western region gas conference august 21, 2012 corrosion 101

WESTERN REGION GAS CONFERENCE AUGUST 21, 2012

CORROSION 101

BASIC CORROSIONMADE

CLEAR AS MUDPRESENTED BY John Brodar P.E. of the Salt River Project

IGNITION SOURCE

FUEL OXYGEN

METALLIC PATH

ELECTROLYTE

ANODE CATHODE

FIRE TRIANGLE CORROSION RECTANGLE

IGNITION SOURCE

FUEL OXYGEN

METALLIC PATH

ELECTROLYTE

ANODE CATHODE

FIRE TRIANGLE CORROSION RECTANGLE

Just as Fire requires all three conditions (Fuel, Oxygen and an Ignition Source) to burn, several conditions must be present for Corrosion to occur.

Corrosion requires an anode, a cathode, an electrolyte and a metallic path connecting the anode and cathode. If any one of these conditions is not present or prevented, corrosion will not occur. Corrosion is electrochemical in nature: the electrolyte and metallic path are necessary for current to flow. If there is no current flow there is no corrosion.

METALLIC PATH

ELECTROLYTE

ANODE CATHODE

CORROSION RECTANGLE

METALLIC PATH

ELECTROLYTE

ANODE CATHODE

CORROSION RECTANGLE

ACMECAMEMECAECAM … REMOVE ANYONE AND THERE IS NO CORROSION.

METALLIC PATH

ELECTROLYTE

ANODE CATHODE

CORROSION RECTANGLE

REMOVE THE ANODEREMOVE THE CATHODE

REMOVE THE METALLIC PATHREMOVE THE ELECTROLYTE AND YOU

STOP CORROSION.

WHAT MAKES SOMETHING AN ANODE?


WHAT MAKES SOMETHING A CATHODE?


WHAT MAKES SOMETHING A CATHODE?

DIFFERENCES!

Illustration of Ohm’s Law_ +

E = 1 volt

R = 1000 ohmsI

milliampsorampsohms

volt1001.

1000

1I


I

milliampsorampsohms

volt1001.

1000

1I


I

Illustration of Ohm’s Law_ + The “I” is

conventional current.

I



Conventional current always

leaves the positive side of

the battery.

I



Conventional current always leaves the positive side of the

battery.

I

In Cathodic Protection the direction of conventional current is incredibly

important!

METALLIC PATH

ELECTROLYTE

ANODE CATHODE

CORROSION RECTANGLE

Electrochemical Circuits

C

e-Metallic Path

+ ions

- ions

Electrolytic Path

Conventional Current Flow

A C

Metallic Path

+ ions

ions

Electrolytic Path


Components of a Corrosion Cell

• Anode (oxidation reaction)

– corrosion

• Cathode (reduction reaction)

– no corrosion

• Electrolyte (cations and anions)

• External path (usually metallic)

Electron and Ion Flow

++

+

+

ELECTROLYTE

e-

e-

e-

e-

e-

e-e-

e-

e-

e-

e-e-

e-e-

e-

Direction of Electron Flow

ELECTROLYTEELECTROLYTE

CATHODE ANODE

e-

e-

e-

e-e-

e-

e-

e-

e-e-

e-e-

e-

Direction of Electron Flowe-

e-

e-e-e- e- e-

e-

+

Electron and Ion Flow

++

+

+

ELECTROLYTE

e-

e-

e-

e-

e-

e-e-

e-

e-

e-

e-e-

e-e-

e-



CATHODE ANODE

e-

e-

e-

e-e-

e-

e-

e-

e-e-

e-e-

e-


e-

e-e-e- e- e-

e-

+

Direction of Conventional Current Flow


++

+

+

ELECTROLYTE

e-

e-

e-

e-

e-

e-e-

e-

e-

e-

e-e-

e-e-

e-



CATHODE ANODE

e-

e-

e-

e-e-

e-

e-

e-

e-e-

e-e-

e-


e-

e-e-e- e- e-

e-

+


IN THE ELECTROLYTE, AS CONVENTIONAL CURRENT

LEAVES THE ANODE

IT TAKES IRON IONS INTO SOLUTION:

