CP Criteria Practice Questions

These questions test CP criteria interpretation, including fixed potential criteria, instant-off readings, 100 mV polarization, reference electrodes, and limitations.

Study Focus

Focus on matching the criterion to the correct structure, reference electrode, test condition, and governing requirement.

Practice Questions

  1. Why is a potential reading incomplete without a reference electrode type?

    1. Because different reference electrodes use different potential scales
    2. Because reference electrodes supply rectifier current
    3. Because all readings must be AC
    4. Because soil resistivity cannot be measured

    Answer: A. A potential value must identify the reference electrode scale.

  2. What does an instant-off potential attempt to reduce?

    1. Metallic continuity
    2. IR drop from CP current flow
    3. Coating thickness
    4. Pipe diameter

    Answer: B. Instant-off readings reduce voltage drop caused by CP current flow.

  3. A structure shifts from −700 mVCSE depolarized to −825 mVCSE polarized. What is the polarization shift?

    1. 75 mV
    2. 125 mV
    3. 700 mV
    4. 1,525 mV

    Answer: B. The magnitude of the shift is 125 mV.

  4. Why is the 100 mV polarization criterion not automatically valid whenever −850 mVCSE is not achieved?

    1. Because it requires valid data and must be permitted by the applicable requirement
    2. Because it never applies to any CP structure
    3. Because it does not require measurements
    4. Because it only applies to AC voltage

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

  5. A pipeline ON reading is −1,050 mVCSE and instant-off is −820 mVCSE. Which value is more appropriate for a polarized potential criterion?

    1. The ON value only
    2. The instant-off value
    3. The pipe diameter
    4. The rectifier nameplate voltage

    Answer: B. The instant-off value better represents polarized potential when current interruption is valid.

  6. Why can one passing test point fail to prove full structure protection?

    1. Because current distribution can vary by location
    2. Because all test points are identical
    3. Because coatings eliminate all current demand
    4. Because reference electrodes cannot be used in soil

    Answer: A. Current distribution, shielding, coating condition, and continuity can vary across the structure.

  7. Which statement is correct?

    1. ON, instant-off, native, and depolarized readings all mean the same thing
    2. The test condition must be documented because it affects interpretation
    3. Reference electrode type is optional
    4. Criteria do not depend on structure type

    Answer: B. Test condition must be documented because criteria are tied to measurement methods.

  8. What can invalidate a depolarization test?

    1. Leaving significant CP current sources active
    2. Recording the reference electrode type
    3. Using consistent test locations
    4. Documenting the timing

    Answer: A. Remaining current sources can prevent valid depolarization.

  9. Why should CP criteria not be applied from memory?

    1. Because exact language, applicability, and exceptions must be checked in the official requirement
    2. Because criteria never change field conclusions
    3. Because only color coding matters
    4. Because all standards are identical

    Answer: A. Official standards and project requirements control exact applicability and language.

  10. Which is the best report statement?

    1. The pipe passed CP
    2. The structure satisfied the applicable criterion at the tested locations based on the stated readings and test conditions
    3. The rectifier was on, so everything passed
    4. The most negative reading proves the whole system

    Answer: B. A defensible conclusion identifies scope, criterion, readings, and limitations.

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