Copper Nickel Flanges and the Bolting & Gasket That Seal Them: EEMUA 145 / ASME B16.5 Compatibility, Galvanic Pitfalls, and a One-PO Bundled Sourcing Playbook for Marine and Offshore Piping

1. What "copper nickel flanges" actually covers in marine and offshore procurement

In a marine-classed procurement file, "copper nickel flange" is a functional bucket that covers at least three sub-categories, each with its own UNS number, manufacturing route, and selection logic. EZ Steel Industrial groups them under a single Cu-Ni line so the buyer can pull the flange, the tube, the bolt, the nut, the gasket, and the matching 90/10 or 70/30 backing ring from one MTC chain:

1.1 EEMUA 145 Composite Flanges (Steel Body + Cu-Ni Facing)

An EEMUA 145 composite flange is a carbon steel or austenitic stainless-steel flange body, machined to the ASME B16.5 Class 150 or PN 16 outer dimensions, with the gasket face and the bore weld-overlaid or roll-bonded with a 3–6 mm layer of UNS C70600 (90/10) or C71500 (70/30) copper-nickel alloy. The composite route is the cost-effective default for sizes DN50 and above, where a solid Cu-Ni forging becomes prohibitively expensive. The composite route also lets the procurement team standardise the bolt circle and the outside diameter on ASME B16.5 — a copper-nickel composite flange marked "EEMUA 145 / ASME B16.5 Class 150" is dimensionally interchangeable with a carbon steel ASME B16.5 Class 150 weld-neck flange of the same nominal size. That interchangeability is the single most important procurement fact in this guide; it is the reason a shipyard can keep one flange drawing instead of two.

1.2 EEMUA 145 Solid Flanges (Forged UNS C70600 / C71500)

A solid Cu-Ni flange is forged from a single billet of UNS C70600 (90/10) or UNS C71500 (70/30) and machined to the same EEMUA 145 / ASME B16.5 Class 150 envelope. Solid Cu-Ni flanges are specified for sour hydrocarbon service, refinery overhead condensing, and any line where a wetted face cannot tolerate a steel substrate showing through at any point during the design life. The cost premium over a composite flange is meaningful (typically 3× to 6× at DN100) but the metallurgical guarantee is total. Solid flanges also tolerate the EEMUA 145 weld-repair procedure without exposing a steel substrate, which makes them the default for offshore classed service where the surveyor's pencil matters more than the procurement budget.

1.3 Cu-Ni Backing Rings, Backing Flanges, and Companion Flanges

A backing ring is a flat steel or Cu-Ni ring slipped behind a lap-joint or loose Cu-Ni flange to provide the bolt-clamping surface; it does not contact the service fluid. Backing flanges (also called "companion flanges" in some catalogues) are the drilled-and-tapped steel flanges that carry the bolt load while the Cu-Ni stub or lap carries the corrosion duty. The EEMUA 145 / ASME B16.5 Class 150 PCD is identical for the Cu-Ni stub and the steel backing, so the bolt, the nut, and the gasket are all shared components. This is the procurement-friendly detail that allows a single stud-bolt specification to cover both the corrosion-alloy and the structural-alloy joints on the same drawing.

2. EEMUA 145 vs ASME B16.5: how the PCD compatibility actually works

EEMUA 145 was written in 1987 by the Engineering Equipment and Materials Users' Association as the marine counterpart to ASME B16.5. The two documents were deliberately aligned on the four dimensions that matter for flange interchangeability: outside diameter, PCD (pitch circle diameter), number of bolt holes, and bolt-hole diameter. The flange thickness, the gasket face finish (RF — raised face — 1.6 mm to 2.0 mm serration), and the hub dimensions are also harmonised within practical tolerance. The result is that an EEMUA 145 DN100 Class 150 flange and an ASME B16.5 NPS 4 Class 150 flange share the same 190.5 mm OD, the same 149.2 mm PCD, the same 8-hole pattern, and the same 19.1 mm (3/4 in) bolt-hole diameter. A gasket cut to ASME B16.21 for NPS 4 Class 150 RF seats on the EEMUA 145 flange; a stud bolt threaded 3/4-10 UNC (the ASME B16.5 default) threads into either flange without modification.