CORROSION OCCURS

Fe++

Fe++

Fe++

Fe++

Fe++

Fe++

Fe++

Fe++

Fe++

e-

e- e-

e-

e-e-

e-

e-

e-

e-

e-

e-

e-e-

e-

e-e-

e-

ANODE

ELECTROLYTE

Anodic Process (half reaction)

AS CONVENTIONAL CURRENT LEAVES THE ANODE IN THE ELECTROLYTE CORROSION OCCURS

++

+

+

ELECTROLYTE

e-

e-

e-

e-

e-

e-e-

e-

e-

e-

e-e-

e-e-

e-



CATHODE ANODE

e-

e-

e-

e-e-

e-

e-

e-

e-e-

e-e-

e-

e-e-

e-e-e- e- e-

e-

+



Conventional current always leaves the positive side of the

battery.

I

In Cathodic Protection the direction of conventional current is incredibly

important!

Voltmeter Circuit Connection

+ _

+_

VOLTS

Parallel Connection

RA RBRC

E

I

Voltage Sign

Current

+_

Voltage measurement is positive20 mV

20 mV

Potential Measurement Between Two Reference Electrodes

+ Reading

+ _

ReferenceElectrode

Voltmeter with+ Reading

ReferenceElectrode

Current

Sign of Voltage for Dissimilar Metals

Noble Active

+_

Voltage measurement is positive

.600 V

Sign of Voltage for Dissimilar Metals

Noble Active

+_

Voltage measurement is positive

.600 V

ANODENEGATIVE -OXIDATIONRUSTLOSE ELECTRONSLOSE POSITIVE IONSGAIN NEGATIVE IONS

CATHODEPOSITIVE +REDUCTIONDOES NOT RUSTGAINS ELECTRONSGAINS POSITIVE IONSREPELS NEGATIVE IONS

Electrochemical Circuits

C

e-Metallic Path

+ ions

- ions

Electrolytic Path


A C

Metallic Path

+ ions

ions

Electrolytic Path


Voltmeter ConnectionsPipe-to-Soil Potential Measurement

.900 v

+_

Pipe

Electrolyte

ReferenceCell

Voltmeter Meter display is apostive reading.Record a negativeP/S Potential.

-.900 v

+ _

Pipe

Electrolyte

ReferenceCell

Voltmeter Meter display is anegative reading.Record a negativeP/S Potential.

WHAT ARE THE FOUR MOST COMMONLY USED METALS

UNDERGROUND?


UNDERGROUND?

STEEL (IRON)


UNDERGROUND?

STEEL (IRON)

COPPER


UNDERGROUND?

STEEL (IRON)COPPER

GALVANIZED STEEL (ZINC)


UNDERGROUND?

STEEL (IRON)COPPER

GALVANIZED STEEL (ZINC)

MAGNESIUM


UNDERGROUND?

STEEL (IRON)COPPER

GALVANIZED STEEL (ZINC)MAGNESIUM


UNDERGROUND?

WHICH IS AN ANODE?


UNDERGROUND?

WHICH IS AN ANODE?WHICH IS A CATHODE?


UNDERGROUND?

WHICH IS AN ANODE?WHICH IS A CATHODE?

ALL OF THEM CAN BE EITHER!

DID YOU KNOW THAT EACH OF THESE METALS HAS A

DIFFERENT NATURAL VOLTAGE OR POTENTIAL?

STEEL (IRON)COPPER

GALVANIZED STEEL (ZINC)MAGNESIUM

COMPARE OTHER METALS TO STEEL

INTRODUCE THE REFERENCE CELLTYPICAL POTENTIALS RELATIVE TO

CSE

Reference Electrodes (Half Cells)Reference Electrodes (Half Cells)

Portable Reference Electrodes

Copper-Copper Sulfate Reference Electrode

Copper Rod

Saturated CopperSulfate Solution

Undissolved CopperSulfate Crystals

PorousPlug

ClearWindow

Removal Cap

Connection for Test Lead

CORROSION IS AN ELECTRO-CHEMICAL PHENOMENON.

