corrosion and corrosion control - c.ymcdn.com · pdf file4/25/2012 4 corrosion is an economic...

4/25/2012

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Corrosionand

Corrosion Control

Examples of Corrosion

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What is Corrosion……….

•Corrosion – The

deterioration of a material,

usually a metal, due to a

reaction in its environment.

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Corrosion is an Economic Issue

e.g. What is the Cost of Corrosion?

Cost of Corrosion

NACE International (National Association of Corrosion Engineers) -- 1972 Estimate?

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Cost of Corrosion

NACE -- 1972Est. @ $10 Billion

Cost of Corrosion

Battelle Columbus -- 1976 Estimate?

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Cost of Corrosion

NACE -- 1972 -- Est. @ $10 Billion

Battelle Columbus -- 1976Est. @ $70 Billion

Cost of Corrosion

U.S. Dept. of Commerce -- 1982 Estimate?

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Cost of Corrosion

NACE -- 1972 -- Est. @ $10 BillionBattelle Columbus -- 1976 -- $70 Billion

U.S. Dept. of Commerce --1982

Est. @ $123.6 Billion

Cost of Corrosion

NACE International (National Association of Corrosion Engineers) -- 1987 Estimate?

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Cost of Corrosion

NACE -- 1987Est. @ $250 Billion

Cost of Corrosion

NACE -- 1972 -- Est. @ $10 BillionBattelle Columbus -- 1976 -- $70 Billion

U.S. Dept. of Commerce - 1982 - $123.6 B

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Cost of Corrosion

What does this tell us

about

the years to come?

Cost of Corrosion - US Annually

0

100

200

300

400

500

600

US Dollars

($Billions)

$10B$70B

$124B

$250B

$500B

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Cost of Corrosion - US annually

�5% of the Gross National Product (GNP)

5%

Cost of Corrosion - US annually

�More than any other disaster presently

occurring in US each year– > Fires– > Floods– > Theft– > Auto Accidents– > Failure of the S&L's

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Cost of Corrosion - US Annually in 1993

�US Population = 250 million


�US Population = 250 million�Corrosion Cost = $500 billion

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�US Population = 250 million�Corrosion Cost = $500 billion�Cost per person per year = $2000


�US Population = 250 million�Corrosion Cost = $500 billion�Cost per person per year = $2000�For a family of four, the family must generate at

least $8000 each year just to pay for the cost of corrosion

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Basic CorrosionPrinciples

Ver. 3.0

Naturally OccurringCorrosion Process

� Metals Corrode in an attempt to achieve a Balance of Energy

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METALS HAVE DIFFERENT ENERGY LEVELS

NOBLE OR PASSIVE (+)

ACTIVE (-)

THE ENERGY HILL

Relative Energy Levels of Various Refined Metals

GOLD

COPPER

STEEL IN CONCRETE WITHOUT Cl

ZINC

MAGNESIUM

ALUMINUM

CARBONSILVER

PLATINUM

STEELSTEEL IN CONCRETE WITH Cl

-

-


ACTIVE (-)

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Corrosion of Iron

ELECTROLYTE

METALLICPATH

COPPERCATHODE

IRONANODE

OH-

Fe++

H+ H

Conventional Current Flow

+-


Galvanic Corrosion Process

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� Anode - Corroding Metal Surface



� Anode - Corroding Metal Surface� Cathode - Non-Corroding Metal Surface


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� Anode - Corroding Metal Surface� Cathode - Non-Corroding Metal Surface� Metal Connection - Path for electrons transfer



� Anode - Corroding Metal Surface� Cathode - Non-Corroding Metal Surface� Metal Connection - Path for electron energy

transfer� Electrolyte Connection - Path for ions transfer


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FOUR ITEMS REQUIRED FOR CORROSION

ANODE

CATHODE

ELECTROLYTE

METAL CONDUCTOR

Eliminate any one (1) of these elementsand corrosion is stopped!