A second compatibility layer is the pressure-temperature rating. EEMUA 145 publishes 16 bar at 50 °C for 90/10 and 70/30 Cu-Ni flanges from DN15 to DN500; ASME B16.5 publishes Class 150 = 19.6 bar at 38 °C, falling to 13.8 bar at 200 °C, for the same envelope. At 50 °C the two are within ~22 % of each other; at 100 °C the gap narrows to under 10 %. The conservative procurement practice is to mark the line "EEMUA 145 / ASME B16.5 Class 150" on the isometric and to use the lower of the two pressure envelopes for the design check. This is exactly how a shipyard operating under DNV, LR, BV, ABS, or CCS rule can accept both specifications on the same line.

3. The Cu-Ni 90/10 vs 70/30 decision and what it means for the bolt, the nut, and the gasket

Cu-Ni 90/10 (UNS C70600, CuNi10Fe1Mn) is the workhorse marine alloy — ~10 % nickel, 1–2 % iron, 0.5–1 % manganese. It is specified for shipbilge, firefighting main, seawater cooling, HVAC heat-exchanger tubing, and port-service tugboat ballast lines. Cu-Ni 70/30 (UNS C71500, CuNi30Fe1Mn) is the higher-nickel upgrade for higher-velocity seawater (≥ 2.5 m/s), for refinery overhead condensing, and for any service where the iron-content in the 90/10 alloy is insufficient to form a stable protective film. The 70/30 alloy is roughly 50 % more expensive per kilogram and is harder to forge, so most shipyards keep it in reserve for the high-velocity, high-corrosion circuits.

3.1 Bolting material by alloy selection

EEMUA 145 §6.3 and the marine-class practice (DNV, LR, BV) recommend austenitic stainless steel stud bolts and nuts for both Cu-Ni 90/10 and 70/30 flanges. The default is ASTM A193 Grade B8M (316 stainless) bolts with ASTM A194 Grade 8M (316 stainless) heavy hex nuts. The Class 2 fit of the A194 8M nut is required (rather than Class 1) to prevent the nut from galling on the bolt thread during the four-pass torque-up. For sizes DN100 and above, A193 B8M Class 2 is also the practical choice because the torque required for a 3/4-10 UNC bolt is large enough that a Class 1 nut may strip.

For Cu-Ni 70/30 in refinery sour service, the bolting can be upgraded to ASTM A193 Grade B7 (Cr-Mo alloy steel) with ASTM A194 Grade 2H nuts, but only when the design temperature exceeds 200 °C and the operating pressure approaches the Class 150 limit. The risk of using B7 + 2H on a Cu-Ni flange in ambient seawater is the galvanic mismatch: the bare B7 surface is a different electrochemical potential than the C71500 face, and any electrolyte (seawater splash, condensate) will drive a small but continuous galvanic current. In practice, shipyards avoid B7 + 2H on Cu-Ni flanges altogether; the cost savings on the bolt do not justify the corrosion-monitoring burden on the inspector.

3.2 Gasket material by alloy selection

For Cu-Ni 90/10 Class 150 RF service in seawater and firefighting water at temperatures up to 95 °C, the default gasket is a soft-cut non-asbestos compressed fibre sheet (CFS) cut to ASME B16.21, 1.5 mm thick, with aramid fibre and NBR binder. The CFS is inexpensive, the cutting tolerance is forgiving, and the procurement file is short. The next step up is a flexible graphite sheet with stainless steel foil ｉｎｓｅｒｔ — preferred for steam at 150–200 °C and for any line that sees thermal cycling.

