Stainless Steel Coil Tube for Fan Coil Unit (FCU) Applications
Product Overview
The Stainless Steel Coil Tube is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd., specifically designed for integration into Fan Coil Units (FCU) and other hydronic heat exchange systems. As a critical structural and functional element within the evaporator and condenser assemblies of FCU systems, this coil tube facilitates efficient thermal transfer between circulating refrigerant or hydronic fluid and ambient air.
Based on extensive research into the significance analysis of factors affecting cooling capacity of fan coil units, this product is engineered to optimize heat transfer performance, minimize pressure drop, and ensure long-term operational reliability under varying thermodynamic conditions. The coil geometry, material selection, and surface finish are all calibrated to maximize the coefficient of performance (COP) within the complete FCU assembly.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional corrosion resistance, mechanical durability, and thermal conductivity characteristics. The primary alloy grades utilized include:
- 304 (UNS S30400) — General-purpose grade with balanced corrosion resistance and formability, suitable for non-chloride environments.
- 316 (UNS S31600) — Enhanced molybdenum content (2.0–3.0%) provides superior resistance to pitting and crevice corrosion in aggressive or humid environments.
- 316L (UNS S31603) — Low-carbon variant (C ≤ 0.03%) optimized for welded coil assemblies requiring post-fabrication heat treatment resistance.
| Property | Specification (Grade 316L) | Test Method |
|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa (74,700 psi) | ASTM A270 / A269 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (29,700 psi) | ASTM A270 / A269 |
| Elongation (at fracture) | ≥ 40% | ASTM A270 / A269 |
| Thermal Conductivity (at 25°C) | 16.3 W/(m·K) | ASTM E1461 |
| Corrosion Potential (vs. SCE) | ≥ +150 mV | ASTM G5 |
| Pitting Resistance (PREN) | ≥ 24 | ASTM G48 |
| Hardness (Rockwell B) | 80 – 100 HRB | ASTM E18 |
The material exhibits a stable face-centered cubic (FCC) crystal structure across the operational temperature range of −196°C to +870°C, ensuring no phase transformation-induced degradation during normal FCU operating cycles. The passive chromium oxide film (Cr₂O₃) self-repairs in the presence of oxygen, providing continuous protection against electrochemical attack.
Specifications
| Parameter | Specification Range | Notes |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (1/4") – 25.4 mm (1") | Standard increments per ASME B36.19M |
| Wall Thickness (WT) | 0.50 mm – 1.65 mm (0.020" – 0.065") | Tolerance: ±0.05 mm |
| Coil Pitch (Row Spacing) | 15 mm – 50 mm (0.59" – 1.97") | Customizable per thermal load requirement |
| Tube Pass Configuration | 2-pass, 4-pass, 6-pass, 8-pass | Determined by cooling capacity target |
| Surface Finish | 2B / BA (Bright Annealed) / Polished (Ra ≤ 0.4 μm) | BA finish recommended for enhanced heat transfer |
| Coil Length | 1.0 m – 12.0 m (3.3 ft – 39.4 ft) | Continuous coil or segmented assembly |
| Operating Pressure | Up to 1.6 MPa (232 psi) working; 2.4 MPa burst | Per EN 10216-5 |
| Operating Temperature | −40°C to +150°C (−40°F to +302°F) | Extended range with Grade 316L |
| Refrigerant Compatibility | R-410A, R-32, R-134a, R-407C, Water/Glycol mixtures | Non-reactive with all listed media |
| Corrosion Allowance | 0.0 mm (inherent material resistance) | No additional coating required |
Manufacturing Process
The production of high-performance stainless steel coil tubes follows a rigorously controlled multi-stage manufacturing sequence:
- Coil Unwinding & Straightening — Precision unwinding of cold-rolled stainless steel strip or seamless tubing blanks from industrial coils, followed by mechanical straightening to achieve dimensional accuracy within ±0.05 mm tolerance.
- Forming & Bending — Computer Numerical Control (CNC) tube bending machines form the tube into the designated coil geometry using a multi-axis mandrel system. The bending radius is calculated to maintain uniform wall thickness (no thinning below 85% of nominal) and prevent ovalization exceeding 5% of nominal OD.
- Welding — U-bend connections and header integrations are performed via Tungsten Inert Gas (TIG) welding in accordance with ASME Section IX, using ER316L filler wire and argon gas shielding (99.99% purity). Weld penetration is verified through radiographic testing (RT) or ultrasonic testing (UT) per AWS D1.6.