SOME POSSIBLEANODIC REACTIONS

4 OH O + H O + 4e 22

--

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224 OH O + H O + 4e --

Al Al + 3e+ + + -


Zn Zn + 2e++ -


4 OH O + H O + 4e 22

--

Al Al + 3e+ + + -

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22

Zn Zn + 2e++ -

4 OH O + H O + 4e --

Al Al + 3e+ + + -

Fe Fe + 2e+ -2


SOME POSSIBLECATHODIC REACTIONS

2H + 2e H+ -

2

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SOME POSSIBLE CATHODIC REACTIONS

CI + 2 e 2 CI 2

--

2H + 2e H+ -

2


2H + 2e H+ -

2

CI + 2 e 2 CI 2

--

O + H O + 4e 4 OH22

--

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H + 1e H+ -


2H + 2e H+ -

2

CI + 2 e 2 CI 2

--

O + H O + 4e 4 OH22

--

Electro-Chemical Corrosion Cell

ANODE

CURRENT FLOW

CATHODE

STEEL PIPE WALL

ELECTROLYTE

POSITIVE

HHHHHHH

Fe(OH)3

Fe(OH)2

H+ H+ H+

OH-

OH-

OH-

H+

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DISSIMILAR SURFACE CORROSION

ANODIC AREA (corrodes)

CATHODIC AREA (protected)

METAL STRUCTURE ELECTROLYTE

e-

H+

OH-

H + e H+

Fe + 2OH Fe(OH)++

2

-

� CAUSED BY VARIATIONS IN SOIL CHEMISTRY AND PHYSIOLOGY

DISSIMILAR ELECTROLYTE CORROSION

PIPE

HI pH HI pH

HighResistivity

Low Resistivity

LOW pH

HighResistivity

PIPE

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� OCCURS WHEN THE METAL STRUCTURE IS IN CONTACT WITH SOILS HAVING DIFFERENT OXYGEN LEVELS

OXYGEN CONCENTRATION CORROSION


� THE AREA WITH HIGH OXYGEN CONTENT BECOMES A CATHODE


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� THE AREA WITH HIGH OXYGEN CONTENT BECOMES A CATHODE

� THE AREA WITH LOW OXYGEN CONTENT BECOMES AN ANODE AND CORRODES


Oxygen Concentration Corrosion

OXYGEN STARVED COMPACTED CLAY SOIL

PAVEMENT

Corrosion Current caused by difference in Oxygen Concentrations

CORROSION

PIPE

Oxygen RichSand Backfill

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� STONE UP AGAINST PIPE SURFACE WITHIN SAND BACKFILL

OXYGEN CONCENTRATION CORROSION EXAMPLES


� CLAY LUMP ON PIPE SURFACE WITH OXYGEN RICH BACKFILL


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� DEEPEST POINT IN CREVICE




� DEEPEST POINT IN CREVICE– LAPPED PLATES– THREADED COUPLINGS– BOTTOM OF PITS– UNDER BOLT HEADS AND WASHERS


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1. Stray Current

2. Naturally Occurring

THERE ARE ONLY TWO (2) BASIC FORMS OF ELECTROLITIC CORROSION

STRAY CURRENT

�MAN MADE CORROSION

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� MAN MADE CORROSION� AN EXTERNAL SOURCE OF DIRECT CURRENT

(DC) TRAVERSING THROUGH THE SOIL (ELECTROLYTE) STRAYS ONTO THE STRUCTURE

STRAY CURRENT



� CATHODIC REACTIONS OCCUR (protection) WHERE THE CURRENT IS PICKED UP BY THE STRUCTURE

STRAY CURRENT

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� CATHODIC REACTIONS OCCUR (protection) WHERE THE CURRENT IS PICKED UP BY THE STRUCTURE

� ANODIC REACTIONS OCCUR (corrosion) WHERE THE CURRENT LEAVES THE STRUCTURE

STRAY CURRENT

+

-DC

GENERATOR

TRANSIT POWER LINE

ANODIC AREA

CATHODIC AREA

RAIL

EARTH

Steel Pipe

CORROSION PASSIVATION

STRAY CURRENT

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FARADAY'S LAW: Wt = KIT

WHERE:Wt = Weight Lost

I = Current (amps)T = Time (yrs.)K = Electrochemical

Equivalent #/A/yr.

