CuNi 90/10 & CuNi 70/30 Threaded Flanges — ASTM B151, ASME B16.5, ANSI, DIN 2566. Class 150–2500 | NPS ½" to 4". No welding required.
A Copper Nickel Threaded Flange (CuNi Screwed Flange) has internal pipe threads (NPT — National Pipe Taper Thread per ASME B1.20.1) machined into the bore, allowing it to be screwed directly onto an externally threaded pipe without any welding. This makes it suitable for locations where welding is not permitted due to hazardous or flammable atmospheres.
Sunflex Metalloy manufactures CuNi Threaded Flanges in CuNi 90/10 (UNS C70600) and CuNi 70/30 (UNS C71500) per ASTM B151, conforming to ASME B16.5, ANSI B16.5, and DIN 2566 dimensional standards.
Ship seawater cooling circuits, air conditioning sea water lines
Ballast water systems, bilge, fire main and general service piping
Low-pressure intake and outfall piping, auxiliary seawater circuits
Utility seawater headers, non-critical process piping on platforms
Cooling water distribution headers in coastal power generation facilities
Jetty seawater supply systems, port utility piping installations
All CuNi flanges are forged from ASTM B151 billets, heat treated (annealed) to restore ductility per ASTM B151 requirements, then CNC machined to ASME B16.5 / B16.47 dimensional tolerances. Full quality records and heat treatment certificates accompany every delivery.
XRF-based Positive Material Identification per ASTM B151 for Cu, Ni, Fe, Mn chemistry verification on every heat number.
Shell hydrostatic testing at 1.5× rated pressure per ASME B16.5 / API 598 with hold time verification and certified results.
Volumetric UT per ASTM A388 / EN 10228-3 on all forgings to detect internal flaws before and after machining.
Surface DPT per ASME Section V / ASTM E165 on flange faces and bore after final machining operations.
100% dimensional check per ASME B16.5 / B16.47 tables using calibrated vernier, micrometers, and CMM instruments.
Tensile, yield, elongation, and Brinell hardness per ASTM B151 on test coupons from each production heat.
Threaded joints are not considered fully leak-proof without thread sealant compound (PTFE tape or anaerobic sealant). For high-pressure, high-temperature, or vibrating service, a seal weld is often added over the thread engagement area per ASME B31.3 to supplement the threaded connection.
| Property | CuNi 90/10 (C70600) | CuNi 70/30 (C71500) |
|---|---|---|
| Tensile Strength (UTS) | 275 MPa (40 ksi) min | 380 MPa (55 ksi) min |
| Yield Strength (0.2%) | 105 MPa (15 ksi) min | 170 MPa (25 ksi) min |
| Elongation (50 mm GL) | 30% minimum | 30% minimum |
| Brinell Hardness (HB) | ≤ 100 HB | ≤ 120 HB |
| Density | 8.94 g/cm³ | 8.94 g/cm³ |
| Modulus of Elasticity | 132 GPa | 152 GPa |
| Element | CuNi 90/10 (C70600) | CuNi 70/30 (C71500) |
|---|---|---|
| Copper (Cu) | Remainder (~88–90%) | Remainder (~65–70%) |
| Nickel (Ni) + Co | 9.0 – 11.0% | 29.0 – 33.0% |
| Iron (Fe) | 1.0 – 1.8% | 0.40 – 1.0% |
| Manganese (Mn) | 1.0% max | 1.0% max |
| Lead (Pb) | 0.02% max | 0.02% max |
| Zinc (Zn) | 0.50% max | 0.50% max |
| Carbon (C) | 0.05% max | 0.05% max |
| Sulfur (S) | 0.02% max | 0.02% max |
Every CuNi flange is manufactured with full heat traceability. Chemical composition is verified by OES (Optical Emission Spectrometry) on each heat and confirmed by XRF-based PMI prior to dispatch. MTC provided per EN 10204 3.1 (standard) or 3.2 (third-party witnessed) per project requirements.
| Standard | CuNi 90/10 Designation | CuNi 70/30 Designation |
|---|---|---|
| UNS (ASTM) | C70600 | C71500 |
| DIN / W.Nr. | CuNi10Fe1Mn / 2.0872 | CuNi30Mn1Fe / 2.0882 |
| EN (CW No.) | CW352H | CW354H |
| BS | CN102 | CN107 |
| MIL Spec | MIL-T-16420 (Comp B) | MIL-T-16420 (Comp A) |
| NORSOK MDS | C-600 (CuNi 90/10) | C-601 (CuNi 70/30) |
CuNi Threaded Flanges are used when: (1) Welding is not permitted due to hazardous atmosphere (Ex-Zone classification per IEC 60079); (2) The piping system requires frequent removal of flanges for maintenance; (3) The service is low-to-medium pressure where threaded joint integrity is proven sufficient; (4) Quick installation without welding equipment is required on remote sites or during commissioning. They are not recommended for high-temperature service above 260°C where differential thermal expansion can loosen threaded joints.
Standard CuNi Threaded Flanges per ASME B16.5 use NPT (National Pipe Taper Thread per ASME B1.20.1). For UK, Australian, Middle East, and offshore North Sea projects, BSPT (British Standard Pipe Taper Thread per BS 21 / ISO 7-1) is often specified. Sunflex Metalloy can supply both NPT and BSPT threaded CuNi flanges — the thread form must be specified at time of order.
Yes. ASME B31.3 allows and sometimes requires a seal weld to be applied over the threaded joint for additional leak tightness in certain service categories. For CuNi 90/10 and CuNi 70/30, seal welding is performed using ERCuNi filler wire. Seal-welded threaded flanges provide added security against leakage in vibrating or high-cycle service while retaining the threaded connection benefits.
Per ASME B16.5, CuNi Threaded Flanges are rated in all pressure classes from Class 150 to 2500. However, practical use of threaded flanges is typically limited to Class 150 to 600 for sustained pressure service. Class 900 and above threaded connections require very careful torquing and are often seal-welded for added confidence. The pressure-temperature rating chart per ASME B16.5 Table 2-1.1 (CuNi Group 3.3) applies.
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