1. Why copper nickel flanges are the highest-leverage line item on a seawater RFQ

A copper nickel flange rarely costs more than a few hundred US dollars per piece, yet it carries a disproportionate share of the corrosion risk on any seawater, desalination, shipboard, or offshore chemical-injection line. Get the grade wrong and the joint leaks inside the first dock-trial. Get the bolting wrong and the stud bolts disappear by the first dry-dock. Get the gasket wrong and the whole flange has to be re-torqued within six months. The economics of a copper nickel flange are not in the flange itself; they are in the system-level cost of avoiding these failures.

That is exactly why EEMUA (the UK Engineering Equipment and Materials Users' Association) published its copper-nickel piping series in 1987 and why those documents have remained the de-facto marine standard almost forty years later. EEMUA 144 covers tubes, EEMUA 145 covers flanges (composite and solid), EEMUA 146 covers pipe fittings, and EEMUA 234 covers the high-iron, high-manganese 66/30/2/2 variant used in naval and offshore pipework. Together, they form a single, self-consistent specification system that a shipyard, an offshore fabricator, or a coastal power plant can adopt without re-inventing the chemistry at every RFQ.

2. The two grades that pay for themselves: C70600 and C71500

There are two copper nickel alloy grades that dominate the B2B flange market, and the choice between them is the single most consequential decision on the RFQ.

C70600, also known as 90-10, CuNi90/10, B10, or BFe10-1-1, carries 9.0-11.0 % Ni, 1.0-1.8 % Fe, 0.5-1.0 % Mn, and the balance copper. It is the workhorse of seawater cooling, shipboard bilge and ballast, desalination intake, and chlorinated chemical loops. Thermal conductivity sits around 50 W/(m·K), which keeps flange faces from running hot, and the protective oxide film forms within hours of first exposure to clean seawater.

C71500, also known as 70-30, CuNi70/30, B30, or BFe30-1-1, carries 29.0-33.0 % Ni, 0.4-1.0 % Fe, and the balance copper. The extra nickel pushes the corrosion envelope up sharply in hot brine, high-velocity seawater, and chloride-bearing refinery cooling water. Thermal conductivity drops to roughly 29 W/(m·K), and the alloy costs 30-50 % more than C70600 because of the nickel content. C71500 is the right call on pump discharges above 3.5 m/s, refinery overhead condensers with brackish cooling water, and offshore platform pipework where sand and suspended solids are in the flow.

A third grade occasionally shows up in navy and offshore RFQs: BFe10-1.6-1, a modified B10 with iron pushed to 1.6 % and manganese around 1 %. The extra iron and manganese improve resistance to impingement attack in turbulent zones like pump discharges and elbow flanges, so BFe10-1.6-1 often appears in pipework immediately downstream of seawater lift pumps. The fourth variant, defined by EEMUA 234, is the 66/30/2/2 alloy with 30 % Ni, 2 % Fe, 2 % Mn — the standard naval Cu-Ni for surface ships and submarines, where the higher iron content protects against cavitation erosion.

3. EEMUA 145 vs ASME B16.5: the cross-reference every buyer needs

EEMUA 145 and ASME B16.5 describe two different worlds, but they are not in conflict. EEMUA 145 was written specifically for marine and offshore Cu-Ni 90/10 and 70/30 piping and includes the corrosion, bolting, and gasket guidance that ASME B16.5 (a dimensional standard for general-purpose flanges) deliberately leaves out. ASME B16.5 gives you the bolt circle, the bolt-hole count, and the facing dimensions; EEMUA 145 gives you the chemistry, the bolting materials, the gasket types, and the operating envelopes that those dimensions will actually see in seawater service.

The practical implication is that an EEMUA 145 flange is dimensionally interchangeable with an ASME B16.5 Class 150 flange of the same nominal size, provided the PCD (pitch circle diameter), the bolt-hole count, and the bolt-hole diameter all match. For DN15 to DN500, EEMUA 145 explicitly aligns to the BS 2871 Part 2: 1972 outside-diameter series, and the PCD was chosen to match ASME B16.5 Class 150. A buyer can therefore order a Cu-Ni weld-neck flange to EEMUA 145 and bolt it to a carbon-steel ASME B16.5 Class 150 flange on the connecting pipe spool without any dimensional adapter.

For Class 300 and PN 40 service, the picture is more nuanced. EEMUA 145 stops at Class 150 / PN 16 for Cu-Ni 90/10 and extends to PN 40 for Cu-Ni 70/30 in larger sizes, so a 300# Cu-Ni flange must be cross-checked against ASME B16.5 Class 300 or EN 1092-1 PN 40 dimensions on a case-by-case basis. EZ Steel Industrial maintains a working cross-reference table for this transition that the engineering team can share on request.

