corrosion mechanisms and prevention rev8

8/7/2019 Corrosion Mechanisms and Prevention Rev8

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Corrosion Mechanisms Corrosion Mechanisms Corrosion Mechanisms Corrosion Mechanisms

Prevention Prevention

Prevention Prevention



Introduction to Water Chemistr Introduction to Water Chemistr Introduction to Water Chemistr Introduction to Water Chemistr



Atomic StructureAtomic Structure

10 P Valence ShellValence Shell

Protons are positively charged and are contained in the nucleus

Protons are positively charged and are contained in the nucleus

The outermost orbital of an atom is called the “Valence Shell”

The outermost orbital of an atom is called the “Valence Shell”

os a oms e o ave e ec rons n e nnermos or a an

require 8 electrons in their outermost orbital to be stable

os a oms e o ave e ec rons n e nnermos or a an

require 8 electrons in their outermost orbital to be stable



Com oundsCom ounds

Compounds are atoms that have bonded toform a molecule

Compounds are atoms that have bonded toform a molecule

There are two types of compounds: There are two types of compounds:

.

2. Ionic Compounds

.

2. Ionic Compounds



Covalent BondsCovalent Bonds

- ’ - ’

electrons

electrons

enough electrons in their valence shell

enough electrons in their valence shell



Covalent BondsCovalent Bonds

8 P

1 P

Example : An oxygen atom has 8 proton and 8 electrons. ItExample : An oxygen atom has 8 proton and 8 electrons. It

as e ec rons n e rs or a an on y n e ou er orbital.as e ec rons n e rs or a an on y n e ou er

orbital.

fulfill its requirement of 8 electrons in the outer orbital. This is

how H2O is formed.

fulfill its requirement of 8 electrons in the outer orbital. This is

how H2O is formed.



The Properties of Water The Properties of Water Polar Covalent BondPolar Covalent Bond

Οδ ¯

Hδ+

Hδ+

Ο

Hδ+Hδ+

When Oxygen and two hydrogen atoms share electrons to formΟ

When Oxygen and two hydrogen atoms share electrons to formΟ

,Ο

they are to the smaller H atoms. For this reason, they spend mostof their time orbiting the Ο atoms and less time around the H atom.

,Ο

they are to the smaller H atoms. For this reason, they spend mostof their time orbiting the Ο atoms and less time around the H atom.

As a result, the Ο atom in water has a PARTIAL NEGATIVE charge,

and the H atoms each have a PARTIAL POSITIVE charge.

As a result, the Ο atom in water has a PARTIAL NEGATIVE charge,

and the H atoms each have a PARTIAL POSITIVE charge.



Ionic BondIonic Bond

++ ¯ ¯

11 P 17 P

Ionic bonds involve at least one metal and one non-metal Ionic bonds involve at least one metal and one non-metal

e me a on as more pro ons an e ec rons so s pos ve y c arge(Cation: Ca++, K+, Ba++, Fe++).

The non-metal atom will have more electrons that protons so it is negatively ¯ ¯

e me a on as more pro ons an e ec rons so s pos ve y c arge(Cation: Ca++, K+, Ba++, Fe++).

The non-metal atom will have more electrons that protons so it is negatively ¯ ¯ , .

The non-metal anions can also be compounds (OH ¯ , HCO3¯ , CO3¯ ¯ , SO4 ¯ ¯ )

, .

The non-metal anions can also be compounds (OH ¯ , HCO3¯ , CO3¯ ¯ , SO4 ¯ ¯ )



Ionic BondIonic BondCl¯ Cl¯ Na+Na+

–+

The charged ions are attracted to each other like magnets The charged ions are attracted to each other like magnets



The Properties of WaterThe Properties of WaterDissolution of SaltsDissolution of Salts

Οδ ¯ Οδ ¯

Οδ ¯

Οδ ¯ δ

¯ Cl ¯ Na+

Οδ ¯

Οδ ¯ δ ¯

The partial negative charge of the oxygen atom in the H2Omolecule is attracted to the positively charged sodium

The partial negative charge of the oxygen atom in the H2Omolecule is attracted to the positively charged sodium

is attracted to the chloride.

This is known as dissociation of the ions.

is attracted to the chloride.

This is known as dissociation of the ions.



