CSLB C-36 Plumbing ContractorService, Repair, and MaintenanceHard
A technician is installing a new water heater and notices that the old galvanized steel nipples connecting the water heater to the copper supply lines are significantly corroded. What is the primary reason for replacing these galvanized nipples with dielectric unions or brass nipples?
- ATo comply with aesthetic preferences for modern plumbing systems.
- BGalvanized steel is prone to bursting under high pressure.
- CGalvanized steel nipples restrict water flow due to their smaller inner diameter.
- DTo prevent galvanic corrosion between dissimilar metals.
Show answer & explanationAnswer & explanation
Correct answer: D. To prevent galvanic corrosion between dissimilar metals.
Connecting galvanized steel directly to copper creates a galvanic couple, where the less noble metal (galvanized steel) corrodes preferentially. Dielectric unions or brass nipples prevent this electrochemical reaction, extending the life of the connection and preventing leaks.
Why the other options are wrong
- A. Aesthetics are not a primary plumbing code or functional concern for these connections; preventing corrosion is a critical functional requirement.
- B. While older galvanized pipes can fail, bursting under normal pressure is not their primary failure mode, and corrosion is a more common issue than bursting due to pressure.
- C. While older pipes can accumulate deposits and restrict flow, the primary reason for replacing galvanized steel connected to copper is galvanic corrosion, not inherent smaller diameter.
Galvanic Corrosion Prevention
Measures taken to prevent the electrochemical degradation that occurs when two dissimilar metals are connected in the presence of an electrolyte.
- Occurs between dissimilar metals (e.g., galvanized steel and copper)
- Requires an electrolyte (water)
- Causes the more active metal to corrode
- Prevented by dielectric unions or brass fittings
Memory trick: Metal mix? Dielectric's the trick, corrosion it'll kick!