Brass-to-lead junction: Utility 1.

Dezincification of brass at junction

Surface water supply; chloramine disinfection; phosphate corrosion control

brass corrosion chloramine

Note the apparent reversal of the normal galvanic series. That is the brass, not the lead is corroding. This could be explained by the much lower potential of Zn relative to Pb, leading to lead acting as the cathode instead of the anode:

Cathode (iron)                                            ½O2  + H2O  + 2e- →  2OH-

Anode (zinc component of brass)           Zn → Zn2+  +  2e-