For Cu-Ni 70/30 in refinery condensing or in high-velocity seawater (≥ 2.5 m/s), the gasket is upgraded to a spiral-wound gasket to ASME B16.20 with an outer ring (carbon steel or 316 SS) and an inner ring (316 SS or Monel 400). The inner ring prevents the winding from being eroded by the high-velocity flow; the outer ring acts as a centring guide and a compression stop. A spiral-wound gasket is the right answer whenever the line pressure approaches 10 bar or the operating temperature exceeds 150 °C.

For Class 300 / PN 40 service (which is uncommon on Cu-Ni marine lines but does occur in refinery and offshore-package use), the gasket is a spiral-wound with graphite filler or a kammprofile (camprofile) with graphite facing. RTJ (ring-type joint) is not normally specified on Cu-Ni flanges because the Cu-Ni material is not hard enough to bite into the RTJ groove without permanent deformation of the gasket face; a kammprofile gives the high-pressure sealing without that risk.

4. The stud-bolt length calculation that shipyard fitters keep getting wrong

The most common reason a Cu-Ni flanged joint leaks in service is not the gasket selection — it is the stud-bolt length. A bolt that is too short does not engage enough nut threads; a bolt that is too long bottoms out on the nut face before the joint is tight. EEMUA 145 §6.4 follows ASME B16.5 in publishing a Table that gives the stud-bolt length for each nominal size and class, but the table assumes the standard flange thickness and the standard nut thickness. If the procurement file has a raised-face weld overlay 3 mm thicker than the standard, the bolt must be 3 mm longer; if a backing flange is fitted behind a Cu-Ni stub flange, the bolt must be longer by the thickness of the backing ring.

A practical rule of thumb for EEMUA 145 / ASME B16.5 Class 150 RF with two solid flanges of the same size:

• Bolt length = 2 × flange thickness + gasket thickness + 1.5 × nut thickness + 3 mm clearance
• Flange thickness per ASME B16.5 Table 2 (or EEMUA 145 Annex B for Cu-Ni specific)
• Gasket thickness: 1.5 mm for CFS, 4.5 mm for spiral-wound with rings
• Nut thickness: ASTM A194 8M heavy hex, per ASME B18.2.2

The 3 mm clearance is the gap that allows the nut to be tightened without bottoming on the bolt thread. The fitter should be able to see at least one to two threads protruding past the top of the nut after torque-up. If the threads are flush with the top of the nut, the bolt is too short; if more than 6 mm of thread protrudes, the bolt is too long and a shorter bolt should be fitted before the next torque pass.

5. ASME PCC-1 bolt-up: the four-pass method for a Cu-Ni joint

The Cu-Ni flange and the Cu-Ni tube are ductile; the 316 SS bolt and the 316 SS nut are elastic. The gasket — whether CFS or spiral-wound — has a nonlinear stress-strain curve and a permanent deformation under sustained load. The combination of a ductile flange and a compressible gasket means the bolt-up cannot be done in a single pass. ASME PCC-1 (Guidelines for Pressure Boundary Bolted Flange Joint Assembly) defines four tightening methods: manual, torque, tension, and stretch. For shipyard Cu-Ni flanges, the torque method is the practical default because it requires only a calibrated torque wrench — a tool that every shipyard fitter has on the bench.

The four-pass sequence is:

• Pass 1 — 40 % of target torque. Hand-snug all bolts, then torque each to 40 % of the calculated target in a star (four-way cross) pattern. The pass seats the gasket and verifies that the flanges are parallel.
• Pass 2 — 60 % of target torque. Same star pattern, 60 % target. The gasket is now at 80 % of its design seating stress.
• Pass 3 — 100 % of target torque. Final design stress on the gasket.
• Pass 4 — 100 % of target torque, clockwise pattern. Verification pass. The clockwise (rather than star) pattern checks for any bolt that was over-torqued in the first three passes and is now storing a higher load than the rest of the bolt circle.

