Stainless Steel Coil Tube (盘管) — HVAC & Heat Exchanger Grade
1. Product Overview
The Stainless Steel Coil Tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed specifically for use in Heating, Ventilation, and Air Conditioning (HVAC) systems, particularly in Fan Coil Unit (FCU) systems and fresh air handling applications. This coil tube serves as the core heat exchange element within energy-efficient air conditioning systems, enabling optimal thermal transfer between refrigerant and air streams.
In modern HVAC architectures, particularly the Fan Coil Unit plus Fresh Air System (FCU + Fresh Air System), the coil tube plays a critical role in achieving superior energy efficiency. Research and field analyses, including studies on the energy-saving performance of Fresh Air Heat Exchangers (FAHE) replacing conventional Fresh Air Handling Units (FAHU), have demonstrated that the selection of appropriate coil tube geometry, material grade, and surface treatment significantly influences the overall system's Coefficient of Performance (COP) and Seasonal Energy Efficiency Ratio (SEER).
Wenzhou Jixing Metal Materials Co., Ltd. supplies coil tubes that meet the demanding requirements of both residential and commercial HVAC applications, offering consistent wall thickness tolerances, superior corrosion resistance, and reliable thermal conductivity across a wide range of operating conditions.
2. Material & Properties
2.1 Base Material Grades
- AISI 304 (UNS S30408) — Austenitic stainless steel with excellent general corrosion resistance; the most widely used grade for HVAC coil tube applications. Composition: 18–20% Chromium (Cr), 8–10.5% Nickel (Ni), ≤0.08% Carbon (C).
- AISI 316 (UNS S31603) — Enhanced austenitic grade with 2–3% Molybdenum (Mo) addition for superior resistance to chlorides and acidic environments; recommended for coastal installations and aggressive atmospheric conditions.
- AISI 316L (UNS S31603L) — Low-carbon variant of 316 (C ≤ 0.03%) suitable for welding-intensive applications where sensitization must be avoided.
- AISI 321 (UNS S32100) — Titanium-stabilized austenitic grade (0.4–0.9% Ti) providing enhanced resistance to intergranular corrosion at elevated temperatures.
2.2 Key Mechanical and Thermal Properties
- Tensile Strength: ≥ 515 MPa (304); ≥ 515 MPa (316)
- Yield Strength (0.2% offset): ≥ 205 MPa (304); ≥ 205 MPa (316)
- Elongation: ≥ 40% (304); ≥ 35% (316)
- Thermal Conductivity: 16.3 W/(m·K) at 25°C (304); 16.3 W/(m·K) at 25°C (316)
- Thermal Expansion Coefficient: 17.2 × 10⁻⁶ /°C (20–100°C) (304)
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, mild acids, and organic compounds; 316 grade exhibits superior pitting and crevice corrosion resistance per ASTM G48 Standard Practice.
2.3 Surface Finish Options
- No. 1 Finish — Hot-rolled, annealed, and pickled; suitable for industrial applications where surface appearance is not critical.
- 2B Finish — Cold-rolled, annealed, pickled, and bright passivated; the standard finish for HVAC coil tube applications, providing a smooth, non-directional surface with enhanced corrosion resistance.
- BA (Bright Annealed) Finish — Cold-rolled and annealed in a controlled atmosphere; offers superior surface quality for high-visibility or hygienic applications.
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | Φ 3.0 mm – Φ 12.7 mm (standard); custom ranges available | ASTM A213 / A269 |
| Wall Thickness | 0.30 mm – 1.00 mm (standard); tolerance ±0.02 mm | ASTM A213 / A269 |
| Coil Length (Standard) | 5 m – 25 m per coil; continuous lengths available upon request | — |
| Coil Weight (Standard) | 50 kg – 500 kg per coil | — |
| Roundness Tolerance | ≤ 2% of OD | ISO 4427 |
| Flatness / Ovality | ≤ 1.5% of OD | ISO 4427 |
| Maximum Bend Radius | 3D (3 × OD) cold bending without cracking | ASTM A213 |
| Operating Temperature Range | −196°C to +870°C (304); −196°C to +870°C (316) | — |
| Pressure Rating | Up to 1.6 MPa (design pressure for HVAC applications) | EN 10216 |
| Welding Compatibility | TIG (GTAW), MIG (GMAW), orbital welding; no preheat required | ASME BPV Section IX |
| Coating / Passivation | Acid pickling and passivation treatment (ASTM A967) | ASTM A967 |
| Packaging | Wooden pallet with VCI (Vapor Corrosion Inhibitor) wrapping; seaworthy export packaging available | — |
4. Manufacturing Process
The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Strip Preparation: Cold-rolled stainless steel strip (2B or BA finish) is sourced from certified mills and inspected for chemical composition (per ASTM A240), mechanical properties, and surface quality. Incoming material undergoes spectrometric analysis for trace element verification.
- Sewing / Longitudinal Welding: The strip edges are joined via High-Frequency Resistance Welding (HFRW) or TIG longitudinal welding to form a continuous tube blank. Weld quality is verified through visual inspection and, where applicable, dye penetrant testing (DPT) per ASTM E709.
