1. Why Copper Nickel Alloy Is Still the Default for Seawater Service

Long before stainless steels were qualified for chlorides, the Cu-Ni family — primarily the 90/10 (UNS C70600) and 70/30 (UNS C71500) grades — was already performing in ship seawater piping, offshore platform cooling, and power plant condensers. The reasons have not changed: the alloys resist general corrosion, are highly tolerant to pitting and crevice attack in clean seawater, and — uniquely among common engineering metals — release copper ions that suppress biofouling. That second property alone saves operators the cost of biocide dosing and routine mechanical cleaning of intake lines.

For a procurement engineer, the practical takeaway is that 90/10 Cu-Ni (C70600, CW 352H, BFe10-1-1) covers the majority of shipboard and offshore seawater piping. 70/30 Cu-Ni (C71500, CW 354H, BFe30-1-1) is reserved for higher velocities, more aggressive service, and applications where the additional nickel content is required by specification. The chart below is the version we use internally to map these grades across the standards most often written into a datasheet.

2. Where the Project Bundle Usually Breaks Down

Most buyers correctly specify the tube. The breakdown happens when the rest of the system is sourced from a different supplier, on a different lead time, with different MTC discipline. The four risk points we see most often on real projects:

Velocity limits. 90/10 Cu-Ni is rated for continuous service up to about 3.5 m/s in clean seawater; 70/30 allows higher. Once you overshoot, erosion-corrosion strips the protective film and the wall loss accelerates. The valve or fitting that creates a local high-velocity zone can do this even when the line velocity is conservative.

Galvanic mismatch at the joint. Bolting a Cu-Ni flange directly to a steel flange without isolating gaskets and insulating sleeves will eat the Cu-Ni side. The same is true when industrial valves with steel trim are dropped into a Cu-Ni line.

Sulfide and stagnation. Seawater polluted with H₂S from a nearby source attacks Cu-Ni aggressively, especially under deposit or stagnation. The standard defense is ferrous sulfate dosing during commissioning — but the dosing regime is rarely written into the procurement spec.

Welding procedure mismatch. Cu-Ni welds need controlled heat input and matching filler (Cu-Ni 30 or 70, not stainless). When the welder on site is handed Cu-Ni pipe and stainless consumables because the consumables box "looked similar," the joint fails first.

3. Building the Datasheet Around the Bundle, Not the Tube

A robust Cu-Ni seawater datasheet has to carry four parallel sets of requirements, not one. The first set covers the copper nickel alloy tube and pipe itself: alloy designation, UNS number, standard (EEMUA 144/234, ASTM B466/B467, JIS H3300, GB/T26291, MIL-T-16420K, DIN 86019, BS 2871), temper, dimensional tolerances, and NDT scope. For a 90/10 marine line, EEMUA 234 is still the most complete reference; for power and desalination, EN 12451 is more common.

The second set covers the pipe fittings — elbows, tees, reducers, end caps. These should be Cu-Ni to the same UNS as the pipe, with butt-weld ends matching the pipe schedule. Mixing Cu-Ni pipe with steel fittings is a recurring source of failure, because the steel fitting becomes the sacrificial anode in the line.

The third set covers the pipe flanges. For Cu-Ni seawater service, the typical choice is a Cu-Ni weld-neck flange with a non-metallic gasket (compressed non-asbestos or PTFE) and isolation grommets on the bolting. If a steel companion flange is unavoidable, the joint must be electrically isolated. We carry both steel flanges and copper nickel flanges, so the project can pick the combination that matches the isolation strategy.

The fourth set is the fastener and gasket package: stud bolts, nuts, and gaskets sized to the flange class, in a material compatible with the Cu-Ni system. Plain carbon steel stud bolts in a Cu-Ni flange will fail by galling and corrosion long before the flange does. This is where gasket stud bolt nut packages — sourced together, MTC-matched, and bagged per joint — save more field hours than any other change we have seen in seawater work.

4. Procurement Specifications That Actually Get Read on Site

The difference between a datasheet that lives in a binder and one that gets used on the receiving dock is whether it can be checked against the MTC in under a minute. We recommend the following for every Cu-Ni seawater shipment:

Certify to EN 10204 3.1 as a baseline, 3.2 when specified. The MTC must carry the heat number, alloy UNS, full chemical composition (Cu, Ni, Fe, Mn, Zn, Pb, S, C, and trace elements), mechanical properties, and the NDT results that were actually performed. A generic "complies with ASTM B466" line is not enough when you need to trace a weld procedure back to a specific heat.

