Stainless Steel Coil Tube — HVAC Fan Coil Application Grade
Product Overview
The Stainless Steel Coil Tube (Model Series: SS-CT) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered coiled tubing product designed specifically for use in Fan Coil Units (FCUs) within commercial HVAC (Heating, Ventilation, and Air Conditioning) systems. These coil tubes serve as the primary heat exchanger elements in chilled water and hot water distribution circuits, enabling efficient thermal transfer between the working fluid and the ambient air stream.
This product line addresses the critical requirements identified in advanced HVAC engineering studies, particularly those concerning five-star hotel fan coil control methodologies and temperature regulation panel positioning. The coil tubes are engineered to maintain thermal performance consistency under variable load conditions, ensuring precise temperature control at the terminal unit level.
Material Composition & Mechanical Properties
The coil tubes are fabricated from austenitic stainless steel grades selected for their superior corrosion resistance, thermal conductivity, and long-term structural integrity in aqueous environments.
- Primary Alloy Grade: AISI 304 / SUS 304 (1.4301) — General purpose HVAC applications
- Enhanced Alloy Grade: AISI 316L / SUS 316L (1.4401) — High-chloride or aggressive water environments
- Carbon Equivalent (CE): ≤ 0.04% — Ensures excellent weldability and resistance to intergranular corrosion
- Chromium (Cr) Content: 18.0–20.0% — Provides robust passive oxide film formation
- Nickel (Ni) Content: 8.0–11.0% — Stabilizes austenitic crystal structure
- Molybdenum (Mo) Content: 2.0–3.0% (316L grade) — Enhances pitting and crevice corrosion resistance
| Property | AISI 304 (SUS 304) | AISI 316L (SUS 316L) |
|---|---|---|
| Density (g/cm³) | 7.93 | 8.00 |
| Thermal Conductivity at 20°C (W/m·K) | 16.3 | 14.6 |
| Specific Heat at 20°C (J/kg·K) | 500 | 500 |
| Tensile Strength (MPa, min) | 515 | 485 |
| Yield Strength (MPa, min) | 205 | 170 |
| Elongation (% A50, min) | 40 | 40 |
| Operating Temperature Range (°C) | −196 to +870 | −196 to +870 |
| Corrosion Resistance (ASTM G48) | Good | Excellent (Pitting Resistance No. ≥ 4) |
Dimensional Specifications
| Parameter | Specification | Tolerance | Reference Standard |
|---|---|---|---|
| Outer Diameter (OD) | 6.35 mm / 9.52 mm / 12.70 mm (1/4" / 3/8" / 1/2") | ±0.05 mm | ASTM A269 / EN 10217-7 |
| Wall Thickness | 0.50 mm / 0.80 mm / 1.00 mm | ±10% | ASTM A269 |
| Coil Bending Radius (Min.) | 10× OD | — | Internal Design Standard |
| Coil Length per Spool | 50 m – 200 m (configurable) | ±2 m | — |
| Surface Finish | No. 1 / 2B / BA (Bright Annealed) | Ra ≤ 0.4 μm (BA finish) | ASTM A478 |
| Pressure Test Rating | 2.5 MPa (hydrostatic) | — | ISO 4434 |
| Helical Pitch | 12 mm – 25 mm (adjustable per design) | ±0.5 mm | — |
| End Preparation | Plain cut / Beveled / Threaded (optional) | — | ASME B1.20.1 |
Manufacturing Process
The production of the SS-CT coil tubes follows a rigorous multi-stage manufacturing sequence to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Strip Preparation: Cold-rolled stainless steel strip is inspected for surface defects, chemical composition, and mechanical properties in accordance with ASTM A478.
- Forming & Welding: The strip is cold-formed into a tubular shape and longitudinally welded using Resistance Welding (RW) or Orbital TIG Welding (Gas Tungsten Arc Welding) to achieve a continuous, leak-tight seam.
- Coil Bending: The straight tube is helically coiled using precision CNC coil bending machinery. The bending process is carefully controlled to prevent cross-sectional ovality exceeding 2% and to avoid material thinning beyond acceptable limits.
- Stress Relief Annealing: Coiled tubes are subjected to a controlled furnace annealing cycle (typically 1050°C – 1100°C for 304 grade) followed by rapid water quenching. This eliminates residual bending stresses and restores full austenitic microstructure.
- Pickling & Passivation: The annealed coils undergo acid pickling (nitric-hydrofluoric acid blend) to remove oxide scale, followed by passivation treatment to establish a uniform chromium oxide passive film.
