CuNi 90/10 & CuNi 70/30 Slip-On Flanges — ASTM B151, ASME B16.5, ANSI, DIN 2576, EN 1092-1. Class 150–600 | NPS ½" to 24".
A Copper Nickel Slip-On Flange (CuNi SO Flange) is a forged flange with a bore slightly larger than the pipe OD, allowing the pipe to "slip" into the flange bore before welding. It is fillet-welded both inside and outside to provide strength and prevent leakage. CuNi Slip-On Flanges offer a cost-effective solution for marine, offshore, and seawater piping systems where full penetration butt welds (weld neck) are not mandated.
Sunflex Metalloy manufactures CuNi Slip-On Flanges in CuNi 90/10 (UNS C70600) and CuNi 70/30 (UNS C71500) per ASTM B151, conforming to ASME B16.5, ANSI B16.5, DIN 2576, and EN 1092-1 Type 01 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.
Slip-On flanges are typically limited to Class 150–600 service. For higher pressure classes (Class 900 and above), Weld Neck Flanges are strongly recommended. The weld joint for SO flanges is not readily inspectable by radiography.
| 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 Slip-On Flanges per ASME B16.5 are commonly specified for Class 150 to Class 600 service. While the standard technically allows SO flanges in higher classes, Class 900 and above service almost always specifies Weld Neck flanges due to fatigue and stress concentration considerations. For seawater service at moderate pressures (up to ~100 bar), SO flanges are fully suitable.
The double fillet weld of Slip-On flanges is not as amenable to radiographic examination as the butt weld of Weld Neck flanges. ASME B31.3 Code allows fillet welds in certain service categories, but critical high-pressure or high-temperature applications typically require the full-penetration butt weld of Weld Neck flanges for RT inspection. DPT (Dye Penetrant) examination of the fillet welds is standard practice for CuNi SO flanges.
Per ASME B16.5, the bore of a Slip-On flange must be sized to the pipe OD being used. The bore is typically furnished to match Schedule 10S to Schedule 80 pipe OD per ASTM B466 (CuNi seamless tube/pipe dimensions). Sunflex Metalloy can supply SO flanges bored to match any specified CuNi pipe schedule.
Yes — CuNi Slip-On Flanges are extensively used in seawater service systems on ships, offshore platforms, and coastal plants. The CuNi 90/10 grade is the industry standard for seawater piping per NORSOK MDS C-600, IMO guidelines, and naval specifications. The double fillet weld joint provides a reliable, corrosion-resistant connection that performs excellently in seawater cooling and utility circuits.
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