IN WATER IMMERSION SERVICE IT IS RELATIVELY EASY, UNDER SOME CONDITIONS, TO WORK WITH THE CHEMICAL PORTION

OF THIS PHENOMENON.

ITS CALLED WATER TREATMENT AND IS USED IN MANY DIFFERENT

INDUSTRIES.

CORROSION IS AN ELECTRO-CHEMICAL PHENOMENON. IN WATER IMMERSION SERVICE IT IS RELATIVELY EASY, UNDER

SOME CONDITIONS, TO WORK WITH THE CHEMICAL PORTION OF THIS PHENOMENON.

UNDERGROUND IT IS VERY DIFFICULT TO WORK WITH THE CHEMICAL PORTION. THAT’S WHY IT IS SO

IMPORTANT TO UNDERSTAND AND BE ABLE TO WORK WITH THE ELECTRICAL

PORTION.

LET’S LOOK AT IRON

WHEN AN IRON ATOM CORRODES SEVERAL THINGS HAPPEN AT THE

SAME TIME


SAME TIME

THE IRON ATOM GIVES OFF TWO ELECTRONS AND BECOMES POSITIVE


SAME TIME


THE IRON IS NO LONGER CALLED AN ATOM IT IS NOW AN ION WITH A

PLUS TWO VALIANCE.


SAME TIME


THE IRON IS NO LONGER CALLED AN ATOM IT IS NOW AN ION WITH A PLUS TWO VALIANCE.

THE IRON ION NO LONGER STICKS TO THE OTHER IRON ATOMS, IT GOES

INTO SOLUTION.


SAME TIME



THE IRON ION NO LONGER STICKS TO THE OTHER IRON ATOMS, IT GOES INTO SOLUTION.

THE IRON ATOM CORRODES AND THE CORROSION PRODUCT IS AN IRON ION.

CORROSION 101

FREE SAMPLES:LET’S MAKE RUST

PRESENTED BY John Brodar P.E. of the Salt River Project


SAME TIME



THE IRON ION NO LONGER STICKS TO THE OTHER IRON ATOMS, IT GOES INTO SOLUTION.

THE IRON ATOM CORRODES AND THE CORROSION PRODUCT IS AN IRON ION.

++ ++ ++ ++ ++++ ++ ++ ++ ++ ++ ++ ++ +++ ++ ++ ++

++ ++ ++ ++ ++ ++ ++++ ++ ++ ++ ++ ++ ++

WHEN WILL THIS END?++ ++ ++ ++ ++ ++ ++ ++ +++ ++ ++ ++

++ ++ ++ ++ ++ ++ ++++ ++ ++ ++ ++ ++ ++

WHAT CAN WE DO?++ ++ ++ ++ ++ ++ ++ ++ +++ ++ ++ ++

++ ++ ++ ++ ++ ++ ++++ ++ ++ ++ ++ ++ ++

METALLIC PATH

ELECTROLYTE

ANODE CATHODE

CORROSION RECTANGLE

YOU’RE RIGHT. THE FIRST LINE OF DEFENSE AGAINST CORROSION IS COATINGS.

THEY ARE RELATIVELY CHEAP AND AMAZINGLY EFFECTIVE.

EXCEPT..

COATINGS ARE EFFECTIVE EXCEPT

AT HOLIDAYS (COATING DEFECTS AT THE TIME OF APPLICATION).

OR AT DAMAGED AREAS.DAMAGE MAY OCCUR DURING

MANUFACTURE, TRANSPORTATION, INSTALLATION OR IN SERVICE.

HOW BAD CAN THE CORROSION AT A

DAMAGED AREA OF THE COATING BE?

