CuNi 70/30 (C71500) Stainless Steel Coil Tube
Product Overview
The CuNi 70/30 (UNS C71500) Coil Tube is a high-performance copper-nickel alloy tubing product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This alloy, composed of approximately 70% copper (Cu) and 30% nickel (Ni), is engineered to deliver superior corrosion resistance, mechanical strength, and durability in the most aggressive aqueous environments. The coil tube format offers significant advantages in processing efficiency, material utilization, and downstream fabrication flexibility compared to straight-length tubing alternatives.
This product represents a material upgrade from the more commonly specified CuNi 90/10 (C70600) alloy, providing enhanced performance characteristics that make it the preferred choice for high-velocity seawater systems, offshore platform infrastructure, and other demanding marine and industrial applications.
Material & Properties
Chemical Composition (UNS C71500 / CuNi 70/30)
- Nickel (Ni): 29.0% – 31.0%
- Copper (Cu): Balance (approximately 68.0% – 70.5%)
- Iron (Fe): ≤ 1.0%
- Zinc (Zn): ≤ 0.25%
- Lead (Pb): ≤ 0.05%
- Tin (Sn): ≤ 0.05%
- Carbon (C): ≤ 0.03%
Key Performance Characteristics
- Corrosion Resistance: Significantly superior to CuNi 90/10 in chloride-rich and high-flow seawater environments. Exhibits excellent resistance to crevice corrosion, pitting, and stress corrosion cracking (SCC).
- Mechanical Strength: Higher yield strength and tensile strength compared to the 90/10 variant, enabling thinner wall designs while maintaining structural integrity under elevated pressures.
- Erosion Resistance: Optimally suited for high-velocity fluid flow conditions where erosion-corrosion is a primary degradation mechanism.
- Biological Resistance: Natural fouling resistance inhibits marine organism attachment and growth on tube surfaces.
- Thermal Conductivity: Excellent heat transfer properties facilitate efficient thermal exchange in condensers, coolers, and heat exchangers.
- Weldability: Good weldability with appropriate filler metals and techniques, supporting field repair and fabrication.
- Temperature Range: Suitable for service temperatures up to 100°C (212°F) in seawater applications.
Specifications
| Parameter | Specification |
|---|---|
| Alloy Designation | UNS C71500 / CuNi 70/30 / CuNi30 |
| Product Form | Coil Tube (Continuous Coiled Tubing) |
| Outer Diameter (OD) | 6.35 mm – 101.6 mm (1/4" – 4") |
| Wall Thickness | 0.5 mm – 5.0 mm (0.020" – 0.197") |
| Coil Diameter | Standard: 1,200 mm – 2,400 mm (configurable) |
| Coil Length per Roll | 50 m – 300 m (customizable upon request) |
| Surface Finish | Mill Finish / Bright Annealed / Pickled & Passivated |
| Hardness (Annealed) | ≤ 90 HB (Brinell) |
| Hardness (Hard Drawn) | 90 – 140 HB |
| Tensile Strength (Annealed) | 310 – 450 MPa (45 – 65 ksi) |
| Yield Strength (0.2% Offset) | ≥ 145 MPa (21 ksi) |
| Elongation (Annealed) | ≥ 40% (in 50 mm / 2") |
| Density | 8.9 g/cm³ (0.322 lb/in³) |
| Electrical Resistivity | 6.8 × 10⁻⁶ Ω·cm (20°C) |
| Thermal Conductivity | 18 W/(m·K) (32°F) |
| Applicable Standards | ASTM B151 / B196 / B751; ASME SB151 / SB196; EN 12412; JIS H3602 |
| Delivery Condition | Annealed (M) or Cold Worked / Hard Drawn (Y) |
Manufacturing Process
The production of CuNi 70/30 Coil Tube at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorously controlled multi-stage manufacturing sequence:
- Raw Material Sourcing & Ingot Casting: High-purity copper and nickel feedstocks are verified through spectroscopic analysis. Ingot casting is performed under vacuum or argon atmosphere to minimize oxide inclusions and ensure compositional homogeneity.
- Hot Extrusion: Preheated billets are extruded through precision dies to produce seamless tube blanks with the desired outer diameter and wall thickness ratios. This process ensures uniform microstructure and absence of weld seams.
- Piercing & Sizing: The extruded blanks undergo piercing to form hollow tubing, followed by sizing operations to achieve dimensional tolerances within ±0.05 mm.
