What material grades are available for copper nickel flanges?

Choosing the right material grade is the single most important decision when you specify copper nickel flanges for a piping system. The grade controls corrosion resistance, mechanical strength, allowable velocity in seawater, weldability, and ultimately the service life of the joint. The wrong grade can mean premature pitting, erosion at the flange face, or a costly retrofit during commissioning. This guide walks you through the UNS designations, ASTM/ASME references, and selection logic used by EPC engineers, shipyards, and desalination plant operators.

What Is a Copper Nickel Flange?

A copper nickel flange is a forged or wrought pipe flange made from a copper-nickel alloy, a family of materials in which nickel is the principal alloying element (typically 10%, 30%, or higher) with iron and manganese additions to improve corrosion and erosion resistance in seawater. Copper-nickel flanges are most commonly specified under the UNS designations C70600, C70620, C71500, C71520, and C71640, and they are manufactured to standards such as ASTM B151, B466, B564, ASME SB564, ASME B16.5, ASME B16.24, ASME B16.47, EN 1092-1, and EEMUA 145.

Because the material combines the thermal conductivity of copper with the corrosion resistance of nickel, copper-nickel flanges have become the default choice for shipbuilding, offshore platforms, desalination plants, power plant condensers, and naval seawater systems. The selection of the right grade, however, depends on the water chemistry, flow velocity, fabrication route (forged vs. cast), and the dimensional standard required by the project specification.

The Main UNS Grades Used for Copper Nickel Flanges

Below is a practical breakdown of the grades that appear most often on material test certificates and project data sheets.

C70600 — 90/10 Copper Nickel (Wrought)

C70600 contains roughly 90% copper, 10% nickel, plus 1–1.8% iron and up to 1% manganese. It is the most widely specified grade for general seawater service, firewater ring mains, ballast lines, and heat exchanger water boxes. C70600 flanges are typically produced from plate, bar, or forgings to ASME B16.5 dimensional tolerances and are accepted under EEMUA 145, DIN 86037, and most naval specifications. For a typical marine cooling line, C70600 handles seawater velocities up to about 3.5 m/s with excellent resistance to biofouling and general corrosion.

C70620 — 90/10 Copper Nickel (Forging Grade)

C70620 is the forging-grade counterpart of C70600. It has a tighter chemical composition (with stricter limits on lead and zinc) and is specifically intended for hot-forged components such as weld-neck flanges, ring-joint flanges, and valve bodies. When the project specification calls for ASME B16.5 weld-neck flanges in 90/10 Cu-Ni, C70620 is usually the correct UNS on the MTR rather than C70600. It carries the same seawater velocity limit and corrosion behavior as C70600.

C71500 — 70/30 Copper Nickel (Wrought)

C71500 contains about 70% copper and 30% nickel, with 0.4–1.0% iron and up to 1% manganese. The higher nickel content gives better resistance to high-velocity seawater, ammonia-bearing cooling water, and sour service. C71500 flanges are commonly used in naval combatants, offshore FPSOs, refinery overhead condensers, and any system where the design velocity exceeds the 3.5 m/s limit of 90/10. The mechanical strength is also higher, which allows thinner gasket seating and higher pressure classes without increasing the flange weight.

C71520 — 70/30 Copper Nickel (Forging Grade)

C71520 is the forging-grade version of C71500. It is the correct UNS for hot-forged 70/30 weld-neck flanges, blind flanges, and integral flange bodies. Specifications that reference ASME SB564 for nickel-copper alloy forgings almost always mean C71520 (or C96400 for cast) rather than C71500. Both C71500 and C71520 share the same corrosion envelope in service.

C71640 — Copper Nickel 30% with High Iron (CuNi30Fe2Mn2)

C71640 is the high-iron variant, with 1.5–2.5% iron. The extra iron dramatically improves resistance to impingement attack and erosion, which is why C71640 is often selected for condenser water-box covers, pump discharge flanges, and other high-velocity or sand-laden brine services. It is the grade to choose when the flow regime is turbulent and the chloride content is elevated, such as in multi-stage flash desalination.

C96200 and C96400 — Cast Copper Nickel

For large-diameter or non-standard flange geometries, cast grades come into play. C96200 is the cast equivalent of 90/10, and C96400 is the cast equivalent of 70/30. Cast flanges are produced to ASTM B584 or ASME B16.24 and are common in pump casings, valve bodies, and large seawater manifolds where forging would be uneconomical. Cast flanges have slightly lower mechanical strength than forged equivalents, so the pressure class may need to be derated.