Fe = 20 #/A/YrCu = 45 #/A/YrPb = 75 #/A/Yr

STRAY CURRENT

� FOR EACH AMPERE OF CURRENT THAT FLOWS OFF THE PIPE SURFACE, MORE THAN 20 POUNDS OF STEEL WILL BE CORRODED EACH YEAR……………….

– For Std wall 2 - inch = 5.48 feet removed– For Std wall 4 - inch = 1.85 feet removed– For Std wall 6 - inch = 1.05 feet removed

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STRAY CURRENT

� FOR EACH AMPERE OF CURRENT THAT FLOWS OFF THE PIPE SURFACE, MORE THAN 20 POUNDS OF STEEL WILL BE CORRODED EACH YEAR

– For Std wall 2 - inch = 5.48 feet removed– For Std wall 4 - inch = 1.85 feet removed– For Std wall 6 - inch = 1.05 feet removed

� TYPICALLY PRODUCES THE HIGHEST CORROSION RATES EXPERIENCED UNDERGROUND

Impressed CurrentCathodic Protection System

18-16

RectifierGround

Bed

+

-Pipeline

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STRAY CURRENT

IF YOU REVERSE THE LEADS OF A RECTIFIER WITH A 10 AMP LOADYOU WILL LOSE:

54.8 FEET OF 2 - INCH MAIN18.5 FEET OF 4 - INCH MAIN10.5 FEET OF 6 - INCH MAIN

NATURALLY OCCURRING CORROSION

� 3 BASIC MECHANISMS

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� 3 BASIC MECHANISMS– DISSIMILAR METAL


� 3 BASIC MECHANISMS– DISSIMILAR METAL– DISSIMILAR ELECTROLYTE


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� 3 BASIC MECHANISMS– DISSIMILAR METAL– DISSIMILAR ELECTROLYTE– OXYGEN CONCENTRATION



GOLD

COPPER


ZINC

MAGNESIUM

ALUMINUM

CARBONSILVER

PLATINUM

STEELSTEEL IN CONCRETE WITH Cl

-

-


ACTIVE (-)

--

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-1.7

+1.2GOLD

-0.1COPPER

-0.1STEEL IN CONCRETE WITHOUT Cl

-1.0ALUMINUM

MAGNESIUM

-1.1ZINC

+0.4CARBON

+0.5SILVER

+0.9PLATINUM

-0.6STEEL

-0.5STEEL IN CONCRETE WITH Cl-

-

Energy Level in Volts vs. Cu/CuSO Reference in soil

4

GALVANIC SERIES OF METALENERGY LEVELS

�Measured Potential Depends Upon:– Electrolyte

� Seawater� Fresh Water/Soil� Other

– Temperature

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GALVANIC SERIES OF METALENERGY LEVELS

�There is a Range in Measured Potential Not an Absolute Value

– 316 Passive Stainless - 50 mV to - 200 mV– Copper - 50 mV to - 300 mV– Carbon Steel -400 mV to - 750 mV– Zinc -900 mV to -1100 mV

ENERGY LEVEL DIFFERENCE BETWEEN CARBON AND ZINC

GOLD

COPPER


ZINC

MAGNESIUM

ALUMINUM

CARBON

SILVER

PLATINUM

STEEL

STEEL IN CONCRETE WITH Cl

-

-

Energy Level in Volts vs. Cu/CuSO Reference4

?

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ENERGY LEVEL DIFFERENCE BETWEEN CARBON AND ZINC

GOLD

COPPER


ZINC

MAGNESIUM

ALUMINUM

CARBON

SILVER

PLATINUM

STEEL

STEEL IN CONCRETE WITH Cl

-

-

Energy Level in Volts vs. Cu/CuSO Reference4

1.5V

-1.1

+0.4

A COMMON DRY CELL BATTERYIS A GALVANIC CORROSION CELL

CARBON ROD(CATHODE)

ZINC CASE(ANODE)

MOIST PASTE(ELECTROLYTE)

WIRE(CONDUCTOR)