- Cold Drawing & Coiling: Tubes are cold-drawn through progressively reducing dies to achieve final dimensions and mechanical properties. The continuous coiling process is performed on precision coiling equipment that maintains uniform bend radius and prevents surface damage.
- Solution Annealing: Tubes are solution-annealed at 750°C – 800°C followed by controlled cooling to relieve residual stresses, restore ductility, and achieve a uniform, strain-free microstructure.
- Pickling & Passivation: Surface treatment involves acid pickling to remove oxide scale and contamination, followed by passivation to establish a protective surface film.
- Hydrostatic & Non-Destructive Testing: Every coil is subjected to hydrostatic pressure testing (typically 1.5× working pressure) and ultrasonic inspection to verify wall integrity and absence of internal defects.
- Dimensional Verification & Coiling: Final dimensional checks confirm compliance with specified tolerances before controlled coiling, bundling, and protective packaging.
Applications
Primary Application Areas
- High-Velocity Seawater Systems: The defining application domain for CuNi 70/30. Superior erosion-corrosion resistance makes this alloy the material of choice for seawater intake systems, cooling water circuits, and heat exchangers operating at flow velocities exceeding 2.5 m/s.
- Offshore Platform Infrastructure: Integral components in offshore oil and gas platforms, including production water cooling systems, process condensers, and thermal management circuits exposed to continuous seawater immersion.
- Marine Propulsion Systems: Used in shipboard cooling systems, sea chests, and auxiliary heat exchangers where long service life and minimal maintenance are critical.
- Power Generation: Condenser tubing in coastal power plants, nuclear facilities, and thermal power stations utilizing seawater as a cooling medium.
- Chemical Processing: Heat exchangers and process piping in chemical plants handling non-oxidizing acids and reducing environments.
- Desalination Plants: Tubing for evaporators, condensers, and preheaters in multi-stage flash (MSF) and reverse osmosis (RO) desalination facilities.
- Desalination & Water Treatment: Components in brackish water treatment systems and industrial water recycling installations.
Comparative Advantage Over CuNi 90/10
| Performance Parameter | CuNi 90/10 (C70600) | CuNi 70/30 (C71500) | Advantage |
|---|---|---|---|
| Corrosion Resistance in Seawater | Good | Excellent | Significantly superior |
| Maximum Recommended Flow Velocity | ≤ 2.5 m/s | ≤ 4.0 m/s | ~60% increase |
| Tensile Strength | ~310 MPa | ~350 MPa | ~13% higher |
| Service Life in Aggressive Environments | 10–15 years | 20–30+ years | Doubled service life |
| Resistance to Erosion-Corrosion | Moderate | Excellent | Substantially improved |
Quality Certifications & Compliance
- Manufacturing Certification: ISO 9001:2015 Quality Management System certified production facility.
- Material Standards Compliance: ASTM B151 (Seamless Copper-Nickel Alloy Tubes for Heat Exchangers); ASTM B196 (Seamless Copper-Nickel Alloy Tubes for Condenser and Heat Exchanger Service); ASME SB151 / SB196.
- European Standards: EN 12412 (Copper and copper alloys – Seamless tubes for heat exchangers and heat transfer purposes).
- Japanese Standards: JIS H3602 (Copper and copper alloys – Seamless tubes for heat exchangers).
- Offshore Industry Compliance: DNV-GL certified for offshore platform applications; NORSOK M-501 compliant.
- Testing & Inspection: 100% hydrostatic testing; ultrasonic flaw detection (UT); dimensional measurement verification per ASTM E1526.
- Material Traceability: Full mill test certificates (MTC) provided per EN 10204 Type 3.1; heat-number traceability from raw material through final product.
- Environmental Compliance: RoHS compliant; REACH compliant; free of restricted hazardous substances.
Unique Selling Points
Performance Superiority: The CuNi 70/30 alloy provides demonstrably enhanced corrosion resistance and mechanical strength compared to the conventional CuNi 90/10 alloy, translating into extended asset life and reduced total cost of ownership (TCO) in demanding marine environments.
Coil Format Efficiency: Continuous coil tube eliminates field butt-welding requirements, reducing installation time by up to 40%, minimizing leak points, and enabling rapid deployment in offshore and remote locations.
Cost-Effective Solution: While the material cost per unit weight is higher than CuNi 90/10, the extended service life, reduced maintenance frequency, and elimination of unplanned shutdowns provide a compelling economic advantage over the product lifecycle.
Proven Track Record: CuNi 70/30 has a decades-long history of reliable performance in offshore platforms, naval applications, and marine engineering worldwide, validating its suitability for critical infrastructure.