Cathodic Protection Equipment and Measurement
Basic Corrosion Course 2017
February 21-23, 2017 Luke Harris – Integrity Solutions 1
Period #6
Overview
• Safety • Pipe-to-Soil Potentials • CP Current Flows • Resistance Measurements • Rectifier Readings • Surveys • Soil Resistivity
February 21-23, 2017 Luke Harris – Integrity Solutions 2
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Safety
• Traffic • Slips, Trips, and Falls • Shock Hazards • Chemicals
February 21-23, 2017 Luke Harris – Integrity Solutions 3
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Pipe-to-Soil Potential
• What is a pipe-to-soil potential? • What equipment is required? • Why do we take them? • Regulations
February 21-23, 2017 Luke Harris – Integrity Solutions 4
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Pipe-To-Soil Measurements
• Used to determine the effectiveness of CP • Locate stray current • Check for shorts. Electrical isolation, electrical
continuity • Taken with CP
– ON – Off – Cycling – Native State
February 21-23, 2017 Luke Harris – Integrity Solutions 5
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Components to take a P/S Measurement
• Volt Meter • Lead Wires • Reference Electrodes • Electrolyte • Pipeline or Structure
February 21-23, 2017 Luke Harris – Integrity Solutions 6
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Voltmeters
• Available in various types • Digital
• Numerical read-out • Analog (D’ Arsonval movement)
• Moving needle • Computerized Data Logger
• Computer chip stores the readings • Can collect other data
• GPS • Must be high input resistance (10 megaohms or more) • Durable/Rugged • Temperature Stable
February 21-23, 2017 Luke Harris – Integrity Solutions 7
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Common Voltmeters used for CP
• Digital
February 21-23, 2017 Luke Harris – Integrity Solutions 8
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Common Voltmeters used for CP
• Analog
February 21-23, 2017 Luke Harris – Integrity Solutions 9
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Common Voltmeters used for CP
• Computerized Data Logger
February 21-23, 2017 Luke Harris – Integrity Solutions 10
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Lead Wires
• Connections Secure – To the Structure – Low Resistance – Tight Connections
• Loose connections – High Resistance – Unstable or incorrect reading
• Contact point – Clean – Electrically continuous
February 21-23, 2017 Luke Harris – Integrity Solutions 11
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Reference Electrodes (Half-Cells)
• Two Common Types – Copper Sulfate – Silver-Silver Chloride
• Contaminant free • Saturated solution • Solution should be clear, not milky or cloudy • Reference electrodes are also called half-cells:
– Reference cell forms one-half of an electrical cell – pipeline being the other half of the cell
February 21-23, 2017 Luke Harris – Integrity Solutions 12
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Copper Sulfate Reference Electrode
• Come in various sizes and types • Most commonly used for pipeline work • Temperature sensitive • Do not leave in direct sunlight for long periods of time
or subjected to high temperatures – cover it from direct sunlight – overheating will cause a voltage shift in the potential readings – may cause it to leak or become unsaturated
February 21-23, 2017 Luke Harris – Integrity Solutions 13
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Half-Cells • 2A Pencil
• 8A Flat Tip
• 6A Flat Tip
• 6B Pointed Tip
• 8B Pointed Tip
• 3A Flat Bottom
• W7 Waterproof connector
• DBA Direct burial
February 21-23, 2017 Luke Harris – Integrity Solutions 14
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Placement of Electrodes • Important for accurate readings • Directly over the pipeline
– The closer the better • Good electrolyte contact • Do not place the electrode over an anode
– get readings in between anodes whenever possible – don’t take readings directly at test stations that have an
anode connected through them – do not place the electrode near the anode when testing
service lines that have anodes attached to them – get the reading somewhat remote from the anode
• readings over an anode will yield an erroneous reading because of the voltage (IR) drop
• Close to the pipeline as possible without touching it
February 21-23, 2017 Luke Harris – Integrity Solutions 15
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Good Electrolyte Contact • Good contact between the half-cell and the electrolyte • Wetting the electrolyte with water can help improve contact
– A wet sponge can also be used – The “Fat Boy” electrode
• Issues with taking readings through concrete or asphalt surfaces • Get the tip through the top layers of the soil for better contact.
– Good contact; potential readings will settle down • Gravel or stones
– may have to scrape away a couple of inches to get to the soil underneath
– may need to install a tube through the stone to get to the soil • Landscaping may have plastic for drainage or architectural effects
with mulch or stone – puncture the plastic and get the electrode down to the soil or
use a tube to get through the plastic
February 21-23, 2017 Luke Harris – Integrity Solutions 16
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Sign Convention
• Pipeline connected to the voltmeter (-) and your half-cell is connected to the voltmeter (+), the value would read +VDC
• Pipeline connected to the voltmeter (+) and your half cell is connected to the voltmeter (-) the value would be -0.850 VDC.