FARADAY’S LAW

FOR STEEL FARADAY’S LAW SAYS THAT ONE AMPERE OF CURRENT FLOWING OFF OF STEEL FOR ONE

YEAR WILL CAUSE THE CORROSION OF 20 POUNDS OF STEEL.

FARADAY’S LAW IS VERY MUCH A MATHEMATICAL RELATIONSHIP.

½ AMP FOR ONE YEAR WILL CONSUME 10 POUNDS OF STEEL

½ AMP FOR TWO YEARS WILL CONSUME 20 POUNDS OF STEEL

2 AMPS FOR ½ YEAR WILL CONSUME 20 POUNDS OF STEEL

CURRENT FLOWING OFF OF YOUR PIPELINE WILL CONSUME STEEL.

HOW MUCH DOES A ½” DIAMETER HOLE IN A ¼” WALL PIPE WEIGH?

NOT MUCH!

JUST 0.0558 LBS.

HOW MUCH CURRENT DOES IT TAKE TO MAKE THAT ½” HOLE?

1 YEAR @ 0.0028 AMPS

2 YEARS @ 0.0014 AMPS OR 1.4 MILLIAMPS

5 YEARS @ 0.6 ma

10 YEARS @ 0.28 ma that’s little more than ¼ ma

Why coatings?

Why coatings?

BECAUSE COATINGS ARE THE CHEAPEST THING WE CAN DO

TO STOP CORROSION.

Why cathodic protection?


Since coatings are not perfect we have to do something to protect

the holidays and damaged areas. AND


CATHODIC PROTECTION IS THE EASIEST THING TO DO TO A PIPELINE

AFTER IT IS INSTALLED.

DEMO PROTECTED PIPE

AnodeCathode

Microscopic Corrosion Cell on the Surface of a Pipeline

Microscopic View of a Corrosion Cell

AnodeCathode

Metallic Connection

Electrolyte

Cathodic Protection Anode

Cathodic Protection Current Applied

Cathodic Protection on a Structure (Macroscopic

view)

84 of 40

-.5 -.6 -.65 -.6 -.7 -.58

-.5 -.6 -.65 -.6

-.6

-.5

NativePotentials

CorrosionMitigated

Polarization of a Structure

NATURALLY OCCURING CATHODE. MORE POSITIVE

NATURALLY OCCURING ANODE. MORE NEGATIVE

-.7 -.58

APPLY (PARTIAL) CATHODIC PROTECTION!!

Prepare to duck.

86 of 40

-.5 -.6 -.65 -.6 -.7 -.58

-.58 -.6 -.65 -.6 -.7 -.58

NativePotentials

CorrosionMitigated



APPLY MORE CATHODIC PROTECTION

88 of 40

-.5 -.6 -.65 -.6 -.7 -.58

-.58 -.6 -.65 -.6 -.7 -.58

-.6 -.6 -.65 -.6 -.7 -.6

NativePotentials

CorrosionMitigated




APPLY EVEN MORE CATHODIC PROTECTION

90 of 40

-.5 -.6 -.65 -.6 -.7 -.58

-.58 -.6 -.65 -.6 -.7 -.58

-.6 -.6 -.65 -.6 -.7 -.6

-.65 -.65 -.65 -.65 -.7 -.65

NativePotentials

CorrosionMitigated




APPLY SUFFICIENT CATHODIC PROTECTION

92 of 40

-.5 -.6 -.65 -.6 -.7 -.58

-.58 -.6 -.65 -.6 -.7 -.58

-.6 -.6 -.65 -.6 -.7 -.6

-.65 -.65 -.65 -.65 -.7 -.65

-.7 -.7 -.7 -.7 -.7 -.7

NativePotentials

CorrosionMitigated


AnodeCathode

Metallic Connection

Electrolyte

Cathodic Protection Anode

Cathodic Protection Current Applied

Cathodic Protection on a Structure (Macroscopic

view)