Corrosion MechanismsCorrosion MechanismsCorrosion MechanismsCorrosion Mechanisms



CorrosionCorrosionCorrosionCorrosion

•• Metal exposed to aerated water is oxidizedMetal exposed to aerated water is oxidized

•• Oxidation is defined as a loss of electronsOxidation is defined as a loss of electrons

•• Metal exposed to aerated water is oxidizedMetal exposed to aerated water is oxidized

•• Oxidation is defined as a loss of electronsOxidation is defined as a loss of electronsand can only occur in the presence of anand can only occur in the presence of anelectron acceptor known as the “oxidizer” electron acceptor known as the “oxidizer” and can only occur in the presence of anand can only occur in the presence of anelectron acceptor known as the “oxidizer” electron acceptor known as the “oxidizer”

•• The most well known oxidizer is oxygen.The most well known oxidizer is oxygen.•• The most well known oxidizer is oxygen.The most well known oxidizer is oxygen.



Ionization of Solid MetalsIonization of Solid Metals

++++

Οδ ¯ δ ¯

26 P26 P

ΟΗ ¯ Η ¯

Hδ+Hδ+

CathodicCathodic

Οδ ¯ δ ¯ Anodic Anodic

Hδ+

Hδ+

ΟΗ ¯ Η ¯



Anodic ReactionAnodic ReactionAnodic ReactionAnodic Reaction

•• For example, if iron (Fe) was exposed to anFor example, if iron (Fe) was exposed to anaerated, corrosive water, the anodic reactionaerated, corrosive water, the anodic reaction•• For example, if iron (Fe) was exposed to anFor example, if iron (Fe) was exposed to anaerated, corrosive water, the anodic reactionaerated, corrosive water, the anodic reactionwou e:wou e:

FeFe

FeFe2+2+

+ 2e+ 2e--

wou e:wou e:

FeFe

FeFe2+2+

+ 2e+ 2e--

•• Ferrous Ions (FeFerrous Ions (Fe2+2+) would dissolve in water) would dissolve in water

••

•• Ferrous Ions (FeFerrous Ions (Fe2+2+) would dissolve in water) would dissolve in water

•• ....



Dissolution of Ferrous ion in Water Dissolution of Ferrous ion in Water

Οδ ¯ Οδ ¯

Οδ ¯ Fe2+

Fe2+

The partial negative charge of the oxygen atom in the H2Omolecule is attracted to the positively charged ferrous ions

The partial negative charge of the oxygen atom in the H2Omolecule is attracted to the positively charged ferrous ionsΟδ ¯

..Οδ ¯



Anodic ReactionAnodic Reaction

Aerated Water

O2

O2

O2

O2

O2O

2

+ +- Cathode - - Cathode -

22

O2O2

O2

O2

Fe2+Fe2+

Fe2+

Fe2+

Fe2+Fe2+Fe2+

Fe2+

e-e-

e-e-

e-e-

e-e-

e-e-e-e-

e-

e-

e-Fe2+

Fe2+

e-

e-e-

Fe Fe2+ + 2 e-Fe Fe2+ + 2 e-



Cathodic ReactionCathodic ReactionCathodic ReactionCathodic Reaction

•• Hydrogen evolution (acids):Hydrogen evolution (acids):2 H2 H++ + 2 e+ 2 e-- HH22

•• Hydrogen evolution (acids):Hydrogen evolution (acids):2 H2 H++ + 2 e+ 2 e-- HH22

•• Oxygen reduction (acids):Oxygen reduction (acids):½ O½ O22 ++ 2H2H++ ++ 2 e2 e-- HH22OO

•• Oxygen reduction (acids):Oxygen reduction (acids):½ O½ O22 ++ 2H2H++ ++ 2 e2 e-- HH22OO

•• Oxygen reductionOxygen reduction (neutral or base):(neutral or base):

½ O½ O + H+ H OO ++ 2 e2 e-- 2 OH2 OH--

•• Oxygen reductionOxygen reduction (neutral or base):(neutral or base):

½ O½ O + H+ H OO ++ 2 e2 e-- 2 OH2 OH--

Note Note: : More than one oxidation and more than one More than one oxidation and more than one Note Note: : More than one oxidation and more than one More than one oxidation and more than one



Cathodic ReactionCathodic ReactionCathodic ReactionCathodic Reaction

•• At the cathode, reduction of oxygen At the cathode, reduction of oxygen•• At the cathode, reduction of oxygen At the cathode, reduction of oxygen

½½ OO22 + H+ H22O + 2eO + 2e-- 2(OH)2(OH)--

½½ OO22 + H+ H22O + 2eO + 2e-- 2(OH)2(OH)--

•• Reduction is defined as the acceptanceReduction is defined as the acceptance

of electrons by an oxidizer.of electrons by an oxidizer.