- Hydrostatic Testing: Each coil spool undergoes 100% hydrostatic pressure testing at 2.5 MPa with a minimum dwell time of 60 seconds to verify weld integrity and absence of leakage pathways.
- Final Inspection & Packaging: Dimensional verification, surface inspection, and chemical analysis are performed. Coils are wrapped in protective film and packaged on wooden pallets with desiccant protection.
Applications
The SS-CT coil tubes find extensive application in the following domains:
- Five-Star Hotel HVAC Systems: Used as heat exchanger coils in Concealed Ceiling Fan Coil Units (CCFCUs) and VAV (Variable Air Volume) terminal units, where precise temperature control and silent operation are paramount. The coil geometry directly influences the effectiveness of the temperature control panel's feedback loop.
- Commercial Building Air Conditioning: Chilled water and hot water coil assemblies for large-scale commercial and institutional buildings.
- Industrial Process Cooling: Heat exchanger components in chemical processing, pharmaceutical manufacturing, and food processing facilities requiring hygienic-grade stainless steel.
- Marine & Offshore HVAC: Corrosion-resistant coil tubes for marine air conditioning systems where high-chloride seawater exposure is present (316L grade recommended).
- Data Center Cooling: Precision cooling coil assemblies for server room temperature management.
- Medical Facility HVAC: Hospital-grade air handling units requiring clean, hygienic, and corrosion-resistant heat exchange elements.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system and ensures all products conform to internationally recognized standards:
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System — Full manufacturing process |
| ISO 14001:2015 | Environmental Management System |
| ASTM A269 / A269M | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for General Use |
| EN 10217-7 | Technical Delivery Conditions for Tubes for Mechanical and Technical Purposes — Heat Resistant Steels |
| ASME B31.5 | Pressure Piping — Hydraulic and Pneumatic Power Transmission |
| GB/T 14976 | Chinese National Standard for Cold-Rolled Seamless Stainless Steel Tubes |
| CE Marking (PED 2014/68/EU) | European Pressure Equipment Directive — Where applicable for pressure-rated assemblies |
| Mill Test Certificate (MTC) — EN 10204 3.1 | Third-party inspection and material certification for each production batch |
Unique Selling Points
Engineered for Precision Thermal Control: The coil geometry and material properties are optimized to deliver consistent heat transfer coefficients across variable flow rates, directly supporting advanced fan coil control algorithms — including PID (Proportional-Integral-Derivative) modulation and multi-zone temperature management systems employed in premium hospitality environments.
- Superior Corrosion Resistance: The austenitic stainless steel construction provides exceptional resistance to condensation-induced corrosion, chemical scaling, and microbial growth (Legionella risk mitigation in cooling water circuits).
- Low-Fouling Surface: Bright Annealed (BA) surface finish minimizes biofilm adhesion and scaling, reducing maintenance intervals and preserving long-term thermal efficiency.
- Customizable Coil Geometry: Variable helical pitch, diameter, and length configurations allow OEM integration with diverse fan coil unit designs and temperature control panel architectures.
- Full Traceability: Each coil spool is accompanied by a complete material traceability record including heat number, chemical analysis, mechanical test results, and dimensional inspection data.
- Compliance with Hotel-Specific HVAC Standards: Products are designed to meet the stringent performance requirements outlined in technical literature regarding five-star hotel fan coil control methodologies, ensuring seamless integration with advanced Building Management Systems (BMS).
Technical Notes on Fan Coil Integration
In accordance with established engineering literature on five-star hotel HVAC systems, the selection of coil tube parameters — including outer diameter, wall thickness, helical pitch, and row configuration — directly impacts the overall thermal performance of the fan coil unit. Key performance considerations include:
- Heat Transfer Efficiency: Optimized coil geometry maximizes the surface-area-to-volume ratio, enhancing the overall heat transfer coefficient (U-value) and enabling precise temperature regulation at the terminal.
- Pressure Drop Characteristics: Coil design must balance thermal performance against acceptable pressure drop (ΔP) to minimize pumping energy consumption.
- Condensate Management: The coil tube surface temperature relative to the dew point of the ambient air determines condensate formation rates, which must be managed through proper coil sizing and temperature control panel programming.
- Temperature Control Panel Positioning: The coil's thermal response characteristics influence the optimal placement of temperature sensors and control panels, ensuring accurate feedback for the control system.
Wenzhou Jixing Metal Materials Co., Ltd provides full technical support and engineering consultation for coil tube specification and integration into custom HVAC fan coil assemblies.