- Pipe Forming (Roll Forming): The welded blank passes through a series of precision forming rolls that progressively reduce the diameter to the target OD. Roll sets are calibrated to maintain wall thickness uniformity within ±0.02 mm tolerance.
- Coil Winding: The formed tube is wound onto a mandrel at controlled tension to produce the coil configuration. Winding parameters (tension, speed, layer-to-layer contact pressure) are optimized to prevent inter-coil damage and ensure consistent coil geometry.
- Solution Annealing (if required): Tubes intended for post-forming or post-welding applications may undergo solution annealing at 1050–1100°C in a protective atmosphere (Argon or controlled Nitrogen), followed by controlled cooling to restore full austenitic structure and maximum corrosion resistance.
- Pickling and Passivation: The coil is subjected to acid pickling (mixed HNO₃/HF solution) to remove mill scale and oxidation, followed by nitric acid passivation to establish a uniform, protective chromium oxide passive layer on the surface per ASTM A967.
- Quality Inspection: Each coil undergoes comprehensive inspection including:
- Dimensional measurement (OD, wall thickness, roundness) using ultrasonic thickness gauges and micrometers
- Chemical composition verification via Optical Emission Spectroscopy (OES)
- Hydrostatic pressure testing per ASTM A213 (test pressure = 1.5 × design pressure)
- Visual and surface inspection for weld quality, scratches, and surface defects
- Mechanical property verification (tensile test, hardness test) per lot
- Packaging and Marking: Each coil is wrapped with protective film and VCI paper, secured on wooden pallets, and clearly marked with heat number, grade, dimensions, and traceability information.
5. Applications
5.1 HVAC Systems (Primary Application)
- Fan Coil Units (FCU): The stainless steel coil tube is the primary heat exchanger element in FCU systems, facilitating heat transfer between chilled water/cooling water and the air stream. In the FCU + Fresh Air System architecture, coil tubes with optimized geometry contribute to improved system COP by 15–25% compared to conventional configurations.
- Fresh Air Heat Exchangers (FAHE): Stainless steel coil tubes are used in plate-fin and tube-fin heat exchangers within fresh air handling units, enabling energy recovery from exhaust air streams and reducing the overall cooling/heating load.
- Chilled Water Coils: Used in air handling units (AHU) for sensible and latent cooling in commercial and industrial facilities.
- Condensing Coils: Applied in refrigeration condensers where stainless steel's corrosion resistance extends service life in humid or chemically aggressive environments.
5.2 Additional Applications
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration equipment, food processing plants, and cold storage facilities.
- Marine HVAC: 316/316L grade coil tubes are used in marine air conditioning systems where saltwater corrosion resistance is critical.
- Food and Pharmaceutical Processing: Heat exchange coils in sanitary-grade equipment requiring compliance with FDA and EHEDG standards.
- Chemical Processing: Heat exchanger tubes in chemical plants where resistance to corrosive media is required.
- Automotive and Aerospace: Precision coil tubes for thermal management systems in advanced vehicle platforms.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and product certifications to ensure that all stainless steel coil tubes meet international standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and process control throughout the manufacturing chain. |
| ISO 14001:2015 | Environmental Management System certification demonstrating commitment to sustainable manufacturing practices. |
| ASTM A213 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for High-Temperature Service — dimensional and mechanical requirements. |
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipe and Tubing for Chemical and Similar Uses. |
| ASTM A967 | Standard Practice for Chemical Cleaning and Passivation of Stainless Steel Parts. |
| EN 10216 | European standard for welded and seamless steel tubes for mechanical and thermal uses. |
| GB/T 12771 | Chinese National Standard for welded stainless steel tubes for general use. |
| MTC (Mill Test Certificate) | Each shipment is accompanied by a full Mill Test Certificate (EN 10204 Type 3.1) documenting chemical composition, mechanical properties, and heat treatment records. |
| Third-Party Inspection | Products are available for third-party inspection by SGS, BV, or TÜV upon customer request. |
7. Unique Selling Points
- Energy Efficiency Contribution: The precise manufacturing tolerances and optimized geometry of these coil tubes directly contribute to improved thermal efficiency in HVAC systems. Studies on FCU + Fresh Air systems have confirmed that coil tube quality is a key determinant of system-level energy savings, with FAHE-equipped systems achieving up to 20% reduction in cooling energy consumption compared to conventional fresh air handling approaches.
- Superior Corrosion Resistance: Available in 304, 316, and 316L grades, these coil tubes provide exceptional longevity in humid, corrosive, and chemically aggressive environments — significantly outperforming carbon steel alternatives in HVAC applications.
- Customization Capability: Wenzhou Jixing Metal Materials Co., Ltd. offers custom OD, wall thickness, coil length, and surface finish configurations to meet project-specific requirements.
- Full Traceability: Every coil is traceable to its heat number and manufacturing batch, with complete documentation available for regulatory and quality assurance purposes.
- Welding and Forming Performance: The austenitic microstructure provides excellent formability and weldability, enabling downstream fabrication without cracking or loss of corrosion resistance.
- Wide Operating Range: Maintains mechanical and corrosion performance from cryogenic temperatures (−196°C) to elevated temperatures (up to 87