Typical Chemical Composition Reference Table

UNS Grade	Cu	Ni	Fe	Mn	Form
C70600	Balance	9.0–11.0%	1.0–1.8%	≤ 1.0%	Wrought plate/bar
C70620	Balance	9.0–11.0%	1.0–1.8%	≤ 1.0%	Forgings
C71500	Balance	29.0–33.0%	0.4–1.0%	≤ 1.0%	Wrought plate/bar
C71520	Balance	29.0–33.0%	0.4–1.0%	≤ 1.0%	Forgings
C71640	Balance	29.0–33.0%	1.5–2.5%	1.5–2.5%	Wrought / tube
C96200	Balance	9.0–11.0%	1.0–1.8%	≤ 1.5%	Cast
C96400	Balance	28.0–32.0%	0.25–1.5%	≤ 1.5%	Cast

Values shown are typical ranges; the exact limits must be confirmed against the applicable ASTM, ASME, or EN standard referenced in the project specification.

How to ｓｅｌｅｃｔ the Right Grade for Your Project

A practical selection path looks like this. First, define the fluid and operating environment: clean seawater, brackish water, sand-laden brine, or chemical service. Second, calculate the maximum continuous flow velocity at the flange face. Third, confirm the pressure class and dimensional standard (ASME B16.5, B16.47, B16.24, EN 1092-1, or EEMUA 145). Fourth, decide whether the flange will be forged from bar or cast. Fifth, match the result to a UNS grade using the rules below.

For general marine & ship-building seawater systems with velocities under 3.5 m/s, C70600 plate flanges or C70620 forged weld-neck flanges are the most economical and widely accepted choice. For high-velocity service on naval combatants, FPSOs, or refinery overhead condensers, step up to C71500 or C71520. Where impingement or sandy brine is present, specify C71640. For very large diameters or non-standard geometries, consider cast C96200 or C96400 to keep machining and forging costs in check.

Matching Standards to Grades

ASTM B151 / B466 — Plate, bar, and seamless tube for 90/10 and 70/30 copper nickel.
ASTM B564 / ASME SB564 — Wrought nickel-copper alloy forgings (C70620, C71520).
ASME B16.5 / B16.47 — Pipe flanges in NPS ½ through 48, classes 150 to 2500.
ASME B16.24 — Cast copper alloy flanges, classes 150 to 600.
EN 1092-1 — European standard for circular flanges with PN designations.
EEMUA 145 / 234 — Specification for 90/10 and 70/30 copper-nickel pipework, including flanges.
DIN 86037 — German standard for 90/10 Cu-Ni flanges commonly used in shipyards.

Common Applications by Grade

C70600 and C70620 dominate shipbuilding seawater cooling, fire-fighting ring mains, and ballast lines because they balance cost, weldability, and proven in-service track records. C71500 and C71520 are found in naval combatants, offshore platforms, and refinery overhead systems where higher velocities and stricter corrosion margins are required. C71640 is specified for power plant condensers, MSF desalination plant reject brine sections, and pump discharge flanges where erosion and impingement are real risks. Cast C96200 and C96400 are used in large seawater manifolds, pump casings, and valve bodies on offshore platforms.

Why Buyers Pair Flanges with the Same-Grade Pipe and Fittings

Galvanic compatibility is the most overlooked reason to match the flange grade to the pipe and fittings. A 90/10 Cu-Ni flange welded to a 70/30 Cu-Ni pipe, or a copper-nickel flange mated to a carbon-steel fitting, creates a galvanic cell that accelerates corrosion at the less-noble side. Specifying the entire run in the same UNS family, and isolating the system from carbon steel with dielectric flanges or rubber gaskets, is the standard practice on commercial vessels and offshore platforms. This is why integrated project suppliers, such as EZ Steel Industrial, package the same material grade across pipes, fittings, flanges, and stud bolts to keep the corrosion cell balanced.

Quality Checks to Verify Before You Order

A few checkpoints separate a good copper-nickel flange supplier from a risky one. First, the mill test certificate should report the UNS designation, heat number, full chemical composition, mechanical properties, and hydrostatic or pneumatic test result. Second, dimensional inspection should reference ASME B16.5, B16.47, or EN 1092-1 as called out in the RFQ. Third, surface finish and bevel preparation should comply with ASME B16.5 paragraph on flange facing finish (typically 125–250 RMS for RF serrated finish). Fourth, packaging and marking must be suitable for export sea freight, including heat-number traceability on each flange.

Key Takeaways

The five most common UNS grades for copper-nickel flanges are C70600, C70620, C71500, C71520, and C71640, plus cast C96200 and C96400.
90/10 (C70600 / C70620) is the workhorse for general seawater service under 3.5 m/s; 70/30 (C71500 / C71520) handles higher velocities and ammonia-bearing service.
C71640 is the high-iron grade for erosion- and impingement-prone service such as condensers and pump discharges.
Cast grades (C96200, C96400) are used for large-diameter or non-standard geometries; wrought forging grades (C70620, C71520) are used for hot-forged weld-neck and blind flanges.
Always match the flange grade to the connected pipe and fittings, and verify the MTR against ASTM B151, B466, B564, ASME SB564, or the project-specific standard.

For more information on the full range of big diameter steel pipe and copper-nickel flange options, send your RFQ with operating temperature, pressure class, fluid, and dimensional standard to the EZ Steel Industrial engineering team.