For Cu-Ni flanges in seawater service, an additional pass is recommended 24 hours after the joint is first put into service. The 24-hour pass re-torques to 100 % target and compensates for the gasket stress relaxation that occurs as the gasket reaches its steady-state creep. The class surveyor (LR, DNV, BV, ABS, CCS) will witness the 24-hour pass and stamp the joint book.

6. Composite Cu-Ni flange vs solid Cu-Ni flange: cost, life, and when to specify which

A composite Cu-Ni flange (steel body + Cu-Ni weld overlay) is the cost-effective default for the typical shipyard Cu-Ni Class 150 line. A solid Cu-Ni flange is the metallurgical default for high-integrity service. The cost gap between the two is meaningful but it is not the only variable. The procurement decision should weigh four factors: the design life, the inspection regime, the fluid corrosivity, and the surveyor's preference.

A common procurement mistake is to specify composite Cu-Ni flanges for a refinery Cu-Ni 70/30 condensing service. The overlay is more than capable of carrying the corrosion duty in steady-state service, but the refinery environment is not steady-state — thermal cycling between 50 °C and 200 °C, the occasional H₂S excursion, the periodic chemical cleaning pass. Each of those events is a stress on the overlay bond. A solid Cu-Ni flange removes the overlay from the failure equation. The same logic applies to naval frigate and submarine seawater systems, where the design life is 30 years and the survey regime is annual.

7. The single-PO bundled sourcing model: how a mill-direct supplier ties Cu-Ni flanges, bolting, and gaskets together

The traditional marine procurement file sources the Cu-Ni tubes, the Cu-Ni flanges, the stud bolts, the nuts, and the gaskets from four or five separate vendors. Each vendor issues its own MTC, its own commercial invoice, and its own material certificate. The class surveyor then has to reconcile four MTCs into a single joint book, and the procurement officer has to chase five different PO numbers, five different delivery dates, and five different payment milestones. The risk is not in the components — each component is fine on its own — but in the integration. A bolt that arrives two weeks before the gasket creates a storage problem; a flange that arrives with a 3.1 certificate when the class surveyor wants a 3.2 creates a paperwork problem; a tube that arrives with a different heat number from the flange creates a traceability problem.

A mill-direct bundled model — exemplified by EZ Steel Industrial's marine Cu-Ni package — collapses all five line items into a single PO, a single MTC chain, a single heat number, and a single PIQ (Product Inspection and Quality plan). The Cu-Ni 90/10 tube (EEMUA 144 or ASTM B466) is drawn from the same heat that the Cu-Ni 90/10 flange (EEMUA 145) is forged from. The 316 SS stud bolts (ASTM A193 B8M Class 2) and the 316 SS heavy hex nuts (ASTM A194 8M) are pulled from a single bolt order and matched to the flange PCD by the supplier's engineering team. The spiral-wound gaskets (ASME B16.20 with 316 SS inner ring and carbon steel outer ring) are cut to the same NPS as the flanges, packed in the same crate, and shipped with the flange MTC as a single cover document.

The class surveyor sees one MTC file, not five. The procurement officer sees one PO, one delivery, one invoice. The shipyard fitter opens one crate at the bench, not five. The cost saving is not in the unit price of any one component — it is in the integration. A typical bundled marine Cu-Ni package saves 8–15 % on the total delivered cost of the assembled joint compared with the same components bought separately, and it cuts the procurement lead time by 4–6 weeks.

8. Class society paperwork: EN 10204 3.1 vs 3.2, and the LR/DNV/BV/ABS/CCS file

The class surveyor does not sign off on the material — the material is the supplier's responsibility. The class surveyor signs off on the documentation that proves the material. The documentation is built on EN 10204, the European standard that defines four types of material certificate: 2.1 (declaration of compliance with the order), 2.2 (test report), 3.1 (independent test report issued by the mill's own QC department, with the mill's authorized signatory), and 3.2 (independent test report issued by a third-party inspector, usually a classification society surveyor or an IACS-accredited body). For Cu-Ni marine and offshore service, the minimum is 3.1; for any line that carries a class-required test (hydrostatic, NDT, PMI), the surveyor will want 3.2.

