CP 3 Practice Questions

These CP 3 practice questions focus on theory, design logic, calculations, criteria interpretation, current distribution, and troubleshooting judgment.

Study Focus

CP 3-level study requires moving beyond definitions. Focus on why criteria apply, how calculations are built, how current distributes, and how field data supports or fails to support conclusions.

Practice Questions

  1. A pipeline has an ON potential of −1,120 mVCSE and an instant-off potential of −790 mVCSE. What is the best interpretation?

    1. The ON value alone proves the pipeline satisfies a polarized −850 mVCSE criterion
    2. The instant-off value suggests the polarized potential does not satisfy −850 mVCSE
    3. The reference electrode is unnecessary
    4. The pipeline is overprotected everywhere

    Answer: B. If the criterion requires a polarized potential, the instant-off value is the relevant value and it is less negative than −850 mVCSE.

  2. A structure has an instant-off potential of −760 mVCSE and a depolarized potential of −640 mVCSE. What is the depolarization?

    1. 120 mV
    2. 640 mV
    3. 760 mV
    4. 1,400 mV

    Answer: A. The magnitude of the change is 120 mV.

  3. A rectifier operates at 48 volts and 4 amps. What is the effective circuit resistance?

    1. 192 ohms
    2. 12 ohms
    3. 0.083 ohms
    4. 52 ohms

    Answer: B. R = V ÷ I = 48 ÷ 4 = 12 ohms.

  4. A coated structure has 20,000 ft² total area and 2 percent coating breakdown. What exposed area is assumed?

    1. 40 ft²
    2. 400 ft²
    3. 2,000 ft²
    4. 10,000 ft²

    Answer: B. 20,000 × 0.02 = 400 ft².

  5. Using 400 ft² exposed area and 3 mA/ft², what current is required?

    1. 120 mA
    2. 1,200 mA
    3. 12,000 mA
    4. 0.013 mA

    Answer: B. 400 × 3 = 1,200 mA, or 1.2 amps.

  6. Why is the 100 mV polarization criterion not a universal fallback?

    1. Because it requires valid data and must be permitted by the governing requirement
    2. Because it never applies to CP
    3. Because it does not require current interruption or documentation
    4. Because reference electrodes are not used

    Answer: A. The criterion must be allowed and supported by valid polarization or depolarization data.

  7. A galvanic anode has 20 amp-years usable capacity and discharges 0.5 amps. What is estimated life?

    1. 10 years
    2. 20 years
    3. 40 years
    4. 100 years

    Answer: C. Life = 20 ÷ 0.5 = 40 years.

  8. What condition can increase CP current requirement over time?

    1. Coating deterioration
    2. Improved coating isolation from electrolyte
    3. Reduced exposed metal area
    4. Removal of unintended continuity

    Answer: A. Coating deterioration increases exposed area and current demand.

  9. Why can a low-resistance groundbed still be a poor design?

    1. Because current distribution and interference risk also matter
    2. Because low resistance prevents all current flow
    3. Because rectifiers only work at infinite resistance
    4. Because anodes cannot discharge current in soil

    Answer: A. Low resistance is useful, but current distribution and interference must also be evaluated.

  10. What is the most defensible response to conflicting CP data?

    1. Select the most favorable reading
    2. Average unrelated readings
    3. Classify readings by structure, test condition, reference electrode, and criterion
    4. Ignore readings that fail

    Answer: C. Conflicting data must be organized by what was measured and which criterion it supports.

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