Stainless Steel Coil Tube — Fan Coil & Radiant Cooling System Grade
Product Code: 439 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Classification: HVAC & Thermal Exchange Coil Products
1. Product Overview
The Stainless Steel Coil Tube (盘管 / Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed for integration into fan coil units (FCU — Fan Coil Units) and floor radiant cooling/heating systems. These coil tubes serve as the primary heat exchange medium in combined cooling configurations, transferring thermal energy between a circulating working fluid (typically water or refrigerant) and the ambient air or structural substrate.
The product is specifically engineered to meet the performance demands identified in advanced research on the combined cooling characteristics of floor radiation and fan coil systems (《地板辐射与风机盘管联合供冷特性实验研究》). This research-driven design philosophy ensures that the coil tubes deliver optimal heat transfer efficiency, thermal stability, and long-term mechanical reliability under continuous cyclic thermal loading conditions.
Unlike conventional carbon steel or copper coil alternatives, the stainless steel construction provides superior corrosion resistance, extended service life, and compliance with stringent hygiene and environmental standards required in modern building services engineering.
2. Material & Properties
2.1 Material Grades
The coil tubes are fabricated from high-grade austenitic stainless steel, with the following primary grade options available:
- Grade 304 (UNS S30408 / 06Cr19Ni10): The standard grade offering excellent general corrosion resistance, formability, and weldability. Suitable for most HVAC and radiant system applications.
- Grade 316 (UNS S31603 / 022Cr17Ni12Mo2): Enhanced grade with molybdenum addition providing superior resistance to pitting and crevice corrosion, recommended for coastal, industrial, or chemically aggressive environments.
- Grade 316L (UNS S31603 / 022Cr17Ni12Mo2 Low Carbon): Low-carbon variant of 316 for improved weldability and resistance to intergranular corrosion in welded assemblies.
2.2 Key Mechanical & Physical Properties
| Property | Grade 304 | Grade 316 / 316L | Test Standard |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa | ≥ 520 MPa | ASTM A270 / GB/T 12771 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 205 MPa | ASTM A270 / GB/T 12771 |
| Elongation (% Elong.) | ≥ 40% | ≥ 40% | ASTM A270 / GB/T 12771 |
| Thermal Conductivity (λ, at 20°C) | ~16.3 W/(m·K) | ~14.6 W/(m·K) | ASTM E1530 |
| Specific Heat (cp, at 20°C) | ~500 J/(kg·K) | ~500 J/(kg·K) | ASTM E1225 |
| Thermal Expansion Coefficient (α, 10–100°C) | ~17.3 × 10⁻⁶ /K | ~16.8 × 10⁻⁶ /K | ASTM E228 |
| Operating Temperature Range | −196°C to +870°C | −196°C to +870°C | — |
| Corrosion Resistance (Acidic/Alkaline) | Good | Excellent | ASTM G48 (Pitting) |
2.3 Surface Finish
The inner and outer surfaces of the coil tubes are supplied in one of the following finish conditions to optimize heat transfer performance and fluid dynamics:
- 2B Finish: Cold-rolled, annealed, and pickled — smooth, non-reflective matte surface suitable for general applications.
- No. 4 Brushed Finish: Directional brushed surface providing enhanced aesthetic appearance for visible installations.
- BA (Bright Annealed) Finish: High-purity, reflective surface with minimal oxide layer, recommended for high-efficiency heat exchange applications where low surface roughness is critical.
3. Technical Specifications
| Specification Parameter | Value / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6 mm – 51 mm (custom sizes available) | ASTM A270 / GB/T 12771 |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm | ASTM A270 / GB/T 12771 |
| Coil Winding Diameter (CWD) | 50 mm – 500 mm (configurable) | Manufacturer Specification |
| Coil Pitch (Center-to-Center Spacing) | 10 mm – 80 mm | Manufacturer Specification |
| Coil Length (Unwound) | 1 m – 50 m per coil (standard); up to 100 m (special order) | Manufacturer Specification |
| Number of Turns | 10 – 500 turns (configurable) | Manufacturer Specification |
| OD Tolerance | ±0.10 mm (OD ≤ 12 mm); ±0.15 mm (OD > 12 mm) | ASTM A270 |
| Wall Thickness Tolerance | ±10% of nominal | ASTM A270 |
| Roundness | ≤ 5% of OD tolerance | ASTM A270 |
| End Straightness | ≤ 1.5 mm/m | Manufacturer Specification |
| Surface Roughness (Ra) | ≤ 0.8 μm (inner surface, BA finish); ≤ 1.6 μm (2B finish) | ISO 4287 |
| Pressure Test | Hydrostatic test at 1.5× working pressure, minimum 60 seconds | GB/T 24511 / ASME B31.5 |
| Working Pressure (Typical) | ≤ 1.6 MPa (16 bar) at 25°C | Manufacturer Specification |
| Heat Transfer Coefficient (U-value, air-water) | 25 – 45 W/(m²·K) (depending on configuration) | ASHRAE Handbook — HVAC Systems & Equipment |
| Maximum Operating Fluid Temperature | 120°C (water); −40°C (refrigerant) | Manufacturer Specification |
4. Manufacturing Process
4.1 Raw Material Selection & Incoming Inspection
Stainless steel strip or seamless pipe blanks are sourced from certified mill suppliers and subjected to rigorous incoming inspection including spectroscopic chemical analysis (per ASTM E415), mechanical property verification, and visual surface examination. Each lot is traceable via heat number and mill certificate.
