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# Columbia Gas of Ohio/Kentucky Tim Jenkins Corrosion Front Line Leader

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Columbia Gas of Ohio/Kentucky Tim Jenkins Corrosion Front Line Leader
AC Interference Columbia Gas of Ohio/Kentucky Tim Jenkins Corrosion Front Line Leader

Objectives Develop a basic understanding of the principles and components of AC Develop an understanding of the different types and effects of AC Influence Develop methods of mitigation Understand safety protocols Cover AC calculations

Basic Electric - AC SINE WAVE Single Phase
Peak of positive side of cycle. SINE WAVE AC - alternating current will reverse in polarity 120 times per second. A full cycle is considered one hertz. Typical AC has 60 hz per second. Half Cycle You’re typical AC sine wave will switch polarity 120 times a second Half Cycle Single Phase Peak of negative side of cycle

Basic Electric - AC SINE WAVE Three Phase
Peak of positive side of cycle. SINE WAVE AC – Three Phase, each conductor has the same amount of current and are 120 degrees out of phase Half Cycle Half Cycle Three Phase Peak of negative side of cycle

Fault Currents If any of the AC waveforms are to get of frequency with each other greater than or less than 120°, then a possible fault current can occur. Fault currents are large magnitude of current that can occur in brief amount of time (normally in milliseconds, typically .1 second) Normally electrical towers or structure has grounding and protection devices for this situation that limits the fault current to a brief amount of time

Fault Currents It’s not possible to know when, how or where fault currents will occur, in which makes it difficult to predict the effects of the fault and the mitigation required to protect both the pipeline and personnel Need to calculate locations of more acceptable for fault currents to occur, such as – Electrical storms, ice storms, & high winds Distance from the Power lines Information provided from the electric company

Fault Currents Even though the fault current is brief, it still presents a danger to personnel and the pipeline Coating damage can occur Pipeline failure due to melting or cracking of the pipeline wall Discuss more in Conductive coupling

Three Phase – Three conductors Shielded wires
Counterpoise Lines – Used for the grounding system, normally buried and above connected to each tower to provide grounding

Method of measuring AC voltage on Structures
Connect to ground with one lead and measure the AC volts onto the structure with the other lead. Use an accurate volt meter, set meter on AC volts Use rubber gloves during measurement and/or Use a rubber mat for added insulation High dielectric boots are available as well Common method, use a copper-copper sulfate half cell with the meter set at AC volts Must have good soil contact with half cell

Effects of AC Influence
Two key factors to consider with AC Influence Safety Corrosion

Effects of AC Influence
Two key factors to consider with AC Influence Safety Corrosion

Safety Electrical Shocks Arcing Ignition of volatile liquids
Step voltages Touch voltages Arcing Ignition of volatile liquids

Safety Maximum allowable AC voltage = 15 Vac
Based on a typical individual is at 1000 ohms body resistance And the individual can tolerate up to 15 mA Ohms law = 15 volts Anything above 15 Vac, could cause muscular contractions Prevents the person from letting go

Safety Electrical Shock, such as fault currents
Can occur by physical contact or standing in the vicinity of an energize structure in contact with earth Short time frames of electrical shocks are a concern when currents are above 50mA or greater Can cause ventricular fibrillation Certainly occurs at body currents of greater than 100 mA Death will occur unless De-fibrillation is given

Safety Electrical Shock
Fault currents - passes from the structure to ground creating a voltage gradient Step Voltage – Is the potential difference between two points on earth’s surface separation by a distance of 1 pace (approx. 1 meter) in the direction of max. potential gradient Touch Voltage – Potential difference between the grounded metallic structure and the point of earth’s surface separated by a distance equal to the normal maximum horizontal reach (approx. 1 meter)

Safety I (Fault Current) Ouch!!! Potential Touch voltage = 2kV 9 kV
The potential difference of the structure and the point on earth 9 kV 8 kV 7 kV

Safety I (Fault Current) Ouch!!! Potential Step voltage = 1kV 9 kV
The potential difference between the two points on the earth where the person is standing. 9 kV 8 kV 7 kV