9 of 40

-.5 -.6 -.65 -.6 -.7 -.58

-.58 -.6 -.65 -.6 -.7 -.58

-.6 -.6 -.65 -.6 -.7 -.6

-.65 -.65 -.65 -.65 -.7 -.65

-.7 -.7 -.7 -.7 -.7 -.7

NativePotentials

CorrosionMitigated


Cathodic ProtectionCathodic protection is the cathodic polarization of all noble potential areas (cathodes) to the most active potential on the metal surface. Cathodic protection is achieved by making the structure the cathode of a direct current circuit. The flow of current in this circuit is adjusted to assure that the polarized potential is at least as active as the most active anode site on the structure. NACE CP 1

When the potential of all cathode sites reach the open circuit potential of the most active anode site, corrosion on the structure is eliminated. NACE CP2 Slides

Cathodic protection is the polarization of the most cathodic areas on a structure to a potential equal to or more negative than the most anodic potential on the structure. When all areas are polarized to a potential equal to or more negative than -850 mv relative to a copper copper sulfate reference electrode, all corrosion has been halted.

DEMO TEST REELS

Close Interval Potential Survey Close Interval Potential Survey Reading

+_

Cu/Cu SO4

Ref. Cell

Voltmeter

Pipe

Electrolyte

CIS Potential ProfileCIS Potential Profile

DEMO TWO WIRES

Shunts

Current Shunts

• Measure voltage drop across a known resistance.

• Current is calculated using Ohm’s Law.

Shunt Measurement

Vmeasured

Rshunt

Icalculated =+ _

+_

VOLTS

RA

RB

RC

E

I

Current Shunt with known resistance value is in series with the circuit

Voltmeter is connected in parallel across the current shunt

Vmeasured

Rshunt

Icalculated =Vmeasured

Rshunt

Icalculated =+ _

+_

VOLTS

RA

RB

RC

E

I



+ _

+_

VOLTS

RA

RB

RC

E

I



+ _

+_

VOLTS

RA

RB

RC

E

I



Current Shunt Calculations #1

Given:Shunt = .01 ohmsVoltage across shunt = 50 mV

Calculate Current:1. Convert units of voltage, 50mV = .05 v2. Calculate current using Ohm’s Law,

I = .05 v /.01 ohms = 5 amps

Current Shunt Calculations #2

I = 28 mV x 15 amps 50 mV

= 8.4 amps

Given:Shunt = 15 amps 50 millivoltsVoltage across shunt = 28 mV

Calculate Current:

Direction of Current Flow

+ _

+_

VOLTS

RA

RB

RC

E

I

Current Flow is from Left to Right

Up Scale Deflection

Typical Current MeasurementsTypical Current Measurements

There are several current measurements commonly made in cathodic protection surveys:

• Current output of a galvanic anode system• Rectifier current output• Test current for determining current

requirement of a structure• Current on a structure (this is a voltage

measurement, and current is calculated)• Current across a bond

Current Along a Pipeline

+_

+_

Voltage measurement is positive20 mV

2-Wire Line Current Test

Pipe Span in Feet

Wires must be color coded

0.17 mV

+ _

Pipe size and wall thickness or weight per foot must be known

Pipeline

N

West East

Pipe Span in Feet


0.17 mV

+ _


Pipeline

N

Pipe Span in Feet


0.17 mV

+ _


Pipeline

Pipe Span in Feet


0.17 mV

+ _


Pipeline

N

West East

Example of 2-Wire Current Line CalculationsExample of 2-Wire Current Line Calculations

• Pipe span = 200 feet• Pipe is 30-inch weighing 118.7 pounds/ foot • Voltage drop across span = 0.17 millivolts• Determined resistance of span = 4.88 x 10-4 ohms• Calculated current flow = 348 milliamps from west to

east

4-Wire Line Current Test4-Wire Line Current Test

Pipe Span for Measuring Current


0.17 mV

+ _

Pipeline

PowerSource

+_

CurrentInterrupter +

_

AMPS

VOLTS

CLEARLLY THE 4 WIRE LINE CURRENT TEST IS MORE COMPLEX. YOU ONLY HAVE TO DO IT ONCE

FOR ANY PARTICULAR PIPE SEGMENT TO DETERMINE THE

RESISTANCE.

