AskCodeMan

Jerry - do you have any idea when the requirement for using brass or dielectric fittings when connecting copper pipe to galvanized nipples (on water heaters) was first instated? I'm about ready to start lobbying the state legislature to require all plumbers to take a course in basic chemistry and physics.

Stuart Brooks
Virginia Inspection Service, LLC
Fredericksburg, VA

I'm not sure when dissimilar metal corrosion was first addressed, but I am sure it was some time between the Roman Empire with their lead pipes and modern day plumbing systems (meaning pre-1970s). The dielectric fitting is not the best way to address dissimilar metals contacting each other at a connection point, not only are dielectric fittings not "the best way", they are not even "a good way", albeit dielectric fitting are better than nothing - I think.

By "dielectric fittings" I am referring to the modern conception of this in that they take a steel nipple and line it with a plastic liner, which is somehow supposed to re-orient mother nature's strive for equilibrium and be 'the next best thing since sliced bread'.

What is really needed is the use of fittings which are not "dissimilar metals" but are 'similar enough metals' on the cathode/anode chart that they are compatible with the other metals being connected together. I.e., when connecting steel to copper (by far the greatest "dissimilar metal" combination found in construction) the use of brass or bronze fittings solves the problem as brass and bronze are compatible with a) copper and b) steel as steel is made with zinc and brass and bronze are made with copper and zinc - brass and bronze is 'similar enough' to copper to be compatible for domestic water uses, and brass and bronze is 'similar enough' to steel to be compatible for domestic water uses. Now, there are specialized uses for which brass and bronze is not 'similar enough' to the other metals to resist the corrosive actions, but we are talking about domestic water systems, not specialized chemical systems. Keep in mind that brass and bronze also have two categories: 'high' or 'yellow' and 'low' or 'red' - depending on the zinc content. 'High' brass is more compatible with steel and zinc due to its higher zinc content - at least as I learned it some time ago.

Here are some dissimilar metals order charts: (in no particular order)
http://npfasteners.com/pdfs/galvanic-co ... -chart.pdf
http://www.galvanizeit.org/aga/designin ... in-contact
http://www.galvanizeit.org/aga/designin ... in-contact
http://www.engineersedge.com/galvanic_capatability.htm

Before starting to push for dielectric fittings, consider pushing for brass or bronze fittings - dielectric fitting go fairly quickly under high corrosion conditions.