• Either case is correct • Must track the polarity • Safety note: Connect reference cell first and place it on
the ground before connecting to the test lead.
February 21-23, 2017 Luke Harris – Integrity Solutions 17
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Why Do We Take P/S Potentials • Regulations
– Department of Transportation (DOT) – State
• Monitoring CP levels • Criteria
– Two most common • Pipe-to-Soil Potential of at least -0.85 Volts With Respect
to a Copper-Copper Sulfate Reference Electrode – Measured with Cathodic Protection Applied – Measured with Cathodic Protection Off
• 100mV (0.1) Volts Polarization – IR Drop
February 21-23, 2017 Luke Harris – Integrity Solutions 18
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Effect of Voltage (IR) Drop • Ohm’s Law defines the relationship among the three electrical
quantities, voltage (E), current (I) and Resistance (R). Ohm’s Law states that voltage equals current times resistance, or E=IxR. Voltage is frequently referred to as simply IR.
• A voltage drop occurs whenever a current passes through a resistance
• The earth has resistance – Place the reference cell close to the pipe
• The voltage at the location of the electrode will be more negative than that at the location of the pipe – an erroneous reading, more negative than that the voltage at
the pipeline – cathodic protection criteria require that the IR drop be
“considered” in the reading; taking steps to obtain the most accurate, IR drop free data
February 21-23, 2017 Luke Harris – Integrity Solutions 19
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
-.850V Criterion
• Commonly used criterion • Applicable to steel and cast/ductile iron • Useful on coated pipelines because of the
relatively small current required to protect them • Bare pipelines may require excessive current to
polarize them up to this potential • There are two versions of this criterion.
February 21-23, 2017 Luke Harris – Integrity Solutions 20
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
-.850 with Cathodic Protection Applied
• Applicable to pipelines that have galvanic anodes connected directly to them –No way of disconnecting or interrupting
the protective current –Consider IR Drop
• IR Drop Free Coupon Test Station • Placement of Reference Cell
February 21-23, 2017 Luke Harris – Integrity Solutions 21
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
-.850 with Cathodic Protection Off • Pipe-to-soil potential measurements taken with the
cathodic protection current momentarily interrupted, or turned off – Usually easy to accomplish with impressed current
systems • Interrupters • Also be done when galvanic systems are
connected to the structure through a test station • When the cathodic protection is off, there is no current
flow in the earth and thus no IR drop (since voltage drop [E] = IxR [Ohm’s Law], if I=0, E must = 0) – These “off” readings are accurate measurements of
the actual structure-to-soil potential
February 21-23, 2017 Luke Harris – Integrity Solutions 22
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
100mV (.1V) Polarization
• Applicable to steel and cast/ductile iron as well as aluminum and copper
• Useful for steel structures that are poorly coated or bare and which would require an excessive amount of protective current to meet one of the -0.850V criteria – frequently used for well casings
• The 100mV (0.1V) polarization refers to the difference between – 1) the original, unprotected potential and the “off” potential
after cathodic protection has been installed or: – 2) the difference between the “instant off” potential and a
potential reached after a period of depolarization
February 21-23, 2017 Luke Harris – Integrity Solutions 23
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Cathodic Protection Current Flow
• Direct Readings with an Ammeter – Inconvenient – Slow – Dangerous – Meter in Series with Circuit – Off Too Long – Skew Readings
February 21-23, 2017 Luke Harris – Integrity Solutions 24
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Cathodic Protection Current Flow
• Using a Shunt – Accurate and Fast – Voltmeter Across Known Resistance – Ohms Law
• E=IR
February 21-23, 2017 Luke Harris – Integrity Solutions 25
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Shunt Ratings
February 21-23, 2017 Luke Harris – Integrity Solutions 26
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Shunt Styles
February 21-23, 2017 Luke Harris – Integrity Solutions 27
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Shunt Styles
February 21-23, 2017 Luke Harris – Integrity Solutions 28
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Shunt Styles
February 21-23, 2017 Luke Harris – Integrity Solutions 29
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
OHM’S LAW
February 21-23, 2017 Luke Harris – Integrity Solutions 30
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
• Mathematically it can be stated three ways:
(1) I = E/R (2) R = E/I (3) E = I x R or E = IR I = Current in Amperes
E = Voltage in volts R = Resistance in Ohms
Volt
The volt is the basic unit of electrical pressure which forces an electrical current (electrons) to flow through an electrical circuit.
