Stainless Steel Coil Tube (Coil Tube) — Product No. 511
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Category: Literature Study & Technical Reference — Severe Cold Region Fan Coil and Floor Radiation Combined Cooling Application
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed for demanding thermal-fluid applications, particularly in severe cold region HVAC (Heating, Ventilation, and Air Conditioning) systems. This product is integral to the combined cooling architecture that integrates Fan Coil Units (FCUs) with Floor Radiation Cooling (FRC) systems, enabling efficient heat exchange under extreme low-temperature operating conditions.
Coil tubes are formed by winding seamless or welded stainless steel tubes into helical or spiral configurations, providing maximum heat transfer surface area within a compact volumetric envelope. This geometry is critical for applications requiring high thermal efficiency in confined installation spaces, such as embedded floor systems, rooftop condensers, and cryogenic heat exchangers.
The product has been extensively studied in the context of "Research on the Application of Fan Coil and Floor Radiation Combined Cooling in Severe Cold Regions", where it demonstrates superior thermal performance, corrosion resistance, and long-term structural integrity compared to conventional carbon steel alternatives.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from high-grade austenitic stainless steel, with the following primary material grades available:
- 304 (UNS S30400 / 1.4301): General-purpose grade with excellent corrosion resistance and formability
- 316 (UNS S31600 / 1.4401): Enhanced chloride resistance due to molybdenum addition (2.0–2.5% Mo)
- 316L (UNS S31603 / 1.4404): Low-carbon variant optimized for welding applications and cryogenic service
- 321 (UNS S32100 / 1.4541): Titanium-stabilized grade for elevated temperature applications
2.2 Mechanical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa (304); ≥ 515 MPa (316) | ASTM A213 / EN 10216-5 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ASTM A213 / EN 10216-5 |
| Elongation (A) | ≥ 40% (minimum) | ASTM A213 / EN 10216-5 |
| Cold Bend Test | 180° bend, no cracking or splitting | ASTM A213 / GB/T 246 |
| Impact Toughness (Charpy V-Notch) | ≥ 47 J at −196 °C (LN2 temperature) | ASTM E23 |
2.3 Physical Properties
- Density: 7.93 g/cm³
- Thermal Conductivity: 16.3 W/(m·K) at 20 °C (304 grade)
- Coefficient of Thermal Expansion: 17.3 × 10⁻⁶ /K (20–100 °C)
- Specific Heat Capacity: 500 J/(kg·K) at 20 °C
- Operating Temperature Range: −196 °C to +870 °C (304 grade)
2.4 Corrosion Resistance
The austenitic stainless steel matrix provides exceptional resistance to:
- Pitting Corrosion: PREN (Pitting Resistance Equivalent Number) ≥ 19 (316 grade)
- Intergranular Corrosion: Passes ASTM A262 Practice E (100 h test, 63% HCl, 71 °C)
- Crevice Corrosion: Excellent resistance in chloride-containing environments
- Stress Corrosion Cracking (SCC): High resistance in dilute chloride solutions at ambient temperature
3. Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Product No. | 511 | — |
| Product Name | Coil Tube (Coiltube) | — |
| Tube Outer Diameter (OD) | Φ6 – Φ32 | mm |
| Wall Thickness | 0.5 – 3.0 | mm |
| Coil Pitch (Helical Winding) | 5 – 50 | mm |
| Coil Diameter | 50 – 500 | mm |
| Tube Length (Per Coil) | 10 – 100 | m |
| Surface Finish | Ba ≤ 0.4 μm (electropolished); Ra ≤ 1.6 μm (mechanical polished) | μm |
| Surface Roughness | ≤ 0.8 μm Ra (standard); ≤ 0.2 μm Ra (mirror finish available) | μm |
| Winding Tolerance | ± 0.5 mm (pitch); ± 1.0 mm (coil diameter) | mm |
| Pressure Rating | Up to 4.0 MPa (PN40) | MPa |
| Operating Fluid | Water, Glycol Solutions, Refrigerants (R134a, R410A, R404A), Ammonia | — |
| Standards Compliance | ASTM A213, ASTM A269, EN 10216-5, GB/T 12771, JIS G3459 | — |
| Heat Treatment | Solution Annealed at 1050–1150 °C, followed by water quench | — |
| Welding Suitability | GTAW (TIG), GMAW (MIG), ORBW — full weldability without pre/post-heat treatment | — |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: High-purity stainless steel billets or slabs sourced from certified suppliers, with full chemical composition verification via Spectroscopic Analysis (Optical Emission Spectroscopy, OES).
- Hot Rolling / Forging: Billets are heated to 1150–1250 °C and hot-rolled or forged into seamless tube blanks with precise dimensional control.
