Stainless Steel Coil Tube — Fan Coil Unit (FCU) System Application
Product Code: 1406 | Supplier: Wenzhou Jixing Metal Materials Co., Ltd.
This technical specification document provides a comprehensive overview of the stainless steel coil tube product manufactured by Wenzhou Jixing Metal Materials Co., Ltd., specifically engineered for Fan Coil Unit (FCU) system applications. The product has been rigorously evaluated against water leakage failure modes identified in FCU systems, ensuring superior performance, durability, and long-term reliability in HVAC (Heating, Ventilation, and Air Conditioning) environments.
1. Product Overview
The Stainless Steel Coil Tube is a precision-engineered tubular component formed into a serpentine or helical coil configuration, designed to serve as the heat exchange core within Fan Coil Unit (FCU) systems. Unlike conventional copper or aluminum coil tubes, the stainless steel variant offers exceptional resistance to corrosion, chemical degradation, and mechanical fatigue — addressing the critical failure mode of water leakage observed in FCU systems over extended operational cycles.
Through systematic analysis of FCU water leakage incidents, it has been determined that material degradation at solder joints, corrosion-induced wall thinning, and thermal cycling fatigue are the primary contributors to system failure. The stainless steel coil tube product from Wenzhou Jixing Metal Materials Co., Ltd. is specifically formulated to mitigate these failure mechanisms, delivering a robust solution for commercial and industrial HVAC installations.
2. Material & Properties
The coil tube is manufactured from high-grade austenitic stainless steel, selected for its optimal balance of corrosion resistance, formability, and thermal conductivity within HVAC operating conditions.
- Base Alloy Grade: SUS304 (ASTM A269 TP304) / SUS316L (ASTM A269 TP316L) — available per project specification
- Chemical Composition (SUS304): Carbon (C) ≤ 0.08%, Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Manganese (Mn) ≤ 2.0%, Silicon (Si) ≤ 1.0%
- Chemical Composition (SUS316L): Carbon (C) ≤ 0.03%, Chromium (Cr) 16.0–18.0%, Nickel (Ni) 10.0–14.0%, Molybdenum (Mo) 2.0–3.0%
- Corrosion Resistance: Superior resistance to chloride-induced pitting and crevice corrosion, critical for humid HVAC environments
- Thermal Conductivity: 14–16 W/(m·K) at 20°C — adequate for heat exchange applications with compensating geometric design
- Operating Temperature Range: −40°C to +250°C continuous service
- Mechanical Strength: Yield strength ≥ 205 MPa; Tensile strength ≥ 520 MPa (annealed condition)
- Surface Finish: No. 4 brushed finish (standard) or electropolished (optional) for enhanced hygiene in sensitive applications
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (¼"), 9.52 mm (⅜"), 12.70 mm (½") | ASTM A269 |
| Wall Thickness | 0.50 mm – 1.50 mm (selectable) | ISO 3506 |
| Coil Diameter | 50 mm – 300 mm (customizable) | Per drawing |
| Coil Pitch | 15 mm – 50 mm (adjustable per thermal load) | Per drawing |
| Tube Length (Developed) | 1.0 m – 10.0 m (standard); up to 20.0 m (special order) | Per project requirement |
| Number of Rows | 1 – 6 rows (configurable) | ASHRAE 15 |
| Fin Material | Aluminum (Al 1100) or Stainless Steel (SUS304) | ASTM B209 / ASTM A269 |
| Fin Spacing | 1.5 mm – 3.0 mm (FPI: 20–36) | Per thermal design |
| End Connection | Flared, soldered, brazed, or compression fitting | ISO 4910 |
| Surface Treatment | Pickled & passivated; optional PTFE (Polytetrafluoroethylene) coating | ASTM A967 |
| Pressure Rating | PN16 (1.6 MPa) standard; PN25 (2.5 MPa) available | EN 12266 |
| Weight | 0.8 kg/m – 4.5 kg/m (depending on configuration) | — |
4. Manufacturing Process
The production of the stainless steel coil tube follows a tightly controlled multi-stage process to ensure dimensional accuracy, metallurgical integrity, and resistance to the leakage failure modes identified in FCU system analyses:
- Raw Material Selection & Inspection: Stainless steel strip or seamless tube is sourced from certified mills, undergoing spectroscopic analysis (PMI — Positive Material Identification) to verify alloy composition compliance with ASTM A269 specifications.
- Coil Forming (Rolling): Precision CNC-controlled rolling machines form the straight tube into the required serpentine or helical coil geometry. Tension-controlled rollers prevent work-hardening and ensure uniform bend radii, critical for avoiding stress concentration points that could lead to fatigue cracking.
- Heat Treatment (Annealing): Solution annealing at 1050–1150°C followed by controlled cooling relieves residual stresses introduced during cold forming, restoring full ductility and corrosion resistance of the austenitic microstructure.
- Fin Insertion & Crimping: Aluminum or stainless steel fins are inserted into the coil tubes using high-precision crimping equipment. The crimp depth is controlled to within ±0.05 mm to ensure uniform metal-to-metal contact, preventing micro-gap formation that could lead to corrosion-induced separation (a root cause of FCU leakage).
- Welding & Brazing (if applicable): End connections and header joints are welded using TIG (Tungsten Inert Gas) welding with argon shielding to prevent oxidation. Joint quality is verified through radiographic testing (RT) or dye penetrant inspection (DPI).
