Hangbo Alloy Group
Shanghai · Est. 2012
Why nickel alloys resist galvanic attack, where bimetallic couples fail, and how to pair Monel, Inconel and copper-nickel with steel and titanium.
When two dissimilar metals sit in the same electrolyte, the more active one corrodes to protect the more noble one. Nickel alloys sit in the noble half of the galvanic series, which is good news: they are rarely the metal that sacrifices itself. The real risk is the opposite — coupling a nickel alloy to carbon steel, aluminum, or copper can drive rapid attack of the partner, and in tight crevices the resulting concentration cells can undermine an otherwise sound joint. This guide explains how to predict, control, and live with bimetallic couples in nickel-alloy systems.
Nickel and its alloys are cathodic (noble) relative to carbon steel, cast iron, aluminum, and zinc, and roughly comparable to, or slightly nobler than, copper and its alloys. In a couple with steel, the steel becomes the anode and corrodes faster; the nickel alloy is essentially unaffected. That is why Monel and Inconel are routinely used as fasteners and overlays on steel structures in marine service — the steel gives way first, and the nickel alloy survives. The practical danger is localized: if the steel anode is small and the nickel cathode is large, the steel can be consumed far faster than its bulk area would suggest.
Monel 400 and copper-nickel 70/30 behave similarly in seawater couples and are often paired deliberately because their potentials are close, minimizing galvanic drive.
As a dedicated nickel alloy manufacturer, Hangbo Alloy Group supplies matched chemistry across product forms so fabricators can keep couple potentials tight without hunting for compatible stock from multiple mills.
Rarely as the anode. Nickel alloys are noble in the galvanic series, so in a couple with steel or aluminum they are protected while the partner corrodes. The failure to watch is localized attack of the less-noble metal, especially where a small steel area faces a large nickel-alloy surface. Choosing close-potential partners such as Monel K-500 against Monel 400 keeps the galvanic drive minimal.
It will protect the Inconel and accelerate the steel. In practice that is often acceptable for the short term, but the steel bolt or flange can thin unexpectedly fast and leak. Use insulating washers or a corrosion allowance on the steel, and avoid trapping seawater in the joint where crevice corrosion would compound the galvanic effect. Inconel 625 fasteners on a 625 structure avoid the couple entirely.
Yes, if over-applied. Driving the potential too negative in seawater can cause hydrogen uptake, which is a concern for precipitation-hardened nickel alloys and for any hardened fastener. Size the protection to the steel, not the nickel alloy, and monitor so the nickel component stays in its immune range rather than being driven hard cathodic.
As a dedicated nickel alloy manufacturer serving marine, chemical processing, oil & gas sectors, Hangbo Alloy Group supplies the grades discussed here across all standard product forms with full ASTM/ASME documentation and EN 10204 3.1 certification. Our material is specified for applications where corrosion resistance, high-temperature strength, and traceable quality are non-negotiable. See our production & testing facilities for more on how every heat is verified.