Marine Seawater Cooler Coil Tubes — CuNi 70/30 & Duplex 2205
1. Product Overview
The Marine Seawater Cooler Coil Tube (Ref. No. 159) is a high-performance coil tube engineered for shipboard seawater cooling systems operating under demanding marine environments. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product is specifically designed to withstand continuous exposure to seawater at temperatures exceeding 30 °C, aggressive biological fouling (biofouling), and high flow velocities of 2–3 m/s. The coil tube integrates an anti-marine organism attachment design to mitigate biofouling-induced efficiency degradation, ensuring sustained thermal performance and extended service life in harsh offshore and maritime conditions.
These coil tubes serve as critical heat exchange elements within marine seawater cooling circuits, where seawater acts as the cooling medium for onboard machinery including main engines, auxiliary generators, turbochargers, and HVAC systems. The product is categorized under the application domain of Marine Engineering (一级分类: 应用场景) with a secondary classification of Marine Engineering (二级分类: 海洋工程) and a tertiary subdivision of Seawater Systems (三级细分: 海水系统).
2. Material Selection & Properties
Material selection for marine seawater cooler coil tubes is governed by the extreme corrosivity of seawater, which contains approximately 3.5% dissolved salts (predominantly NaCl), dissolved oxygen, and biological contaminants. Two primary alloy systems are specified:
2.1 CuNi 70/30 (Copper-Nickel 70/30)
- UNS Designation: C70600 / C70700
- Composition: 70% Copper (Cu), 30% Nickel (Ni), with trace Fe
- Corrosion Resistance: Excellent resistance to flowing seawater; forms a protective Cu₂O/Cu₃O₄ oxide film
- Thermal Conductivity: ~48 W/(m·K) — superior heat transfer efficiency
- Limitations: Not recommended for stagnant or low-velocity seawater (<0.5 m/s) due to erosion-corrosion risk; susceptible to ammonia attack
- Service Temperature Range: Up to 90 °C in seawater service
2.2 Duplex 2205 (UNS S32205 / S31803)
- Composition: ~22% Cr, ~5% Ni, ~3% Mo, ~1.5% N, ~1.5% Mn
- Microstructure: Dual-phase (austenite + ferrite) approximately 50/50 balance
- Corrosion Resistance: Superior resistance to pitting and crevice corrosion (Pitting Resistance Equivalent Number, PREN ≈ 34–38)
- Yield Strength: ≥ 450 MPa (2× that of 316L austenitic stainless steel)
- Thermal Conductivity: ~18 W/(m·K)
- Advantages: Enhanced mechanical strength permits thinner wall designs; excellent resistance to chloride-induced stress corrosion cracking (SCC)
2.3 Comparative Material Properties
| Property | CuNi 70/30 (C70600) | Duplex 2205 (S32205) |
|---|---|---|
| Density (g/cm³) | 8.9 | 7.8 |
| Thermal Conductivity (W/(m·K)) | ~48 | ~18 |
| Tensile Strength (MPa) | 280–400 | ≥ 550 |
| Yield Strength (MPa) | 140–250 | ≥ 450 |
| PREN (Pitting Resistance Equivalent Number) | N/A | 34–38 |
| Seawater Corrosion Rate (mm/year) | < 0.05 (flowing) | < 0.02 (flowing) |
| Maximum Service Temperature (°C) | 90 (seawater) | 250 |
| Biofouling Resistance | Moderate (Cu ion release) | Low (requires anti-fouling design) |
| Typical Wall Thickness (mm) | 0.5–1.2 | 0.4–1.0 |
3. Technical Specifications
| Parameter | Specification |
|---|---|
| Product Reference No. | 159 |
| Product Name | Coil Tube (盘管) |
| Application Category | Marine Engineering → Seawater Systems → Ship Seawater Cooler |
| Operating Seawater Temperature | ≥ 30 °C (tropical and subtropical waters) |
| Design Seawater Flow Velocity | 2–3 m/s |
| Design Seawater Salinity | 30–40 g/L (standard oceanic conditions) |
| Material Options | CuNi 70/30 (C70600/C70700) or Duplex 2205 (S32205/S31803) |
| Outer Diameter (OD) Range | 12.7 mm – 25.4 mm (½" – 1") |
| Wall Thickness Range | 0.4 mm – 1.2 mm |
| Coil Diameter | 200 mm – 600 mm (configurable per vessel design) |
| Coil Length | Up to 50 m continuous coil |
| Surface Finish | Polished (Ra ≤ 0.8 μm) with anti-fouling treatment |
| Anti-Fouling Design | Specialized surface geometry / coating to inhibit marine organism attachment |
| End Forming | Flared, rolled, or brazed per customer specification |
| Applicable Standards | EN 12449, ASTM B151, ASTM B665, ISO 11907 |
| Design Life | ≥ 10 years in continuous seawater service |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
4. Manufacturing Process
4.1 Raw Material Preparation
Material sourcing follows strict mill certification protocols. CuNi 70/30 and Duplex 2205 stock is procured from certified mills with full chemical and mechanical property documentation. Incoming material undergoes positive material identification (PMI) via X-ray fluorescence (XRF) spectroscopy and chemical spot testing to verify alloy composition compliance.