- Heat Treatment & Annealing — Post-weld solution annealing at 1050°C – 1150°C with rapid water quenching restores full solution-solidified microstructure, eliminates residual stresses, and re-establishes the passive film. This ensures maximum corrosion resistance and mechanical properties.
- Pickling & Passivation — The annealed surface is pickled using a mixed acid solution (HNO₃/HF) to remove oxide scale, followed by passivation treatment to enhance the chromium oxide passive layer thickness to ≥ 2 nm.
- Pressure Testing & Leak Detection — Each coil assembly undergoes hydrostatic pressure testing at 1.5× working pressure (minimum 2.4 MPa) for a hold time of 30 minutes, followed by helium leak detection at sensitivity of 1×10⁻⁹ Pa·m³/s.
- Final Inspection & Packaging — Dimensional verification using laser measurement systems, visual inspection under 10× magnification, and protective packaging with moisture-absorbent desiccants prior to shipment.
Applications
The stainless steel coil tube serves as the primary heat transfer element in a wide range of HVAC and industrial thermal management systems:
- Fan Coil Units (FCU) — Central application domain; the coil tube functions as the evaporator or condenser core, directly influencing the cooling capacity, heating efficiency, and energy consumption of the complete FCU system.
- Chilled Water Systems — Coil tubes in air handling units (AHU) and fan coil terminals for commercial buildings, hospitals, and cleanroom environments.
- Industrial Process Cooling — Heat exchangers in chemical processing, food and beverage manufacturing, and pharmaceutical production where corrosion resistance is critical.
- Marine & Offshore Systems — HVAC coils for vessel applications exposed to high-chloride marine atmospheres, leveraging Grade 316L's superior pitting resistance.
- Refrigeration & Cryogenic Systems — Low-temperature coil assemblies for cold storage facilities and industrial refrigeration plants operating down to −40°C.
- Heat Pump Systems — Evaporator and condenser coils for air-source and ground-source heat pump installations requiring high thermal efficiency and long service life.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring adherence to international standards:
| Standard / Certification | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System — Full production lifecycle |
| ISO 14001:2015 | Environmental Management System — Sustainable manufacturing |
| EN 10216-5 | Welded stainless steel tubes for heat exchangers and boilers |
| ASTM A270 / A269 | Stainless steel tubing — seamless and welded, cold-formed |
| ASME B31.3 | Process piping — design and construction standards |
| EN 1279 / EN 12828 | Heat exchangers for HVAC — design and test requirements |
| UL 1995 / CE Marking | Electrical safety and conformity for HVAC components |
| Material Test Report (MTR) | Mill-certified chemical composition and mechanical property verification per lot |
Unique Selling Points
Research-Driven Thermal Optimization: Product design incorporates findings from advanced thermodynamic analysis of FCU cooling capacity influencing factors — including air-side heat transfer coefficient, refrigerant-side flow distribution, and coil geometry parameters — ensuring the coil tube achieves optimal thermal performance within the complete system architecture.
- Zero-Corrosion Lifetime: Inherent stainless steel passivity eliminates the need for anti-corrosion coatings, reducing total cost of ownership (TCO) by eliminating periodic re-coating and extending service life beyond 25 years.
- Precision Bending Tolerance: CNC-controlled manufacturing ensures uniform wall thickness retention (≥ 85% nominal) throughout all bends, preventing localized flow restriction and ensuring balanced refrigerant distribution across all coil passes.
- High PREN (≥ 24): Superior pitting resistance number provides exceptional protection in high-humidity, chlorinated, or chemically aggressive environments — a critical advantage over copper and carbon steel alternatives in coastal or industrial settings.
- Hygienic Surface Finish: Bright Annealed (BA) or polished finish with Ra ≤ 0.4 μm minimizes fouling accumulation, maintaining design heat transfer efficiency over extended operating periods and reducing maintenance intervals.
- Full Traceability: Every coil assembly is accompanied by a complete material traceability dossier including mill certificate, heat number, chemical analysis, mechanical test results, weld procedure qualification records, and pressure test documentation.
Conclusion
The Stainless Steel Coil Tube from Wenzhou Jixing Metal Materials Co., Ltd. represents a state-of-the-art heat transfer component engineered to maximize the cooling capacity and energy efficiency of Fan Coil Unit systems. By integrating rigorous materials science, precision manufacturing processes, and compliance with the most stringent international standards, this product delivers dependable thermal performance, exceptional corrosion resistance, and extended service life — making it the definitive choice for high-reliability HVAC and industrial thermal management applications worldwide.