CuNi 90/10 & CuNi 70/30 Lap Joint Flanges — ASTM B151, ASME B16.5, ANSI, EN 1092-1. Class 150–600 | NPS ½" to 24". Used with CuNi Stub Ends.
A Copper Nickel Lap Joint Flange (CuNi LJ Flange) is used in conjunction with a CuNi stub end (lap joint fitting). The flange has a flat face with a bore large enough to slide freely over the pipe OD. It backs up against the stub end (which is welded to the pipe) and rotates freely around it — allowing the bolt holes to be aligned with the mating flange regardless of the rotational position of the pipe weld.
Sunflex Metalloy manufactures CuNi Lap Joint 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 EN 1092-1 Type 02 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.
The sealing integrity of a Lap Joint connection depends entirely on the stub end face quality and gasket selection. The backing flange only provides bolt-up clamping force. Stub ends must be manufactured to ASME B16.9 or MSS SP-43 with a smooth, flat face matching the gasket bore and OD.
| 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) |
The pipe and stub end (lap joint fitting) must be CuNi since these are the process-wetted components. The backing (lap joint) flange itself does not contact the process fluid — it sits behind the stub end. In many projects, carbon steel backing flanges are used behind CuNi stub ends for cost savings, especially in larger sizes. However, in seawater or corrosive external environments, CuNi backing flanges are preferred for total corrosion resistance. All-CuNi assemblies are specified for subsea and full immersion service.
A stub end (also called a lap joint fitting) is a short pipe nipple with a lap on one end — the lap has the same OD as the flange facing diameter and serves as the sealing surface. The stub end is butt-welded to the pipe, and the backing (Lap Joint) flange slides over the pipe before welding and backs up against the completed stub end lap. The gasket sits on the stub end face, and the flange provides clamping force when bolted up. CuNi stub ends are manufactured per ASME B16.9 / MSS SP-43.
CuNi Lap Joint Flanges are typically manufactured in Class 150 to Class 600. Higher pressure classes (Class 900 to 2500) use Weld Neck flanges due to strength requirements. Most seawater cooling systems, utility piping, and marine systems operate well within Class 150 to 300 ratings, making Lap Joint flanges fully suitable for these applications.
CuNi Lap Joint Flanges are suitable up to approximately 260°C service temperature in line with ASME B16.5 pressure-temperature ratings for CuNi Group 3.3. Above this temperature, or in high-cycle thermal service, the freely rotating interface between the stub end and backing flange can be a concern — Weld Neck flanges are preferred for high-temperature cyclic service.
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