Few material decisions on a seawater project are as consequential — or as routinely oversimplified — as the choice between copper nickel alloy, stainless steel, and titanium. All three families are marketed as “seawater resistant,” and all three will, under the right conditions, deliver twenty or thirty years of service. The differences show up at the margins: in the velocity at which the pipe wall starts to thin, in the chloride concentration at which pitting begins, in the dollar cost per metre of installed line, and in the welding procedure the fabrication yard has to follow.

This guide is written for the engineer or buyer who has to make that call on a real project. It compares the three material families on the attributes that actually drive service life and total cost, and explains how the right answer is usually a hybrid — different materials in different parts of the same system — rather than a single material across the whole plant.

Copper nickel alloy (90/10 and 70/30)

A copper-base alloy containing 10% or 30% nickel, plus small additions of iron and manganese for corrosion resistance and weldability. The 90/10 grade (UNS C70600, CuNi10Fe) handles sustained seawater velocities around 3.5 m/s; the 70/30 grade (UNS C71500, CuNi30Fe) holds up to roughly 4.5 m/s. Both grades develop a thin, adherent, self-healing oxide film in seawater that resists pitting, crevice corrosion, and biofouling. Standards that govern the alloy include ASTM B466, ASTM B111, ASTM B395, EEMUA 144, EEMUA 234, EN 12451, and JIS H 3300. The matching copper nickel flanges are produced in the same two grades so that the flange and the pipe are metallurgically compatible.

Stainless steel (304, 316, 6Mo super-austenitic, duplex)

Austenitic stainless steel pipe in the 304/316 family is widely available and easy to fabricate, but its chloride tolerance is limited; 316 will pit in warm seawater above roughly 1000 ppm chloride unless velocity is carefully controlled. The 6% molybdenum super-austenitic grades (AL-6XN, 254 SMO) and the duplex grades (2205, 2507) push that ceiling much higher, but the cost rises sharply with each step. Stainless is also susceptible to microbially influenced corrosion (MIC) in stagnant or low-flow seawater dead legs, which is why most marine pipe codes limit its use to systems that flow continuously.

Titanium (Grade 1, 2, and 7)

Commercially pure titanium (Grade 1 and Grade 2) and the palladium-stabilized Grade 7 are essentially immune to general corrosion, pitting, and crevice attack in natural seawater, including warm, chlorinated, and polluted water. The ceiling velocity is high, and the alloy is light. The trade-off is cost: titanium tube and pipe run several times the price of copper nickel alloy in the same diameter and wall, the welding procedure requires inert gas shielding on both sides, and the supply chain is thinner than for copper-base alloys. Titanium is therefore most often specified for the highest-velocity or most safety-critical parts of a system, with copper nickel doing the bulk of the run.

The table below summarizes the comparison on the attributes that drive the engineering decision. Numbers are typical for the most common grade in each family; project specifications can shift the answer for any single attribute.

When copper nickel is the default

For long runs of moderate-velocity seawater pipework on board a ship, on an offshore platform, or in a coastal power station, copper nickel is the most cost-effective and the most forgiving choice. The alloy is tolerant of long idle periods, polluted harbor water, and brackish estuarine conditions, and the matching copper nickel flanges eliminate the galvanic risk that comes with mixing a copper-base tube to a carbon steel or stainless flange. EZ Steel Industrial manufactures both 90/10 and 70/30 copper nickel tubes, pipes, and flanges to ASTM B466, EEMUA, EN 12451, JIS, and GB/T 8890, which covers the specification regime of most shipyards and offshore operators.

When stainless is the right call

Stainless is the right answer for process pipework inside a plant where the fluid is not raw seawater — for example, treated cooling water, demineralized water, food-grade fluids, or pharmaceutical service — where its cleanliness, availability, and lower installed cost outweigh its limited chloride tolerance. Within the seawater envelope itself, super-austenitic and duplex grades extend the alloy's reach into hotter, more chloride-rich streams, but the cost premium is meaningful and the biofouling issue remains.