Safety – (Maximum Current Calculation)
Maximum current IB a human body can tolerate depends on shock duration ts (seconds) and body weight calculated as follows: IB = 0.157/  ts ( for a 70 kg body) IB = 0.116/  ts ( for a 50 kg body)

Safety – Step and Touch Voltage Calculation
Maximum voltage that human body can tolerate by touch or step – Step formula - VStep = ( ) 0.157/  ts ( for a 70 kg body) VStep = ( ) 0.116/  ts ( for a 50 kg body) Touch formula - VTouch = ( ) 0.157/  ts ( for a 70 kg body) VTouch = ( ) 0.116/  ts ( for a 50 kg body) Resistance is considering the human body resistance and the contact resistance of the feet and earth (which depends on soil resistivity (m)

Safety – Step and Touch Voltage Calculation
Pipe line running parallel to a power line may exhibit 500 volts for a duration of ½ second during line to ground fault What is the tolerable touch voltage for a 50 kg individual with a soil resistivity of 50 ohms m touching the structure during the fault?

Safety – Step and Touch Voltage Calculation
VTouch = ( ) 0.116/  ts - ( for a 50 kg body) VTouch = ( • 50) 0.116/  (.5) = 176 VAC Since the possible fault voltage is 500 V then we need to raise the soil resistance Try 3000 Ω-m of crush stone added to the site Now the calculation equals to 902 VAC Which exceeds the maximum pipe to earth voltage of 500 VAC, the pipe is now safe Voltage gradient mats could provide a higher earth voltage to decrease the potential difference between the hand or feet touching the pipe

Safety I (Fault Current) Cool !!! Potential Step voltage = 0 kV 10 kV
Voltage gradient Mat = 10 kV The potential difference between the two points on the earth where the person is standing. 10 kV 10 kV 7 kV

Gradient control mats – Placed at all test station locations in the AC Corridor

Zinc Grounding Mat Cut hole for Test station Dimensions = 4’x4’
Wire connected to the zinc ribbon Cut hole for Test station Dimensions = 4’x4’ 12” crushed gravel Zinc ribbon 6” Low resistance material – Coke breeze or benonite 6” Low resistance material – Coke breeze or benonite Note : You can use the native soil, providing soil has good moisture content

Zinc Grounding Mat Connected to pipeline in Test station box
Wire connected to the zinc ribbon Connected to pipeline in Test station box Copper rods installed to get low resistance with grounding mat

Safety (Calculation for Arcing)
One of the greatest concern in dealing with fault currents between a power line structure and the pipeline is whether or not there is enough energy available to create an electric arc through the soil. Could result in pipeline damage

Safety (Calculation for Arcing)
Greatest prevention of Arcing with fault currents is to maintain safe distance between power lines and the pipeline One must obtain information from the electric company or producer such as fault currents maximum measurements Need to find soil resistivity in area Perform sufficient amount of testing samples in order to accurate obtain average

Safety - (Calculation for Arcing)
One Safe distance calculation by Sunde - for prevention of arcing Distance r (m) over which an arc could occur, based on soil resistivity  in (Ω-m) and fault magnitude If (kA).

Safety - (Calculation for Arcing)
R(m) = 0.08 Use this formula with lower resistivity R(m) = If •  ( = > 1000-m) Use this formula with extremely high resistivity R(m) = Distance measured in meters If = Magnitude of fault current  = Soil resistivity measured in meters If •  ( = < 100-m)

Safety - (Calculation for Arcing)
For an example, Soil  = 6700 ohms-cm = 67 ohms -m Fault Current If =17.9 kA Use formula R(m) = 0.08 R(m) = 87.6 meters If •  ( = < 100-m)

Lightening Pipeline 90 Meters Fault Currents

Lightening 90 Meters Pipeline Fault Currents Zinc Ribbon

Safety - (Calculation for Arcing)
If safe distance can not be obtain, Screening electrodes between the pipeline and towers maybe used to intercept the fault currents Such as zinc ribbon, or banks of sacrificial anodes

Lightening Fault Currents Pipeline

Lightening Fault Currents Zinc Pipeline Zinc Ribbon

Effects of AC Influence
Two key factors to consider with AC Influence Safety Corrosion

AC Corrosion on Pipelines
AC influence can cause corrosion to take place on coated steel pipe line Study performed in Germany, recently in the 1990’s, had determined that corrosion occurs at specific AC current density - (>100 A/m²) = Corrosion will result (20 A/m² A/m²) = Corrosion is unpredictable (< 20 A/m²) = Corrosion will not result

AC Corrosion on Pipelines
There has been documented cases of pipe to soil potentials being above VCSE with pH samples at 11, indicating pipe being cathodically protected, but corrosion was found due to AC current density in the range of 800 A/m² Pipe must be mitigated by dropping the AC voltage with the use of grounding devices such as zinc ribbon, copper wire, etc..

