Stainless Steel Coil Tube (Coiltube) — HVAC Air Treatment Series
Product Code: JX-CT-1546 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
This document provides a comprehensive technical specification for the Stainless Steel Coil Tube product line developed and manufactured by Wenzhou Jixing Metal Materials Co., Ltd. The product is engineered specifically for integration into Fan Coil Unit (FCU) plus Fresh Air System architectures, where thermal efficiency, corrosion resistance, and hygienic performance are critical design parameters. The coil tube serves as the primary heat exchange element within air treatment systems, facilitating precise temperature control through convective and radiative heat transfer mechanisms.
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular heat exchanger component fabricated from high-grade austenitic stainless steel. Designed for deployment in commercial, industrial, and institutional HVAC (Heating, Ventilation, and Air Conditioning) systems, this product delivers superior thermal conductivity, long-term structural integrity, and resistance to the corrosive environments commonly encountered in air treatment applications.
Within the context of a Fan Coil Unit plus Fresh Air System, the coil tube performs two essential functions:
- Primary Air Treatment: The coil tube absorbs or rejects thermal energy from the circulating air stream, achieving precise temperature regulation in conditioned spaces.
- Secondary Fresh Air Conditioning: When integrated with fresh air handling units, the coil tube conditions incoming outdoor air to maintain indoor air quality (IAQ) standards while minimizing energy consumption.
The product is manufactured in continuous coil form, allowing for seamless integration into coil assemblies with minimal waste and maximum thermal surface area utilization. The coil geometry is optimized to balance pressure drop across the air stream with maximum heat transfer coefficient, in accordance with the principles outlined in ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) standards.
Material & Properties
Base Material Composition
The coil tube is fabricated from 316L Austenitic Stainless Steel (UNS S31603) as the standard grade, with 304L (UNS S30403) available upon request for cost-sensitive applications. The material composition adheres to ASTM A269 / ASME SA-269 specifications for seamless stainless steel tubes.
| Element | Specification Range | Typical Value |
|---|---|---|
| Carbon (C) | ≤ 0.03 | 0.015 |
| Chromium (Cr) | 16.0 – 18.0 | 17.0 |
| Nickel (Ni) | 10.0 – 14.0 | 12.0 |
| Molybdenum (Mo) | 2.0 – 3.0 | 2.5 |
| Manganese (Mn) | ≤ 2.0 | 1.2 |
| Silicon (Si) | ≤ 1.0 | 0.5 |
| Phosphorus (P) | ≤ 0.045 | 0.020 |
| Sulfur (S) | ≤ 0.030 | 0.010 |
Mechanical Properties
| Property | Specification (ASTM A269) | Unit |
|---|---|---|
| Tensile Strength (UTS) | ≥ 485 | MPa |
| Yield Strength (0.2% offset) | ≥ 170 | MPa |
| Elongation at Break | ≥ 40 | % |
| Hardness (Brinell) | ≤ 217 | HB |
Thermal Properties
| Property | Value (at 20°C) | Value (at 100°C) |
|---|---|---|
| Thermal Conductivity | 16.3 W/(m·K) | 18.5 W/(m·K) |
| Specific Heat Capacity | 500 J/(kg·K) | 540 J/(kg·K) |
| Thermal Expansion Coefficient | 17.3 × 10⁻⁶ /K | 18.0 × 10⁻⁶ /K |
| Density | 8.00 g/cm³ | — |
Corrosion Resistance Characteristics
The inclusion of 2.0–3.0% Molybdenum in the 316L grade provides exceptional resistance to:
- Pitting and crevice corrosion in chloride-containing environments (e.g., coastal or industrial air streams)
- Intergranular corrosion due to the low carbon (≤ 0.03%) composition, eliminating the risk of chromium carbide precipitation at weld boundaries
- Condensate corrosion from acidic condensate (pH 4.0–5.5) commonly formed in cooling coil applications
- Galvanic corrosion when paired with compatible aluminum or copper fin materials
Specifications
Dimensional Specifications
| Parameter | Standard Range | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (¼"), 9.52 mm (⅜"), 12.70 mm (½"), 15.88 mm (⅝") | ±0.10 mm |
| Wall Thickness | 0.50 – 1.50 mm | ±10% |
| Coil Length (per coil) | 100 – 500 m (continuous) | ±1.0% |
| Coil Winding Diameter | 300 – 1200 mm | ±5 mm |
| Minimum Bend Radius | ≥ 3 × OD | — |
