Stainless Steel Dry Coil Tube — Wenzhou Jixing Metal Materials Co., Ltd.
Product Code: No. 1193 | Classification: Technical Literature & Application Study
1. Product Overview
The Stainless Steel Dry Coil Tube (also referred to as Coiltube or Free-Cooling Coil) is a precision-engineered stainless steel tubing product designed specifically for dry cooling and heat exchanger systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube is formed into compact spiral or serpentine configurations to maximize surface area within a minimal footprint, enabling highly efficient heat transfer in industrial and HVAC applications.
The dry coil technology eliminates the need for evaporative water consumption, distinguishing it from conventional wet cooling towers. Instead, ambient air passes directly over the stainless steel coil surfaces to absorb heat from the process fluid flowing through the tubes. This approach offers superior energy efficiency, reduced water usage, and enhanced operational reliability in water-scarce or hygienically sensitive environments.
Key Concept: The applicability of dry coil technology and systems is determined by ambient dry-bulb temperature conditions, system design parameters, and the thermal performance requirements of the end application. When ambient dry-bulb temperatures are below the process fluid temperature, dry cooling can serve as a primary or supplemental heat rejection method, significantly reducing overall energy consumption.
2. Material & Properties
The dry coil tube is fabricated from high-grade austenitic stainless steel, selected for its outstanding combination of corrosion resistance, mechanical strength, and thermal conductivity.
2.1 Common Grade Options
- AISI 304 (UNS S30408): General-purpose grade offering excellent corrosion resistance in most atmospheric and industrial environments. Chromium (Cr) content: 18–20%; Nickel (Ni) content: 8–10.5%.
- AISI 316 (UNS S31608): Enhanced corrosion resistance with Molybdenum (Mo) addition (2–3%), suitable for marine, chemical, and coastal applications.
- AISI 316L (UNS S31603): Low-carbon variant of 316 with improved resistance to intergranular corrosion, ideal for welding-intensive coil assemblies.
- AISI 321 (UNS S32100): Titanium-stabilized grade for elevated-temperature applications (up to 870°C) where thermal cycling is a concern.
2.2 Mechanical & Thermal Properties (Typical — AISI 304)
| Property | Symbol | Value | Unit |
|---|---|---|---|
| Tensile Strength (Ultimate) | UTS | ≥ 520 | MPa |
| Yield Strength (0.2% Offset) | YS | ≥ 205 | MPa |
| Elongation (in 50 mm gauge length) | EL | ≥ 40 | % |
| Thermal Conductivity (at 20°C) | λ | 16.3 | W/(m·K) |
| Specific Heat Capacity (at 20°C) | cp | 500 | J/(kg·K) |
| Thermal Expansion Coefficient (20–100°C) | α | 17.3 × 10−6 | 1/K |
| Density (at 20°C) | ρ | 8000 | kg/m³ |
| Operating Temperature Range | Top | −196 to +870 | °C |
2.3 Corrosion Resistance
- Excellent resistance to atmospheric corrosion, urban and industrial atmospheres
- Resistance to dilute organic and inorganic acids (316/316L grades)
- Resistance to chloride-induced pitting and crevice corrosion (Mo-bearing grades)
- Non-magnetic in the annealed condition (austenitic microstructure)
- Free from hydrogen embrittlement risk
3. Technical Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 6.0 mm – 50.8 mm (¼" – 2") | ASTM A213 / ASTM A269 |
| Tube Wall Thickness | 0.5 mm – 3.0 mm (0.020" – 0.118") | ASTM A213 / EN 10216-5 |
| Coil Inner Diameter (Bundling ID) | 100 mm – 1,200 mm (configurable) | Custom / OEM Specification |
| Coil Length per Bundle | 5 m – 150 m (configurable) | Custom / OEM Specification |
| Surface Finish | 2B Annealed / Bright Annealed & Pickled (BAP) / Mirror Polish (Ra ≤ 0.4 μm) | ASTM A478 / GB/T 4237 |
| Coil Pitch | 1.2 × OD – 2.5 × OD (design-dependent) | ASME PTC 22 / Custom |
| Tube-to-Tube Welding | TIG (GTAW) / Orbital Welding — Full-Penetration Butt Welds | ASME Section IX / AWS D10.9 |
| Hydrostatic Test Pressure | 1.5 × Maximum Operating Pressure (MOP) | ASTM A213 / EN 10216 |
| Maximum Operating Pressure | Up to 4.0 MPa (580 psi) — grade and wall thickness dependent | ASME B31.3 |
| Maximum Operating Temperature | −196°C to +870°C (AISI 304); up to +1100°C (310/310S) | ASTM A213 |
| Heat Transfer Coefficient (Air Side) | 20 – 60 W/(m²·K) (natural convection); 50 – 200 W/(m²·K) (forced convection) | ASHRAE Fundamentals Handbook |
| Fin Configuration (Optional) | Integral Lugs / External Aluminized Fins / None (bare tube) | Custom / OEM Specification |
| End Connections | Flanged (ASME B16.5) / Threaded (NPT/BSP) / Welded (Socket/Butt) | ASME B16.5 / ISO 7-1 |
4. Manufacturing Process
The production of high-quality stainless steel dry coil tubes follows a rigorous, multi-stage manufacturing process ensuring dimensional accuracy, metallurgical integrity, and thermal performance.
