Stainless Steel Coil Tube — Wenzhou Jixing Metal Materials Co., Ltd.
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 formed into continuous helical or spiral configurations. Designed for thermal management and fluid transport applications, this coil tube is integral to Variable Frequency Drive (VFD) Fan Coil Unit (FCU) systems, where it serves as the primary heat exchange medium. The coil geometry maximizes the surface-area-to-volume ratio, enabling efficient thermal transfer in compact installations. The product is engineered to meet rigorous demands in HVAC (Heating, Ventilation, and Air Conditioning), refrigeration, and industrial process cooling systems.
Wenzhou Jixing Metal Materials Co., Ltd. leverages advanced cold-forming technology and strict metallurgical controls to produce coil tubes that deliver superior mechanical integrity, corrosion resistance, and thermal conductivity — critical attributes for systems operating under variable frequency modulation and dynamic load conditions.
2. Material & Properties
The coil tube is fabricated from high-purity austenitic stainless steel, with the following material options available:
- 304 Stainless Steel (UNS S30400 / 1.4301): Contains 18% Chromium (Cr) and 8% Nickel (Ni). Offers excellent general-purpose corrosion resistance, weldability, and formability. Suitable for non-aggressive chemical environments and food-grade applications.
- 316 Stainless Steel (UNS S31600 / 1.4401): Contains 16–18% Cr, 10–14% Ni, and 2–3% Molybdenum (Mo). Provides enhanced resistance to pitting and crevice corrosion, particularly in chloride-rich environments.
- 316L Stainless Steel (UNS S31603 / 1.4404): Low-carbon variant of 316, with Carbon (C) ≤ 0.03%. Eliminates intergranular corrosion risk during welding, ideal for heat-exchange applications involving brazing or welding.
- 321 Stainless Steel (UNS S32100 / 1.4541): Titanium-stabilized grade with excellent resistance to intergranular corrosion at elevated temperatures (up to 870°C / 1598°F).
2.1 Key Mechanical Properties
| Property | 304 Grade | 316 Grade | 316L Grade |
|---|---|---|---|
| Tensile Strength (Ultimate Tensile Strength, UTS) | ≥ 520 MPa (≥ 75,400 psi) | ≥ 515 MPa (≥ 74,700 psi) | ≥ 485 MPa (≥ 70,300 psi) |
| Yield Strength (0.2% Proof Stress) | ≥ 205 MPa (≥ 29,700 psi) | ≥ 205 MPa (≥ 29,700 psi) | ≥ 170 MPa (≥ 24,700 psi) |
| Elongation (at Break) | ≥ 40% | ≥ 40% | ≥ 45% |
| Hardness (HB) | ≤ 217 HB | ≤ 217 HB | ≤ 217 HB |
| 16.3 W/(m·K) | 14.6 W/(m·K) | 14.6 W/(m·K) | |
| Density | 8.00 g/cm³ | 8.03 g/cm³ | 8.03 g/cm³ |
| Maximum Service Temperature | 870°C (1598°F) | 870°C (1598°F) | 870°C (1598°F) |
| Corrosion Resistance | Good (general) | Excellent (chloride-resistant) | Excellent (chloride-resistant, low C) |
3. Specifications
| Parameter | Specification / Range |
|---|---|
| Product Name | Stainless Steel Coil Tube (盘管, Coiltube) |
| Material Grades | 304, 316, 316L, 321 (Custom grades available upon request) |
| Outer Diameter (OD) | Φ 3.0 mm – Φ 50.8 mm (0.118 in – 2.000 in) |
| Wall Thickness | 0.3 mm – 3.0 mm (0.012 in – 0.118 in) |
| Coil Pitch (Helix Pitch) | 5 mm – 50 mm (0.197 in – 1.969 in), customizable |
| Coil Diameter (Bundled) | Φ 100 mm – Φ 600 mm (3.94 in – 23.62 in) |
| Coil Length per Roll | Up to 100 m (328 ft) per continuous coil |
| Surface Finish | BA (Bright Annealed), No. 4 Brushed, 2B Mill Finish, Custom |
| Internal Surface Roughness (Ra) | ≤ 0.8 μm (BA finish); ≤ 1.6 μm (2B finish) |
| Pressure Rating | Up to 2.5 MPa (362.6 psi) at 20°C / 68°F |
| Operating Temperature Range | −196°C (−321°F) to +870°C (+1598°F) |
| Standards Compliance | ASTM A213, ASTM A269, GB/T 12771, GB/T 13296, EN 10216-5, JIS G3459 |
| Welding Process | Orbital TIG (Tungsten Inert Gas) welding; laser welding available |
| Packaging | Wooden crates with moisture-proof wrapping; custom export packaging |
| Customization | OD, wall thickness, pitch, length, surface finish, and grade — all customizable |
4. Manufacturing Process
The production of the Stainless Steel Coil Tube at Wenzhou Jixing Metal Materials Co., Ltd. follows a multi-stage precision manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and consistent surface quality.
- Raw Material Selection & Inspection: Cold-rolled stainless steel coils are sourced from certified mills. Incoming material undergoes spectroscopic analysis (via Optical Emission Spectrometry, OES) to verify chemical composition compliance with ASTM/GB standards. Mechanical properties are validated through tensile testing and hardness measurement.
- Tube Forming (Cold Drawing): The stainless steel strip is cold-formed into tubular profiles using precision rolling mills. This process induces beneficial work hardening, improving yield strength by up to 30% without compromising ductility.
