Photo Gallery B1: Galvanic Induced Failures
Galvanic induced piping failures are due to the direct connection of two dissimilar metals having sufficiently different electrical potential. Copper to brass represents virtually no concern, while galvanized steel to brass will almost always produce an advanced failure. Galvanic activity is rarely a concern for well maintained closed piping systems operating under low corrosion conditions of 0.5 MPY or less, with 60 year old properties still showing no measurable impact. For newer piping systems, however, the threat is far greater due to the generally lower quality of today’s carbon steel pipe along with higher system corrosion levels.
Corrosion activity of greater than 2.0 MPY are generally necessary for galvanic activity to introduce a threat, which is why this problem is mostly associated with open condenser water systems. As system-wide corrosion activity increases beyond that amount, the impact of galvanic activity accelerates greatly Blue-green deposits around the threads between a brass valve and steel pipe nipple, while showing no leaks or discolorization at the steel nipple to steel threadolet side, almost always confirms a galvanic condition and the higher probability of failure at the threads to the valve.
Galvanic corrosion is widely misunderstood, commonly misinterpreted, and its result frequently manipulated in order to misdirect responsibility or justify pipe replacement. The lack of dielectric fittings to isolate dissimilar metals have been cited as the source of a system-wide 12 MPY corrosion condition when in fact it only impacts a very localized area. Surprisingly often, dielectric insulators installed to remedy a problem are installed incorrectly – thereby providing no benefit whatsoever. Photo Galleries G5 and G6 illustrate this common issue.
Undersized pipe, lower pipe quality, and a greater vulnerability to corrosion, combined with less effective corrosion controls have increased the frequency of this problem. An issue almost unheard of decades ago even at the most problematic piping systems, galvanic activity now requires serious planning to avoid.
