Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product formed into a continuous helical or spiral configuration. This product is primarily designed for use in Fan Coil Units (FCU), heat exchangers, refrigeration systems, and HVAC (Heating, Ventilation, and Air Conditioning) applications where efficient heat transfer under variable operating conditions is critical.
Coiltubes offer superior surface-area-to-volume ratios compared to straight pipe sections, enabling enhanced thermal exchange efficiency. The continuous coiling geometry eliminates joint points, reducing the risk of leakage and improving structural integrity under cyclic thermal loading. Wenzhou Jixing Metal Materials Co., Ltd. applies rigorous quality control throughout the manufacturing process to ensure dimensional accuracy, surface finish, and metallurgical consistency in every coil tube produced.
2. Material & Properties
2.1 Base Alloy Grades
- Austenitic Stainless Steels: SUS304 (UNS S30400), SUS316 (UNS S31600), SUS316L (UNS S31603)
- Duplex Stainless Steels: SUS329JD (UNS S32900) — for high-corrosion and high-pressure environments
- Super-Austenitic Stainless Steels: 904L (UNS N08904) — for extreme chemical resistance applications
2.2 Mechanical Properties (Typical Values for SUS304 Grade)
| Property | Symbol | Value | Unit |
|---|---|---|---|
| Tensile Strength (Ultimate) | σb | ≥ 520 | MPa |
| Yield Strength (0.2% Offset) | σ0.2 | ≥ 205 | MPa |
| Elongation (at Break, 50 mm gauge) | A50 | ≥ 40 | % |
| Hardness (Rockwell B) | HRB | ≤ 95 | — |
| Thermal Conductivity (at 100°C) | λ | 16.3 | W/(m·K) |
| Linear Thermal Expansion (20–100°C) | α | 17.3 | ×10-6 K-1 |
| Density | ρ | 7.93 | g/cm³ |
2.3 Corrosion Resistance
The austenitic stainless steel coil tubes exhibit excellent resistance to atmospheric corrosion, dilute acids, and alkaline solutions. SUS316 and SUS316L grades, containing 2–3% Molybdenum (Mo), provide enhanced pitting and crevice corrosion resistance, making them suitable for marine environments and chemical processing applications. The passive chromium oxide film (Cr₂O₃) formed on the tube surface self-repairs in the presence of oxygen, ensuring long-term durability.
3. Specifications
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 50.8 mm | GB/T 14976, ASTM A213 |
| Wall Thickness | 0.3 mm – 3.0 mm | GB/T 14976, ASTM A213 |
| Coil Diameter (CD) | 100 mm – 1000 mm | Manufacturer Standard |
| Pitch (Coil Spacing) | 3.0 mm – 25.0 mm | Per Application Requirement |
| Coil Turns | 5 – 500 | Per Application Requirement |
| Tube Length (Straight, Pre-Coil) | Up to 6000 mm | Per Order Specification |
| Surface Finish | 2B, BA (Bright Annealed), No. 4 Brushed, Mirror (8K) | ASTM A480 |
| End Condition | Plain, Beveled, Threaded, Flanged, U-Bend | Per Application Requirement |
| Tolerance (OD) | ±0.05 mm – ±0.10 mm | GB/T 14976 |
| Tolerance (Wall Thickness) | ±10% of nominal | GB/T 14976 |
| Operating Temperature Range | -196°C to +870°C (SUS304); -196°C to +425°C (SUS316L) | Material Specification |
| Maximum Operating Pressure | Up to 4.0 MPa (design dependent) | ASME B31.3 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: Cold-rolled stainless steel strip or seamless tubing stock conforming to ASTM A270 / GB/T 14976 chemical composition and mechanical property requirements.
- Surface Preparation: Acid pickling and passivation treatment to remove mill scale and establish a uniform chromium oxide passive layer.
- Precision Forming: Computer Numerical Control (CNC) coiling machine forms the tube into the specified helical geometry with controlled coil diameter, pitch, and turn count. The forming process employs multi-roller guidance to prevent ovality and cross-sectional distortion.
- In-Process Inspection: Online dimensional monitoring via laser displacement sensors and coordinate measuring machines (CMM) ensures conformance to specified tolerances.
- Post-Forming Stress Relief: Solution annealing at 1050°C – 1150°C followed by rapid water quench to eliminate residual stresses introduced during cold coiling and restore full austenitic microstructure.