IT IS A MULTI STEP PROCESS.

AFTER YOU BECOME AN OHM’S LAWYER AND CAN WORK WITH

E=IRI=E/RR=E/I

YOU WILL UNDERSTAND THAT IF YOU PASS A KNOWN CURRENT

AND MEASURE A VOLTAGE YOU CAN USE OHM’S LAW TO CALCULATE RESISTANCE.

ONCE YOU KNOW THE RESISTANCE FOR A SECTION OF PIPE, YOU CAN NOW MEASURE A VOLTAGE DROP AND, AGAIN USING OHM’S LAW,

CALCULAE THE ACTUAL CURRENT FLOWING IN THE PIPE.




0.17 mV

+ _

Pipeline

PowerSource

+_


_

AMPS

VOLTS

Example of 4-Wire Current Line Calculations

Example of 4-Wire Current Line Calculations

• Test current = 10 amps• Potential shift due to test current (ON= 5.08millivolts

and OFF = 0.17 millivolts) = 4.91 millivolts• Calibration factor (10/4.91) = 2.04 amps/millivolts• Voltage drop across span = 0.17 millivolts• Calculated current flow (2.04 x 0.17) = 347 milliamps

from east to west

WHY ARE ANODES SOMETIMES NEGATIVE

AND SOMETIMES POSITIVE?????

Galvanic Anode Cathodic Protection SystemA Cathodic Protection System

ANODE

CURRENT

Impressed Current Cathodic ProtectionImpressed Current System

ANODE

CU

RR

EN

T

PowerSource

+-

CU

RR

EN

T



APPLY SUFFICIENT CATHODIC PROTECTION

OVER PROTECT A SEGMENT OF PIPELINE

Electrical Shielding due to Shorted Casing

Pipe Lying on Casing due toPipe Lying on Casing due toLack of Insulating SpacersLack of Insulating Spacers

Vent PipeVent Pipe

End SealCasingCasing

PavementPavement




0.17 mV

+ _

Pipeline

PowerSource

+_


_

AMPS

VOLTS

Criteria for Cathodic Protection

• Cathodic protection is a polarization phenomenon.• Cathodic protection is achieved when the open circuit

potential of the cathodes are polarized to the open circuit potential of the anodes.

• Practical application makes use of structure-to-electrolyte potentials.

NACE Standards for Underground or Submerged Iron and Steel

• SP0169 Control of External Corrosion on Underground or Submerged Metallic Piping Systems

• SP0285 Corrosion Control of Underground Storage Tank Systems by Cathodic Protection

Criteria for Underground or Submerged Iron or Steel Structures

• –0.850 volt potential--Negative (cathodic) potential of at least 850 mV with the cathodic protection applied

• –0.850 volt polarized potential--Negative polarized potential of at least 850 mV

• 100 millivolts polarization--Minimum of 100 mV of cathodic polarization

Resistances

Measuring Lead (+)

Contact Lead (+)/Ref. Cell

Reference Cell

Contact Reference Cell

to Electrolyte

Electrolyte

Polarization

Structure

Contact Test Lead/Structure

Test Lead

Contact Test/Measuring Lead

Measuring Lead (-)

Internal Meter

Voltage (IR) Drops Across a Measuring CircuitVoltage (IR) Drops Across a Measuring Circuit

Cathodic Protection Tutorial Three NACE International, 2001

.900 v

+ _

PolarizationFilm Structure

Electrolyte

ReferenceCell

Voltmeter

Measurement & C.P. current across electrolyte

IR Drops Across Electrolyte

• Reference electrode placement• Current interruption

Time

Pote

nti

al

+

-

t=0

-850 mV On

-850 mV Instant Offor IR Corrected

IR

Depolarization

Depolarized Potential

100 mVPolarization

Pipe-to-Soil PotentialsPipe-to-Soil Potentials

Santan Raw Water Tank Potentials 8/2/79

0.81 0.81

0.74

0.69

0.680.675

0.67

0.74

0.75

0.76

0.77

0.78

0.6

0.65

0.7

0.75

0.8

0.85

0 10 20 30 40 50 60 70 80 90

Time in Minutes

Po

ten

tial

to

Cu

Cu

So

4 (N

egat

ive

Nu

mb

ers)


