Stray and Telluric Current Correction

1. Stray and TelluricCurrent Correction Peter Nicholson Managing Director Cathodic Technology Limited Bolton, Ontario, Canada

2. Close Interval Potential Surveys • CIPS surveys are the mainstay of pipeline integrity • CIPS Surveys may be influenced by stray or telluric currents

3. Pipeline Integrity • Measuring structure-to-electrolyte potentials at test stations can give a false indication of the level of cathodic protection on a pipeline - only a CIPS survey can provide assurance of cathodic protection

4. Static Stray Current • This paper does not cover static stray current such as interference from foreign cathodic protection systems or HVDC systems

5. Dynamic Stray Current • Dynamic stray currents may originate from electric transit systems, mining operations and other operations using DC current

6. Dynamic Stray Currents • Dynamic stray currents which originate from electrified transit systems usually show maximum activity during the morning and afternoon rush hour

7. Telluric Currents • Telluric currents are dynamic currents induced on a pipeline due to disturbance of the earth’s magnetic field as a result of sun spot activity

8. Telluric Currents • Telluric currents affect the potential of a pipeline and generate IR drops in the pipe wall resulting in errors in CIPS data

9. Stray Current Correction • CIPS data affected by dynamic stray currents or telluric currents can be corrected to yield meaningful results

10. GPS Timed Data Logger • Stationery data loggers such as the Cath-Tech “Smart Logger” set out in the survey area to record the rectifier ON and OFF structure-to-electrolyte potential of each rectifier interruption provide the deviation from the average potential

11. CIPS Survey • In areas influenced by dynamic stray currents or telluric currents, the close interval survey proceeds while the stationary data loggers record the rectifier ON and OFF potential of each interruption

12. GPS Timed Current Interrupters • By utilizing GPS timed Data Loggers, Interrupters and Survey Equipment accurate time based data can be compared for Telluric and Stray Current Correction

13. Deviation from Average Potential • Calculate the average rectifier ON and OFF potentials of the data recorded by the static logger, then calculate the deviation from the average for each logged value =(B4-Average(B$4:B$9872))

14. CIPS Data Compromised by Stray Currents • Even with severe stray currents CIPS data can be corrected

15. CIPS Survey Data Correction =(Lookup (Time of CIPS Data Recording), (Data Recording Times On Stationary Data Logger), (Deviation Value For Each Recording Interval)) • Enter a Formula on your CIPS data spread sheet to acquire the Potential Deviation for each recorded survey value

16. CIPS Survey Data Correction • By utilizing the GPS System, precise time can be obtained to allow correction of CIPS data from the deviation of the potential recorded at one or more Stationary Loggers

17. Verifying Interruption Timing • Waveforms can be taken to verify the accuracy of the rectifier interruption and any electrical activity that would affect the Stray or Telluric Current Correction

18. CIPS Correction Requires Precise Timing • Precise timing from the GPS engine of 365 nano seconds allows for stray and telluric correction

19. Corrected CIPS Data

20. Thank You From The Staff At Cathodic Technology Limited Cathodic Technology Limited 15-1 Marconi Court Bolton, Ontario Canada L7E 1E2 Phone ++1 905 857-1050 Fax ++1 905 857-3499 Email ctl@corrosion-rust.com Web Site www.cath-tech.com