For a project that combines EEMUA, ASME, and GB/T deliverables — which is most international shipyards today — the safe practice is to dual-certify the flange to both EEMUA 145 (for chemistry, bolting, and corrosion) and ASME B16.5 (for the connecting pipe spool dimensions). EZ Steel Industrial routinely dual-certifies its Cu-Ni flange production to both standards on the same heat.

4. Composite vs solid Cu-Ni flanges: when to pick which

EEMUA 145 defines two flange constructions, and the choice between them is a question of service, schedule, and budget.

A composite Cu-Ni flange uses a carbon-steel or low-alloy-steel forging as the structural body, with a Cu-Ni 90/10 or 70/30 weld-overlay (cladding) on the gasket-sealing face and the hub-bore. The overlay is typically 3-5 mm thick and is deposited by hot-wire TIG or plasma-transfer arc. The structural body carries the bolt-load and pressure; the overlay carries the corrosion. Composite flanges are roughly 40-60 % cheaper than solid Cu-Ni flanges in sizes above DN100 because the body uses a cheaper base material.

A solid Cu-Ni flange is forged from a single Cu-Ni 90/10 or 70/30 billet. There is no cladding interface, no risk of overlay disbonding, and the entire cross-section resists corrosion. Solid flanges are mandatory in services where the overlay could be damaged — for example, in heat-exchanger channels where the gasket face sees repeated make-and-break cycles, or in sour-service modules where NACE MR0175 requires the wetted surface to be a single alloy.

A practical procurement rule: specify composite flanges for static seawater lines (cooling water, ballast, firewater) where the joint is made once and left alone. Specify solid flanges for heat-exchanger channels, pump suction and discharge headers, and any joint that will be broken and remade more than twice in the equipment life. EZ Steel Industrial's copper nickel flanges are produced in both constructions with the same EN 10204 3.1 certificate package.

5. Dimensional specification — the lines that should appear on every RFQ

Most RFQ failures on Cu-Ni flanges start with an incomplete dimensional line. A complete RFQ should call out, at minimum, the following items — and a complete mill quotation should mirror them.

Dimensional standard: ASME B16.5 (Class 150 or 300), EN 1092-1 (PN 16, PN 25, or PN 40), or GB/T 17241. Pressure class must match the connecting pipe on both sides of the joint; down-classing to save cost is the most common procurement mistake on Cu-Ni flanges and almost always results in a leakage event within the first hot cycle.

Material standard: ASTM B151 (rod and bar for solid flanges), ASTM B171 (plate for rolled-plate flanges), EEMUA 145 (composite and solid marine flanges), or EEMUA 234 for the 66/30/2/2 naval grade. EEMUA 145 should appear by name on the RFQ even if the project also references ASME B16.5; the chemistry, bolting, and quality requirements in EEMUA 145 are not duplicated in the ASME dimensional standard.

Facing type and finish: raised face (RF) is the default, with stock finish Ra 3.2-6.3 µm for spiral-wound or compressed non-asbestos gaskets. Flat face (FF), tongue-and-groove (TG), and male-female (MFM) are available on request. For FF, specify Ra 0.8-1.6 µm to seat a soft cut gasket without extrusion.

Quality and traceability: EN 10204 3.1 mill test certificate is non-negotiable for any seawater, desalination, or chemical service. The 3.1 certificate must list actual ladle chemistry, mechanical properties, the heat treatment chart, dimensional inspection results, NDT reports, and the hydrostatic test record. For classed vessels, add the class-society certificate line (ABS, DNV, LR, BV, RINA, CCS, KR).

6. Bolting the Cu-Ni joint — the EEMUA 145 decision tree

The bolting is where most Cu-Ni flange joints fail in service, and the EEMUA 145 / EEMUA 234 bolting rules are explicit because the failure mode is galvanic corrosion. A zinc-plated carbon-steel stud bolt on a Cu-Ni 90/10 flange in seawater will lose the zinc in months and then lose the steel in a year, leaving the joint to leak at the first thermal cycle.

EEMUA 145 Section 6.3 sets the rule: the bolt material must be electrochemically compatible with the flange, with a galvanic potential difference below 0.25 V in the operating electrolyte. The practical translation, used in shipyards from Korea to Norway, is the four-step decision tree below.