- Pickling & Passivation: The finished coil tube assembly undergoes chemical pickling (HNO₃/HF mixture) to remove oxide scale, followed by passivation treatment to establish a protective chromium oxide layer (Cr₂O₃), essential for long-term corrosion resistance in humid environments.
- Pressure Testing & Leak Detection: Each unit undergoes hydrostatic pressure testing at 1.5× the maximum operating pressure (2.4 MPa for PN16 units) held for a minimum of 30 minutes. Electronic leak detection (helium sniffing) is performed on all joints to ensure zero-permeability integrity.
- Final Inspection & Packaging: Dimensional verification, visual inspection, and surface quality assessment are conducted per ISO 9001 quality management protocols. Units are packaged in moisture-barrier containers with desiccant to prevent pre-installation corrosion.
5. Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. is specifically engineered for the following applications, with particular emphasis on FCU systems where water leakage prevention is critical:
- Commercial HVAC Systems: Fan Coil Units in office buildings, shopping malls, hotels, and hospitals requiring reliable, maintenance-free heat exchange components
- Industrial Process Cooling: Precision temperature control in manufacturing facilities where corrosive atmospheres (chlorides, sulfides) would degrade copper-based alternatives
- Food & Pharmaceutical Processing: Hygienic applications requiring food-grade (FDA-compliant) materials with resistance to acid washdown cycles
- Marine & Coastal Environments: HVAC installations in coastal regions or maritime facilities where high chloride exposure accelerates corrosion of conventional materials
- Long-Life Infrastructure Projects: Government and institutional buildings designed for 25–30 year service life with minimal component replacement
- Chilled Water Systems: Secondary loop coil tubes handling glycol-water mixtures where copper alloy dezincification is a concern
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring that all stainless steel coil tube products meet or exceed international standards:
- ISO 9001:2015 — Quality Management System certification for manufacturing processes
- ISO 14001:2015 — Environmental Management System for sustainable production practices
- CE Marking — Conformity with European Union machinery and pressure equipment directives (PED 2014/68/EU)
- ASTM A269/A269M — Standard specification for seamless and welded austenitic stainless steel tubing
- EN 10217-7 — European standard for welded stainless steel tubes for pressure purposes
- GB/T 14976 — Chinese national standard for seamless stainless steel tubes (where applicable)
- NSF/ANSI 61 — Drinking water system components certification (for potable water applications)
- ASME B31.9 — Compliance for medical gas piping systems (where applicable)
7. Unique Selling Points & Technical Advantages
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. represents a paradigm shift in FCU heat exchange component design, directly addressing the water leakage failure modes identified through systematic analysis of commercial HVAC system failures.
- Superior Corrosion Resistance: Compared to copper coil tubes, the stainless steel variant exhibits 5–10× longer service life in aggressive HVAC environments, eliminating the primary root cause of water leakage — corrosion-induced wall perforation.
- Elimination of Galvanic Corrosion: When paired with stainless steel fins (available option), the elimination of dissimilar metal contact removes the electrochemical driving force for galvanic corrosion, a common failure mode in mixed copper-aluminum FCU coils.
- Thermal Cycling Fatigue Resistance: The austenitic microstructure of SUS304/316L provides exceptional resistance to thermal fatigue cracking, addressing the stress-induced failure at coil bends observed in FCU systems operating with variable temperature differentials.
- Joint Integrity: TIG-welded connections with verified weld penetration provide mechanical and metallurgical continuity, eliminating the micro-leakage pathways at brazed joints that contribute to progressive water accumulation in FCU drip trays.
- Reduced Total Cost of Ownership (TCO): Although the initial material cost is 1.5–2.0× that of copper coil tubes, the extended service life (25+ years vs. 8–12 years for copper), reduced maintenance frequency, and elimination of leakage-related damage costs result in a 40–60% reduction in lifecycle costs.
- Customizable Geometry: CNC-controlled coil forming allows precise optimization of coil pitch, diameter, and row configuration for specific thermal load requirements, enabling engineers to fine-tune heat transfer performance without compromising structural integrity.
- Environmental Compliance: Stainless steel is 100% recyclable with no loss of material properties, supporting green building certifications (LEED, BREEAM, Green Star) and corporate sustainability objectives.
8. Technical Notes — FCU Water Leakage Prevention
Based on the analysis of Fan Coil Unit system water leakage problems, the following design considerations are incorporated into the stainless steel coil tube product to prevent and mitigate leakage:
- Minimum Wall Thickness: Wall thickness is selected to provide a minimum 10-year corrosion allowance of 0.1 mm/year even under aggressive conditions, ensuring the tube maintains structural integrity throughout its design life.
- Drainage Compatibility: Coil geometry is designed to promote uniform condensate drainage to the FCU drain pan, preventing standing water that accelerates corrosion at the tube-to-fin interface.
- Anti-Scale Coating (Optional): A PTFE-based internal coating reduces mineral scale deposition in hard-water regions, maintaining heat transfer efficiency and preventing blockage-induced pressure buildup that can cause tube rupture.
- Thermal Expansion Accommodation: Flexible end connections and expansion loops are designed to accommodate differential thermal expansion between the coil tube and connecting piping, preventing stress-induced joint separation.
Wenzhou Jixing Metal Materials Co., Ltd. commits to delivering stainless steel coil tube products that meet the highest standards of quality, reliability, and performance for critical HVAC applications. For detailed project-specific specifications, custom engineering support, or sample evaluation, please contact the technical sales department directly.