How long after the initial cathodic readings should the next tests be performed?

• A. 6 months
• B. 12 to 18 months
• C. 24 months
• D. 36 months

Answer: (B)

Periodic verification of cathodic protection is essential to keep underground steel tanks from corroding. After the initial readings establish the baseline, the next tests are done within a window of about 12 to 18 months. This interval strikes a balance: it’s long enough for the protection system to respond to soil conditions and for readings to settle into a steady state, but not so long that corrosion could advance significantly before any needed adjustments are caught. If you test too soon, you might see misleading results from transient conditions; if you wait much longer than 18 months, you risk letting problems go undetected. During the test, a reference electrode measures the tank’s potential relative to the soil, and you’re checking that the protection level remains within the design range. If the readings aren’t in range, you adjust the protective system and re-test to confirm the protection is now adequate.