CONVENTIONAL CURRENT

Zn++

H+

OH-

OH-

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CORROSION IS AN ELECTROCHEMICAL PROCESS

� THE CHEMICAL PART IS THE UNWANTED REVERSION OF THE METAL TO IT'S OXIDE FORM


� THE CHEMICAL PART IS THE UNWANTED REVERSION OF THE METAL TO IT'S OXIDE FORM THAT IS INTRODUCED TO THE ELECTROLITE

� THE ELECTRO PART IS THE TRANSFER OF ENERGY (ELECTRONS) WHICH OCCURS DURING THE CORROSION PROCESS FROM ANODE TO THE CATHODE. THE ELECTRONS ARE TRANFERRED INSIDE THE METAL STRUCTURE

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� THE ELECTRO PART IS THE TRANSFER OF ENERGY WHICH OCCURS DURING THE CORROSION PROCESS

� WHAT WE UNDERSTAND, WE CAN CONTROL



� THE ELECTRO PART IS THE TRANSFER OF ENERGY WHICH OCCURS DURING THE CORROSION PROCESS

� WHAT WE UNDERSTAND, WE CAN CONTROL� TO UNDERSTAND CORROSION, WE MUST

UNDERSTAND BASIC ELECTRICITY

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CURRENT FLOW

ELECTRONIC IONIC

CAN BE EITHER:

ION

�Charged Atom or Molecule

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ION

�Charged Atom or Molecule

OH -

H + is a Hydrogen Atom without one electronwhich carries a positive charge of +1

is a Hydroxyl Molecule with an excess electronwhich carries a negative charge of -1

Both Electronic and Ionic Current Charge Transfer Occurs in Corrosion Cell

ELECTROLYTE (Solution containingcharged atoms or molecules)

METALLIC

PATH

COPPER

CATHODEIRON

ANODE

OH-

Fe++

H+ H

+-

e-

e-

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CURRENT

� Ampere

CURRENT

� Ampere� Electrical Charge Transfer through Distance per

Unit Time

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CURRENT


Unit Time� 1 Coulomb per Second transferred between two

points

CURRENT



points� 6.24 x 10 electrons per Second transferred

between two points

18

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CURRENT




between two points� SYMBOL = I

18

CURRENT




between two points� SYMBOL = I

– analogous to gas flow -- e.g. Cubic Feet per Hour

18

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ELECTRO-MOTIVE FORCE

� VOLT


� VOLT� The Potential (or energy) Difference between

the terminals of a source of electrical energy

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the terminals of a source of electrical energy� Basic Unit of Force which causes electric

charge transfer thru distance per unit time




charge transfer thru distance per unit time� SYMBOL = E or V

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charge transfer thru distance per unit time� SYMBOL = E or V

– analogous to gas pressure -- e.g. Pounds per Square Inch

RESISTANCE

� OHMS

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RESISTANCE

� OHMS� Impedance to Electric Charge Transfer through

distance per unit time

RESISTANCE


distance per unit time� The tendency of a conductor to oppose the flow

of current, causing electrical energy to be changed into heat

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RESISTANCE




� The unit of resistance which will limit the current flow to 1 Ampere from an applied EMF of 1 Volt

RESISTANCE





� Symbol = R or

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� Symbol = R or – analogous to the restriction of gas flow

caused by a given pipe diameter and length

RESISTANCE

Electrical Circuit Calculations

� We will learn how to use Ohm's Law to calculate either the current, volt or resistance factors in both series and parallel circuits.

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OHMS LAW

� The Current Flow in an Electrical Circuit (DC Circuit) is Directly Proportional to the EMF applied to the circuit and Inversely Proportional to the Resistance of the Circuit

I =ER

OHMS LAW

E

RI

I = ER

E = I x R

R = EI

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UNITS OF MEASURE

MILLIVOLT = 0.001 VOLTSVOLT = 1.000 VOLTSKILOVOLT = 1,000.000 VOLTSMEGAVOLT = 1,000,000.000 VOLTS

DO NOT MIX UNITS, i.e., MILLIVOLTS WITH AMPS

OR VOLTS WITH MILLIAMPS

SAMPLE CALCULATION

9 VOLT BATTERYR1 = 1 OHMR2 = 2 OHMS

WHAT ISTHE

CURRENTFLOW?

