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.

Dielectric unions are use to join pipes made from dissimilar metals to avoid electrolysis which leads to corrosion and pipe failure. Persistent failures leakage were observed in the brass portion of dielectric unions after a relatively short service period. Each includes a union nut 2 tailpieces and a gasket. It is a voltage which a dielectric material insulator will withstand without breaking down.

A dielectric union is a pipe connection with a 1 16 thick plastic washer and a piece of rubber between the two. This is nearly the same as dielectric withstand. 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. Its only intended use is to break continuity.

All insulating materials undergo breakdown when the electric field caused by an applied voltage exceeds the material s dielectric strength. They seem to think that the main failure mode is overtightening of the union which results in metal metal contact and galvanic 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. It is the highest voltage at which the specific insulation will not break down.

This union is made from galvanized steel and lead free brass. 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. A dielectric union pipe fitting is designed to hold two types of metal pipe together without actually soldering them. View entire discussion 7 comments more.

Failure is the over firing of the dielectric resulting in the formation of a low resistance batio. Dielectric flanges are installed between pipes made from dissimilar metals to help prevent accelerated deterioration and corrosion. 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. What is electric strength.

To order call 800 769 0503. Metallographic examination revealed evidence of severe stress corrosion cracking within the brass as well as dealloying on the surface. They are ideal for use in air and water conditioners hot water storage tanks processing tanks and steam gas and water piping. Evaluations using stress calculations and the dynamics of freezing water indicated that the unions were not overtightened during.

Plumbing codes in all states require the use of dielectric unions when connecting dissimilar metals.