Stainless Steel Coil Tube — Fan Coil Heat Exchanger Product Series
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Catalog Reference: No. 561 | Classification: Literature-Based Technical Reference
Product Overview
The Stainless Steel Coil Tube is a precision-engineered coiled heat exchanger element designed primarily for fan coil units (FCUs) and terminal air handling systems in commercial, industrial, and residential HVAC (Heating, Ventilation, and Air Conditioning) applications. This product series leverages the inherent corrosion resistance, thermal conductivity, and mechanical durability of austenitic stainless steel to deliver superior heat transfer performance under dynamic operating conditions.
Grounded in empirical research on the actual operating-state heat exchange performance of fan coil units, this coil tube product line addresses critical real-world challenges including variable air-side flow rates, condensation management, fouling resistance, and long-term degradation of thermal efficiency. The design philosophy emphasizes maintaining consistent heat transfer coefficients across the full operational envelope — from low-load part-load conditions to peak design capacity.
Material & Properties
Primary Alloy Grades
- ASTM A213 TP304 (UNS S30408): The standard grade for general HVAC coil tube applications, offering excellent corrosion resistance, weldability, and formability. Chromium (Cr) content of 18–20% and Nickel (Ni) content of 8–10.5% provide robust passivation against atmospheric and condensing water corrosion.
- ASTM A213 TP316L (UNS S31603): Enhanced grade incorporating 2–3% Molybdenum (Mo) for superior resistance to chlorided condensation, acidic condensate, and aggressive industrial atmospheres. Preferred for coastal installations and process cooling applications.
- ASTM A213 TP321 (UNS S32100): Titanium-stabilized grade (Ti ≥ 5×C) for applications requiring elevated-temperature stability and resistance to intergranular corrosion during welding or high-temperature operation.
Key Performance Properties
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C, providing efficient heat transfer between the refrigerant/water circuit and the air stream.
- Corrosion Resistance: Excellent resistance to pitting, crevice corrosion, and stress corrosion cracking in chloride-containing environments (up to ~500 ppm Cl⁻ for 316L grade).
- Mechanical Strength: Minimum tensile strength of 515 MPa (0.2% offset); yield strength ≥ 205 MPa for annealed condition.
- Temperature Range: Continuous operation from −196°C (cryogenic) to +870°C (oxidizing atmosphere), covering the full spectrum of HVAC and industrial process requirements.
- Fouling Resistance: Smooth, passivated inner surface with Ra ≤ 0.8 μm minimizes biofilm adhesion and scale deposition, preserving heat transfer efficiency over extended service intervals.
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 3.0 mm, 4.0 mm, 5.0 mm, 6.0 mm, 8.0 mm, 10.0 mm | ASTM A213 / GB/T 12771 |
| Tube Wall Thickness | 0.3 mm – 1.5 mm (typical: 0.5 mm – 0.8 mm for FCU coils) | ASTM A213 / EN 10217 |
| Coil Pitch (Row Spacing) | 10 mm – 25 mm (customizable per thermal load requirement) | Manufacturer Specification |
| Coil Length (Uncoiled) | 1.0 m – 15.0 m (continuous coil lengths up to 500 m) | — |
| Coil Diameter (Wound) | 150 mm – 800 mm | — |
| Fins per Inch (FPI) | 8 FPI – 14 FPI (aluminum or stainless steel fins) | ASHRAE Standard 34 |
| Fouling Factor (Design) | 0.0001 m²·K/W (water side); 0.0003 m²·K/W (air side) | TEMA Standards |
| Design Pressure (Water Side) | 1.0 MPa – 1.6 MPa (standard); up to 4.0 MPa (reinforced) | GB/T 150 / ASME VIII |
| Surface Treatment | Passivated (citric acid or nitric acid); optional electropolished | ASTM A967 / ASTM A986 |
| Finish (Inner Surface) | Mirror polished (Ra ≤ 0.4 μm) for food-grade; commercial (Ra ≤ 1.6 μm) for HVAC | ASTM A967 |
| Heat Transfer Efficiency (LMTD-based) | η ≥ 0.85 under nominal operating conditions | ASHRAE RP-1490 |
| Welding Method | Orbital TIG (GTAW); resistance-welded fin-to-tube joints | ISO 15614-1 |
| Hydrostatic Test Pressure | 1.5× design pressure (minimum 3.0 MPa) | ASTM A213 / GB/T 24511 |
Manufacturing Process
Process Flow
- Raw Material Procurement & Inspection: Cold-rolled stainless steel strip (304/316L) sourced from certified mills, verified via spectroscopic analysis (PMI) and mechanical testing per ASTM A240/A213 requirements.
- Forming & Sizing: Precision roll-forming converts strip into seamless tube blanks with controlled OD and wall thickness tolerances (±0.05 mm). The process preserves the material's cold-worked strength while ensuring uniform geometry.