Step 1 — default for marine and offshore: ASTM A193 B8M (316 stainless) stud bolts with ASTM A194 8M (316 stainless) nuts. This is the workhorse bolting for Cu-Ni 90/10 and 70/30 flanges in seawater and brackish water, and is accepted by DNV, Lloyd's Register, Bureau Veritas, and CCS. Avoid B8 (304 stainless) in marine service — the chloride content of seawater will pitting-corrode 304 long before 316 shows any attack.

Step 2 — higher strength at Class 150 RF/FF: ASTM A193 B7 (quenched and tempered alloy steel) stud bolts with ASTM A194 2H nuts. This combination is acceptable at Class 150 RF and FF facings only and must not be used above Class 150 or above 200 °C. B7/2H is also the right call for Cu-Ni flanges in non-marine service where chloride exposure is low.

Step 3 — sour service and chloride-free chemistry: Monel 400 (N04400) stud bolts and nuts. Monel bolting matches the Cu-Ni flange potential almost exactly and is the default for refinery and chemical-plant service where chloride-induced bolt failure is a concern and budget allows the upgrade. The cost premium is roughly 5-8x over B7/2H and roughly 3-4x over B8M/8M.

Step 4 — what never to use: zinc-plated or hot-dip galvanized carbon-steel bolts. The zinc coating creates a large cathodic area relative to the Cu-Ni flange and dissolves rapidly, leaving the underlying steel to corrode. This is the single most common bolting failure on Cu-Ni flange joints and is almost always a procurement error rather than a metallurgical one.

Tightening follows ASME PCC-1 with the four-pass sequence (40 %, 60 %, 80 %, 100 % of target bolt stress) and a final 360-degree pass to equalise gasket seating. In seawater and Cl⁻-bearing service, retorque the joint within 6 months of first commissioning and again at the 12-month turnaround; Cu-Ni gaskets relax as the protective oxide film matures.

7. Gasket selection — matching the facing to the medium

Gasket choice is the third leg of the joint and the one most often under-specified on Cu-Ni flanges. The general rule: a Cu-Ni flange face (either solid Cu-Ni or weld-overlay) should be paired with a gasket whose metal wetted surface is no less noble than the flange face. A graphite-filled spiral-wound gasket with a 316 stainless inner ring is the default and works on virtually every Cu-Ni service. A carbon-steel inner ring is not acceptable because the carbon steel will corrode in seawater and contaminate the Cu-Ni face.

For Class 150 / PN 16 raised-face Cu-Ni flanges in seawater, firewater, or desalination, the standard gasket is a spiral-wound gasket with 316L stainless inner and outer rings and a graphite or non-asbestos filler (ASME B16.20). For Class 150 flat-face, use a soft-cut non-asbestos gasket (ASME B16.21) with a binder suitable for the operating temperature — aramid fibre for water service, graphite for higher temperatures.

For Class 300 / PN 40 and above, the spiral-wound gasket stays the workhorse, but the inner ring is upgraded to a higher nickel alloy (Monel 400 or alloy 825) where the chemistry demands it, and the outer ring may need to be PTFE-coated to prevent crevice corrosion in stagnant seawater pockets.

For Class 600 and above, ring-type joint (RTJ) gaskets are common on Cu-Ni flanges in refinery and high-pressure steam service. RTJ gaskets are metal-to-metal seals and require an RTJ groove on the flange face — the gasket cannot be retrofitted to a raised-face flange. The gasket material should match or exceed the flange material: soft iron (low carbon) for Cu-Ni 90/10, 304 stainless for Cu-Ni 70/30, Monel 400 for sour or chloride-critical service. EZ Steel Industrial's gasket, stud bolt and nut product line covers spiral-wound, soft-cut, ring-type joint, and Kammprofile gaskets in the full ASME / EN pressure-class range, all dual-certified to EN 10204 3.1.

8. Manufacturing route: why forged bar stock plus solution anneal is the only safe answer

The cheapest Cu-Ni flanges on the open market are cast — and the cheapest cast flanges are the most expensive Cu-Ni flanges a buyer will ever own. Cast Cu-Ni suffers from two problems: microporosity that acts as a corrosion initiation site in seawater, and a coarse grain structure that reduces impact toughness and fatigue life. Both failure modes appear as through-wall leaks within the first two to three years of service, exactly the timeline that falls outside most suppliers' warranty coverage.

The correct manufacturing route for a Cu-Ni flange that will live in seawater is hot forging plus solution annealing. Hot forging at 900-950 °C breaks up the as-cast structure and refines the grain, and solution annealing at the same temperature range followed by a water quench puts the alloy into a uniform single-phase condition. The forging is then finish-machined on CNC to bring the flange faces, bolt circle, and hub dimensions into ASME B16.5 or EN 1092-1 tolerance.

