Close-Interval Survey
Near-continuous structure-to-electrolyte potential data for evaluating CP levels, interruptions, gradients, and locations missed by test-station-only surveys.
Cathodic Protection Survey Methods
Survey methods are where cathodic protection theory becomes field evidence. This hub organizes the main CP survey techniques by what they measure, what they can prove, and what errors can mislead interpretation.
Use the Right Survey for the Question
Different surveys answer different questions. A structure-to-electrolyte potential survey evaluates CP level at accessible points. A close-interval survey improves spatial resolution. A DCVG or ACVG survey helps locate coating faults. Coupons help reduce voltage-drop error at a representative exposed surface. Current requirement testing estimates the current needed to polarize a structure or area.
The mistake is treating every survey as if it proves the same thing. A coating survey does not automatically prove adequate protection, and a test-station reading does not prove what happens between test stations.
Primary Survey Method Pages
Electrical Isolation Testing
Technical practice guide for evaluating electrical isolation, continuity, shorts, bonds, casing interaction, and CP current distribution.
Pipe-to-Soil Potential Survey
Technical practice guide for structure-to-electrolyte potential measurements, including ON, instant-off, native, and depolarized readings, data quality, IR drop, and interpretation.
Depolarization Testing
Technical practice guide explaining cathodic polarization, depolarization, calculated polarization, and the 100 mV polarization criterion.
DCVG Survey
Direct current voltage gradient surveys used to locate coating defects and evaluate current discharge patterns near holidays.
ACVG Survey
Alternating current voltage gradient surveys used to locate coating defects using AC signal leakage in the electrolyte.
CP Coupons
Technical practice guide for coupon measurements, instant-off coupon readings, depolarization, calculated polarization, and interpretation.
UST CP Testing
Technical practice guide for UST cathodic protection testing, direct-connect galvanic systems, coupons, criteria, and interpretation.
AST CP Testing
Technical practice guide for tank-bottom reference cells, rectifier interruption, criteria, and AST CP interpretation.
Current Requirement Testing
Temporary-current testing used to estimate current needed for polarization, distributed protection, and CP system design decisions.
CP Troubleshooting
How survey findings connect to rectifier output, current distribution, isolation problems, shielding, interference, and coating condition.
Casing Testing
Technical practice guide for evaluating casing isolation, casing shorts, electrolytic contact, and CP current distribution.
Galvanic Anode Testing
Technical practice guide for evaluating galvanic anode output, current, anode life, and CP interpretation.
Soil Resistivity Testing
Technical practice guide covering the Wenner four-pin method, data quality, and CP interpretation.
Survey Selection Matrix
| Question | Useful Method | Primary Caution |
|---|---|---|
| Is the pipeline meeting a potential criterion between test stations? | CIS / interrupted CIS | Requires valid contact, interruption control, and careful handling of dynamic current. |
| Where are coating holidays likely located? | DCVG or ACVG | Holiday indication is not the same as proving corrosion severity. |
| How much current may be needed to polarize the structure? | Current requirement test | Temporary groundbed location and current distribution can bias the result. |
| Can IR drop be reduced at a representative exposed surface? | Coupon testing | Coupon area, placement, connection, and environment must represent the intended condition. |
| Is stray current affecting the structure? | Time-based potentials, line current, side-drain, mutual/exposure surveys | Static snapshots can miss dynamic pickup and discharge cycles. |
Field Interpretation Priorities
- Confirm the structure under test and the electrical continuity path before trusting readings.
- Record measurement condition: native, ON, instant-off, depolarized, interrupted, or affected by dynamic current.
- Separate CP performance questions from coating-condition questions.
- Consider voltage drop, reference electrode placement, shielding, adjacent structures, and changing current sources.
- Use survey data to create a defensible interpretation, not just a pass/fail table.
Related Measurement Pages
Measurements
Cathodic protection measurement hub covering reference electrodes, structure-to-electrolyte potentials, instant-off potentials, IR drop, CP coupons, shunts, current measurement, and reference electrode conversion.
IR Drop
Guide to IR drop and voltage-drop error in cathodic protection measurements, including soil voltage gradients, pipeline current, reference electrode placement, interruption, and coupons.
Instant-Off Potential
Technical practice guide to instant-off potential testing, current interruption, IR drop, valid data conditions, criterion interpretation, worked examples, and common field errors.
CP Coupons
Guide to cathodic protection coupons, including coupon purpose, placement, connection, instant-off readings, current density, depolarization, and limitations.