AC Calculation for Current Density
Calculation to determine AC current density - Iac = 8◦Vac/ ••d Iac = Current density  = soil resistivity in meters d = holiday area in cm’s

AC Calculation for Current Density
Calculation to determine AC current density - Iac = 8Vac/ ••d Resistance and area of holiday will be the key factors in determining the AC current density For an example – 1cm² holiday found with 5 Vac in a soil resistivity of 10 Ohms m (1000 ohms CM) = 127 amp/m² ((( Corrosive))) But below the 15 Vac

Documented cases of AC Corrosion Found -
Pipe to soil potential readings were above –1.0v CSE DC Pipe met DOT criteria for CP – above V CSE

Documented cases of AC Corrosion Found -

AC Stray Current – Interference Methods
Electromagnetic Coupling – Inductive Electrostatic Coupling – Capacitive Conductive Coupling - Direct path

AC Stray Current – Interference Methods
Electromagnetic Coupling – Inductive Electrostatic Coupling – Capacitive Conductive Coupling Direct path

Electromagnetic Coupling – Inductive
Works in the same capacity of a inductive pipeline locator – Induces an audio signal onto the buried pipeline Or in the same capacity of a transformer Primary coils inducing current by a electromagnetic field to the secondary windings

Electromagnetic Coupling - Inductive
Primary characteristics include: Medium to High Voltages High induced current levels

Electromagnetic Coupling - Inductive
The level of interference decreases with increasing separation of conductors The strength of the magnetic flux is in direct proportional to the current magnitude and inversely proportional to the distance of the conductor Induction effects experienced during power line faults can be a hazard to personnel Normally peaks at the point of entry of AC corridor and at the point of exit

Electromagnetic Coupling - Inductive (Remediation)
Installation of a low resistance grounding systems to reduce current and voltage levels Grounding mats for test stations (safety) Zinc ribbon Copper wire with the use of PCR or ISP Achieve at least a 25 ohm impedance system Ideally one ohm system Normally deeper is better

AC Stray Current – Interference Methods
Electromagnetic Coupling – Inductive Electrostatic Coupling – Capacitive Conductive Coupling Direct path

Electrostatic Coupling – Capacitive
Any two conductors separated by a dielectric material (insulator) is considered a capacitor Electrical Field Gradient between the transmission line and conductor takes place, builds up a electrical charge on the structure Such as a capacitor function Primary characteristics include : Very High Voltage peaks on power lines

Electrostatic Coupling – Capacitive
Conductors acceptable to capacitive coupling Pipelines suspended above ground on skids Any above ground equipment isolated such as vehicles or backhoes with rubber tires Electrostatic Coupling does not penetrate the earth Long parallel exposure of buried metallic structures to power lines

Electrostatic Coupling – Capacitive
Electromagnetic charge ( Voltage Gradient – electrom-agnetic field VAC VAC The voltage builds up until it has path to ground to discharge Ground

Electrostatic Coupling – Capacitive
Circuit is open, the voltage charge will build to high voltage static capacity, until a ground source is provided. Electromagnetic charge ( Voltage Gradient – electrom-agnetic field VAC VAC The voltage builds up until it has path to ground to discharge Ground

Electrostatic Coupling – Capacitive
Direct Path to ground – You…… By touching the structure and ground at the same time. Electromagnetic charge Voltage Gradient – electrom-agnetic field ( VAC VAC The voltage discharges Ground

