DielectricUnion stainless steel to Brass

For general plumbing needs, a dielectric union consists of a steel connector mated to a brass connector with an electrical insulator between the differing metals. While instrumentation dielectric unions are designed in a similar fashion, they’re actually stainless on both sides. This is because they’re designed to help with a different aspect of corrosion mitigation.

This process begins with a piece of material (referred to as the anode) that is buried in the ground near the component that requires protection (referred to at the cathode). Both the anode and cathode are connected to a machine called a rectifier.

Ordinary dielectric unions are designed to reduce or eliminate the corrosive effects of electrolysis. Electrolysis happens when water (or any other electrolytic liquid) is passed through a system that consists of two or more dissimilar metals.

Dielectricinsulatedunions

Dielectric Unions are a crucial tool used to greatly reduce the effects of corrosion in a plumbing network. A dielectric union used in instrumentation is similar to a dielectric connector that might be on top of a hot water heater. There are, however, a few key differences.

Dielectricunion stainless steel to carbon steel

Dielectricunion stainless steel to copper

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Instrumentation dielectric unions are for electrical isolation of sensitive electronics. Unlike dielectric unions for plumbing, they do not prevent corrosion on their own. They must be used in conjunction with an active corrosion mitigation system and should not be used to connect dissimilar metals.

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The rectifier then cycles an electric current through the system causing electrolysis. This flowing electrical current replenishes the electrons that would normally be lost to oxidation. In doing so, it protects the cathode from the corrosion that it would naturally experience.

Dielectricunion for gas piping

Instrumentation dielectric unions are not designed to prevent the natural electrolysis between varying types of metals. Rather, they provide a barrier between sensitive electronics and the electrical current that must pass through the cathode (the component requiring protection). Connecting metering or testing equipment directly to the electrified cathode could cause false readings or equipment damage and failure.

If applied correctly, the natural phenomenon of electrolysis can be harnessed to prevent corrosion in certain applications. Two examples of this are metal components like underground piping systems and storage tanks that are in contact with the ground.

This can generate a small electrical current that causes the less noble material to corrode and wither away over time. A secondary effect of electrolysis is that the more noble material will be less susceptible to corrosion.