•• Reduction is defined as the acceptanceReduction is defined as the acceptance

of electrons by an oxidizer.of electrons by an oxidizer.

•• In this case, oxygen accepts theIn this case, oxygen accepts theelectrons lost b the iron.electrons lost b the iron.

•• In this case, oxygen accepts theIn this case, oxygen accepts theelectrons lost b the iron.electrons lost b the iron.



Reduction of Oxygen at CathodeReduction of Oxygen at Cathode

++++

Οδ ¯ δ ¯ 26 P26 P

Ο

ΟΗ ¯ Η ¯

Hδ+Hδ+

ΟΗΗ

CathodicCathodic

Οδ ¯ δ ¯ Anodic Anodic

Hδ+

Hδ+

ΟΗ ¯ Η ¯



CorrosionCorrosionCorrosionCorrosion

•• The anodic and cathodic reactions would be:The anodic and cathodic reactions would be:•• The anodic and cathodic reactions would be:The anodic and cathodic reactions would be:

2Fe2Fe00 2Fe2Fe2+2+ + 4e+ 4e-- (anodic(anodic -- oxidation)oxidation)2Fe2Fe00 2Fe2Fe2+2+ + 4e+ 4e-- (anodic(anodic -- oxidation)oxidation)

22 ++ 22 + e+ e-- -- ca o cca o c -- re uc onre uc on

----------------------------------------------------------------------------------------------------

22 ++ 22 + e+ e-- -- ca o cca o c -- re uc onre uc on

----------------------------------------------------------------------------------------------------2Fe + O2Fe + O22 + 2H+ 2H22OO 2Fe2Fe ++ + 4(OH)+ 4(OH)--2Fe + O2Fe + O22 + 2H+ 2H22OO 2Fe2Fe ++ + 4(OH)+ 4(OH)--

,,as high as 10as high as 10 – – 11.11.,,as high as 10as high as 10 – – 11.11.

•• FeFe2+2+

+ 2OH+ 2OH--

Fe(OH)Fe(OH)22 (Ferrous Hydroxide)(Ferrous Hydroxide)•• FeFe2+2+

+ 2OH+ 2OH--

Fe(OH)Fe(OH)22 (Ferrous Hydroxide)(Ferrous Hydroxide)



Oxidation of Dissolved IronOxidation of Dissolved IronOxidation of Dissolved IronOxidation of Dissolved Iron

•• Ferrous ions (FeFerrous ions (Fe2+2+) are oxidized to less soluble) are oxidized to less soluble

4Fe4Fe2+2+ 4Fe4Fe3+3+ + 4e+ 4e--

OO22 + 2H+ 2H22OO + 4e+ 4e-- 4(OH)4(OH)--

----------------------------------------------------------------------------------------------

4Fe4Fe2+2+ + O+ O22 + 2H+ 2H22OO 4Fe4Fe3+3+ + 4(OH)+ 4(OH)--

Precipitates:Precipitates:

3+3+



Formation of Passive Layer at CathodeFormation of Passive Layer at CathodeFormation of Passive Layer at CathodeFormation of Passive Layer at Cathode

FeFe2+2+ + 2OH+ 2OH-- Fe(OH)Fe(OH)22 (Ferrous Hydroxide)(Ferrous Hydroxide)

6Fe OH6Fe OH s + Os + O 4H4H O l + 2FeO l + 2Fe OO .H.H O sO s

Green Hydrated MagnetiteGreen Hydrated MagnetiteFeFe OO .H.H OO HH O + FeO + Fe OO Black Ma netite assive la erBlack Ma netite assive la er

4Fe(OH)4Fe(OH)22 + O+ O22 + 2H+ 2H22OO 4Fe(OH)4Fe(OH)33 (Ferric Hydroxide)(Ferric Hydroxide)

ee 33 e .e . 22 ee 22

2FeO(OH)2FeO(OH) FeFe22OO33.H.H22O Hydrated Ferric OxideO Hydrated Ferric Oxide

Re Brown RustRe Brown RustFeFe22OO33.H.H22OO FeFe22OO33+ 2H+ 2H22O (O (alpha or gammaalpha or gamma))



