Stainless Steel Coil Tube (Coiltube) — HVAC Fan Coil Unit Application Grade
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-formed tubular product designed specifically for use in Fan Coil Units (FCUs) and All-Air Constant Volume (CAV) systems deployed in large commercial spaces such as shopping malls, convention centers, and public buildings. These coil tubes serve as the critical heat exchange elements within fan coil assemblies, facilitating efficient thermal transfer between circulating refrigerant/heat transfer fluid and ambient air.
Coiltube products in this category are engineered to meet the demanding requirements of modern HVAC (Heating, Ventilation, and Air Conditioning) systems, where reliability, corrosion resistance, and thermal conductivity are paramount. The integration of stainless steel coil tubes into hybrid HVAC architectures—combining all-air systems with fan coil units—enables superior temperature control, energy efficiency, and occupant comfort in large-volume commercial environments.
Material & Properties
Material Grades
- Austenitic Stainless Steel: Primary grades include AISI 304 (UNS S30400) and AISI 316L (UNS S31603), selected for their excellent corrosion resistance and formability.
- Alloy Composition: Chromium (Cr) content of 18–20%, Nickel (Ni) content of 8–12%, with optional Molybdenum (Mo) addition of 2–3% for enhanced chloride resistance in 316L grade.
- Carbon Limit: Maximum carbon content ≤ 0.08% (304) or ≤ 0.03% (316L) to ensure resistance to intergranular corrosion during welding operations.
Mechanical Properties
- Tensile Strength: 515–720 MPa (annealed condition)
- Yield Strength: 205–290 MPa (0.2% offset)
- Elongation: ≥ 40% (minimum, per ASTM A213/A269)
- Hardness: ≤ 92 HRB (annealed)
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C
- Thermal Expansion Coefficient: 16–18 × 10⁻⁶ /°C
Corrosion Resistance
- Excellent resistance to atmospheric corrosion, mild aqueous environments, and HVAC condensate
- 316L grade provides superior resistance to pitting and crevice corrosion in chloride-containing environments
- Resistance to stress corrosion cracking (SCC) at operating temperatures below 60°C
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Code | 1007 | — |
| Product Name | Coiltube (盘管) | — |
| Material Grade | AISI 304 / AISI 316L | ASTM A269, ASTM A213 |
| Outer Diameter (OD) | 7.0 mm – 12.7 mm (typical range) | ASME B36.19M |
| Wall Thickness | 0.5 mm – 1.5 mm | ±10% tolerance |
| Bend Radius | ≥ 3D (minimum bend radius) | ASTM A213 |
| Surface Finish | 2B / No. 4 Hairline / Electropolished | ASTM A480 |
| Maximum Operating Temperature | −40°C to +150°C | — |
| Maximum Working Pressure | 1.6 MPa (16 bar) | ASME BPV Code Section I |
| Coil Diameter | 200 mm – 800 mm (customizable) | — |
| Tolerance on OD | ±0.05 mm (precision grade) | ISO 4287 |
| Forming Method | Continuous cold bending / CNC coil forming | — |
| Delivery Condition | Annealed and pickled (solution treated) | ASTM A269 |
Manufacturing Process
- Raw Material Selection: High-purity stainless steel strip or seamless tube blanks are sourced from certified mills, with full chemical composition verification via Optical Emission Spectrometry (OES) and confirmation of mechanical properties through tensile testing per ASTM A370.
- Coil Forming (Cold Bending): Continuous CNC-controlled coil forming machines bend the tube into precise helical or serpentine patterns. The forming process is conducted at ambient temperature to preserve the metallurgical integrity of the austenitic microstructure. Bend radii are controlled to prevent wall thinning below 90% of original thickness and to avoid micro-cracking at the outer bend surface.
- Stress Relief Annealing: Following forming, the coiltube assemblies undergo solution annealing at 1050°C – 1150°C followed by rapid water quenching. This eliminates residual stresses introduced during cold forming, restores full ductility, and dissolves any carbide precipitation that may have occurred at deformation zones.
- Pickling & Passivation: The annealed product is subjected to pickling (removal of oxide scale using mixed acid solutions) and passivation (treatment with nitric acid or citric acid) to restore the passive chromium oxide layer and ensure maximum corrosion resistance.
