POLARITY

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POLARITY / -
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Meter Polarity

• It is extremely important to record the polarity
  (and unit) displayed on the voltmeter.
• It is equally important to understand what that
  polarity means.
• Polarity is basically understanding the flow of
  current in a circuit.
• This will help us determine anodic areas,
  cathodic areas, and direction of current flow.

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Polarity of Two Electrodes
Positive
V DC
Anode (Active Metal)
Cathode (Noble Metal)
Current
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Building a Galvanic Series
Active B D A E C
V B/A 240 mV
V C/A - 680 mV
V DC
V D/A 10 mV
V E/A - 200 mV
A
E
B
C
D
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Galvanic Series
More Active Magnesium -1.750 V Zinc -1.100
V Aluminum -1.050 V Clean Steel - 0.500 V to
- 0.800 V Rusted Steel - 0.200 V to 0.500
V Copper - 0.200 V Graphite 0.300 V More
Noble
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Current Flow on a Pipeline
Negative
V DC
Current
Pipeline
Current Span
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Polarity When Measuring SHUNTS

• Example
• V 26 mV
• 50 mV 25 A shunt
• Shunt factor 0.5 A/mV
• Current 26 mV x 0.5 A/mV 13 A
• Current Direction ??????

26
mV DC
Right - Left
50 mV 25A Shunt
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Pipe-to-Soil Potential Measurements
Negative
- 0.650
Positive to Pipe
Negative to CSE
Reference Electrode
Pipeline
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Pipe-to-Soil Potential Measurements
- 0.910
0.805
Reference Electrode
Cathodic Area
Anodic Area
El Paso Pipeline Under Cathodic Protection
Foreign Pipeline Crossing
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Polarity Interference Bond

• Meter Reads - 42 mV
• Bond Current 42/0.01 4200 mA
  4.2 Amps
• Direction of Current ? (hint Ck polarity)
• Is this a Critical Bond to El Paso ???

- 42
mV DC
NO
0.01 Ohm Shunt
Bond Box
Foreign Pipeline
El Paso Pipeline
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Side Drains
Pipeline
- 7
Reference Electrode
Reference Electrode

• Positive means current is right-to-left

- 2

• Largest gradient coating holiday

- 19
196
- 40
_

- 196
- 45
Current pickup Cathodic Area
- 6
12
Side Drains
Pipeline
- 7
-15
_

- -5
Pipeline DISCHARGING Current (i.e. Anodic Area)
- -15
- 0
- 19
Current Discharge, Anodic Area
Pipeline Receiving Current
- 15
- 6
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Summary

• ALWAYS, ALWAYS record polarity and unit of
  measurement. Example -42 mV, or 210 mA.
• Polarity indicates direction of current
  movement.
• Be consistent with how you connect your meter.

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QUIZ
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Quiz Question 1
- 1.200
V DC
Magnesium
Steel
Current
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Quiz Question 2
0.135
V DC
Current
Pipeline
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Quiz Question 3

• Direction of Current ? (hint Ck polarity)
• Is this a Critical Bond to El Paso ???

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YES
mV DC
50mV- 50A Shunt
Bond Box
Foreign Pipeline
El Paso Pipeline
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Quiz Question 4
Reference Electrodes
- 7
- -5
Pipeline DISCHARGING Current (i.e. Anodic Area)
- -15
- 0
- 19 -
- 15
Pipeline RECEIVING Current (i.e. Cathodic Area)
- 6 -
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THANK YOU