When titanium earns its premium

Titanium pays for itself in the highest-velocity sections of a once-through cooling system, in safety-critical firewater deluge on an offshore platform, in plate heat exchangers handling polluted harbor water, and in any service where the cost of a failure (downtime, environmental cleanup, or replacement at sea) dwarfs the material premium. The material is also the right call when the chemistry rules out copper — for example, in systems carrying ammonia or strong reducing agents — because copper alloys are vulnerable under those specific conditions.

In practice, almost every large seawater plant is a hybrid. Copper nickel handles the long shipboard and platform runs at moderate velocity. Stainless handles the process-side and freshwater-side pipework. Titanium handles the high-velocity headers, plate heat exchangers, and safety-critical firewater sections where the design velocity exceeds what copper nickel can sustain.

The procurement implication is that the buyer is rarely buying a single alloy. They are buying a coordinated piping package in which tube, pipe, fitting, flange, and joint assembly have to come from the same metallurgical conversation. That is where EZ Steel Industrial's bundled approach pays off: the company can deliver copper nickel, stainless, titanium, the matching copper nickel flanges and steel flanges, the pipe fittings that connect them, and the stud bolts, nuts, and gaskets that complete the joint, on a single purchase order, with mill certificates that line up heat for heat.

Whether you are buying copper nickel, stainless, or titanium, the questions to put to a supplier are the same. A serious quotation should answer all of them in writing, not on the phone.

– Material standard. ASTM, EN, EEMUA, JIS, GB/T — whichever governs the project. If the supplier is vague about this, treat the quote as incomplete.

– Exact alloy and UNS number. “Stainless” is not a specification; 316L, 6Mo, 2205, and 2507 behave very differently in seawater.

– Chemical composition and mechanical properties. Within the standard's tolerance, including any residual limits the project imposes (lead and zinc in copper nickel, for example).

– Dimensional tolerances and testing regime. Hydrostatic test, eddy current or ultrasonic NDT, flattening test, and grain size where applicable.

– Mill certificate to EN 10204 3.1 or 3.2. Traceable to the heat number marked on each tube or pipe.

– Matching fittings, flanges, and joint components. Whether the supplier can deliver the whole package or only the tube. Half a package is harder to manage than no package at all.

If the system runs continuously and the design velocity stays below 3.5 m/s, start with copper nickel 90/10. It is the lowest-cost, lowest-fabrication-cost option that still gives full seawater immunity, and it is the default the major shipyards and offshore operators have trusted for decades.

Move up to copper nickel 70/30 when the velocity, the temperature, or the water chemistry (polluted harbor water, higher chloride, hotter condensers) pushes past the 90/10 envelope. The cost increment is small compared with the cost of an erosion failure.

Move to stainless only when the service rules out copper — high-purity or food-grade fluids, ammonia-bearing streams, or process pipework that is not in direct seawater contact. Within the stainless family, match the grade to the chloride concentration and the temperature, and remember that 316 is not a seawater alloy.

Specify titanium in the sections where the design cannot tolerate any compromise: high-velocity condenser headers, safety-critical firewater on offshore platforms, plate heat exchangers in polluted harbor water. The premium is high, but so is the cost of a failure in those services.

Throughout, treat the system as a package. Buy the copper nickel alloy tube, the matching flanges, the pipe fittings that connect them, and the stud bolts, nuts, and gaskets that seal the joint, from the same supplier against the same specification. The metallurgy, the documentation, and the schedule all become someone else's problem in the right way.

EZ Steel Industrial has been producing industrial steel and alloy products since 1994 from its base in Changsha, China. The product line covers carbon and carbon alloy steel, stainless steel, copper and nickel alloy, heat efficiency tubes, pipe fittings, pipe flanges, gasket / stud bolt / nut assemblies, and industrial valves — which means a hybrid seawater system can be sourced as a single package rather than four or five separate orders.

The copper nickel alloy range is delivered to ASTM B466, EEMUA, EN 12451, JIS H 3300, and GB/T 8890, with mill certificates to EN 10204 3.1 as standard and 3.2 where the project requires third-party inspection. The matching copper nickel flanges are produced in 90/10 and 70/30 grades so the flange metallurgy matches the pipe. The adjacent stainless steel pipe and titanium tube, together with the pipe fittings, gaskets, and stud bolts, can be added to the same order and shipped on the same documentation set, which simplifies both procurement and the QA trail at site.