The first time a procurement officer confuses Cu-Ni 90/10 with Cu-Ni 70/30 on a purchase order, the project does not fail loudly. It fails slowly — as accelerated wall thinning in a condenser, as a flange that will not seat against the gasket it was matched with, or as a heat exchanger that the class society refuses to sign off because the mill certificate names the wrong edition of the standard. Copper nickel alloy tubing is forgiving in service but unforgiving in specification. This guide is written for the people who write the RFQ, not just the people who weld the tube.

Across shipbuilding, offshore platforms, desalination plants, petrochemical cooling water systems and power station condensers, the same family of alloys is specified again and again. The Copper Development Association highlights that copper and its alloys are essential to the marine industry because of their resistance to corrosion and biofouling in saltwater environments, while also delivering the thermal and electrical conductivity that propulsion, navigation and heat exchange systems depend on. Understanding where each grade fits — and where it does not — is the single most cost-saving skill a buyer can develop.

Start With the Service, Not the Alloy

The most common procurement mistake is to lead with material code. Starting with the service condition is faster and produces fewer rejections. Three questions cover roughly 90 percent of real cases:

1. What is flowing through the pipe? Clean seawater, brackish water, deaerated water, or a process fluid with trace hydrocarbons? Each medium has its own preferred alloy family.

2. What is the design flow velocity? Cu-Ni 90/10 is comfortable up to roughly 3.5 m/s in seawater; Cu-Ni 70/30 tolerates about 4.5 m/s. Push past those limits and erosion-corrosion becomes the limiting factor.

3. What is the consequence of failure? A firewater line on a commercial vessel has different documentation requirements than a primary condenser in a nuclear auxiliary system. The latter may need RCC-M compliance, the former usually does not.

Answering these three questions first lets the specifier ｄｒｏｐ a grade before a single drawing is checked, which is why experienced EPC teams build them into the front page of every piping datasheet.

90/10 vs. 70/30: A Decision Table That Actually Works

Both alloys rely on the same self-healing oxide film for corrosion resistance, so the decision usually comes down to mechanical strength, flow velocity and budget. EZ STEEL INDUSTRIAL produces both grades to ASTM B466, EEMUA 144, EEMUA 234, DIN 86019 and GB/T 8890, which means the same mill can supply a shipyard in Korea, an offshore yard in Brazil and a refinery in the Middle East from one quality plan.

The rule of thumb that holds up across most shipyards: if the line is hull-penetration, firemain, or general seawater service, stay with 90/10. If the line enters a condenser shell, feeds a desalination evaporator, or sees sustained high flow rates in a power plant, move to 70/30. Specifying 70/30 everywhere is technically safe but it inflates the bill and can actually hurt weldability on small-bore branches.

The Tubing Is Only Half the System

A seawater circuit is a chain, and a chain is only as strong as its weakest component. The tube gets most of the attention in the datasheet, but the pipe fittings, pipe flanges, gaskets and stud bolts around it decide whether the system holds pressure for thirty years or starts weeping at the first hot commissioning. Specifying all of these from the same manufacturer — and from the same heat of material where possible — keeps the metallurgical story consistent and the documentation chain short.

This is one of the reasons EZ STEEL INDUSTRIAL positions its Cu-Ni range alongside carbon and stainless lines. On a typical offshore platform the seawater cooling train sits next to a carbon steel pipe riser for the firewater ring main and a stainless steel pipe network for the higher-pressure injection system. Pulling all three families from a single mill simplifies welding procedure qualification, reduces the number of partial shipments, and gives the EPC document controller one set of EN 10204 3.1 certificates instead of three.

Five Things to Lock Down in the RFQ

Most disputes between buyers and mills come from RFQs that are 80 percent complete. The remaining 20 percent is where warranty claims, late deliveries and rejected heat numbers are born. Locking down these five items before issuing the inquiry removes nearly all of them.

Common Pitfalls Worth Naming Out Loud

Three procurement mistakes show up again and again, even with experienced teams. The first is mixing Cu-Ni tube with carbon steel flanges on a long seawater line. The galvanic couple accelerates wall loss at the tube end. The fix is to use Cu-Ni flanges or to add a dielectric gasket and insulating kit at every transition.

The second is welding Cu-Ni 90/10 with the wrong filler. AWS A5.7 ERCuNi or equivalent nickel-rich filler is mandatory; using a copper filler on 90/10 produces a joint that is weaker than the parent tube and prone to hot cracking. The third is ordering to "schedule" rather than to actual wall thickness. Cu-Ni tubes are typically specified by gauge or millimetre wall, not by ASME B36.10/B36.19 schedule, and conflating the two has cost more than one project its pressure-test signature.

None of these issues are exotic. They are the small disciplines that separate a piping package that runs for three decades from one that ends up in a warranty claim spreadsheet.

Where Copper Nickel Alloy Fits in the Wider Materials Map

Cupronickels do not ｒｅｐｌａｃｅ every alloy in a piping book. The Britannica entry on cupronickel places the family firmly in seawater condenser tubes and similar corrosion-resistant service, which is still the right framing today. On a modern project, Cu-Ni 90/10 and 70/30 are specified where the fluid is raw seawater or brackish cooling water, where biofouling would otherwise dominate maintenance cost, and where weldability and formability matter as much as raw strength.

Outside that envelope, the specifier typically moves to other families. Higher-pressure process lines ｄｒｏｐ down to carbon steel pipe in ASTM A106 or API 5L. Corrosive chemical services move to stainless steel pipe in ASTM A312 or its duplex equivalent. Heat-recovery circuits move to finned or U-bent tubes on the heat efficiency tubes side. Knowing when to switch families is as valuable as knowing how to specify one.

A Short Pre-Issue Checklist for the Buyer

Before the RFQ goes out, run through this short list. If the answer to any line is "not sure", go back to the piping lead before sending the inquiry — not after the quotations come in.

Confirm the service fluid, design temperature and design pressure. Confirm the required flow velocity and whether 90/10 is mechanically adequate. Confirm the standard, edition and UNS code. Confirm the testing scope and the inspection body. Confirm the documentation language and the file format. Confirm the flange and pipe fittings specification matches the tube specification. Confirm the delivery schedule, including any mill-specific production windows that might push lead time.