4.2 Coil Forming
- Tube Straightening: Incoming straight tubes are fed through multi-roller straightening machines to achieve dimensional uniformity.
- Coil Winding: A precision CNC coil forming machine winds the tube into the specified helical geometry with controlled pitch and diameter. Forming forces are calibrated to prevent ovality exceeding ≤ 2% of OD.
- Welding (if segmented): Butt-weld joints (where applicable) are performed via orbital TIG (Tungsten Inert Gas) welding with argon backing gas, followed by 100% visual and dye penetrant inspection (DPI).
4.3 Surface Treatment & Anti-Fouling Design
The anti-marine organism attachment design is a critical differentiator for this product:
- Mechanical Surface Optimization: The internal bore surface is polished to a Ra ≤ 0.8 μm finish, reducing adhesion sites for biofilms, barnacles, and tube worms.
- Anti-Fouling Coating (Optional): A biocompatible, non-toxic anti-fouling coating may be applied internally to inhibit microbial colonization and biofilm formation, compliant with IMO (International Maritime Organization) environmental regulations.
- CuNi Alloy Inherent Protection: CuNi 70/30 releases trace copper ions into the seawater film, providing a natural biocidal effect that discourages biofouling attachment.
- Flow Velocity Optimization: The coil geometry is engineered to maintain a minimum internal flow velocity of 2 m/s, which mechanically inhibits organism settlement and adhesion.
4.4 End Forming & Assembly
Tube ends are formed according to the vessel manufacturer's specification — flared, rolled, or prepared for brazing. Brazing is performed using silver-bearing brazing alloys (e.g., BAg-5, BAg-7) in a controlled atmosphere to ensure leak-tight, corrosion-resistant joints compatible with seawater service.
4.5 Quality Control & Testing
- Dimensional Inspection: 100% inspection of OD, wall thickness, coil diameter, and pitch using calibrated micrometers, ultrasonic thickness gauges, and laser profilometers.
- Hydrostatic Pressure Testing: Each coil assembly is pressure-tested at 1.5× design pressure (typically 1.0–1.5 MPa for seawater systems) with zero leakage tolerance, held for a minimum of 30 seconds.
- Leak Testing: Helium leak detection or air pressure decay testing on all weld and brazed joints.
- Visual & Surface Inspection: 100% visual examination of all joints; dye penetrant testing (DPI) on critical welds.
- Material Verification: PMI (XRF) verification of final product alloy composition.
- Corrosion Testing (Sample-Based): Periodic salt spray testing (ASTM B117) and immersion testing in simulated seawater to validate corrosion resistance claims.
5. Applications
The Marine Seawater Cooler Coil Tube (Ref. No. 159) is deployed in the following marine engineering applications:
- Ship Main Engine Cooling: Seawater coolers for four-stroke and two-stroke marine diesel engines, where seawater absorbs waste heat from engine jacket water and lube oil circuits.
- Auxiliary Generator Cooling: Heat exchangers for auxiliary diesel generators and gas turbine generators powering onboard electrical systems.
- Turbocharger Cooling: Seawater-cooled intercoolers and aftercoolers for turbocharged marine engines.
- HVAC & Air Conditioning Systems: Seawater chillers for onboard climate control in passenger vessels, cruise ships, and offshore platforms.
- Offshore Platform Cooling: Seawater cooling loops for process equipment on oil and gas platforms, FPSOs (Floating Production Storage and Offloading), and FPSOs (Floating Production, Storage, and Offloading) units.
- Naval Vessel Systems: Seawater cooling circuits for military naval vessels requiring high-reliability, corrosion-resistant components.
- Subsea Equipment Cooling: Cooling circuits for subsea production systems and umbilical-managed equipment.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains the following quality and regulatory certifications for marine-grade coil tube production:
| Certification / Standard | Scope & Relevance |
|---|---|
| ISO 9001:2015 | Quality Management System — ensures consistent manufacturing quality and process control |
| ISO 14001:2015 | Environmental Management System — ensures environmentally responsible production practices |
| EN 12449 | Stainless steel tubes for heat exchangers — dimensional and material specifications |
| ASTM B151 | Standard specification for copper-nickel alloys (C70600/C70700) — material conformance |
| ASTM B665 | Standard specification for seamless wrought austenitic and duplex stainless steel tubes — material conformance for 2205 |
| ISO 11907 |