Formation of Passive Layer at CathodeFormation of Passive Layer at CathodeFormation of Passive Layer at CathodeFormation of Passive Layer at Cathode

composed of Fecomposed of Fe33OO44 (magnetite) with an outer(magnetite) with an outer-- --

composed of Fecomposed of Fe33OO44 (magnetite) with an outer(magnetite) with an outer-- -- ..

oxide film inhibits diffusion of Feoxide film inhibits diffusion of Fe2+2+ and Oand O22--

..

oxide film inhibits diffusion of Feoxide film inhibits diffusion of Fe2+2+ and Oand O22--

•• The passive film acts as a barrier to preventThe passive film acts as a barrier to prevent•• The passive film acts as a barrier to preventThe passive film acts as a barrier to prevent

•• Magnetite is also extremely soluble under normalMagnetite is also extremely soluble under normal•• Magnetite is also extremely soluble under normalMagnetite is also extremely soluble under normal....



Types of CorrosionTypes of CorrosionTypes of CorrosionTypes of Corrosion

•• General corrosionGeneral corrosion•• General corrosionGeneral corrosion

•• Galvanic CorrosionGalvanic Corrosion•••• Galvanic CorrosionGalvanic Corrosion••

•• DealloyingDealloying

•• DealloyingDealloying

•• Erosion CorrosionErosion Corrosion

•• Microbiolo icall Influenced CorrosionMicrobiolo icall Influenced Corrosion

•• Erosion CorrosionErosion Corrosion

•• Microbiolo icall Influenced CorrosionMicrobiolo icall Influenced Corrosion



General CorrosionGeneral CorrosionGeneral CorrosionGeneral Corrosion

•• General corrosion is when anodic dissolutionGeneral corrosion is when anodic dissolution•• General corrosion is when anodic dissolutionGeneral corrosion is when anodic dissolution

surface.surface.surface.surface.

•• Microscopic ano es an cat o es areMicroscopic ano es an cat o es arecontinuously changing their electrochemicalcontinuously changing their electrochemical

•• Microscopic ano es an cat o es areMicroscopic ano es an cat o es arecontinuously changing their electrochemicalcontinuously changing their electrochemical

resulting in a corrosion rate that is nearlyresulting in a corrosion rate that is nearlyconstant at all locations.constant at all locations.

resulting in a corrosion rate that is nearlyresulting in a corrosion rate that is nearlyconstant at all locations.constant at all locations.



General CorrosionGeneral Corrosion



Galvanic CorrosionGalvanic CorrosionGalvanic CorrosionGalvanic Corrosion

•• Galvanic corrosion occurs when two differentGalvanic corrosion occurs when two different•• Galvanic corrosion occurs when two differentGalvanic corrosion occurs when two different

environment.environment.

“ ” “ ”

environment.environment.

“ ” “ ” susceptible to oxidation in a given environmentsusceptible to oxidation in a given environmentsusceptible to oxidation in a given environmentsusceptible to oxidation in a given environment

..

•• The less noble metal will become the anode andThe less noble metal will become the anode and

..

•• The less noble metal will become the anode andThe less noble metal will become the anode and

more noble metal (cathode) is protected.more noble metal (cathode) is protected. more noble metal (cathode) is protected.more noble metal (cathode) is protected.



Galvanic Series in Seawater at 25Galvanic Series in Seawater at 25 °°C (77C (77 °°F)F)Galvanic Series in Seawater at 25Galvanic Series in Seawater at 25 °°C (77C (77 °°F)F)

• Magnesium alloys• Zinc• Galvanized steel or galvanized wrought iron

• Magnesium alloys• Zinc• Galvanized steel or galvanized wrought iron

(anodic, or least noble) (anodic, or least noble)

• Mild steel

• Wrought iron• Cast iron

- -

• Mild steel

• Wrought iron• Cast iron

- -• Lead• Tin

• Copper alloy (yellow brass, 65% Cu)•

• Lead• Tin

• Copper alloy (yellow brass, 65% Cu)• • Copper C11000 (ETP copper)• Copper alloys (silicon bronze)• Copper alloy (copper nickel, 30% Ni)•

• Copper C11000 (ETP copper)• Copper alloys (silicon bronze)• Copper alloy (copper nickel, 30% Ni)•

• Type 316 stainless steel (passive)• Type 904 L stainless steel• Duplex 2205 stainless steel•

• Type 316 stainless steel (passive)• Type 904 L stainless steel• Duplex 2205 stainless steel•• Titanium• Gold• Platinum

• Titanium• Gold• PlatinumProtected End(Cathodic, or more noble)Protected End(Cathodic, or more noble)




•• Example: Zinc will corrode when connected to iron.Example: Zinc will corrode when connected to iron.