Pipe suspended 500 VAC

Electrostatic Coupling – Capacitive (Remediation)
Temporary repair – Ground vehicles and equipment Use temporary grounding rods (copper rods) normally in 3 meters in length Use #2 Cable Use ½ in diameter rods in normal soils Refuel away of influence area to prevent accidental ignition, bond to refueling tanks Due to high resistance soil, you need to place multiple rods, space about 6 feet apart Metal chains dragging from the vehicle’s bumper in High AC voltage corridors are commonly used

Pipe is being grounded by making contact to the soil

Electrostatic Interference – Capacitive (Remediation)
Permanent repair – Above ground pipelines or valves Install Zinc ribbon Install Zinc Grounding or voltage gradient Mats Grounding Rods 3 Meters in length Design cable size based on potential fault currents Set depth until achieved a minimum of 25 ohms impedance Lower the impedance as low as possible One ohm is desirable

Electrostatic Interference – Capacitive (Remediation)
In most cases, the Electrostatic charge can not generate enough body current to create a shock hazard, more of a nuisance shock similar to static electricity.

AC Stray Current – Interference Methods
Electromagnetic Coupling – Inductive Electrostatic Coupling – Capacitive Conductive Coupling Direct path

Conductive Coupling Occurs when line to ground shorts or faults take place On High Voltage power lines faults normally occur during lighting strikes Fault currents can occur by accidental contact with other structures Such as construction equipment or cranes Fault currents is conducted to the pipeline through its coating Higher the coating dielectric strength, the less amount of the transfer current on the pipeline

Conductive Coupling Occurs in milliseconds
Voltage and current is higher than steady state but happens very briefly .1 or a tenth of a second is the normal time frame that voltage is present due to the fault protection system

Conductive Coupling Failure to the pipeline Coating damage
Cracking and melting of the pipe wall

Materials Used for AC Mitigation
Two reasons for mitigation of AC influence Prevent corrosion on the pipeline Prevent of hazardous shock from contacting the pipeline Materials commonly used Zinc grounding and/or voltage gradient mats Zinc ribbon or heavy gauge copper wiring Blind face test stations Galvanic anodes PRC or Inductive capacitive coupling

Materials Used for AC Mitigation
Zinc Ribbon – to mitigate the AC currents from the pipeline to the soil Zinc is used in some low resistivity areas as a galvanic anode to protect structures The AC currents will take the path of less resistance to the ground Zinc provides this path Depending of soil resistance, distance to the tower, the location of structure to the towers and the amount of magnitude influence of the towers must be calculated in the design of the amount of Zinc ribbon needed and the location

Materials Used for AC Mitigation
Programs available to profile the pipeline for AC mitigation PRCI

Materials Used for AC Mitigation
Zinc Ribbon – Installation – Placed below the pipeline Depending on soil resistance Place in the lowest resistance area Minimum Two feet away from the pipeline Make connection to the pipeline in a junction box or test station Commonly used, a minimum of a no. 4 gauge wire connected to the pipeline and zinc ribbon May need to increase size of cable due to greater magnitude of fault currents

Materials Used for AC Mitigation
Zinc Ribbon – Installation – Placed between the pipeline and tower To mitigate fault currents and prevent coating damage Splice zinc ribbon by striping the zinc off the wire and crimp the connections together Make crimp repair with epoxy resin kits, heat shrink sleeve, or electrical rubber tape

Chart for Zinc Ribbon

Standard – ½ inch comes in wooden spools
Ribbon is bonded to the main in the test station to be able to test AC mitigation such as AC current density & grounding system resistance

Zinc ribbon is placed below the pipeline and at least two feet away

Installed at test station facility –
Coupon for AC measurements Grounding mat or voltage gradient mat for test point reader safety Zinc ribbon connection Structure connections

What's wrong with the next slide?

Zinc ribbon Slide “B” Pipe line Tower Zinc ribbon Slide “A”

Zinc Ribbon is on the wrong side of the pipeline
Tower Zinc ribbon Zinc ribbon is above the pipeline

Polarization cells or Insulated surge protections are great for grounding the pipeline or structure with out shorting out the DC cathodic protection currents. It will block the DC and allow the AC currents flow to ground.

Dead Front Test Stations
To prevent electrical shock in making contact with wire connection to mainline

Any Questions??? Thank YOU!!!!

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