1000 mV = 1 V
1 mV = 0.001 V
SYMBOL is either V or E
50 mV = _____V 2.5 V = ______mV
250 mV = ______V 10.0 V = _____mV
850 mV = ____ V 3.67 V = _____mV
0.250
0.05
0.85
2,500
10,000
3,670
OHM’S Law • Sample Calculations:
I V R 1. _____ 10 V 5 ohms 2. 3A _____ 2 ohms 3. _____ 10 mV 0.1 ohms 4. 1200 mA 12V _____
2
6
100 mA (.1 A)
10 ohms
Shunts Calculation
50 mV - 50 A Determine Amps/mV 1 mV = ____ A = ____ A / mV mV Shunt Resistance R = E = _____V = _____ Ω I A If Measure - 50 mV I = V = ____ mV = ________mV = _____ A R Ω Ω Additional samples provided at the end of the chapter.
50
50 1
0.050
50
0.001
50
0.001 50,000 50
Shunts Calculation
Determine Shunt Factor (SF)
SF X Measurement (mV) = Amps
50A / 50mV shunt = SF of _____
SF ____ X 4.2 mV = ____ A
50A / 25mV shunt = SF of _____
SF ____ X 4.2 mV = ____ A
1
1 4.2
0.5
0.5 2.1
Shunts Calculation
V / R = I
Measurement (V) / R (0.1Ω, 0.01Ω, or 0.001Ω) = I (A)
Measurement of 32.1 mV = _____V / 0.1Ω = ____ A
Measurement of 32.1 mV = _____V / 0.01Ω = ____ A
Measurement of 32.1 mV = _____V / 0.001Ω = ____ A
.0321 .321
.0321 3.21
.0321 32.1
Rectifier Readings
• AC Input – Voltage at Disconnect or Behind Breaker – Current by Clamp-On Ammeter – Power =(3600x Kh x N) / T
• AC Throughput – Voltage Across Main Lugs of Taps
• DC Output – Voltage Across the Output Lugs – Current: Voltage Across the Shunt
February 21-23, 2017 Luke Harris – Integrity Solutions 36
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
AC Input Voltage
• Safety note: Rectifiers are general charged with AC with 120 volts or more.
• Readings taken at: – Electrical disconnect – Behind main breaker – These are taken ahead of protective devices
February 21-23, 2017 Luke Harris – Integrity Solutions 37
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
AC Throughput
• Measure AC voltage into the stacks • Across the main lugs of the taps • Across input lugs of the stacks
February 21-23, 2017 Luke Harris – Integrity Solutions 38
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
DC Output
• DC voltage across the output lugs • Current through the shunt • Meters on the unit
February 21-23, 2017 Luke Harris – Integrity Solutions 39
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Surveys
• Locating • GPS • Close Interval Survey (CIS) • Direct Current Voltage Gradient (DCVG) • Alternating Current Voltage Gradient (ACVG)
February 21-23, 2017 Luke Harris – Integrity Solutions 40
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Conductive Locating
February 21-23, 2017 Luke Harris – Integrity Solutions 41
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Pipe
Transmitter Receiver
Inductive Locating
February 21-23, 2017 Luke Harris – Integrity Solutions 42
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Pipe
Transmitter Receiver
GPS
February 21-23, 2017 Luke Harris – Integrity Solutions 43
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Close Interval Survey
February 21-23, 2017 Luke Harris – Integrity Solutions 44
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Close Interval Survey Data
February 21-23, 2017 Luke Harris – Integrity Solutions 45
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Direct Current Voltage Gradient
February 21-23, 2017 Luke Harris – Integrity Solutions 46
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Alternating Current Voltage Gradient (ACVG)
February 21-23, 2017 Luke Harris – Integrity Solutions 47
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Soil Resistivity
February 21-23, 2017 Luke Harris – Integrity Solutions 48
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
P1 P2 C1 C2
Resistivity Test Instrument
Review
• Pipe-to-soil potentials • CP Current Flows • Resistance Measurement • Rectifier Reads • Surveys • Soil Resistivity • Safety
February 21-23, 2017 Luke Harris – Integrity Solutions 49
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6
Luke Harris 989-436-3894
February 21-23, 2017 Luke Harris – Integrity Solutions 50
2017 Underground Corrosion Short Course CP Measurements Part 1– Period #6