| Straight Length (cut-to-length) | 1.0 – 12.0 m | ±2 mm |
Performance Specifications
| Parameter | Value | Test Standard |
|---|---|---|
| Maximum Operating Pressure | 1.6 MPa (16 bar) | ASME B31.5 |
| Maximum Operating Temperature | −196°C to +450°C | ASTM A269 |
| Design Pressure (typical HVAC) | 0.6 – 1.0 MPa | EN 12828 |
| Maximum Water Velocity (internal) | 2.5 m/s | ASHRAE 90.1 |
| Heat Transfer Coefficient (water-side) | 4000 – 8000 W/(m²·K) | ASHRAE Handbook |
| Heat Transfer Coefficient (air-side) | 25 – 60 W/(m²·K) | ASHRAE Handbook |
| Surface Roughness (Ra) | ≤ 0.8 μm (internal) | ISO 1302 |
Available Grades and Configurations
| Grade | UNS Designation | Application Focus | Corrosion Resistance Level |
|---|---|---|---|
| 304L | UNS S30403 | General HVAC, indoor applications | Standard |
| 316L | UNS S31603 | High-humidity, coastal, industrial | Enhanced (Mo-added) |
| 316L Ti | UNS S31635 | Welded assemblies, high-temperature | Enhanced (Ti-stabilized) |
| 321 | UNS S32100 | High-temperature applications | Standard (Ti-stabilized) |
Manufacturing Process
Process Flow
- Raw Material Procurement & Inspection: Austenitic stainless steel strip or billet is sourced from certified mills. Incoming material undergoes spectroscopic analysis (OES — Optical Emission Spectroscopy) and chemical composition verification against ASTM A269 requirements.
- Hot Rolling / Cold Drawing: Seamless tubes are produced via the Mannesmann (plastic piercing) method or capillary piercing process. For smaller diameters, cold drawing is employed to achieve precise dimensional tolerances and improved surface finish.
- Pipe Milling & Sizing: Tubes are passed through a series of reducing rolls and calibrating rolls to achieve the target outer diameter and wall thickness within ±0.10 mm tolerance.
- Pickle & Passivate Treatment: Tubes are subjected to acid pickling (HNO₃ + HF mixed acid, 50–80°C, 15–30 minutes) followed by passivation to remove scale, restore the chromium oxide passive layer, and ensure long-term corrosion resistance.
- Coil Winding: Tubes are wound onto precision coils using CNC-controlled winding machines. Winding tension is maintained at 15–30 N to prevent deformation while ensuring uniform coil geometry. The winding diameter is controlled to ±5 mm.
- Heat Treatment (Solution Annealing): Where applicable, coils undergo solution annealing at 1050–1100°C followed by controlled cooling (air or water quench) to achieve a fully austenitic microstructure with no carbide precipitation.
- Internal Surface Treatment: Optional electropolishing reduces internal surface roughness to Ra ≤ 0.4 μm, minimizing fouling potential and improving heat transfer efficiency.
- Final Quality Inspection: Each coil undergoes hydrostatic pressure testing (1.5 × design pressure, hold time ≥ 30 seconds), dimensional verification, visual surface inspection, and optional eddy current testing for wall thickness uniformity.
- Packaging & Dispatch: Coils are wrapped in moisture-proof PE (Polyethylene) film, secured with stainless steel strapping, and placed on wooden pallets for shipping.
Key Manufacturing Controls
- Dimensional Accuracy: Automated laser micrometers provide real-time OD and wall thickness monitoring with ±0.05 mm resolution during production.
- Surface Quality: Internal and external surfaces are inspected for scratches, dents, and oxidation under controlled lighting (≥ 500 lux) at 100% coverage.
- Coil Geometry: CNC winding machines ensure consistent layer-to-layer spacing and edge alignment, preventing tube deformation during downstream coil assembly.
- Traceability: Each coil is assigned a unique heat number and batch code, enabling full traceability from raw material mill certification through final product delivery.
Applications
Primary Application: Fan Coil Unit + Fresh Air Systems
The Stainless Steel Coil Tube is specifically engineered for integration into Fan Coil Unit (FCU) plus Fresh Air System architectures. In this system configuration, the coil tube performs the following critical functions:
- FCU Cooling/Heating Coil: The coil tube, typically finned and assembled into a serpentine or cross-flow coil configuration, absorbs or rejects thermal energy from the recirculated indoor air. The 3