•• he zinc is less noble and will oxidize more easilhe zinc is less noble and will oxidize more easil

•• Example: Zinc will corrode when connected to iron.Example: Zinc will corrode when connected to iron.

•• he zinc is less noble and will oxidize more easilhe zinc is less noble and will oxidize more easil

than the ironthan the iron•• he electrons will flow to the iron makin it thehe electrons will flow to the iron makin it the

than the ironthan the iron•• he electrons will flow to the iron makin it thehe electrons will flow to the iron makin it the

cathode.cathode.

2+2+ --

cathode.cathode.

2+2+ --

½ O½ O22 + H+ H22O + 2eO + 2e-- 2(OH)2(OH)-- (Cathodic reaction)(Cathodic reaction)

½ O½ O22 + H+ H22O + 2eO + 2e-- 2(OH)2(OH)-- (Cathodic reaction)(Cathodic reaction)

•• e ormation o y roxi es increases t e pH ate ormation o y roxi es increases t e pH atthe surface where the iron is in contact with waterthe surface where the iron is in contact with water•• e ormation o y roxi es increases t e pH ate ormation o y roxi es increases t e pH atthe surface where the iron is in contact with waterthe surface where the iron is in contact with water

– –

known as “cathodic protection”.known as “cathodic protection”.

– –

known as “cathodic protection”.known as “cathodic protection”.




•• Differences in composition or surface conditionDifferences in composition or surface conditionof similar metals can result in galvanic corrosionof similar metals can result in galvanic corrosion

•• Differences in composition or surface conditionDifferences in composition or surface conditionof similar metals can result in galvanic corrosionof similar metals can result in galvanic corrosioncells.cells.

•• New pipeline installed in a repaired section willNew pipeline installed in a repaired section will

cells.cells.

•• New pipeline installed in a repaired section willNew pipeline installed in a repaired section willcorrode more rapidly than the old pipe to whichcorrode more rapidly than the old pipe to whichit is connected.it is connected.corrode more rapidly than the old pipe to whichcorrode more rapidly than the old pipe to whichit is connected.it is connected.

•• he old pipe will have a protective rust layerhe old pipe will have a protective rust layerthat will make the iron in the new steel easier tothat will make the iron in the new steel easier to

•• he old pipe will have a protective rust layerhe old pipe will have a protective rust layerthat will make the iron in the new steel easier tothat will make the iron in the new steel easier to

..•• The new pipe will become the anode and willThe new pipe will become the anode and will

..•• The new pipe will become the anode and willThe new pipe will become the anode and will

....



Concentration Cell CorrosionConcentration Cell CorrosionConcentration Cell CorrosionConcentration Cell Corrosion

•• ConcentrationConcentration--cell corrosion occurs becausecell corrosion occurs because•• ConcentrationConcentration--cell corrosion occurs becausecell corrosion occurs because

the metal.the metal.the metal.the metal.

•• s orm o corros on common y occurs ns orm o corros on common y occurs nlocalized areas where small volumes of localized areas where small volumes of

•• s orm o corros on common y occurs ns orm o corros on common y occurs nlocalized areas where small volumes of localized areas where small volumes of

..

•• Normal mechanical construction can createNormal mechanical construction can create

..

•• Normal mechanical construction can createNormal mechanical construction can create

crev ces a s arp corners, spo we s, o n s,crev ces a s arp corners, spo we s, o n s,fasteners, flanged fittings, couplings,fasteners, flanged fittings, couplings,crev ces a s arp corners, spo we s, o n s,crev ces a s arp corners, spo we s, o n s,fasteners, flanged fittings, couplings,fasteners, flanged fittings, couplings,, …, …, …, …



Concentration Cell CorrosionConcentration Cell Corrosion

•• Higher dissolved oxygen provides aHigher dissolved oxygen provides a•• Higher dissolved oxygen provides aHigher dissolved oxygen provides a

•• Reduction of oxygen would occur:Reduction of oxygen would occur:

•• Reduction of oxygen would occur:Reduction of oxygen would occur:

½½ OO22 + H+ H22O + 2eO + 2e-- 2(OH)2(OH)--½½ OO22 + H+ H22O + 2eO + 2e-- 2(OH)2(OH)--

will become the anodewill become the anode

will become the anodewill become the anode

ee ee + e+ e--

ee ee + e+ e--

C t ti C ll C iC t ti C ll C iC t ti C ll C iC t ti C ll C i




tt ngtt ngtt ngtt ng•• Pittin occurs in the resence of an ox en cellPittin occurs in the resence of an ox en cell•• Pittin occurs in the resence of an ox en cellPittin occurs in the resence of an ox en cell

only if a break exists on the passive film (such asonly if a break exists on the passive film (such asa scratch)a scratch)only if a break exists on the passive film (such asonly if a break exists on the passive film (such asa scratch)a scratch)

•• Any area containing stagnant water will consume Any area containing stagnant water will consume

oxygen by cathodic reaction as corrosion occurs.oxygen by cathodic reaction as corrosion occurs.

•• Any area containing stagnant water will consume Any area containing stagnant water will consume

oxygen by cathodic reaction as corrosion occurs.oxygen by cathodic reaction as corrosion occurs.•• While the remainder of the surface is continuouslyWhile the remainder of the surface is continuously

supplied with oxygen rich water, the stagnant areasupplied with oxygen rich water, the stagnant area•• While the remainder of the surface is continuouslyWhile the remainder of the surface is continuously

supplied with oxygen rich water, the stagnant areasupplied with oxygen rich water, the stagnant area

now con a ns a very ow oxygen concen ra onnow con a ns a very ow oxygen concen ra on•• The dissolved oxygen differential causes theThe dissolved oxygen differential causes the

now con a ns a very ow oxygen concen ra onnow con a ns a very ow oxygen concen ra on•• The dissolved oxygen differential causes theThe dissolved oxygen differential causes the

stagnant area to ecome t e ano e.stagnant area to ecome t e ano e.stagnant area to ecome t e ano e.stagnant area to ecome t e ano e.

C t ti C ll C iC t ti C ll C iC t ti C ll C iC t ti C ll C i




•• The surroundin metal surface becomes the cathode,The surroundin metal surface becomes the cathode,•• The surroundin metal surface becomes the cathode,The surroundin metal surface becomes the cathode,

tt ngtt ngtt ngtt ng

and is protected due to the locally increased pH.and is protected due to the locally increased pH.

OO + 2H+ 2H O + 4eO + 4e-- 4 OH4 OH --

and is protected due to the locally increased pH.and is protected due to the locally increased pH.

OO + 2H+ 2H O + 4eO + 4e-- 4 OH4 OH --

•• At the anode, Ferrous ions continue to dissolve into At the anode, Ferrous ions continue to dissolve into

the water.the water.

•• At the anode, Ferrous ions continue to dissolve into At the anode, Ferrous ions continue to dissolve into

the water.the water.

FeFe FeFe2+2+ + 2e+ 2e--FeFe FeFe2+2+ + 2e+ 2e--

cathodic areas, they are oxidized and form a porouscathodic areas, they are oxidized and form a porousferric h droxide reci itate that covers the it.ferric h droxide reci itate that covers the it.

cathodic areas, they are oxidized and form a porouscathodic areas, they are oxidized and form a porousferric h droxide reci itate that covers the it.ferric h droxide reci itate that covers the it.

4Fe4Fe

2+2+

+ 10H+ 10H22OO ++ OO22

4Fe(OH)4Fe(OH)33(s) + 8H(s) + 8H

++

4Fe4Fe

2+2+

+ 10H+ 10H22OO ++ OO22

4Fe(OH)4Fe(OH)33(s) + 8H(s) + 8H

++




•• In the it the ferrous ions h drol ze to ferrousIn the it the ferrous ions h drol ze to ferrous•• In the it the ferrous ions h drol ze to ferrousIn the it the ferrous ions h drol ze to ferrous

tt ngtt ngtt ngtt ng

hydroxide ions, resulting in the formation of acidhydroxide ions, resulting in the formation of acidprotons:protons:hydroxide ions, resulting in the formation of acidhydroxide ions, resulting in the formation of acidprotons:protons:

FeFe2+2+ + 2H+ 2H22OO ↔↔ Fe(OH)Fe(OH)22 + 2H+ 2H++

••

FeFe2+2+ + 2H+ 2H22OO ↔↔ Fe(OH)Fe(OH)22 + 2H+ 2H++

•• a higher rate of dissolution of the iron.a higher rate of dissolution of the iron.

