Photo Gallery I7: Improper Dielectric Fitting Installation
A remarkably common finding in our ultrasonic investigations relates to the incorrect installation of galvanic fittings or isolators, also known as “dielectrics.” Although such fittings were virtually unheard of within the HVAC industry 40 years ago , the much higher levels of corrosion activity occurring today demand control of this added corrosion threat. For that reason, dielectric fittings are often one of the first steps taken in response to a corrosion condition or piping failure.
Dielectric insulators are recommended by chemical treatment providers as well as many corrosion consultants as the solution for many different corrosion conditions even though they offer no possible benefit. The recommendation to replace all smaller threaded pipe nipples with dielectrics is appropriate where thread leaks are occurring at the brass valve connections, but offers no benefit in solving a high system wide 7.5 MPY corrosion condition. The fact that galvanic fittings were not installed to some examples of brass drain valves does not mean that they are responsible for corrosion activity elsewhere given that the impact of galvanic corrosion is very limited to the area of the connection point only. For many corrosion scenarios, and especially where a failure has occurred, the lack of galvanic fittings is the first direction for everyone to throw blame.
After decades of increasing use, however, their functioning and purpose still appears widely misunderstood.
The intent of such fittings is to isolate any electrical contact and transfer of current between dissimilar metals or metals having a different electrical potential, and most notably, between carbon steel or galvanized steel pipe to brass or copper pipe. Of the various combinations, threaded galvanized steel pipe connected to a brass valve produces the most aggressive attack against the zinc finish at the galvanized steel pipe. Even worse are configurations where galvanized steel or carbon steel pipe is sandwiched between two brass valves, or a brass valve and copper run-out pipe.
Yet, we find that approximately 40% of such fittings are installed wrong – with the galvanic insulator placed between copper and brass fittings having no significant dielectric potential, rather than isolating the steel pipe as required. No benefit is realized in such cases; with the potential for failure at steel to brass or copper connections remaining. Pointing out such errors always produces a strong but futile rebuttal.
The below photo gallery illustrates this extremely common mistake made by both in-house maintenance efforts as well as professional plumbing and HVAC contractors. Given that the dielectric insulator should be placed between the steel riser and brass isolation valve, another shutdown to correct the condition is rarely performed once the mistake has been uncovered. No benefit is then realized, and accelerated corrosion to the steel pipe continues.
A review of our many photographs in our “Corrosion Types” photo galleries demonstrates this very widespread threat. But for many installations where piping failures have occurred, it would seem that the appearance to have corrected a corrosion problem is the primary concern. Some almost appear to have been installed randomly.