4.2 Coil Tube Forming
- Slitting & Leveling: Stainless steel strip is slit to the required width and thickness, then passed through a leveling mill to achieve flatness within ±0.2%.
- Coil Winding: The leveled strip is wound onto a precision coil former using CNC-controlled winding equipment to ensure uniform pitch, concentricity, and dimensional accuracy throughout the coil.
- Welding (if applicable): For welded coil tubes, the seam is formed and welded using TIG (Tungsten Inert Gas / GTAW — Gas Tungsten Arc Welding) or laser welding technology under argon shielding to prevent oxidation. Weld seams are ground flush to minimize flow disturbance.
- Alternative — Seamless Coiling: Seamless stainless steel tubing is cold-coiled using hydraulic or mechanical coil-bending machines, eliminating the need for seam welding and providing uniform material properties throughout the tube wall.
4.3 Post-Forming Treatment
- Solution Annealing (if required): Coils are heated to 1050–1150°C and rapidly quenched to relieve residual stresses from cold forming and restore full corrosion resistance.
- Pickling & Passivation: The coil surface is cleaned using a mixed acid pickling solution (HNO₃/HF or H₂SO₄/HNO₃) to remove scale and oxide, followed by nitric acid passivation to form a protective chromium oxide layer.
- Surface Finishing: Final surface treatment (2B, No. 4, or BA) is applied per customer specification.
4.4 Quality Control & Testing
- Dimensional Inspection: Outer diameter, wall thickness, coil pitch, and coil diameter are verified using laser micrometers, ultrasonic thickness gauges, and coordinate measuring machines (CMM).
- Hydrostatic Pressure Testing: Each coil is pressure-tested at 1.5× the rated working pressure to verify integrity and absence of leaks.
- Helium Leak Testing: For high-integrity applications, helium mass spectrometer leak detection is performed to identify micro-porosity or seam defects at sensitivity levels of 1×10⁻⁹ mbar·L/s.
- Visual & Surface Inspection: Full-length visual examination under controlled lighting conditions; eddy current testing (per ASTM E3092) for subsurface defect detection on the inner surface.
- Chemical Composition Verification: Spark OES (Optical Emission Spectroscopy) analysis on each production lot.
- Mechanical Testing: Tensile and hardness testing on representative samples per ASTM A270 requirements.
5. Applications
5.1 Fan Coil Units (FCU) in Commercial & Residential HVAC
The stainless steel coil tubes are the core heat exchange element in fan coil units, which are widely deployed in commercial buildings, hotels, hospitals, and residential complexes. The coil tubes facilitate convective heat transfer between the circulating chilled water or hot water and the air stream forced through the unit by a fan. The combined floor radiation and fan coil cooling configuration leverages the coil tubes' high thermal conductivity and corrosion resistance to achieve uniform temperature distribution and superior indoor thermal comfort.
5.2 Floor Radiant Cooling & Heating Systems
In floor radiant systems, the coil tubes are embedded within the floor slab or suspended below the floor finish. They circulate chilled water (for cooling) or heated water (for heating) to provide surface-based thermal conditioning. The stainless steel construction prevents corrosion from moisture in concrete or soil, ensuring decades of reliable operation without degradation of heat transfer performance.
5.3 Combined Floor Radiation & Fan Coil Cooling Systems
As highlighted in the referenced experimental research (《地板辐射与风机盘管联合供冷特性实验研究》), the combined system integrates both floor radiant panels and fan coil units to achieve superior cooling performance, particularly in addressing latent heat loads. The stainless steel coil tubes in this configuration must withstand:
- Sustained thermal cycling between cooling (12–16°C) and heating (40–60°C) modes
- Pressure fluctuations during seasonal changeover
- Potential condensation on the coil surface during cooling operation
- Long-term exposure to deionized or treated water circuits
5.4 Additional Applications
- Industrial Process Cooling: Heat exchangers in chemical processing, food and beverage production, and pharmaceutical manufacturing.
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration units.
- Automotive HVAC: Compact coil assemblies in vehicle heating and air conditioning systems.
- Solar Thermal Systems: Heat collection coils in solar water heating and solar cooling installations.
- Cleanroom & Laboratory HVAC: Precision temperature control coils where stainless steel hygiene standards are mandatory.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and product certification program ensuring full compliance with international and national standards:
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System — Design, manufacturing, testing, and delivery |
| ISO 14001:2015 | Environmental Management System — Sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health & Safety Management System |
| ASTM A270 / A269 | Standard Specification for Seamless and Wrought Stainless Steel Tubular Products (For Boilers, Heaters, Exchangers, and Similar Applications) |
| GB/T 12771 | Chinese National Standard — Welded Stainless Steel Tubes for Fluid Transport |
| GB/T 24511 | Chinese National Standard — Technical Specification for Pressure Vessels (Pressure Testing) |