I have a question that revolves around the galvanic corrosion mechanism.  If I use threaded bronze valves in a carbon steel boiler feedwater circuit, will there be a concern with galvanic corrosion in the threaded joint?  (Temperature is 400F at 250 psi).

Correct me if I am incorrect, but I think it would be ok.

Since carbon steel is more anodic on the galvanic series than coppor alloys, the corrosion would tend to be in the carbon steel.  

But since the carbon steel will have the greater surface area in the system, won't that protect it?

We commonly put small sections of copper piping on carbon steel sprinkler lines and don't see corrosion.  We do not do the opposite, though which would be a failure waiting to happen.  

Well, on one hand this is feedwater so the conductivity is very low so galvanic corrosion will be minimal.
On the other this is at 400F and galvanic corrosion rates are exponential with temp.

Do you want to use bronze valves at 400F?  Even without the CS pipe I would think that there is a risk of dealloying.

There have been a number of instances of dealloying of copper alloys in these types of services. Copper can plate onto the carbon steel pipe surfaces leading to galvanic corrosion and severley shortened service life.

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