Information from inspection and analysis of electric resistance welded galvanized steel pipe after service in residential water systems has resulted in a compilation of observations concerning the development and severity of corrosion leading to failure. The observations gathered over a fourteen-year period explain the development of corrosion that does not always correlate with the many factors generally thought to be responsible. The inability of the zinc coating to meet its theoretical role of galvanic protection was clearly evident, and this allowed development of localized attack and tuberculation. Both forms of corrosion result from under-deposit corrosion, or the presence of copper ions in the water. Tubercles that covered the weld seam resulted in severe grooving corrosion and accelerated failure regardless of the weld or coating quality. It appears that the corrosion of the plumbing system in each residence is progressive, the most severe attack taking place at the inlet end of the system and diminishing to light or no corrosion at the downstream outlets. Pitting and grooving corrosion found in the downstream plumbing were attributed to the techniques and components used to plumb the system.
Key Words: electric resistance welded, galvanized, domestic water, pitting, grooving, tuberculation, under-deposit attack, copper, zinc, cut end corrosion, crevice corrosion, temperature, galvanic, hardness, water softening, anions, cations, potential reversal, oxygen