150 m | Customizable |
| Surface Treatment | Pickled, Passivated, or Polished (2B/BA finish) | ASTM A468 |
| Winding Pitch | 2.0 mm – 5.0 mm (adjustable per design) | ISO 11979 |
| Tensile Strength | ≥ 520 MPa (304); ≥ 515 MPa (316) | ASTM A240 |
| Yield Strength (0.2% offset) | ≥ 205 MPa (304); ≥ 170 MPa (316) | ASTM A240 |
| Impact Test (Charpy V-notch) | ≥ 47 J at −196°C (304); ≥ 27 J at −196°C (316) | ASTM A262 |
| Hydrostatic Test Pressure | 1.5× Maximum Working Pressure (MWP) | EN 10216-5 Clause 10 |
| Material Certification | EN 10204 Type 3.1 (Mill Test Certificate) | EN 10204 |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorously controlled multi-stage manufacturing process to ensure dimensional accuracy, metallurgical homogeneity, and surface integrity:
- Raw Material Selection: Vacuum Arc Remelted (VAR) or Electro Slag Remelted (ESR) stainless steel wire rod is procured from certified mills with full traceability documentation.
- Wire Drawing: Multi-stage cold drawing through tungsten carbide dies reduces the wire rod to the target tube blank diameter with controlled elongation and grain structure refinement.
- Tube Forming: Cold-seamless or cold-drawn seamless tube production ensures a uniform wall thickness and eliminates weld-induced metallurgical weaknesses.
- Coil Winding: Precision CNC-controlled winding machines form the tube into the specified coil geometry with controlled pitch, diameter, and tension to prevent kinking or ovality deformation.
- Heat Treatment (Solution Annealing): Tubes are annealed at 1050°C – 1150°C followed by controlled water quenching to achieve the required austenitic microstructure and stress relief.
- Pickling and Passivation: Acid pickling removes oxide scale; subsequent passivation treatment establishes a protective chromium oxide film (Cr₂O₃) for enhanced corrosion resistance.
- Quality Inspection: 100% visual inspection, ultrasonic flaw detection (UT), eddy current testing (ECT), hydrostatic pressure testing, and dimensional verification (OD, wall thickness, coil diameter, straightness) are performed in accordance with ISO 9001 quality management protocols.
Applications
The stainless steel coil tube is primarily designed for the following application domains:
- Fan Coil Unit (FCU) Systems: Serves as the core heat exchange coil in unitary fan coil units used in commercial buildings, hospitals, laboratories, and data centers. The coil tube enables efficient thermal energy transfer in both heating and cooling modes, supporting demand-response strategies for building energy management.
- HVAC Heat Exchangers: Integrated into air-handling units (AHUs), rooftop units (RTUs), and chilled beam systems where corrosion-resistant, high-performance heat exchange media are required.
- Refrigeration Systems: Utilized in evaporator and condenser coil assemblies for commercial refrigeration and cold storage applications where ammonia or fluorocarbon refrigerants are employed.
- Process Industry Heat Exchangers: Deployed in chemical processing, pharmaceutical manufacturing, and food processing applications where hygienic-grade (3-A compliant) and corrosion-resistant tubing is mandated.
- Building Energy Management Systems (BEMS): The coil tube's predictable thermal performance characteristics enable precise quantification of demand response metrics, supporting intelligent building control algorithms for peak load shifting and energy cost optimization.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains comprehensive quality assurance infrastructure ensuring full compliance with international standards:
- ISO 9001:2015 — Quality Management Systems certification for manufacturing and supply chain processes.
- ISO 14001:2015 — Environmental Management Systems certification for sustainable manufacturing practices.
- ASTM A213/A213M — Conformance with standard specifications for seamless austenitic stainless steel tubing for heat transfer applications.
- EN 10216-5 — European standard for seamless and welded stainless steel tubes for heat exchangers and similar purposes.
- EN 10204 Type 3.1 — Mill Test Certificate (MTC) providing full traceability of chemical composition and mechanical test results.
- CE Marking — Conformity with European regulatory requirements for construction and mechanical product safety.
- HACCP / 3-A Sanitary Standards — Available for food-grade and pharmaceutical-grade coil tube configurations.
Unique Selling Points
The Wenzhou Jixing stainless steel coil tube distinguishes itself through the following competitive advantages:
- Thermal Performance Optimization: Engineered surface geometry and controlled coil pitch maximize heat transfer coefficients, enabling reduced coil footprint and enhanced system efficiency—critical for demand-response quantification in smart building applications.
- Exceptional Corrosion Durability: The 316-grade option with molybdenum alloying provides superior resistance to condensate-induced corrosion, extending service life beyond 25 years in aggressive HVAC environments.
- Full Traceability: Every coil tube spool is accompanied by a complete material passport including chemical analysis, mechanical test data, and heat treatment records, ensuring regulatory compliance for critical infrastructure projects.
- Customized Coil Geometry: Flexible manufacturing capabilities allow tailored coil diameters, pitches, and lengths to match specific fan coil unit designs and thermal load requirements.
- Hygienic Surface Integrity: Internal surfaces polished to Ra ≤ 0.8 μm minimize biofilm formation and fouling, reducing maintenance intervals and sustaining peak thermal performance throughout the service life.