a higher rate of dissolution of the iron.a higher rate of dissolution of the iron.

intensifies this effect as hydrochloric acid formsintensifies this effect as hydrochloric acid forms

--

intensifies this effect as hydrochloric acid formsintensifies this effect as hydrochloric acid forms

-- 22 22 22 22

Concentration Cell Corrosion PittingConcentration Cell Corrosion Pitting



Concentration Cell Corrosion - PittingConcentration Cell Corrosion - PittingO2

O2 O2

O2 O2

O2

O2

O2

O2

O2

O2

O2O2

O2 O2

- Cathode -Fe2+

OH-

OH-

- Cathode -

H+

Fe2+

H+

Fe2+

OH- OH-

+

H+

Fe2+

Fe2+

OH-

-

Fe2+

H+

H+

FeFe2+2+ + 2H+ 2H22O↔ Fe(OH)O↔ Fe(OH)22 + 2H+ 2H++ (anodic(anodic – – oxidation)oxidation)FeFe2+2+ + 2H+ 2H22O↔ Fe(OH)O↔ Fe(OH)22 + 2H+ 2H++ (anodic(anodic – – oxidation)oxidation)

Concentration Cell Corrosion PittingConcentration Cell Corrosion Pitting



Concentration Cell Corrosion - PittingConcentration Cell Corrosion - Pitting




Aerated Water

O2

O2

O2

O2

O2

O2O2

2

O2

O2

O2

O2

O2

C

FeC

C Fe

C

FeC

FeCFe

C Fe

C

FeC

C

CFe Fe

C

FeC

FeCFe

C Fe

C

Fe++

Fe++

e-e-

-

FeFeC C Fe FeC C Fe C CFe FeC C FeFe++

e-

e-

e-

FeFeCFe C FeCFe C FeC C FeCFe CFe++

e-

e-



Erosion CorrosionErosion CorrosionErosion CorrosionErosion Corrosion

•• Erosion corrosion refers to the repetitive formationErosion corrosion refers to the repetitive formationn r i n f m l' r iv rf film.n r i n f m l' r iv rf film.

•• Erosion corrosion refers to the repetitive formationErosion corrosion refers to the repetitive formationn r i n f m l' r iv rf film.n r i n f m l' r iv rf film.

This typically occurs in a moving liquid.This typically occurs in a moving liquid.••

This typically occurs in a moving liquid.This typically occurs in a moving liquid.••

cathodic process which creates an oxide layer oncathodic process which creates an oxide layer on

the pipe surface.the pipe surface.

cathodic process which creates an oxide layer oncathodic process which creates an oxide layer on

the pipe surface.the pipe surface.•• The destruction of the protective film is mechanicalThe destruction of the protective film is mechanical

due to hi h velocit flow of water es eciall if itdue to hi h velocit flow of water es eciall if it•• The destruction of the protective film is mechanicalThe destruction of the protective film is mechanical

due to hi h velocit flow of water es eciall if itdue to hi h velocit flow of water es eciall if it

contains suspended solids.contains suspended solids.

••contains suspended solids.contains suspended solids.

•• exchanger tubes.exchanger tubes.

exchanger tubes.exchanger tubes.

Erosion Corrosion ProcessErosion Corrosion Process



Erosion-Corrosion ProcessErosion-Corrosion Process

O2 Aerated Water

O2O2

O2

O2

2

O2

2

O2O2

O2

O2

Passive Film

Base Metal



Microbiologically Influenced CorrosionMicrobiologically Influenced CorrosionMicrobiologically Influenced CorrosionMicrobiologically Influenced Corrosion

of oxygenof oxygen

of oxygenof oxygen

•• Anaerobic bacteria can exist in the inner parts Anaerobic bacteria can exist in the inner parts•• Anaerobic bacteria can exist in the inner parts Anaerobic bacteria can exist in the inner partso corros on epos s, w e e ou er par s areo corros on epos s, w e e ou er par s areinhabited by aerobic bacteria.inhabited by aerobic bacteria.o corros on epos s, w e e ou er par s areo corros on epos s, w e e ou er par s areinhabited by aerobic bacteria.inhabited by aerobic bacteria.

Mic obiologicall Infl enced Co osionMic obiologicall Infl enced Co osionMic obiologicall Infl enced Co osionMic obiologicall Infl enced Co osion




•• Sulfate Reducing Bacteria (SRB) are anaerobicSulfate Reducing Bacteria (SRB) are anaerobicbacteria that reduce sulfate to hydrogen sulfide.bacteria that reduce sulfate to hydrogen sulfide.

