CSLB C-36 Plumbing ContractorService, Repair, and MaintenanceMedium
A technician is installing a new water heater and notices that the old galvanized steel nipple connecting to the hot water outlet shows significant corrosion where it was previously connected to copper piping. To prevent this issue in the new installation, what component should be used?
- AA PVC adapter.
- BA dielectric union.
- CA stainless steel flexible connector.
- DA brass nipple.
Show answer & explanationAnswer & explanation
Correct answer: B. A dielectric union.
The corrosion observed is galvanic corrosion, which occurs when two dissimilar metals (like galvanized steel and copper) are in electrical contact in the presence of an electrolyte (water). A dielectric union is specifically designed to isolate these metals and prevent this reaction.
Why the other options are wrong
- A. A PVC adapter is not typically rated for hot water heater connections due to temperature and pressure limitations, and would not be code compliant for this application.
- C. While stainless steel is corrosion-resistant, a stainless steel connector directly connecting galvanized steel and copper would still create a galvanic cell, albeit potentially slower corrosion than direct contact.
- D. A brass nipple would still be a dissimilar metal to galvanized steel, though less reactive than copper, it doesn't fully address the galvanic corrosion issue when connecting to copper.
Galvanic Corrosion Prevention
Methods used to stop the electrochemical reaction that corrodes one metal when it's in contact with a more noble metal in an electrolyte.
- Occurs between dissimilar metals (e.g., galvanized steel and copper) in the presence of water.
- Results in accelerated corrosion of the less noble metal (e.g., steel).
- Dielectric unions are specifically designed to prevent this by providing an electrical break.
Memory trick: Two metals, one corrodes, dielectric intercedes.