GALVANIC CORROSION 1

[mechanical3010]

Black Steel Pipe with threaded fittings is specified for valve package of fan coil units that includes shut off valves, strainer, 3 way valve, balancing valves etc. There is a dielectric union in both the supply and return piping at the point of connection with the copper coil of Fan Coil Units. This dielectric union will indeed protect the copper coil from corrosion. However, there is no protection from galvanic corrosion that would conceivably occur between pipe (of black steel) and valves (of brass), or is the dissimilarity between these two metals not significant enough to set up galvanic current? Furthermore, how long can these dissimilar metals coexist without failure (causing leaks)?

 

[walkes]

Brass valves prevent the corrosion.

 

[ChasBean1]

With good water chemistry control, you probably won't see a result. For dielectrics and control of potential at dissimilar metals, You'd be best off with protection between iron and brass (often mated in pre-formed piping) rather than at brass and copper connections.

I don't know the lifeline of this. I do know that the lifeline is more likely to be longer when using dielectrics between negative (e.g., Fe-2) and positive (e.g., Cu, +3) potentials.

 

[strider6]

It's likely that you'll have some corrosion on steel, but is not possible to say how long it will resist.
Galvanic corrosion is a function of several different factors and the difference in potential of the two metals is just one.

If you want to avoid galvanic corrosion you should avoid dissimilar coupling or using insulation gasket.

http://xpedio.carrier.com/idc/groups/public/documents/marketing/04-581043-01.pdf

http://www.corrosionist.com/Galvanic_Corrosion.htm

V.


Corrosion Control