For large-diameter composite flanges (above DN600) where forging a single Cu-Ni billet becomes impractical, the alternative is rolled-plate flanges cut from ASTM B171 plate and weld-overlaid on the sealing face. The plate must be solution annealed after forming to restore the corrosion-resistant microstructure. This route is acceptable for EEMUA 145 service provided the overlay chemistry and thickness are documented on the MTC and verified by PMI (positive material identification) on the finished face.

EZ Steel Industrial's copper nickel flanges are produced by hot forging of C70600 and C71500 billets, solution annealed in a dedicated non-ferrous furnace line, and finish-machined on five-axis CNC. The mill runs the full inspection stack in-house: ladle chemistry, mechanical testing, ultrasonic testing per ASTM A388, hydrostatic testing at 1.5x design pressure, and dimensional CMM reporting.

9. Inspection and testing — what the MTC must contain

A Cu-Ni flange MTC under EN 10204 3.1 needs to be more than a one-page certificate. For EEMUA 145, ASTM B151, and ASTM B171 service, the MTC should include the items below, and a serious mill will produce all of them as a multi-page document keyed to the heat number stamped on the flange.

Chemistry: actual ladle analysis with Cu, Ni, Fe, Mn, plus impurity limits (Zn, Pb, S, C, P). The iron range is the most-fought-over number on the MTC — too low and the protective oxide film is weak, too high and the alloy loses ductility. For C70600, iron should sit between 1.0 % and 1.8 %; for C71500, between 0.4 % and 1.0 %.

Mechanical properties: tensile strength, yield strength at 0.5 % offset, and elongation. For C70600 in the annealed condition, expect tensile around 275-340 MPa, yield 105-125 MPa, elongation 30 % minimum. For C71500 annealed, tensile 360-490 MPa, yield 125-205 MPa, elongation 30 % minimum.

Heat-treatment record: solution anneal temperature, hold time, quench medium, and furnace chart trace. This is what proves the flange is in the correct metallurgical condition rather than a forged-and-shipped-without-heat-treat reject. EEMUA 145 calls for solution annealing at 900 ± 25 °C with a hold time sufficient to put the entire cross-section into the single-phase field, followed by a water quench rapid enough to suppress secondary-phase precipitation.

Dimensional inspection: actual measured values for outside diameter, bolt circle, number and size of bolt holes, flange thickness, hub length, and facing finish (Ra value).

Non-destructive testing: 100 % ultrasonic testing per ASTM A388 or equivalent, with calibration on a reference block of the same alloy. Any UT indication above the acceptance threshold is a reject. For composite flanges, the overlay bond is tested by shear ultrasonic or by magnetic particle on the machined face.

Pressure test: hydrostatic test at 1.5x the design pressure (or per the applicable code, whichever is higher), held for a minimum of 30 minutes with no leakage or pressure ｄｒｏｐ. For Cu-Ni service, hydrostatic is preferred over pneumatic because the higher thermal conductivity of the alloy makes any leak easier to detect with water than with gas.

Surface finish and cleanliness: pickling and passivation in an acid bath to remove forge scale and embedded iron, followed by a neutralisation rinse. Final surface should be free of iron contamination, verifiable with a ferroxyl test. Any iron contamination picked up after the passivation step — for example, from storage on a carbon-steel rack — is a reject.

10. Bundled sourcing — why the pipe, fittings, flanges and bolting should ship together

A Cu-Ni flange rarely stands alone. On a typical shipboard seawater cooling line, the flange is bolted to a Cu-Ni pipe spool (90/10 for general service, 70/30 for high-velocity sections), sealed with a spiral-wound gasket, and tightened with a matched stud bolt and nut set. Every one of these items carries its own MTC, and a class-society surveyor will reject the assembly if the documentation chain has gaps.

This is the real argument for mill-direct bundled sourcing. When the pipe, the fittings, the flanges, the gasket, the stud bolts, and the nuts all come from the same mill, the MTCs are cross-referenced to the same heat numbers, the class-society certificates are issued under the same audit trail, and the documentation package the surveyor receives is one consistent file. Distributor-sourced flanges paired with mill-direct pipe, on the other hand, fail surveyor reviews more often than not because the MTCs come from different manufacturers, different heat numbers, and different class-society audits.

The trade-off with mill-direct is order minimums and lead time. Most Cu-Ni flange mills require a minimum order value to justify a production run, and lead time for non-stock sizes runs 4-6 weeks. Buyers who can plan ahead and consolidate Cu-Ni pipe, fittings, flanges, gaskets, and bolting into a single mill-direct PO capture the largest savings and the cleanest documentation. EZ Steel Industrial operates a single non-ferrous line that produces all five product groups from the same billet inventory, with EN 10204 3.1 and class-society certificates cross-referenced automatically.

