New England Aquarium sea water piping corrosion

Stainless steel failed (pitting from dirt), Monel was intermediate, titanium would have been best but cost-prohibitive. Used to illustrate the trade-off ladder for seawater service.

Cupro-nickel is just copper-nickel alloy. It's ninety percent copper, ten percent nickel. Monel 400 is thirty percent copper, seventy percent nickel. So if you go across the copper-nickel phase diagram, you've got 90/10 and 70/30. The Navy uses lots of Monel in their seawater piping. Good corrosion resistance, not fantastic. I told you the story about the aquarium — stainless steel wasn't good enough, Monel was intermediate in maintenance, and titanium would have been the best, but it's pricey. So it's a complete trade-off between price and performance and maintenance.