• 3.1 certificate contents: chemical composition, mechanical properties (tensile, yield, elongation, hardness), heat treatment condition, NDT results (where applicable), dimensional inspection, MTC traceable to the heat number.
• 3.2 certificate contents: same as 3.1, but signed by both the mill's authorized signatory and an independent third-party inspector. The third party may be the class surveyor (LR, DNV, BV, ABS, CCS) or an IACS-accredited body such as TÜV, Bureau Veritas, or SGS.
• For Cu-Ni composite flanges: the 3.1 certificate must additionally state the overlay alloy (UNS C70600 or C71500), the overlay thickness (typically 3–6 mm), the overlay process (weld overlay, roll bond, or explosive bond), and the overlay integrity test (typically 100 % dye-penetrant or ultrasonic).
• For stud bolts and nuts: the 3.1 certificate must state the ASTM grade (A193 B8M Class 2, A194 8M heavy hex), the heat treatment condition (solution annealed for B8M, hot-worked for 2H), the thread class (ASME B1.1 2A for bolts, 2B for nuts), and the mechanical test results (tensile, hardness, stress rupture where applicable).

9. Five procurement mistakes that class surveyors flag every quarter

Across several hundred Cu-Ni flange RFQs reviewed for class-society buyers over the past three years, the same five mistakes show up over and over. Each one is fixable in the RFQ, before the PO is issued.

9.1 Specifying the flange standard without the gasket standard

An RFQ that calls for EEMUA 145 / ASME B16.5 Class 150 flanges but does not call out ASME B16.21 (for soft-cut) or ASME B16.20 (for spiral-wound) leaves the gasket choice to the supplier. The supplier will pick a generic compressed fibre, the gasket OD may be 2 mm off the flange RF dimension, and the joint will not seal at design pressure. The RFQ must name the gasket standard and the gasket type in the same line as the flange.

9.2 Specifying the stud-bolt material without the nut grade

An RFQ that calls for ASTM A193 B8M bolts without specifying ASTM A194 8M heavy hex Class 2 nuts will receive a mix of Class 1 and Class 2 nuts. Class 1 nuts will strip on the first torque pass; Class 2 nuts will survive. The RFQ must call out both the bolt grade and the nut grade, and the nut class.

9.3 Specifying Cu-Ni 90/10 overlay without specifying the overlay thickness

A composite Cu-Ni flange RFQ that says "C70600 overlay" without specifying the overlay thickness will receive a 2 mm overlay from one supplier and a 5 mm overlay from another. The 2 mm overlay is borderline for design life in high-velocity seawater; the 5 mm overlay is the marine default. The RFQ should specify "minimum 3 mm C70600 overlay, weld-deposited, 100 % dye-penetrant tested".

9.4 Specifying EEMUA 144 tubes with ASME B16.5 Class 150 flanges without verifying the PCD

EEMUA 144 tubes are sized to the metric DN system, ASME B16.5 flanges are sized to the NPS system. The two systems align on the four interchangeability dimensions for sizes DN15 to DN500, but they diverge at the larger sizes. The RFQ should explicitly state "EEMUA 144 / ASME B16.5 Class 150 interchangeable envelope" and reference the cross-reference table in EEMUA 145 Annex A.

9.5 Issuing a class-society RFQ without naming the class society

A class-society RFQ that does not name the class (LR, DNV, BV, ABS, CCS) will receive a commercial-grade MTC. The supplier cannot issue a 3.2 certificate for a class that was not declared. The RFQ should name the class and the surveyor's role (3.2 witnessing vs. 3.1 acceptance).

10. Frequently asked questions from marine and offshore buyers