Stainless Steel Coil Tube (盘管 / Coiltube) for HVAC Fan Coil Units
1. Product Overview
The Stainless Steel Coil Tube (盘管Coiltube), catalog reference No. 1063, is a precision-engineered heat exchanger component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for use in Air Conditioning Fan Coil Units (FCUs), serving as the core thermal transfer element that enables efficient heat exchange between circulating refrigerant and ambient air.
Unlike conventional copper tube coil assemblies, this stainless steel coil tube offers superior corrosion resistance, extended service life, and enhanced hygiene performance — critical advantages in commercial HVAC systems where exposure to moisture, condensate, and varying chemical environments is constant. The product addresses common abnormal operating conditions identified in fan coil unit deployments, including reduced thermal efficiency, tube fouling, and premature degradation due to galvanic or pitting corrosion.
2. Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional balance of mechanical strength, thermal conductivity, and corrosion resistance. The following material properties define the performance envelope of this product:
- Base Material: Austenitic Stainless Steel — Grade 304 (SAE 304 / AISI 304) or Grade 316L (SAE 316L / AISI 316L) for enhanced chloride resistance
- Chromium Content (Cr): 18–20%, providing a stable passive oxide film for general corrosion protection
- Nickel Content (Ni): 8–10%, ensuring austenitic microstructure and ductility
- Molybdenum Content (Mo): 2–3% (Grade 316L only), conferring superior resistance to pitting and crevice corrosion in condensate-rich environments
- Thermal Conductivity: 14–16 W/(m·K) at 20°C — lower than copper but compensated by optimized fin geometry and tube arrangement
- Operating Temperature Range: −40°C to +150°C, accommodating both cooling and heating cycles in HVAC applications
- Operating Pressure: Up to 1.6 MPa (gauge), compatible with standard refrigerant and hydronic loop pressures
- Surface Finish: Pickled and passivated, achieving a surface roughness (Ra) of ≤ 0.8 μm to minimize fouling and facilitate condensate drainage
- Corrosion Resistance: Passivation treatment per ASTM A967; resistance to intergranular corrosion verified per ASTM A262 Practice E
3. Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 7.0 mm, 8.0 mm, 9.52 mm (3/8"), 10.0 mm (customizable) | ISO 1307 |
| Tube Wall Thickness | 0.5 mm – 1.0 mm (tolerance ±0.05 mm) | ASTM A269 / A270 |
| Fin Material | Aluminum (Al 1100 / Al 3003) or Stainless Steel (304) | ASTM B209 / ASTM B209M |
| Fin Spacing (FPI) | 10 FPI – 14 FPI (Fins Per Inch) | ASHRAE Standard 22 |
| Tube Layout | Staggered (offset) or In-line; 2-row, 3-row, 4-row, or multi-row configurations | — |
| Tube Passes | 2-pass, 4-pass, 6-pass, or custom configurations | — |
| Coil Length (Total Tube Length) | 2 m – 12 m (configurable per unit design) | — |
| End Connections | Flared, brazed, threaded (BSP/NPT), or welded headers | ASME B31.5 |
| Operating Fluid | R-410A, R-32, R-134a, water, or glycol-water mixture | ASHRAE Standard 34 |
| Weight (Typical, per meter of coil) | 0.15 kg – 0.35 kg/m (depending on fin density and tube configuration) | — |
| Surface Treatment | Passivation, optional hydrophilic coating for condensate drainage enhancement | ASTM A967 |
| Hydrostatic Test Pressure | 1.5× maximum operating pressure (typically 2.4 MPa) | ISO 4427 |
4. Manufacturing Process
The production of the stainless steel coil tube follows a rigorous, multi-stage manufacturing protocol designed to ensure dimensional accuracy, thermal performance, and long-term reliability:
- Raw Material Procurement & Inspection: Stainless steel seamless tubes (per ASTM A269 / A270) are sourced from certified mills. Incoming material undergoes chemical composition analysis (per ASTM E415), mechanical property verification, and visual inspection for surface defects.
- Cutting & Forming: Tubes are precision-cut to specified lengths and cold-formed into U-bends or serpentine coil configurations using CNC-controlled bending machines. Bend radii are maintained at a minimum of 3× the tube OD to prevent wall thinning and micro-cracking.
- Fin Insertion & Expansion: Aluminum or stainless steel fins are inserted into the tube array. Mechanical expansion (or orbital welding) is then performed to achieve a tight thermal bond between the fin base and tube OD, ensuring minimal contact thermal resistance (< 0.0001 m²·K/W).
- Fin Stamping & Sizing: Fins are stamped and cut to precise dimensions using high-speed stamping presses. Fin height, thickness, and spacing are controlled to within ±0.1 mm tolerance.
- Header Assembly & Brazing: Inlet and outlet headers are fabricated and brazed to the coil tubes using phosphorus-free copper brazing filler alloy (BCuP-8 per AWS A5.8) for stainless steel-compatible joints, or silver-soldered for critical connections.
