Stainless Steel Coil Tube — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (盘管, Coiltube) is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd., designed primarily for integration into Fan Coil Units (FCUs) and distributed air-conditioning systems. The product is fabricated from high-grade stainless steel wire, cold-formed into a continuous helical or serpentine coil geometry that maximizes heat transfer surface area within a compact volumetric envelope. This design is particularly critical in applications where thermal performance prediction and experimental validation of heat exchangers are essential, as demonstrated in academic research on fan coil unit thermal performance modeling.
Coil tubes serve as the core heat exchange element in fan coil systems, facilitating efficient thermal energy transfer between a working fluid (water, refrigerant, or glycol solution) and ambient air. The geometric configuration—characterized by consistent coil pitch, uniform tube diameter, and smooth curvature radii—directly influences pressure drop, flow distribution uniformity, and overall heat transfer coefficient, making material selection and manufacturing precision paramount.
2. Material & Properties
The coil tube is fabricated from austenitic stainless steel grades selected for their combination of corrosion resistance, thermal conductivity, and mechanical integrity under cyclic thermal loading.
- Primary Grade: SUS304 / ASTM A269 Type 304 (18% Cr, 8% Ni) — the standard grade offering excellent general corrosion resistance and formability.
- Alternative Grade: SUS316 / ASTM A269 Type 316 (16% Cr, 10% Ni, 2% Mo) — selected for environments with elevated chloride ion exposure (e.g., coastal HVAC installations, marine air conditioning).
- Surface Treatment: Pickling and passivation per ASTM A967 to ensure a chromium-rich oxide layer, preventing localized corrosion and maintaining long-term thermal efficiency.
- Key Mechanical Properties: Tensile strength ≥ 515 MPa; Yield strength ≥ 205 MPa; Elongation ≥ 40% (ensuring adequate ductility for coil forming without cracking).
- Thermal Conductivity: Approximately 16.3 W/(m·K) at 25°C, providing reliable heat transfer performance across operating temperature ranges of −20°C to +200°C.
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm / 4.0 mm / 6.0 mm / 8.0 mm / 9.52 mm / 12.7 mm | ASTM A269 / GB/T 12771 |
| Wall Thickness | 0.3 mm – 1.5 mm (customizable) | ASTM A269 |
| Coil Pitch | 6 mm – 25 mm (configurable per design) | Manufacturer Specification |
| Coil Diameter | 100 mm – 800 mm | Project-specific |
| Coil Length | Up to 50 m continuous | — |
| Surface Finish | Mirror polished (Ra ≤ 0.4 μm) or Matte (Ra ≤ 1.6 μm) | ASTM B733 |
| Operating Temperature | −200°C to +870°C | Material-dependent |
| Maximum Operating Pressure | Up to 4.0 MPa (wall thickness dependent) | ASME B31.9 |
| Corrosion Resistance | Excellent in atmospheric, freshwater, and moderate chemical environments | ASTM G48 (pitting resistance) |
| Welding Compatibility | TIG (GTAW), Orbital, Laser welding | ASTM A564 |
| Compliance Standards | GB/T 12771, ASTM A269, EN 10217-7, JIS G3446 | Multi-standard certified |
4. Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage process to ensure geometric accuracy, metallurgical integrity, and consistent thermal performance:
- Material Selection & Incoming Inspection: Raw stainless steel wire rod or seamless tube stock is sourced from certified mill suppliers. Each batch undergoes spectrographic analysis (PMI — Positive Material Identification), chemical composition verification, and mechanical property testing prior to acceptance.
- Wire Drawing / Tube Forming: The raw stock is cold-drawn through precision dies to achieve the target outer diameter and wall thickness with tight dimensional tolerances (±0.05 mm). This step also refines the grain structure and surface finish.
- Coil Winding: The formed tube is wound onto precision mandrels using CNC-controlled winding equipment. Critical parameters—coil pitch, helix angle, and bend radius—are controlled to prevent ovalization, wrinkling, or localized stress concentrations that could compromise structural integrity or heat transfer performance.
- Heat Treatment (if required): Solution annealing at 1040°C–1150°C followed by rapid water quenching may be applied to relieve residual stresses from cold forming, restoring full austenitic microstructure and mechanical properties.
