Galvanic effect of brasses on various steels 1

In potable water lines, the Plumbing Code requires dielectric unions between copper & steel. A rubber or plastic sleeve prevents direct contact of the metals on the inside (wet side).

If you have some sort of closed loop heating or cooling system, add corrosion inhibitors.

There is so much info:

In high purity water systems it isn't a big deal becuase the water isn't very electrically conductive. In potable water systems it is a major issue. I believe that the CDA has papers on the subject.

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Rust never sleeps
Neither should your protection

Perform a web search on the "galvanic table". This will tell you where different metals lie in the galvanic series.

Here are some decent tables:

This one gives a good description of corrosion potential (volts) and material selection based on that potential:

(more info from previous site)

You probably at least need to be aware of the galvanic relationships and basic behaviors (and of course brass by most or all references is “cathodic” to steel, and steel conversely is “anodic” to brass). You have received posts from others with pretty good general advice. In accordance with Faraday’s law (and/or Kirchov’s second law depending on who you talk to), if you electrically couple these materials all exposed in an electrolyte there will be electrical current flow that will accordingly dissolve some steel. I think a few hundred years ago, in the time of folks like Sir Humphrey Davy and Faraday etc. or before, this behavior was found to be particularly bad when the exposed area of the cathodic material was very large and the exposed area of the anodic (and highly stressed) fastener was very small (e.g. when they tried to fasten copper-bearing sheets or plates to the hulls of salt-water sailing ships with say iron fasteners, that additionally were often also quite highly stressed relative to the sheet they fastened?)
Eventually I think some folks quite early on also discovered that at least in some applications they would not get near as drastic localized corrosion (and maybe even reasonable service life in many applications?) when the coupled galvanic areas/relationships were the other way around. I have noticed the fastener site at touches on some of this as well as some prevalent misunderstandings and knee-jerk reactions that occur in this field (probably much more eruditely than I can) and also contains the quote, “The closer together on the table the joined metals are, the less galvanic current is generated. Obviously, the less the current flow, the less corrosion there will be.”
I think some consensus standards, e.g. ANSI/AWWA C111/A21.11, I suspect based on a great deal of experience and testing over decades, also appear to sort of take many of these factors into account (as well as common bolting stress) when they require special alloy steel bolting e.g. to be used for buried mechanical joint fasteners with ductile iron piping systems. The alloy steel, while of course at least some dissimilar, metal is specially compounded with at least a small amount of nickel, copper, and chrome so as to service (remain pretty much at least slightly cathodic over time) pretty well in most normal soil environments, at least when bolted firmly to the ductile iron. I understand other compositions of bolted assemblies (I suspect with many piping materials)have not fared as well.
All that being said, I understand it is possible that even injudicious couples/area ratios might provide suitable service in even aggressive conditions when provided with coating applications and/or life-extending cathodic protection currents, with suitable potential designed and maintained to overrride deleterious galvanic effects.
While I am talking about electrical currents, I would make one other comment – another poster has referred to a plumbing code for “dielectric unions”. The Ductile Iron Pipe Research Association (DIPRA) website at and in the document “DIRECT TAPPING OF DUCTILE IRON PIPE ENCASED IN POLYETHYLENE” provides special precautions/procedures most applicable in some aggressive soil environments for tapping ductile iron pipes and also suggests insulation of the (often copper) service line from the piping system in some circumstances, and particularly when stray DC currents might be imparted to the ductile iron piping by grounding of some electrical devices. This I suspect does not mean there would necessarily be any significant problem at least with a direct couple of the small surface area service etc. to iron pipes in other environments/conditions due to galvanic conditions, but that higher “stray” currents getting onto and then off of the pipes into the soil could exacerbate the conditions (by carrying much more pipe metal with them).