- Seam Welding: Longitudinal seams are welded using Orbital TIG welding under a high-purity Argon (Ar) shield atmosphere (≥ 99.99% purity). The welding parameters — current, voltage, travel speed, and gas flow — are precisely controlled to produce uniform, penetration-complete welds with minimal heat-affected zone (HAZ).
- Coil Bending / Helical Forming: The straight tube is fed through a CNC-controlled coil bending machine that imparts the helical geometry. The bending process is executed at controlled temperatures (typically room temperature for austenitic grades) to prevent cold cracking. Bending radius and pitch are programmatically adjustable to meet application-specific requirements.
- Internal Cleaning & Pickling: Post-welding oxide scale is removed through a combination of mechanical brushing and chemical pickling (using a mixture of nitric acid (HNO₃) and hydrofluoric acid (HF)). This restores the passive chromium oxide layer (Cr₂O₃) essential for corrosion resistance.
- Passivation Treatment: The coil tube undergoes passivation using a 20–30% nitric acid or citric acid solution to further enhance the passive film thickness and uniformity, achieving a minimum critical pitting temperature (CPT) of 25°C for 316/316L grades.
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Final Inspection & Testing: Each batch undergoes:
- Dimensional inspection (OD, wall thickness, pitch tolerance within ±0.1 mm)
- Visual inspection of weld seams (100% coverage)
- Hydrostatic pressure testing (1.5× working pressure, held for 30 seconds)
- Helium leak testing for critical applications (leak rate ≤ 1×10⁻⁹ Pa·m³/s)
- Spectroscopic re-verification of chemical composition
- Packaging & Dispatch: Qualified coil tubes are bundled, wrapped in moisture-proof polyethylene film, and packed in ISPM-15 compliant wooden crates for export or domestic distribution.
5. Applications
The Stainless Steel Coil Tube is deployed across a wide spectrum of thermal and fluid management systems, with particular emphasis on the following domains:
- HVAC Fan Coil Unit Systems: As highlighted in the reference study on AC Variable Frequency Speed Control Fan Coil Unit Systems, the coil tube serves as the core heat exchange element. In VFD-driven FCU systems, the coil tube must withstand variable flow rates and fluctuating thermal loads. The stainless steel construction ensures long-term reliability under dynamic operating conditions, resisting scaling, fouling, and thermal fatigue that degrade copper-aluminum alternatives.
- Industrial Process Cooling & Heating: Used in chemical processing, pharmaceutical manufacturing, and food and beverage production for heat exchangers, condensers, and evaporators where hygiene and corrosion resistance are paramount.
- Refrigeration & Cryogenic Systems: The austenitic stainless steel grades maintain ductility at cryogenic temperatures (down to −196°C), making the coil tube suitable for liquid nitrogen (LN₂) and liquid oxygen (LO₂) systems.
- Marine & Offshore Applications: 316/316L grade coil tubes provide excellent resistance to saltwater corrosion, suitable for shipboard HVAC systems, desalination plants, and offshore platform cooling circuits.
- Medical & Laboratory Equipment: Biocompatible 316L coil tubes are used in medical device cooling systems, autoclaves, and laboratory heating/cooling apparatus.
- Automotive Thermal Management: Lightweight stainless steel coil tubes are increasingly adopted in electric vehicle (EV) battery thermal management systems, offering corrosion resistance and thermal stability under high-voltage environments.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that every batch of Stainless Steel Coil Tube meets international standards and regulatory requirements.
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — certifies systematic quality control across all production stages |
| ISO 14001:2015 | Environmental Management System — ensures environmentally responsible manufacturing practices |
| ISO 45001:2018 | Occupational Health & Safety Management System |
| CE Marking | European Conformity — certifies compliance with EU Machinery Directive, Pressure Equipment Directive (PED 2014/68/EU), and relevant harmonized standards |
| ASTM A213 / A269 | Compliance with American Society for Testing and Materials (ASTM) standards for seamless and welded austenitic stainless steel tubing |
| GB/T 12771 / GB/T 13296 | Chinese National Standards for stainless steel tubes — general technical conditions and specific requirements for heat exchanger tubes |
| EN 10216-5 | European Standard for welded stainless steel tubes — seamless and welded austenitic stainless steel tubes for heat exchangers |
| ASME B31.3 | Compliance with American Society of Mechanical Engineers (ASME) code for process piping — where applicable for pressure-containing applications |
| Material Test Reports (MTR) | Each batch is accompanied by a mill test report documenting chemical composition, mechanical properties, heat number, and traceability information |
7. Unique Selling Points
- Variable Frequency System Compatibility: Engineered specifically to handle the dynamic flow and thermal cycling inherent in VFD-driven fan coil unit systems, ensuring consistent heat transfer performance across the entire speed modulation range.
- Full Traceability: Every coil tube batch is traceable to its mill heat number through a comprehensive MTR system, enabling complete supply chain accountability.
- Superior Corrosion Resistance: The austenitic stainless steel construction with passivated surface finish provides decades of service life in aggressive environments, significantly outperforming carbon steel and copper alternatives.
- Custom Engineering: Flexible customization of OD, wall thickness, coil pitch, and surface finish to meet exact application specifications — reducing downstream processing costs and installation complexity.
- Hygienic Design: BA (Bright Annealed) finish with internal surface roughness Ra ≤ 0.8 μm meets sanitary requirements for food, pharmaceutical, and medical applications.
- Cost-Effective Alternative: Provides a durable, low-maintenance alternative to copper-fin