11. RFQ checklist — the seven questions to send every Cu-Ni flange mill

Before releasing a Cu-Ni flange RFQ, attach the following seven questions. The answers will quickly separate serious mills from trading companies and from distributors who buy to print and resell with no metallurgical control.

1. What material standards do you manufacture to — EEMUA 145, ASTM B151, ASTM B171, EEMUA 234, or a proprietary equivalent? Provide the standard number, the edition year, and the in-house specification reference.
2. What is the manufacturing route — forged bar stock plus solution anneal, rolled plate plus overlay, or cast? Request the heat-treatment chart for the most recent order in the same size and grade.
3. What inspection and testing does the standard MTC package include — chemistry, mechanical properties, UT, MT, hydrostatic, dimensional CMM? Ask for a sample MTC from a previous seawater-service order on the same heat.
4. Can you supply EN 10204 3.1 certificates and class-society certificates (ABS, DNV, LR, BV, CCS, RINA, KR) as required? Confirm which class societies are covered and whether the certificate is a witnessed test or a stamp-only acceptance.
5. What is the recommended bolting material for the requested service, and do you supply matched stud bolts and nuts to ASTM A193 B7, B8M, or Monel 400?
6. What is the lead time for a DN100 PN16 Class 150 C70600 weld-neck flange in standard quantities, and what is the minimum order quantity? A serious mill quotes lead time in weeks and MOQ in single pieces for stock sizes.
7. Can you bundle the Cu-Ni flange order with Cu-Ni pipe, butt-weld fittings, gaskets, stud bolts, and nuts on a single PO with cross-referenced MTCs? If not, the documentation burden stays on the buyer.

12. Frequently asked questions

Q1. Can I use a stainless-steel flange in seawater service instead of Cu-Ni?

For low-chloride, low-temperature service (potable water, mild brackish water), a 316L or super-duplex stainless flange can work. For true seawater with continuous chloride exposure, Cu-Ni is the more cost-effective answer because the corrosion rate is lower over a 20-year service life and the alloy is not subject to chloride pitting or crevice corrosion in the same way.

Q2. Is 90/10 always cheaper than 70/30?

Yes. The nickel content is the main cost driver, and 70/30 carries roughly three times the nickel of 90/10. The price premium is usually 30-50 % on the flange itself. The question is not whether 70/30 is more expensive, but whether the service conditions justify it.

Q3. Do I need a class-society certificate for non-marine Cu-Ni flanges?

No. Class-society certification is only required for flanges going onto classed vessels or offshore structures under class-society survey. For land-based chemical plants, refineries, and desalination plants, EN 10204 3.1 is sufficient.

Q4. Can Cu-Ni flanges be welded?

Yes, but the welding procedure must use a matched filler (CuNi 90/10 for C70600, CuNi 70/30 for C71500), and the weld area must be post-weld solution annealed to restore the protective oxide film. Most buyers avoid welding on Cu-Ni flanges and instead use slip-on, weld-neck, or socket-weld jointing to keep the welding off the flange itself.

Q5. What is the maximum service temperature for Cu-Ni flanges?

For C70600 the practical limit is around 300 °C continuous service. For C71500 the limit is similar, though the alloy retains strength slightly better at the upper end. Above 300 °C, the protective oxide film begins to break down and corrosion accelerates, and a different alloy (Monel 400, or austenitic stainless) becomes the correct choice.

Q6. How do I verify a Cu-Ni flange is genuine C70600 and not a substandard alloy?

A handheld XRF (X-ray fluorescence) analyser will read the copper and nickel content in seconds. Any mill-direct shipment should be tested on receipt, and any reading outside the ASTM B151 / EEMUA 145 envelope is a reject. Visual inspection is not sufficient because the surface colour of a Cu-Ni flange does not reliably distinguish C70600 from C71500 or from a yellow-brass substitute.

Q7. What is the standard PCD for an EEMUA 145 DN100 Class 150 flange?

DN100 (NPS 4) Class 150 PCD is 190.5 mm with 8 x M16 bolt holes. This is identical to the ASME B16.5 Class 150 NPS 4 PCD, which is the basis of the EEMUA 145 / ASME B16.5 interchange rule.

Q8. Are Cu-Ni flanges magnetic?

No. Both C70600 and C71500 are essentially non-magnetic in the annealed condition. This is sometimes used as a quick field check — a strongly magnetic flange claiming to be Cu-Ni is almost certainly a carbon or low-alloy steel substitute.