- Surface Finishing: Depending on application requirements, the coil tube may receive additional surface treatments including electropolishing (for ultra-low roughness surfaces that resist biofilm formation) or mechanical polishing to achieve specified surface roughness (Ra ≤ 0.4 μm for electropolished grade).
- Quality Inspection: Each batch undergoes dimensional verification (CMM measurement), hydrostatic pressure testing (per ASTM A213/A269), visual surface inspection, and non-destructive testing (NDT) including eddy current testing or dye penetrant testing to detect subsurface defects.
Applications
HVAC Fan Coil Units in Large Commercial Spaces
The primary application of this stainless steel coiltube is as the heat exchange coil element within Fan Coil Units (FCUs) deployed in large commercial spaces. As documented in engineering practice regarding the combined application of All-Air Constant Volume (CAV) systems with fan coil units in shopping malls and similar large-volume buildings, these coil tubes provide the following critical functions:
- Zone Temperature Control: Individual fan coil units equipped with stainless steel coils enable precise temperature regulation in distinct zones within large commercial spaces, complementing the bulk air handling provided by central all-air systems.
- Latent and Sensible Heat Removal: The high thermal conductivity and large surface-area-to-volume ratio of helical coil tubes facilitate efficient simultaneous sensible and latent heat transfer, enabling effective dehumidification in high-moisture commercial environments.
- Energy Efficiency: Stainless steel coils maintain long-term thermal performance without degradation, ensuring sustained coefficient of performance (COP) in HVAC systems over extended service life.
- Hygiene and Maintenance: The smooth, non-porous surface of electropolished stainless steel coils resists microbial colonization and facilitates cleaning, which is particularly important in food-service areas within shopping malls.
Additional Applications
- Commercial refrigeration and cold storage systems
- Industrial process heat exchangers in food and pharmaceutical processing
- Marine HVAC systems where chloride-induced corrosion is a concern
- District heating and cooling distribution systems
- Cleanroom environmental control systems
Quality Certifications
- ISO 9001:2015 — Quality Management Systems certification for manufacturing processes
- ISO 14001:2015 — Environmental Management Systems certification
- CE Marking — Conformity with European Union directives for construction products and machinery safety
- EN 10204 3.1 — Manufacturer's Test Report certification for material traceability
- ASTM A269 / ASTM A213 — Compliance with American Society for Testing and Materials standards for austenitic stainless steel tube
- GB/T 14976 — Chinese national standard for seamless stainless steel tubes
- NSF/ANSI 61 — Drinking water system components certification (where applicable for potable water applications)
- Mill Test Certificates (MTC) — Provided with each shipment, including chemical analysis, mechanical test results, and heat number traceability
Unique Selling Points
1. Engineered for HVAC Performance: Unlike generic stainless steel tubing, this coiltube product is specifically designed and optimized for fan coil unit heat exchange applications, with bend geometry and coil pitch parameters validated for maximum air-side and fluid-side heat transfer coefficients.
2. Superior Long-Term Reliability: The combination of 304/316L austenitic stainless steel with precision cold-forming and stress-relief annealing ensures dimensional stability and corrosion resistance exceeding 20 years of service life in aggressive HVAC condensate environments.
3. Energy-Saving Design: Optimized coil geometry minimizes fluid-side pressure drop while maximizing heat exchange surface area, contributing to lower pumping energy requirements and improved overall system COP in large commercial HVAC installations.
4. Hygienic Surface Quality: Electropolished finish with surface roughness Ra ≤ 0.4 μm prevents biofilm accumulation, reducing maintenance frequency and ensuring consistent thermal performance throughout the service life.
5. Full Traceability and Compliance: Complete material traceability from mill to finished product, with comprehensive test documentation conforming to international standards, ensuring seamless integration into certified building systems.
Concluding Remarks
The stainless steel coiltube product (Item No. 1007) from Wenzhou Jixing Metal Materials Co., Ltd. represents a specialized component in the thermal management supply chain for modern commercial HVAC systems. Its application in hybrid All-Air Constant Volume / Fan Coil Unit architectures for large commercial spaces demonstrates the critical role of precision-engineered heat exchange elements in achieving energy-efficient, reliable, and comfortable indoor environmental quality. The metallurgical properties of austenitic stainless steel, combined with advanced cold-forming technology and rigorous quality control, position this product as a premium solution for demanding commercial HVAC applications where long-term performance, corrosion resistance, and hygiene are non-negotiable requirements.