Stainless Steel Coil Tube (盘管) — HVAC Fan Coil Unit Application Series
1. Product Overview
The Stainless Steel Coil Tube (Chinese: 盘管) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered coiled tubular product designed for use in Fan Coil Units (FCU), heat exchangers, and industrial thermal management systems. This product series is specifically optimized for HVAC (Heating, Ventilation, and Air Conditioning) applications where reliable thermal performance, corrosion resistance, and long-term structural integrity are critical requirements.
Unlike conventional copper or aluminum coil tubes, the stainless steel coil tube offers superior resistance to corrosion, chemical degradation, and mechanical fatigue, making it an ideal choice for demanding environments including coastal facilities, industrial plants, and medical buildings where hygiene and durability are paramount.
Key Reference: This product series aligns with the principles outlined in the industry study document "Development and Selection Reference of Fan Coil Unit Thermostats", which emphasizes the importance of matching coil tube material properties with thermostat control strategies for optimal energy efficiency and system reliability.
2. Material & Properties
2.1 Material Composition
The coil tube is fabricated from high-grade austenitic stainless steel, with the following primary material grades available:
- 304 (UNS S30408): General-purpose grade offering excellent corrosion resistance and formability. Suitable for most indoor HVAC applications.
- 316 (UNS S31608): Enhanced molybdenum-containing grade providing superior resistance to chlorides and aggressive chemical environments. Recommended for coastal and marine applications.
- 321 (UNS S32108): Titanium-stabilized grade offering improved resistance to intergranular corrosion at elevated temperatures. Suitable for high-temperature thermal loops.
2.2 Mechanical Properties
- Tensile Strength (抗拉强度): ≥ 520 MPa (304 grade) / ≥ 580 MPa (316 grade)
- Yield Strength (屈服强度): ≥ 205 MPa
- Elongation at Break (断裂伸长率): ≥ 40%
- Hardness (硬度): ≤ 92 HRB (annealed condition)
- Operating Temperature Range (工作温度范围): −196°C to +650°C (304) / −196°C to +870°C (316)
2.3 Thermal Properties
- Thermal Conductivity (热导率): 14.5–16.5 W/(m·K) at 25°C
- Specific Heat Capacity (比热容): 500 J/(kg·K)
- Linear Thermal Expansion Coefficient (线膨胀系数): 17.3 × 10⁻⁶ /°C
2.4 Corrosion Resistance
- Excellent resistance to atmospheric corrosion, water, and most organic acids
- Superior resistance to pitting and crevice corrosion (316 grade)
- Resistance to stress corrosion cracking (SCC) in chloride environments
- Non-magnetic in annealed condition
3. Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Category (产品分类) | Stainless Steel Coil Tube (盘管) | — |
| Material Grade (材质牌号) | SUS 304 / SUS 316 / SUS 321 | ASTM A213 / GB/T 12771 |
| Outer Diameter (外径) | 6 mm / 8 mm / 10 mm / 12 mm / 16 mm (customizable) | ISO 3506 |
| Wall Thickness (壁厚) | 0.5 mm / 0.8 mm / 1.0 mm / 1.2 mm / 1.5 mm | ASTM A269 |
| Coil Diameter (盘管直径) | 100 mm – 500 mm (customizable) | — |
| Coil Length (盘管长度) | Up to 200 m per coil (continuous) | — |
| Surface Finish (表面处理) | Pickled & Passivated (酸洗钝化) / Brushed / Polished | ASTM A967 |
| Welding Method (焊接方式) | Automatic TIG (GTAW) Welding | ISO 15614 |
| Tolerance — Outer Diameter (外径公差) | ±0.1 mm | GB/T 8163 |
| Tolerance — Wall Thickness (壁厚公差) | ±10% of nominal | ASTM A213 |
| End Condition (端部状态) | Cut square / Beveled / Threaded (on request) | — |
| Maximum Operating Pressure (最大工作压力) | ≤ 1.6 MPa (typical HVAC) / ≤ 4.0 MPa (industrial) | ASME B31.9 |
| Design Life (设计寿命) | ≥ 25 years (indoor HVAC) / ≥ 15 years (outdoor) | — |
| Applicable Standards (适用标准) | GB/T 12771, ASTM A213, EN 10216-5, JIS G3459 | — |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Inspection (原材料检验): Incoming stainless steel coil stock is verified for chemical composition (via XRF spectrometry), mechanical properties, and surface quality per ASTM A213 requirements.
- Slitting & Leveling (分条与矫直): The stainless steel strip is slit to the required width and cold-rolled to achieve precise wall thickness tolerances. The strip is then leveled to eliminate residual stresses.
- Tube Forming (制管): The leveled strip is fed through a roll-forming machine to produce a seamless or longitudinally welded tube with the specified outer diameter and wall thickness. The welding process utilizes automatic TIG (Tungsten Inert Gas) Welding under argon shielding gas to ensure a hermetic, oxide-free weld seam.
- Heat Treatment (热处理): Welded tubes undergo solution annealing (固溶处理) at 1050°C – 1150°C followed by controlled cooling to restore full austenitic microstructure and maximum corrosion resistance.