- Surface Treatment: The assembled coil undergoes pickling and passivation to remove any oxide scale, carbon residue, or contamination. Optional hydrophilic nano-coating may be applied to enhance condensate runoff and reduce waterlogging — a key improvement measure for abnormal operating conditions in fan coil units.
- Quality Control & Testing: Every coil unit undergoes hydrostatic pressure testing (1.5× working pressure, held for 15 minutes with zero leakage), dimensional verification, and visual inspection. Random samples are subjected to eddy current testing and corrosion testing (salt spray per ASTM B117, 480 hours minimum for Grade 316L).
5. Applications
The stainless steel coil tube is the primary heat exchange element in a wide range of HVAC and thermal management systems. Its applications include:
- Commercial Air Conditioning Fan Coil Units (FCUs): Concealed ceiling-mounted, wall-mounted, and floor-standing FCUs for office buildings, hotels, hospitals, and retail spaces. The stainless steel construction directly addresses common abnormal operating conditions such as condensate-induced corrosion, tube scale buildup, and reduced cooling capacity over time.
- Industrial Process Cooling & Heating: Temperature control loops in pharmaceutical, food processing, and chemical manufacturing facilities where hygienic and corrosion-resistant heat exchangers are mandated.
- Refrigeration Systems: Evaporator coils in cold storage rooms, walk-in freezers, and refrigerated display cases operating with R-404A, R-507, or R-134a refrigerants.
- Heat Pump Systems: Indoor unit coils in air-source and ground-source heat pumps, where the coil must withstand both evaporative and condensing duty cycles.
- Clean Room & Pharmaceutical HVAC: Applications requiring non-shedding, non-corrosive, and easily cleanable heat exchanger surfaces compliant with GMP (Good Manufacturing Practice) standards.
- Marine & Coastal HVAC: Fan coil units deployed in high-humidity, salt-spray environments (hotels, cruise ships, coastal facilities) where Grade 316L stainless steel provides critical chloride resistance.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications and compliances to ensure product integrity and global market acceptance:
- ISO 9001:2015 — Quality Management System certification, covering all stages of design, manufacturing, and post-sale service
- ISO 14001:2015 — Environmental Management System, ensuring sustainable manufacturing practices
- ISO 45001:2018 — Occupational Health and Safety Management System
- CE Marking — Conformity with European Machinery Directive (2006/42/EC) and Pressure Equipment Directive (PED 2014/68/EU) for pressure-containing components
- UL / CSA Listed — Safety certification for HVAC components per UL 484 (Air-Conditioning and Refrigerating Equipment)
- RoHS Compliance — Restriction of Hazardous Substances (Directive 2011/65/EU), ensuring freedom from lead, mercury, cadmium, and other restricted materials
- REACH Compliance — Registration, Evaluation, Authorisation and Restriction of Chemicals (EC No 1907/2006)
- Material Certifications: Mill Test Reports (MTRs) per ASTM A923, providing full chemical composition and mechanical property documentation for each production batch
- Third-Party Testing: Independent verification by SGS, BV (Bureau Veritas), or TÜV Rheinland for corrosion resistance, thermal performance, and dimensional accuracy
7. Unique Selling Points
Extended Service Life: Stainless steel coil tubes resist the galvanic and pitting corrosion that commonly degrades copper-aluminum coil assemblies, extending replacement intervals from 5–8 years to 15–20 years — directly reducing total cost of ownership (TCO) in commercial HVAC installations.
Hygienic & Non-Toxic: The austenitic stainless steel surface is non-porous, non-shedding, and resistant to microbial colonization, making it ideal for healthcare, food processing, and pharmaceutical HVAC applications where indoor air quality (IAQ) is paramount.
Improved Condensate Management: Optional hydrophilic surface coating promotes rapid condensate drainage, mitigating waterlogging — a primary cause of reduced cooling capacity and mold growth in conventional fan coil units.
Corrosion-Resistant in Harsh Environments: Grade 316L variant provides superior resistance to chloride-induced pitting, enabling reliable operation in coastal, marine, and chemically aggressive environments where standard stainless steel or copper tubes would fail prematurely.
Design Flexibility: Available in multiple tube diameters, fin densities, row configurations, and pass counts to precisely match the thermal load requirements of diverse fan coil unit designs — from compact residential units to large commercial VAV (Variable Air Volume) systems.
8. Conclusion
The Stainless Steel Coil Tube (No. 1063) from Wenzhou Jixing Metal Materials Co., Ltd. represents a high-performance, corrosion-resistant heat exchange solution purpose-built for air conditioning fan coil units and related HVAC applications. By addressing the root causes of common abnormal operating conditions — including corrosion, fouling, condensate accumulation, and thermal degradation — this product delivers superior reliability, energy efficiency, and total lifecycle value compared to conventional copper-based alternatives. Its compliance with international quality, safety, and environmental standards makes it suitable for global deployment across commercial, industrial, and institutional HVAC systems.