Mark the bundle end to end. Each tube, fitting, and flange should carry a permanent mark: alloy grade, heat number, size, and manufacturer. For shipyard work, this is a class requirement; for offshore, it is what allows the joint traceability to survive a yard turnover.

Match the packaging to the storage time. Cu-Ni tubes ship with end caps to keep the bore clean. If the line will sit on the quayside for more than a few weeks before erection, those end caps matter. The same applies to fittings and flanges, which arrive with protective coating that has to come off only at installation.

5. Why a Single-Source Bundle Is Usually Cheaper Than a Split Buy

Split procurement — Cu-Ni tube from one mill, fittings from a second, flanges and gaskets from a third, valves from a fourth — is the industry default, and on the surface it looks like competitive pricing. In seawater service, the hidden cost is integration: four different MTC formats, four different lead times, four different packaging standards, and one common point of failure at the joint where they all meet.

A bundled supply from a single source — tube, pipe, fittings, flanges, gaskets, stud bolts, and the matched industrial valves for the line — collapses all of that. The MTCs follow the same format, the markings use the same convention, the packaging is consistent, and the supplier owns the joint. For project procurement, that translates into a shorter approval loop, fewer RFIs during inspection, and one phone call when something needs to be traced.

This is the model we built the EZ STEEL Cu-Ni bundle around. From a 1994 base in steel manufacturing, expanded into 500+ staff and 480,000+ annual tonnage, the production footprint now covers Cu-Ni tube, pipe, fittings, and flanges to the same MTC discipline as our stainless steel pipe and carbon steel pipe lines, with API, EN, and ASME certification on the pressure-bearing items. That is why a Cu-Ni project can sit next to a carbon-steel line in the same vessel and the same MTC binder.

6. Commissioning — The Step the Datasheet Cannot Skip

The single most common cause of early Cu-Ni failures is not the material, the weld, or the joint. It is the commissioning step. If the line is filled with seawater and left stagnant for days, sulfides and biological activity build up under deposits and the protective film does not form properly. If the line is flushed and then left dry, the film is damaged by oxygen and chlorides cycling.

The standard practice, embedded in the same EEMUA documents that drive the material spec, is a ferrous sulfate treatment during initial wet-up, continuous flow during the first 30 days, and avoidance of stagnant conditions thereafter. Where the project is bundling heat exchangers, the heat efficiency tubes side of the system has to follow the same protocol — Cu-Ni tubes that dry out after wet-up corrode far faster than tubes that never lost their film.

None of this is a manufacturing issue. It is a specification issue, and it belongs in the commissioning document that the supplier hands over with the MTC package. If your datasheet does not yet carry a commissioning clause, add one before the first tube is shipped.

7. A Practical Walkthrough for a Project RFQ

For a project RFQ on a Cu-Ni seawater line, the fastest path to a clean quote is to send the following as one document, even if the buy is split internally:

1. Process conditions — fluid, temperature, max velocity, chloride level, sulfide exposure, intermittent vs. continuous service.
2. Pipe class and material list — line by line, with the UNS pinned, the standard named, and the size / wall / length for each.
3. Fittings list — same UNS, same standard, butt-weld ends matching the pipe schedule.
4. Flanges and bolting — flange type, facing, class, gasket material, stud bolt and nut material and length.
5. Valves — body material, trim material, end connection, and pressure class.
6. Certification scope — EN 10204 3.1 or 3.2, third-party inspection if required, traceability for pressure-bearing parts.
7. Packaging, marking, and delivery sequence — by line, by spool, or by joint, to match the site erection plan.

Send that as a single RFQ, even to multiple suppliers, and the responses will be comparable. Send it as seven separate inquiries, and the responses will not align on MTC format, lead time, or packaging — and the joint at site is where the difference will show up.

8. What We Supply for Cu-Ni Seawater Bundles

EZ STEEL INDUSTRIAL has supplied Cu-Ni tube, pipe, fittings, and flanges to marine, offshore, power, and desalination projects since 1994. The bundle covers 90/10 and 70/30 grades, with manufacturing to EEMUA 144/234, ASTM B466/B467, JIS H3300, GB/T26291, MIL-T-16420K, DIN 86019, and BS 2871. Where the line has to transition into a different alloy system, we supply the matched pipe fittings, pipe flanges, gaskets, stud bolts, and industrial valves so the joint is engineered, not improvised.

The MTC package follows EN 10204 3.1 as standard and 3.2 when the project asks for it. Each item carries permanent marking — alloy grade, heat number, size, and manufacturer — and the bundle is sequenced to match the site erection plan. For a typical seawater cooling line, the same supplier carries the line from tube to the last valve, which is the cleanest way to keep the joint inside one MTC discipline.