Stray and TelluricStray and TelluricCurrent CorrectionCurrent Correction

Peter NicholsonManaging Director

Cathodic Technology Limited

Bolton, Ontario, Canada

Close Interval Potential Close Interval Potential SurveysSurveys

CIPS surveys are the mainstay of pipeline integrity

CIPS Surveys may be influenced by stray or telluric currents

Pipeline IntegrityPipeline 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

Static Stray CurrentStatic Stray Current

This paper does not cover static stray current such as interference from foreign cathodic protection systems or HVDC systems

Dynamic Stray CurrentDynamic Stray Current

Dynamic stray currents may originate from electric transit systems, mining operations and other operations using DC current

Dynamic Stray CurrentsDynamic Stray Currents

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

TelluricTelluric Currents 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

Telluric CurrentsTelluric Currents

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

Stray Current CorrectionStray Current Correction

CIPS data affected by dynamic stray currents or telluric currents can be corrected to yield meaningful results

GPS Timed Data LoggerGPS 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

CIPS SurveyCIPS 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

GPS Timed Current GPS Timed Current InterruptersInterrupters

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

Deviation from Average PotentialDeviation 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))

Top of Mountain South of Rt 114 Rect OFF Rect ON OFF Div ON Div Date Time

720 761 -3.74242 18.02681 281002 194929 44 35.8396 N 71 51.3908 W718 761 -5.74242 18.02681 281002 194930 44 35.8395 N 71 51.3908 W718 761 -5.74242 18.02681 281002 194931 44 35.8395 N 71 51.3908 W718 761 -5.74242 18.02681 281002 194932 44 35.8395 N 71 51.3908 W716 760 -7.74242 17.02681 281002 194933 44 35.8394 N 71 51.3908 W716 761 -7.74242 18.02681 281002 194934 44 35.8394 N 71 51.3909 W716 758 -7.74242 15.02681 281002 194935 44 35.8393 N 71 51.3909 W716 758 -7.74242 15.02681 281002 194936 44 35.8391 N 71 51.391 W

CIPS Data Compromised by Stray CurrentsCIPS Data Compromised by Stray Currents

Even with severe stray currents CIPS data can be corrected

CIPS Survey Data CorrectionCIPS Survey Data Correction

Enter a Formula on your CIPS data spread sheet to acquire the Potential Deviation for each recorded survey value

=(Lookup (Time of CIPS Data Recording),

(Data Recording Times On Stationary Data Logger),

(Deviation Value For Each Recording Interval))

Chainage Rect ON Rect OFF Lat Deg Minutes Long Deg Minutes Elevation UTC Time0 1634 1413 43 48.9246 N 79 16.8898 W 185.4 1518342 1604 1387 43 48.9249 N 79 16.8894 W 185.2 1518354 1555 1364 43 48.925 N 79 16.889 W 185.1 1518366 1578 1359 43 48.925 N 79 16.8887 W 185.2 151837

CIPS Survey Data CorrectionCIPS 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

Rect ON Rect OFF Correct ONCorrect OFFON Div off dIV666146 924 850 905 847 -18.9732 -2.74242666145 917 840 898 837 -18.9732 -2.74242666143 917 834 897 833 -19.9732 -0.74242666139 905 817 886 816 -18.9732 -0.74242666133 891 807 871 804 -19.9732 -2.74242666127 872 790 852 789 -19.9732 -0.74242666120 855 765 835 762 -19.9732 -2.74242666113 829 745 809 745 -19.9732 0.257576666106 847 767 829 766 -17.9732 -0.74242666099 867 785 849 786 -17.9732 1.257576666092 855 760 837 761 -17.9732 1.257576666084 855 767 838 768 -16.9732 1.257576

Verifying Interruption TimingVerifying 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

CIPS Correction Requires Precise TimingCIPS Correction Requires Precise Timing

Precise timing from the GPS engine of 365 nano seconds allows for stray and telluric correction

Corrected CIPS DataCorrected CIPS Data

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

Thank You From The Staff At Thank You From The Staff At Cathodic Technology LimitedCathodic Technology Limited