0.6

0.65

0.7

0.75

0.8

0.85

0 10 20 30 40 50 60 70 80 90

Time in Minutes

Po

ten

tial

to

Cu

Cu

So

4 (N

egat

ive

Nu

mb

ers)

Steady State (48 Amps) Rectifier Turned Off


0.6

0.65

0.7

0.75

0.8

0.85

0 10 20 30 40 50 60 70 80 90

Time in Minutes

Po

ten

tial

to

Cu

Cu

So

4 (N

egat

ive

Nu

mb

ers)

Steady State

Instant Off Potential

Rectifier Turned Off


0.6

0.65

0.7

0.75

0.8

0.85

0 10 20 30 40 50 60 70 80 90

Time in Minutes

Po

ten

tial

to

Cu

Cu

So

4 (N

egat

ive

Nu

mb

ers)

Steady State

Instant Off

IR

DROP


0.6

0.65

0.7

0.75

0.8

0.85

0 10 20 30 40 50 60 70 80 90

Time in Minutes

Po

ten

tial

to

Cu

Cu

So

4 (N

egat

ive

Nu

mb

ers)

Steady State

Instant Off

IR

DROP

Depolarization Occurs Over Time


0.6

0.65

0.7

0.75

0.8

0.85

0 10 20 30 40 50 60 70 80 90

Time in Minutes

Po

ten

tial

to

Cu

Cu

So

4 (N

egat

ive

Nu

mb

ers)

Steady State

Instant Off

IR

DROP


Rectifier Turned On (Adjusted to 36 Amps)


0.6

0.65

0.7

0.75

0.8

0.85

0 10 20 30 40 50 60 70 80 90

Time in Minutes

Po

ten

tial

to

Cu

Cu

So

4 (N

egat

ive

Nu

mb

ers)

Steady State

Instant Off

IR

DROP


Rectifier Turned On

IR

DROP


0.6

0.65

0.7

0.75

0.8

0.85

0 10 20 30 40 50 60 70 80 90

Time in Minutes

Po

ten

tial

to

Cu

Cu

So

4 (N

egat

ive

Nu

mb

ers)

Steady State

Instant Off

IR

DROP


Rectifier Turned On

IR

DROP

Instant On Potential


0.6

0.65

0.7

0.75

0.8

0.85

0 10 20 30 40 50 60 70 80 90

Time in Minutes

Po

ten

tial

to

Cu

Cu

So

4 (N

egat

ive

Nu

mb

ers)

Steady State

Instant Off

IR

DROP


Rectifier Turned On

IR

DROP


Polarization Increases Over Time.


0.6

0.65

0.7

0.75

0.8

0.85

0 10 20 30 40 50 60 70 80 90

Time in Minutes

Po

ten

tial

to

Cu

Cu

So

4 (N

egat

ive

Nu

mb

ers)

Steady State

Instant Off

IR

DROP


Rectifier Turned On

IR

DROP


THIS POTENTIAL INCREASE IS CATHODIC PROTECTION !

Santan Raw Water Tank On Potentials

0

5

10

15

20

25

30

35

40

45

0.80 0.90 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 1.80 1.90

Potential to CuSO4 (Negative Numbers)

Hei

gh

t o

f T

ank

In F

eet

11 V 33.5 Amps 10/19/79 Water Flowing 1800 GPM 11 V 36 A 8/20/79 No Flow

western region gas conference august 21, 2012 corrosion 101

Documents

metallic pathremove

youstop corrosion

anionsexternal path

conditions fuel

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ion flowelectron

john brodar

basic corrosionmadeclear