- Piercing and Drawing: Hot-pierced tubes undergo multi-pass cold drawing to achieve final outer diameter and wall thickness tolerances (typically ± 5% for wall thickness).
- Solution Annealing: Tubes are annealed at 1050–1150 °C in a controlled atmosphere (nitrogen or argon) followed by rapid water quench to dissolve carbide precipitates and restore full austenitic structure.
- Pickling and Descaling: Surface scale is removed using a mixture of nitric acid (HNO₃) and hydrofluoric acid (HF) to expose the passive chromium oxide film.
- Coil Winding (Coiling): The annealed tube is precisely wound into helical or spiral configurations using CNC-controlled coiling machines. The winding parameters (pitch, coil diameter, number of turns) are programmed according to the application-specific heat transfer requirements.
- Welding of Coil Ends: Tube ends are joined using GTAW (Gas Tungsten Arc Welding) with argon shielding to create a hermetic, leak-free seal. Weld quality is verified by radiographic testing (RT) or dye penetrant testing (PT).
- Surface Treatment: Optional electropolishing, passivation, or mechanical polishing to achieve the required surface finish for hygiene or thermal performance optimization.
- Pressure Testing: Each coil tube undergoes 100% hydrostatic or pneumatic pressure testing at 1.5× the maximum working pressure for a minimum of 60 seconds to verify integrity.
- Dimensional Inspection: Final dimensional verification using laser measurement systems to confirm OD, wall thickness, coil pitch, and overall geometry.
4.2 Key Process Parameters for Severe Cold Applications
For applications in severe cold regions (design temperatures as low as −40 °C to −60 °C), additional process controls are implemented:
- Cryogenic Impact Testing: Charpy V-notch impact tests conducted at −60 °C to ensure ductile fracture behavior (≥ 47 J absorbed energy)
- Low-Carbon Specification: Carbon content limited to ≤ 0.03% (L-grade) to prevent intergranular corrosion during welding in cold environments
- Enhanced Winding Tolerances: Tighter pitch tolerances (± 0.3 mm) to maintain consistent heat transfer coefficients at cryogenic temperatures
5. Applications
5.1 Primary Application: Severe Cold Region Combined Cooling Systems
The coil tube is a critical component in the Fan Coil Unit (FCU) and Floor Radiation Cooling (FRC) combined system, a hybrid approach designed for severe cold climate zones (e.g., northern China, Scandinavia, Siberia). In this system:
- Floor Radiation Cooling: Stainless steel coil tubes are embedded in floor screed or concrete slabs, providing sensible cooling through radiation and natural convection. The stainless steel material ensures long-term corrosion resistance against groundwater chlorides and deicing salts.
- Fan Coil Units: Coil tubes serve as the heat exchange core within FCU units, where air is circulated over the coil surface by fans. The helical winding geometry maximizes the heat transfer area per unit volume, enabling compact and efficient air-side cooling.
- Combined Operation: The hybrid system achieves superior indoor thermal comfort by decoupling sensible and latent heat loads — floor radiation handles sensible cooling while fan coils manage moisture removal. The stainless steel coil tube's thermal conductivity and low thermal resistance ensure rapid temperature response.
5.2 Additional Applications
- Cryogenic Heat Exchangers: LNG (Liquefied Natural Gas) processing, liquid nitrogen distribution systems
- Pharmaceutical and Food Processing: Hygienic-grade heat exchangers requiring CIP (Clean-in-Place) and SIP (Sterilization-in-Place) compatibility
- Refrigeration Systems: Evaporators and condensers for industrial refrigeration plants
- Chemical Processing: Reactor cooling jackets, distillation column condensers
- Power Generation: Steam generator tubes, feedwater preheaters
- Automotive Industry: Intercoolers, oil coolers, and battery thermal management systems
6. Quality Certifications & Standards Compliance
6.1 Product Standards
| Standard | Description | Scope |
|---|---|---|
| ASTM A213 / A213M | Standard Specification for Seamless Ferritic, Austenitic, and Ferritic-Austenitic Stainless Steel Tubes for High-Temperature and High-Pressure Boilers and Heaters | Tube material and dimensions |
| ASTM A269 / A269M | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service Applications | Chemical service tubing |
| EN 10216-5 | Non-Alloy and Alloy Steel Tubes for Mechanical and Technical Purposes — Technical Delivery Conditions for Precision Tubes of Non-Alloy and Alloy Steels | European precision tube specifications |
| GB/T 12771 | Stainless Steel Seamless Tubes for General Purposes (Chinese National Standard) | Chinese market compliance |
| JIS G3459 | Stainless Steel Seamless Tubes (Japanese Industrial Standard) | Japanese market compliance |
| ASME BPV Section I | Boiler and Pressure Vessel Code — Section I: Rules for Construction of Power Boilers | Pressure vessel applications |