Dielectric Union Failure

This article describes the building code and practical requirements for a dielectric fitting when connecting copper piping to steel pipes or steel fittings such as at the top of a water heater.

Dielectric union failure. All insulating materials undergo breakdown when the electric field caused by an applied voltage exceeds the material s dielectric strength. To order call 800 769 0503. This failure mode is unique for bme capacitors that normally were. A dielectric union pipe fitting is designed to hold two types of metal pipe together without actually soldering them.

Its only intended use is to break continuity. Evaluations using stress calculations and the dynamics of freezing water indicated that the unions were not overtightened during. This union is made from galvanized steel and lead free brass. Plumbing codes in all states require the use of dielectric unions when connecting dissimilar metals.

Dielectric flanges are installed between pipes made from dissimilar metals to help prevent accelerated deterioration and corrosion. Slow degradation failures are characterized by a gradual increase of leakage current against stress time until a failure criterion is reached 100µa in this study. A dielectric union is a pipe connection with a 1 16 thick plastic washer and a piece of rubber between the two. Dielectric unions are use to join pipes made from dissimilar metals to avoid electrolysis which leads to corrosion and pipe failure.

Metallographic examination revealed evidence of severe stress corrosion cracking within the brass as well as dealloying on the surface. View entire discussion 7 comments more. Electrical breakdown or dielectric breakdown is a process that occurs when an electrical insulating material subjected to a high enough voltage suddenly becomes an electrical conductor and electric current flows through it. They seem to think that the main failure mode is overtightening of the union which results in metal metal contact and galvanic corrosion.

Each includes a union nut 2 tailpieces and a gasket. Failure is the over firing of the dielectric resulting in the formation of a low resistance batio. What is electric strength. Persistent failures leakage were observed in the brass portion of dielectric unions after a relatively short service period.

With a copper and an iron pipe this is necessary as the combination of metals under solder could produce galvanization leading to corrosion and failure of the pipe. It is a voltage which a dielectric material insulator will withstand without breaking down. We explain the effect of galvanic corrosion at copper to steel pipe connections and we include notes on the recommendation for a jumper wire across dielectric fittings or. A dielectric class 3000 union with a dielectric coated a105 carbon steel tailpiece that is 3 4 female npt with a 304 stainless 1 2 male npt threadpiece teflon o ring is coded as follows.

This is the failure of an insulator due to the voltage impressed across it.