Stainless Steel Coil Tube — Heat Transfer Optimized Product Series
Product Overview
The Stainless Steel Coil Tube (Product No. 1210) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered continuous coil tubing product designed for demanding heat transfer applications. This product line represents an advanced evolution in coil tube technology, integrating metallurgical excellence with thermal performance optimization derived from rigorous heat transfer analysis studies, particularly those concerning ice storage tank systems and thermal energy storage applications.
Coil tubes are distinguished from straight seamless tubes by their continuous helical geometry, which provides inherent advantages in thermal management systems including enhanced surface-area-to-volume ratios, improved flow dynamics, and superior heat exchange efficiency. The stainless steel coil tube series from Wenzhou Jixing Metal Materials is engineered to deliver exceptional performance in refrigeration, thermal energy storage, chemical processing, and HVAC (Heating, Ventilation, and Air Conditioning) applications where corrosion resistance, thermal conductivity, and mechanical durability are critical requirements.
Material & Properties
Material Grades
- AISI 304 / ASTM 304 (UNS S30400) — The standard austenitic stainless steel offering excellent corrosion resistance, formability, and weldability. Chromium (Cr) content of 18–20% and Nickel (Ni) content of 8–10.5% provide robust protection against oxidation and general corrosion in a wide range of environments.
- AISI 316 / ASTM 316 (UNS S31600) — Enhanced austenitic grade with 2–3% Molybdenum (Mo) addition, providing superior resistance to pitting and crevice corrosion, particularly in chloride-containing environments and industrial chemical applications.
- AISI 321 / ASTM 321 (UNS S32100) — Titanium-stabilized austenitic grade (Ti ≤ 5×C) offering outstanding resistance to intergranular corrosion at elevated temperatures (450–850 °C), suitable for high-temperature heat exchanger applications.
- AISI 316L / ASTM 316L (UNS S31603) — Low-carbon variant (C ≤ 0.03%) of 316 grade, providing enhanced weldability and resistance to sensitization, ideal for welded heat transfer assemblies.
Key Material Properties
| Property | 304 Grade | 316 Grade | 321 Grade |
|---|---|---|---|
| Density (ρ) | 8.00 g/cm³ | 8.00 g/cm³ | 8.00 g/cm³ |
| Thermal Conductivity (λ) @ 20 °C | 16.3 W/(m·K) | 14.6 W/(m·K) | 16.3 W/(m·K) |
| Specific Heat Capacity (cp) @ 20 °C | 500 J/(kg·K) | 500 J/(kg·K) | 500 J/(kg·K) |
| Tensile Strength (Rm) — Annealed | ≥ 515 MPa | ≥ 515 MPa | ≥ 515 MPa |
| Yield Strength (Rp0.2) — Annealed | ≥ 205 MPa | ≥ 205 MPa | ≥ 205 MPa |
| Elongation (A) — Annealed | ≥ 40% | ≥ 40% | ≥ 40% |
| Maximum Service Temperature | 870 °C | 870 °C | 925 °C |
| Corrosion Resistance (Pitting) | Good | Excellent | Good |
Specifications
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (¼" – 2") | ASTM A778 / ASME B76.4 |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm (Schedules 5S – 40S) | ASTM A778 / ASME B76.4 |
| Coil Diameter | 300 mm – 1200 mm | Manufacturer Specification |
| Coil Length (per coil) | 30 m – 120 m (continuous) | Manufacturer Specification |
| Surface Finish | 2B (Cold Rolled & Annealed), BA (Bright Annealed), No. 4 Brushed, Mirror (8K) | ASTM A480 / ASTM A666 |
| End Condition | Plain, Beveled, or Custom Perforated | Customer Specification |
| Tolerance — OD | ±0.05 mm to ±0.15 mm | ASTM A778 |
| Tolerance — Wall Thickness | ±10% (minimum ±0.05 mm) | ASTM A778 |
| Pressure Rating (typical, 304 grade, 12.7 mm OD × 1.65 mm WT) | ≤ 2.5 MPa at 20 °C | ASME B31.3 / EN 13480 |
| Heat Transfer Coefficient (internal, turbulent flow) | 3,000 – 15,000 W/(m²·K) (dependent on flow regime) | Empirical correlations (Dittus-Boelter, Gnielinski) |
| Maximum Operating Pressure | Up to 6.0 MPa (grade and dimension dependent) | ASME B31.3 / EN 13480 |
| Operating Temperature Range | −196 °C (LN₂) to +870 °C (continuous) | ASME B31.3 |
Manufacturing Process
The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd follows a multi-stage precision manufacturing sequence that ensures dimensional accuracy, metallurgical integrity, and thermal performance consistency:
- Raw Material Selection & Verification — Virgin stainless steel billets or continuously cast slabs sourced from certified mills (e.g., Outokumpu, POSCO, Tsingshan) undergo rigorous incoming inspection including spectrographic analysis (OES), chemical composition verification per ASTM E415, and visual surface examination.
- Hot Rolling & Pickling — Billets are reheated to 1,100–1,200 °C and hot-rolled into semi-finished hollow sections. The resulting oxide scale is removed through acid pickling (HNO₃/HF mixed acid bath) to restore the passive chromium oxide layer essential for corrosion resistance.
- Cold Drawing (Tube Milling) — The hot-rolled tube blanks are cold-drawn through precision tungsten carbide (WC-Co) dies using a plug-assisted drawing process. This process achieves the final outer diameter and wall thickness with tight tolerances while inducing beneficial work hardening that enhances mechanical strength.
