How to ｓｅｌｅｃｔ Copper Nickel Alloy Piping for Marine, Heat Exchanger and Petrochemical Projects

A field-tested engineering guide from EZ STEEL INDUSTRIAL — choosing the right grade, the right standard, and the right partner for long service life.

1. Start with the Service, Not the Alloy

Engineers who jump straight to a UNS number often pay for performance they do not need — or, worse, underspec a system that will fail. Begin with three questions:

• What fluid is being carried (seawater, brackish water, hydrocarbon, condensing steam)?
• What is the design temperature, design pressure, and expected flow velocity?
• Is the system part of a heat exchanger bundle, a hull pipe, a firewater main, or a process line?

For ship hull and offshore piping where seawater velocity is moderate, 90/10 Cu-Ni (UNS C70600) is the default. For hotter or more aggressive service — including hydrocarbon processing and high-temperature condensing — 70/30 Cu-Ni (UNS C71500) is the safer call. Our recommendation matches what standards such as EEMUA Publication 144 outline for 90/10 offshore piping, and the proven field record of ASME SB111 / SB466 70/30 tubes in heat exchanger service.

2. Lock the Standard and the Test Plan Early

Cu-Ni is a specification-driven product. Mismatching the standard between tube, flange, and fitting is one of the most common causes of in-service leaks. For pressure-side service, common references include:

• ASTM B111 / ASME SB111 — seamless condenser and heat exchanger tubes
• ASTM B466 / ASME SB466 — seamless pipe and tube for general service
• EEMUA Publication 144 — 90/10 Cu-Ni tubes for offshore applications (≤ 20" / 508 mm OD)
• BS 2871 Part 2, EN 12451, JIS H 3300 — regional equivalents for sanitary, refrigeration, and process piping

When the project requires nuclear-grade or aerospace-grade Cu-Ni (for example, RCC-M II for pressurized water reactors), confirm traceability and MTR format at the RFQ stage. The earlier the test plan is locked, the fewer surprises appear at receiving inspection.

3. Bundle the Pipe, Fittings and Flanges from One Source

One of the fastest ways to derail a Cu-Ni project is to source tube from one mill, fittings from another, and flanges from a third. Material certificates, heat numbers, and chemical composition may not align — and at site, the joint that matters most is the one with the weakest link. At EZ STEEL INDUSTRIAL, we routinely ship pipe fittings together with the parent tube, so the entire loop is documented under one heat and one MTR.

Our standard Cu-Ni package covers BW elbows, tees, reducers, and caps; SW fittings for small-bore high-pressure branches; and threaded fittings for instrument and utility drops. Pairing them with pipe flanges in matching UNS C70600 / C71500 material eliminates the galvanic risk you would otherwise manage with a bimetallic transition.

4. Don't Forget the Sealing Stack

A Cu-Ni pipe held by carbon steel stud bolts and a non-metallic gasket will not survive a long maintenance interval. The sealing system — gasket, stud bolt, nut — must be matched to the operating temperature, the fluid chemistry, and the bolt torque plan. Spiral-wound gaskets with graphite or PTFE filler are common for Cu-Ni flange joints on offshore piping; ring-type joint (RTJ) gaskets are used for high-pressure hydrocarbon service.

For projects that want a single source of accountability, our gasket stud bolt nut inventory is built to the same lot standards as the Cu-Ni flanges it ships with, so installers do not waste hours cross-checking thread, length, and material.

5. Apply the Same Logic to Heat Exchanger Bundles

In a shell-and-tube exchanger, the tube material carries the design intent. When the shell side is seawater and the tube side is condensing hydrocarbon, 90/10 Cu-Ni tubes (ASTM B111) are usually the right choice. When the duty is hotter — for example, in a power plant feedwater heater — 70/30 or aluminum brass tubes may be considered. The supporting U bend tubes must be drawn, solution-annealed, and hydrostatically tested to the same standard as the straight tubes they are bent from.

Engineers often forget to confirm the bend radius, the thinning allowance, and the post-bend heat treatment. These are exactly the points that decide whether the bundle passes its first hydrostatic test on the shop floor — or returns a year later with a leak at the bend tangent.

6. A Quick Project Checklist Before You Issue the PO

Before releasing a Cu-Ni purchase order, walk through this short list. It captures the questions our project team asks on every inquiry:

• Fluid service, design temperature, design pressure, and maximum flow velocity
• Material standard (ASTM / ASME / EN / BS / JIS / EEMUA) and required UNS number
• Dimensions: OD, wall thickness, length, and — for U-bends — bend radius and tangent
• Required tests: chemical analysis, tensile, hardness, hydrostatic, eddy current, ultrasonic, PMI
• Documentation: MTR format, EN 10204 3.1 / 3.2, third-party inspection agency, traceability
• Bundled items: fittings, flanges, gaskets, stud bolts — all from one source with one heat number