4.1 Process Flow
- Raw Material Selection: Cold-rolled stainless steel strip or seamless tube stock is sourced from certified mills, with each lot accompanied by a Mill Test Certificate (MTC) conforming to EN 10204 Type 3.1 or ASTM equivalent.
- Dimensional Verification: Incoming tube stock undergoes dimensional inspection (OD, wall thickness, roundness) using calibrated micrometers and ultrasonic thickness gauges to ensure compliance with specified tolerances (±0.05 mm for wall thickness).
- Surface Preparation: Tubes are cleaned using mechanical and chemical methods to remove scale, oxide, and contaminants. Bright Annealing & Pickling (BAP) restores the protective chromium oxide layer for optimal corrosion resistance.
- Coil Forming: Precision forming machinery (spiral coil former or serpentine bending machine) shapes the tube into the designated coil geometry. Forming parameters — bend radius, pitch, and coil diameter — are controlled to prevent wall thinning (≤ 8% reduction) and ovality (≤ 2%).
- Welding Assembly: Tube segments are joined using Tungsten Inert Gas (TIG / GTAW) welding or automated orbital welding. Fillers (e.g., ER308L, ER316L) match or exceed the base metal composition. Welding parameters are optimized per ASME Section IX qualification procedures.
- Post-Weld Heat Treatment (if required): Solution annealing at 1040–1120°C followed by rapid water quenching is performed to restore full austenitic microstructure and maximize corrosion resistance in heat-affected zones.
- Fin Attachment (if applicable): External fins are applied via mechanical lugging, brazing (using phosphor copper or nickel-based alloys), or expansion methods to increase effective heat transfer surface area by 3–8×.
- Hydrostatic Testing: Each coil assembly is pressure-tested at 1.5× the maximum operating pressure with a hold time of minimum 30 seconds. Leak detection employs visual inspection and pressure gauge monitoring.
- Final Inspection & Non-Destructive Testing (NDT): Visual inspection, dye penetrant testing (DPT) per ASTM E165, and radiographic testing (RT) per ASTM E94 (where required) verify weld integrity. Surface roughness is measured per ASTM B463.
- Packaging & Dispatch: Completed coil tubes are protected with anti-corrosion coatings, wooden cradles, and moisture-absorbent desiccants for safe transportation.
5. Applications
The stainless steel dry coil tube finds extensive application across multiple industries where energy efficiency, water conservation, and corrosion resistance are paramount.
5.1 Primary Application Sectors
- HVAC & Building Services: Free-cooling systems for chiller plants, data center thermal management, and district cooling networks. Dry coils serve as pre-coolers or primary coolers during favorable ambient conditions.
- Power Generation: Condenser cooling in combined-cycle power plants, auxiliary cooling loops, and steam turbine exhaust heat recovery systems.
- Food & Beverage Processing: Juice cooling, dairy pasteurization circuits, beer/wine fermentation temperature control, and refrigerated storage systems (hygienic-grade 316L coils with sanitary finishes).
- Pharmaceutical & Biotechnology: Cleanroom temperature regulation, bioreactor cooling jackets, and lyophilization (freeze-drying) systems where contamination-free, non-shedding materials are mandatory.
- Chemical & Petrochemical: Reactor cooling loops, distillation column condensers, and heat exchangers handling aggressive process fluids where carbon steel would corrode.
- Marine & Offshore: Engine room cooling, HVAC systems on vessels, and offshore platform temperature control in saltwater-rich environments (316/316L grades).
- Electronics & Semiconductor: High-power equipment cooling, server room thermal management, and precision temperature control in fabrication cleanrooms.
- Renewable Energy: Solar thermal collector loop cooling, geothermal heat exchange systems, and wind turbine generator cooling circuits.
5.2 System Integration Scenarios
- Primary Dry Cooling: Standalone dry coil systems serving as the sole heat rejection method in temperate climates.
- Hybrid Dry-Wet Systems: Dry coils integrated with evaporative coolers for year-round operation, switching modes based on ambient conditions.
- Pre-Cooling Configuration: Dry coils as upstream pre-coolers reducing the load on downstream chillers or cooling towers.
- Heat Recovery Loops: Capturing waste heat from industrial processes and redistributing it via coil-based heat exchangers.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring every dry coil tube product meets international standards and customer requirements.
6.1 Quality Management System
- ISO 9001:2015 — Quality Management Systems (QMS) certification
- ISO 14001:2015 — Environmental Management Systems (EMS) certification
- ISO 45001:2018 — Occupational Health & Safety Management Systems (OH&SMS) certification
6.2 Product & Material Standards
- ASTM A213 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for High-Temperature Service
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and General Industrial Service
- ASTM A778 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Heat-Transfer Equipment
- EN 10216-5 — Non-alloy and Alloy Steel Tubes for Mechanical, Thermal and General Engineering Purposes — Part 5: Non-Heat-Resistant Austenitic Stainless Steel Tubes
- GB/T 12771 — Chinese National Standard for Stainless Steel Tubes for General Application
- ASME Section VIII / Section IX — Pressure Vessel & Welding Code compliance (where applicable)
- ASME B31.3 — Process Piping Code compliance
6.3 Testing & Inspection Certifications
- Mill Test Certificates (MTC) per EN 10204 Type 3.1 with chemical composition and mechanical property data
- Weld Procedure Qualification (WPQ) and Welder Performance Qualification (WPQ) per ASME Section IX
- Third-party inspection available per SGS / TÜV / Bureau Veritas protocols