- Final Surface Treatment: Electropolishing or mechanical finishing to achieve the specified surface roughness (Ra ≤ 0.4 μm for BA finish; Ra ≤ 0.2 μm for mirror finish).
- Non-Destructive Testing (NDT): 100% visual inspection, eddy current testing (ECT) for wall thickness verification, and hydrostatic pressure testing per ASTM A269.
- Packaging: Individual protective wrapping with desiccant, wooden crate or export-grade container packaging with anti-condensation measures.
4.2 Key Process Parameters
- Coiling speed: 5 – 30 m/min (depending on tube diameter and wall thickness)
- Minimum bend radius: ≥ 3× outer diameter (to prevent wrinkling or cracking)
- Post-coil annealing atmosphere: Protective gas (N₂ + 5% H₂) or vacuum (≤ 10⁻² Pa)
- Hydrostatic test pressure: 1.5× maximum working pressure, held for ≥ 5 seconds
5. Applications
5.1 Fan Coil Units (FCU) and HVAC Systems
The primary application of the Coiltube product is in Fan Coil Units, where it serves as the core heat exchange element. The coil tube is brazed into a serpentine or multi-row configuration within the FCU cabinet. Under variable cooling load conditions, the coil tube efficiently transfers thermal energy between the refrigerant/cooling water circulating within the tube and the air flowing across the coil surface. The Grey Prediction Model (GM) approach referenced in associated technical literature enables accurate estimation of FCU cooling capacity under non-steady-state operating conditions, accounting for variations in inlet water temperature, air flow rate, and ambient humidity.
5.2 Additional Applications
- Refrigeration and Air Conditioning: Evaporator and condenser coils for commercial and industrial refrigeration systems.
- Chemical Processing: Heat exchangers for corrosive fluid handling in petrochemical, pharmaceutical, and food processing industries.
- Automotive Industry: Intercooler coils, cabin AC evaporators, and exhaust gas recirculation (EGR) coolers.
- Marine Engineering: Seawater-cooled heat exchangers and ballast water treatment systems.
- Medical Equipment: Cryogenic fluid transfer lines and sterilization equipment heat exchangers.
- Power Generation: Steam generator tubes and feedwater heaters in thermal and nuclear power plants.
6. Quality Certifications & Standards Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — Design, manufacture, and supply of stainless steel products |
| ISO 14001:2015 | Environmental Management System — Sustainable manufacturing practices |
| GB/T 14976 | Chinese National Standard for cold-rolled stainless steel seamless tubes |
| ASTM A213 / A269 | American standards for seamless austenitic stainless steel boiler, heat exchanger, and condenser tubes |
| EN 10216-5 | European standard for stainless steel tubes for pressure purposes |
| JIS G3446 | Japanese Industrial Standard for stainless steel seamless tubes |
| CE Marking | European conformity for pressure equipment (PED 2014/68/EU) |
| NSF/ANSI 61 | Drinking water system components — material safety certification |
| Mill Test Report (MTR) | Provided with each batch — chemical composition, mechanical properties, and heat treatment records |
7. Unique Selling Points
- Variable-Condition Adaptability: The coil tube geometry, when integrated into FCU systems, enables efficient heat exchange across a wide range of operating conditions. Advanced thermal modeling (including Grey Prediction Models) ensures optimal performance prediction under transient loads.
- Leak-Free Continuous Construction: The seamless, continuous coil design eliminates soldered or welded joints that are common failure points in multi-segment heat exchanger assemblies.
- Customizable Geometry: Coil diameter, pitch, turn count, and end configurations are fully customizable to meet specific system integration requirements and space constraints.
- Exceptional Corrosion Resistance: Available in multiple alloy grades from standard SUS304 to super-austenitic 904L, providing decades of service life even in aggressive chemical environments.
- Precision Manufacturing: CNC-controlled coiling with ±0.05 mm dimensional tolerance ensures consistent thermal performance and reliable system integration.
- Comprehensive Quality Documentation: Full traceability from raw material mill certificates through final inspection reports, supporting regulatory compliance in regulated industries.
8. Technical Consultation & Ordering Information
Wenzhou Jixing Metal Materials Co., Ltd. provides full technical support for coil tube selection, thermal performance analysis, and system integration engineering. Custom manufacturing is available for non-standard specifications. Please provide detailed application parameters (medium, operating temperature, pressure, flow rate, and space constraints) for a tailored quotation and engineering assessment.