- Welding: Longitudinal seams are welded using high-purity orbital TIG welding (Ar gas shield, 99.999%) to produce a clean, oxide-free weld zone with penetration integrity verified by 100% visual inspection and periodic radiographic testing (RT).
- Coiling: Tubes are wound into precise helical coils using CNC-controlled coiling machines. Coil pitch, diameter, and turn count are programmable to meet specific thermal performance targets derived from fan coil unit heat exchange models.
- Fin Application: Aluminum or stainless steel fins are inserted into the coil using automated finning machines with controlled insertion depth and uniform fin spacing. Fin-to-tube bonding is achieved via resistance welding or mechanical crimping with optional soldering.
- Heat Treatment & Annealing: Post-forming annealing at 1050°C in a protective atmosphere (dew point < −60°C) relieves cold-work stresses, restores full ductility, and promotes uniform microstructure.
- Surface Passivation & Cleaning: All coils undergo chemical passivation (ASTM A967) to establish a continuous chromium oxide passive film, followed by ultrasonic cleaning to remove particulate contaminants.
- Quality Control & Testing: Each coil batch undergoes hydrostatic pressure testing, dimensional verification, and performance benchmarking against design heat transfer coefficients. Random samples are subjected to intergranular corrosion testing (ASTM A262 Practice E) and salt spray testing (ASTM B117, 1000+ hours).
- Packaging & Dispatch: Coils are packaged with moisture-absorbing desiccants, protective end caps, and UV-stable wrapping to prevent oxidation and mechanical damage during transit.
Applications
Primary Application Domains
- Commercial HVAC Fan Coil Units: Chilled water and hot water coil tubes for split-type, cassette, and concealed FCUs in office buildings, hotels, hospitals, and retail spaces. The stainless steel construction eliminates the corrosion and leakage risks associated with copper tube alternatives in high-humidity environments.
- Industrial Process Cooling & Heating: Heat exchanger coils for chemical processing, pharmaceutical manufacturing, and food & beverage production where sanitary-grade (316L) surfaces and resistance to aggressive process fluids are mandatory.
- Marine & Coastal HVAC Systems: Corrosion-resistant coil tubes for shipboard HVAC, offshore platform climate control, and coastal facility installations exposed to salt-laden atmospheres.
- Data Center Thermal Management: Precision cooling coil tubes for server room air handling units where long service life and minimal maintenance downtime are critical.
- Automotive & Transportation HVAC: Compact coil tube assemblies for vehicle air conditioning systems and rail transit climate control.
Quality Certifications & Compliance
- ISO 9001:2015 — Quality Management System certification covering the entire manufacturing process.
- ISO 14001:2015 — Environmental Management System, ensuring responsible sourcing and waste minimization.
- CE Marking (EU) — Compliance with European Machinery Directive and Pressure Equipment Directive (PED 2014/68/EU) for pressure-containing components.
- ASME "S" Stamp — Certification for Section VIII pressure vessel components where applicable.
- GB/T Standards Compliance — Full conformance with Chinese national standards for stainless steel tubes (GB/T 12771, GB/T 24511) and HVAC components.
- UL / CSA Listing — Safety certification for HVAC heat exchanger components in North American markets.
- SIL / NSF 61 — Optional potable water safety certification for applications involving drinking water contact.
- Material Traceability: Full mill certificate traceability (EN 10204 3.1) with lot-by-lot chemical and mechanical test reports.
Unique Selling Points
1. Research-Validated Thermal Performance: Product design is informed by empirical studies on fan coil unit heat exchange characteristics under actual operating conditions, ensuring that nominal performance ratings translate reliably to real-world duty cycles — addressing the well-documented discrepancy between steady-state test data and dynamic operational performance.
2. Superior Corrosion Longevity: Austenitic stainless steel coil tubes deliver 2–3× the service life of conventional copper tube alternatives in corrosive or high-humidity environments, significantly reducing lifecycle replacement costs and system downtime.
3. Low-Fouling Surface Engineering: Passivated and optionally electropolished inner surfaces minimize scale and biofilm accumulation, maintaining heat transfer efficiency across extended service intervals and reducing cleaning frequency.
4. Customizable Geometry: Full CNC-driven coil winding capability allows precise tailoring of coil pitch, diameter, and fin density to match specific thermal load profiles and space constraints, optimizing the heat transfer area-to-volume ratio for each application.
5. End-to-End Traceability: From raw material mill certificates to final product test reports, complete traceability documentation supports regulatory compliance, warranty claims, and lifecycle performance verification.
Technical Reference
Primary research basis: "Study on Heat Exchange Performance Characteristics of Fan Coil Units under Actual Operating Conditions" (《风机盘管实际运行状态下换热性能特征研究》). This research provides the empirical foundation for thermal performance modeling, fouling factor selection, and operating envelope validation incorporated into the product design specifications above.
Wenzhou Jixing Metal Materials Co., Ltd. — Catalog No. 561 | Product Line: Stainless Steel Coil Tube for HVAC & Industrial Heat Exchange Applications