- Coil Winding & Forming — The drawn straight tubes are wound into continuous helical coils using CNC-controlled coil winding machinery. The winding parameters (coil diameter, pitch, tension) are precisely controlled to ensure uniform geometry and prevent ovality or kinking. The coil winding process maintains the tube's metallurgical properties without introducing residual stresses that could compromise fatigue performance.
- Stress Relief Annealing — Coiled tubes are subjected to solution annealing at 1,010–1,150 °C followed by rapid water quenching. This process eliminates residual stresses from cold forming, restores full austenitic microstructure, and maximizes ductility and corrosion resistance. The annealing atmosphere is strictly controlled (protective atmosphere or vacuum) to prevent decarburization and oxidation.
- Surface Treatment & Finishing — Post-annealing surface conditioning includes:
- 2B Finish: Cold-rolled and annealed in protective atmosphere — smooth, slightly reflective surface
- BA (Bright Annealed): Annealed in controlled reducing atmosphere — high-reflectivity, smooth surface suitable for food and pharmaceutical applications
- No. 4 Brushed: Mechanical brushing with abrasive belts — satin finish with directional grain
- Mirror (8K):em> Electro-polishing and precision grinding — Ra ≤ 0.2 μm surface roughness
- Final Inspection & Testing — Comprehensive quality assurance includes:
- Dimensional inspection (OD, WT, coil diameter, straightness) using laser micrometers and CMM (Coordinate Measuring Machine)
- Hydrostatic pressure testing at 1.5× maximum working pressure per ASTM A778
- Eddy current testing (ASTM E309) for internal and external flaw detection
- Chemical composition verification (ASTM E415 / E1268)
- Mechanical testing (tensile, hardness) per ASTM E8 / E92
- Corrosion testing (salt spray, pitting potential) per ASTM B117 / ASTM G48
- Packaging & Dispatch — Coils are wrapped in VCI (Vapor Corrosion Inhibitor) paper, shrink-wrapped, and secured on wooden or steel pallets. Each coil is accompanied by a mill test certificate (MTC) conforming to EN 10204 Type 3.1.
Applications
Based on rigorous heat transfer analysis, including studies on thermal performance in ice storage systems, the stainless steel coil tube product line from Wenzhou Jixing Metal Materials serves the following critical application domains:
Thermal Energy Storage & Ice Storage Systems
Stainless steel coil tubes are extensively employed in ice storage tank systems (蓄冰槽) for thermal energy storage. The helical coil geometry maximizes the heat transfer surface area within a compact tank volume. Heat transfer analysis demonstrates that coil tubes achieve Nusselt number (Nu) values 15–30% higher than equivalent straight tube arrangements under turbulent flow conditions, owing to secondary Dean vortices induced by the curved geometry. In ice storage applications, the coils facilitate rapid ice formation during off-peak cooling periods and efficient thermal energy release during peak demand, contributing to peak load shifting and energy cost reduction in commercial buildings.
Refrigeration & Air Conditioning (HVAC)
- Evaporator and condenser coils in commercial refrigeration systems
- Chilled water coil assemblies for air handling units
- Heat recovery chiller systems utilizing counter-flow coil configurations
- Freeze-drying equipment condensers
Chemical & Petrochemical Processing
- Reactor jacket cooling/heating coils
- Distillation column internal heat exchangers
- Cooling coils for process fluid temperature control
- Corrosive fluid transfer lines requiring continuous coil routing
Food & Pharmaceutical Industry
- Pasteurization and sterilization coil heat exchangers
- Milk processing cooling coils (BA finish)
- Pharmaceutical clean-in-place (CIP) systems
- Wine and beverage cooling systems
Power Generation
- Heat recovery steam generators (HRSG) in combined cycle plants
- Waste heat recovery systems
- Geothermal heat exchange coils
- Nuclear auxiliary cooling systems (316L grade)
Automotive & Industrial Equipment
- Radiator cooling coils
- Industrial furnace heating elements (321 grade)
- Compressor intercooler assemblies
Unique Selling Points
1. Superior Heat Transfer Performance: The helical coil geometry generates Dean secondary flow patterns that enhance turbulent mixing, resulting in heat transfer coefficients 15–30% higher than straight tube equivalents. This performance advantage has been validated through computational fluid dynamics (CFD) analysis and experimental correlation with established heat transfer models (Dittus-Boelter, Gnielinski, and modified correlations for curved tubes).
2. Precision Dimensional Control: Advanced CNC coil winding technology ensures coil diameter tolerance of ±1% and pitch uniformity of ±0.5 mm, guaranteeing consistent thermal performance across the entire coil length.
3. Comprehensive Grade Availability: Four primary stainless steel grades (304, 316, 321, 316L) cover the full spectrum of corrosion resistance requirements from atmospheric environments to aggressive chemical and chloride-containing media.
4. Full Traceability & Certification: Every coil is traceable to the original mill heat number with complete chemical and mechanical test data, ensuring compliance with international codes and standards.
5. Custom Engineering Capability: Wenzhou Jixing Metal Materials offers custom coil configurations including variable pitch, perforated coils for enhanced mixing, and multi-pass coil arrangements tailored to specific heat transfer requirements.
Quality Certifications & Standards Compliance
| Certification / Standard | Description | Applicable Scope |
|---|---|---|
| ISO 9001:2015 | Quality Management System | All products and processes |
| ISO 14001:2015 | Environmental Management System | Manufacturing operations |
| ISO 45001:2018 | Occupational Health & Safety Management | Workplace safety |
| ASTM A778 | Standard Specification for Seamless and Welded Stainless Steel Coil Tubes | Material specification |
| ASME B76.4 | Dimensional Requirements for Seamless and Welded Stainless Steel Tubes | Dimensional tolerance |
| EN 10216 |