- Pickling & Passivation (酸洗钝化): The annealed tubes are pickled in nitric/hydrofluoric acid solution to remove surface scale and oxide layers. Subsequent passivation treatment forms a protective chromium oxide film on the surface, enhancing corrosion resistance per ASTM A967.
- Coiling (盘绕): The processed straight tube is fed into a precision coiling machine to form the final coil geometry. The coiling process is controlled to maintain consistent coil diameter and prevent material deformation or work hardening.
- End Processing (端部加工): Tube ends are cut square, beveled, or threaded according to customer specifications. Ends may also be capped with protective plugs to prevent contamination during storage and transport.
- Final Inspection & Packaging (终检与包装): Each coil undergoes dimensional verification, visual inspection, and non-destructive testing (NDT) including eddy current testing (涡流检测) and hydrostatic pressure testing (水压试验). Qualified coils are packaged with protective wrapping and moisture-absorbing desiccants.
4.2 Quality Control Points
- In-process monitoring of welding parameters (current, voltage, travel speed) to ensure consistent weld quality
- 100% hydrostatic pressure testing at 1.5× the maximum working pressure for leak detection
- Eddy current inspection of the weld seam for defect detection (pores, cracks, incomplete fusion)
- Surface roughness measurement ensuring Ra ≤ 0.8 μm after passivation
- Salt spray testing (盐雾试验) per ASTM B117: ≥ 500 hours without red rust (304 grade) / ≥ 1000 hours (316 grade)
5. Applications
5.1 HVAC Fan Coil Units (风机盘管)
The primary application of this stainless steel coil tube is in Fan Coil Units (FCU), where it serves as the heat exchange element. The coil tube is arranged in a serpentine or U-bend configuration within a finned tube heat exchanger, facilitating efficient heat transfer between the refrigerant/cooling water and the air stream. The use of stainless steel eliminates the risk of galvanic corrosion when paired with aluminum fins, extending the service life of the heat exchanger significantly.
5.2 Additional Applications
- Chilled Water Systems (冷冻水系统): Coil tubes for air handling units (AHU) and cooling coils in commercial buildings
- Industrial Process Cooling (工业过程冷却): Heat exchangers in chemical processing, pharmaceutical manufacturing, and food processing
- Marine & Offshore HVAC (海洋与海上暖通): Corrosion-resistant coil tubes for shipboard and offshore platform ventilation systems
- Medical & Laboratory Facilities (医疗与实验室设施): Hygienic-grade coil tubes for cleanroom HVAC systems requiring high surface cleanliness
- Geothermal Heat Exchangers (地源热泵换热器): Underground coil tubes for ground-source heat pump systems
- Domestic Hot Water Systems (生活热水系统): Coil immersion heaters for water heating applications
6. Quality Certifications & Standards Compliance
6.1 Factory Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management System
- CE Marking — Conformity with European directives
- RoHS Compliance — Restriction of Hazardous Substances
6.2 Product Standards
- GB/T 12771 — Welded stainless steel tubes for fluid transport (Chinese National Standard)
- ASTM A213 — Specification for austenitic stainless steel tubes for high-temperature service
- ASTM A269 — Specification for seamless and welded austenitic stainless steel tubes, pipes, and fittings
- ASTM A967 — Standard practice for chemical cleaning and passivation of stainless steel parts
- EN 10216-5 — Welded stainless steel tubes for pressure purposes
- JIS G3459 — Stainless steel tubes for general use (Japanese Industrial Standard)
6.3 Third-Party Testing
- Material composition verification by SGS / Intertek / BV (Bureau Veritas)
- Dimensional and mechanical property testing by accredited NABL/CNAS laboratories
- Corrosion resistance testing (salt spray, immersion) per ASTM B117
7. Unique Selling Points
- Superior Corrosion Resistance: Eliminates the galvanic corrosion problem inherent in copper-aluminum fin-tube combinations, extending heat exchanger service life by 3–5× compared to copper coil tubes in aggressive environments.
- HVAC-Specific Optimization: Coil geometry and tube dimensions are engineered specifically for Fan Coil Unit applications, ensuring optimal airflow distribution and heat transfer efficiency when integrated with thermostat control systems (as referenced in the FCU thermostat selection study).
- Full Material Traceability: Each coil tube batch is traceable to the original mill certificate, ensuring complete supply chain transparency and compliance verification.
- Customization Capability: Flexible customization of tube diameter, wall thickness, coil diameter, coil length, and surface finish to meet specific project requirements.
- Hygienic Surface Quality: Post-passivation surface finish with Ra ≤ 0.8 μm meets hygienic requirements for food-grade and pharmaceutical applications.
- Environmental Sustainability: Stainless steel is 100% recyclable with no loss of material properties, supporting green building certifications (LEED, Green Star, BREEAM).
8. Packaging & Delivery
- Individual coils wrapped in moisture-proof PE film with desiccant packs
- Securely strapped and loaded on wooden pallets or steel frames for container shipping
- End caps on tube ends to prevent contamination and damage during transit
- Complete documentation package: Mill Test Certificate (MTC), Certificate of Conformance (CoC), Packing List, and Bill of Lading