I = = = 3 AMPSER

__9__ (1 + 2)

RI

E

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• Basic theory of CP

– Galvanic anodes – metallic element that has a higher natural electromotive

force than that element being protected (i.e. – magnesium, zinc, and

aluminum to protect steel)

– Impressed current anodes – External direct current source connected to the

anode (more positive) and structure.

– Level of protection

• Generally -0.85 to -1.15 vdc typical (per NACE standard RP0169-96,

Section 6) for ground to soil (electrolyte) readings.

• If the system exceeds -1.17 volts area starts to be overprotected with -

1.22 volts generation hydrogen gas causing disbondment of the coating

Corrosion and Cathodic Protection

Types of Coatings• Coal Tar Enamels

• Mill-Applied Tape Systems

• Extruded Polyolefin with Butyl Adhesive

• Fusion-Bonded Epoxy

• Multi-layer Epoxy Extruded Polyolefin

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• A technique to reduce the corrosion rate of a metal surface by making it the

cathode of an electrochemical cell.

• 2 types of cathodic protection methods

– Sacrificial or Galvanic Anode

– Impressed Current

Cathodic Protection

Sacrificial or Galvanic Anode CP System

Anodes

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Corrosion Terms

• A/C – Alternating electrical current which flows first in one direction and then the opposite direction in a fixed pattern

• Amps – Basic unit of flow in an electrical or electronic circuit. Usually indicated as “I” in electrical Formulas

• Anode – The part of the corrosion cell that corrodes, or sacrifices itself, to protect the cathode portion of the corrosion cell.

• Battery – A device that stores an electrical charge for later use.

• Bridge – An electronic semi-conductor or electrical device that converts A/C power into D/C power.

• Cathode – The part of the corrosion cell that receives protection from the anode portion of the corrosion cell

• Cathodic Protection – The process of intentionally corroding one material to protect another material.

• Circuit Breaker – Provides overload protection and serves as an on/off switch for equipment.

• Coating – A di-electric material used to isolate a structure from the surrounding environment.

• Collins Meter – Trade name for an instrument used to measure soil resistivity.

• Conductor – Any material capable of carrying an electrical current.

• Copper-Copper Sulfate Reference Electrode – The standard reference used to measure the voltage potential of underground metallic structures. Commonly known as a Half-Cell, CUCUSO4 Reference Cell, or Reference Cell.

• Corrosion – The deterioration of a material, usually a metal, due to a reaction in its environment.

• Criteria – The rules used that indicate when cathodic protection has been achieved.

• Current Interrupter – Portable battery-operated instrument used to turn current producing equipment on and off in defined cycles during field testing procedures.

• D/C – Current which flows only in one direction.

• Diode – An electronic semi-conductor device that allows current to flow only in one direction.

• Electrolyte – The substance in which ions transverse from the anode to the cathode. Normally the earth surrounding a structure

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Corrosion Terms

• Fuse – An electrical device that protects equipment from damage due to an over-current or over-voltage condition.

• Insulator – A fitting or substance that exhibits a high resistance to electrical current flow.

• I-R Drop – A voltage developed due to current flowing through a resistance.

• Ohms – The term used to indicate the amount of resistance to electrical flow. Usually indicated as “R” in electrical formulas.

• Ohms Law – A mathematical statement describing the relationship of volts, amps, and ohms in an electrical circuit. In basic terms, the law states that:

– Volts = Ohms x Amps; or,

– E=I x R

• Resistance – Opposition to current flow. Usually indicated as “R” in electrical formulas.

• Resistivity – Resistance of an electrolyte such as earth. Usually expressed in “ohms per centimeter” or “Ohms/cM”

• Volts – The term used to describe the amount of pressure in an electrical circuit. Usually indicated as “E” in electrical formulas.

corrosion and corrosion control - c.ymcdn.com · pdf file4/25/2012 4 corrosion is an economic...

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