- Pickling & Passivation: The coil is subjected to acid pickling (nitric/hydrofluoric acid blend) to remove surface oxides, followed by passivation to establish a protective chromium oxide film, ensuring long-term corrosion resistance.
- End Finishing & Brazing/Welding: Coil ends are deburred, beveled, and prepared for brazing or welding to headers, manifolds, or terminal fittings. Brazing is performed under inert atmosphere (nitrogen) to prevent oxidation.
- Quality Control & Testing: Final inspection includes dimensional verification (laser scanning or coordinate measuring), hydrostatic pressure testing at 1.5× working pressure, eddy current flaw detection for wall integrity, and visual surface inspection per ASTM E1417.
5. Applications
The stainless steel coil tube is a versatile component with broad applicability across multiple industries:
- Commercial & Residential HVAC: Core heat exchange element in fan coil units (FCUs), air handling units (AHUs), and unitary air conditioners. The coil geometry directly determines the thermal performance coefficients (U-value, NTU) validated in academic studies on FCU heat transfer prediction.
- Industrial Process Cooling & Heating: Used in condensers, evaporators, and recuperators in chemical processing, food and beverage pasteurization, and pharmaceutical cleanroom environments where corrosion resistance and sanitary compliance are mandatory.
- Automotive & Transportation: Compact coil heat exchangers for vehicle climate control systems and industrial vehicle thermal management.
- Marine & Offshore: SUS316-grade coil tubes in shipboard air conditioning and refrigeration systems exposed to salt-laden atmospheres.
- Medical & Laboratory Equipment: Precision temperature control coils in medical imaging systems, laboratory incubators, and sterilization chambers.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring product traceability and conformance to international standards:
- ISO 9001:2015 — Quality Management System certification covering all manufacturing stages.
- ISO 14001:2015 — Environmental Management System, ensuring sustainable manufacturing practices.
- CE Marking — Conformity with European health, safety, and environmental protection standards.
- Mill Test Certificates (MTC) — EN 10204 3.1 type certificates provided for each production batch, documenting chemical composition, mechanical properties, and heat treatment records.
- Material Traceability: Full lot traceability from raw material mill certification through final product dispatch, enabling root-cause analysis and quality assurance throughout the supply chain.
7. Unique Selling Points
The coil tube product from Wenzhou Jixing Metal Materials Co., Ltd. distinguishes itself through several key advantages:
- Precision Geometry Control: CNC winding ensures coil pitch uniformity within ±0.1 mm, directly translating to predictable and optimized heat transfer performance—critical for engineering applications where thermal performance prediction models must match experimental results.
- Multi-Grade Material Availability: Offering SUS304 and SUS316 grades provides design flexibility to match the coil tube to specific environmental and corrosion requirements without compromising thermal efficiency.
- Customization Capability: Full customization of outer diameter, wall thickness, coil pitch, coil diameter, and total length to meet project-specific thermal-hydraulic design requirements.
- Superior Surface Finish: Mirror-polished surfaces (Ra ≤ 0.4 μm) reduce fouling resistance and enhance convective heat transfer coefficients, extending service life and maintaining design performance over time.
- Comprehensive Quality Assurance: Multi-stage inspection protocols including hydrostatic testing, eddy current NDT, and dimensional laser scanning ensure zero-defect delivery and long-term reliability in demanding applications.
8. Technical Notes & Design Considerations
When integrating coil tubes into fan coil unit or heat exchanger designs, engineers should consider the following:
- The coil pitch-to-diameter ratio (P/D) significantly influences both pressure drop and heat transfer rate. A P/D ratio of 1.5–2.0 is typically optimal for balanced performance in air-side applications.
- Stainless steel's lower thermal conductivity (~16 W/m·K) compared to copper (~400 W/m·K) necessitates careful design consideration. The increased surface area from coil geometry compensates for this, but wall thickness should be minimized where mechanically permissible to reduce conductive thermal resistance.
- Thermal expansion differential between the coil tube and surrounding fin material (typically aluminum) must be accounted for to prevent fatigue cracking at fin-tube interfaces over thermal cycling.
- For applications requiring validated thermal performance, the coil tube geometry parameters (OD, wall thickness, pitch, number of passes) should be precisely documented to enable accurate CFD modeling and experimental correlation, as referenced in the academic literature on fan coil unit thermal performance prediction.