•• Sulfate Reducing Bacteria (SRB) are anaerobicSulfate Reducing Bacteria (SRB) are anaerobicbacteria that reduce sulfate to hydrogen sulfide.bacteria that reduce sulfate to hydrogen sulfide.

SOSO4422-- + 8H+ 8H++ + 8e+ 8e-- SS22-- + 4H+ 4H22OO

•• m m f RBm m f RB--infl n rr i n rinfl n rr i n r

SOSO4422-- + 8H+ 8H++ + 8e+ 8e-- SS22-- + 4H+ 4H22OO

•• m m f RBm m f RB--infl n rr i n rinfl n rr i n r hydrogen sulfide odor, and black iron sulfidehydrogen sulfide odor, and black iron sulfidedeposits.deposits.hydrogen sulfide odor, and black iron sulfidehydrogen sulfide odor, and black iron sulfidedeposits.deposits.

SS22-- + 2H+ 2H++ HH22SS22-- 2+2+

SS22-- + 2H+ 2H++ HH22SS22-- 2+2+





r r r r ur r r r u

aggressive organic and inorganic acids.aggressive organic and inorganic acids.

r r r r ur r r r u

aggressive organic and inorganic acids.aggressive organic and inorganic acids.

•• c s pro uce y acter a acce eratec s pro uce y acter a acce eratecorrosion by dissolving oxides (the passivecorrosion by dissolving oxides (the passive

•• c s pro uce y acter a acce eratec s pro uce y acter a acce eratecorrosion by dissolving oxides (the passivecorrosion by dissolving oxides (the passive

•• Acids also consume the OH Acids also consume the OH-- ions whichions which•• Acids also consume the OH Acids also consume the OH-- ions whichions which

(Le Chatelier’s Principle).(Le Chatelier’s Principle).

(Le Chatelier’s Principle).(Le Chatelier’s Principle).




•• IronIron--oxidizing bacteria are aerobic bacteriaoxidizing bacteria are aerobic bacteriawhich oxidize ferrous ions to less soluble ferricwhich oxidize ferrous ions to less soluble ferricons.ons.

FeFe

2+2+

FeFe

3+3+

+ e+ e

--

•• The resulting ferric ions precipitate as ferricThe resulting ferric ions precipitate as ferrichydroxides forming tubercules in the pipes.hydroxides forming tubercules in the pipes.



Controlling CorrosionControlling CorrosionControlling CorrosionControlling Corrosion

C i P blC i P blC i P blC i P bl



Corrosion ProblemsCorrosion ProblemsCorrosion ProblemsCorrosion Problems

•• onsumer comp a nts a out e ateronsumer comp a nts a out e ater

•• Com liance with EPA’s Lead and Co er RuleCom liance with EPA’s Lead and Co er Rule

DegassifiersDegassifiers: Effect on Alkalinity: Effect on AlkalinityDegassifiersDegassifiers: Effect on Alkalinity: Effect on Alkalinity



gg yygg yy

•• FloridaFlorida groundwatersgroundwaters contain a high amount of Hcontain a high amount of H22SS

•• DegassifiersDegassifiers are used to remove the Hare used to remove the H22S in theS in the

permeate.permeate.

•• DegassifiersDegassifiers also completely remove COalso completely remove CO22..

•• increases more easily, but water has no bufferingincreases more easily, but water has no bufferingcapacity.capacity.

•• The hydroxides are consumed by acids in theThe hydroxides are consumed by acids in thedistribution system resulting in a pH dropdistribution system resulting in a pH drop

DegassifiersDegassifiers: Effect on Alkalinity: Effect on AlkalinityDegassifiersDegassifiers: Effect on Alkalinity: Effect on Alkalinity



gg yygg yy

•• In order to resolve this problem, many plants injectIn order to resolve this problem, many plants inject

22 ..

HH22O + COO + CO22 HH22COCO33

HH22COCO33 + OH+ OH-- HCOHCO33-- + H+ H22OO

-- ++ -- 22-- ++

•• Alkalinity can also be added by blending the permeateAlkalinity can also be added by blending the permeate

with a small amount of feedwater or water from awith a small amount of feedwater or water from aneighboring lime softening plant.neighboring lime softening plant.

AlkalinityAlkalinity –– Effects on CorrosionEffects on CorrosionAlkalinityAlkalinity –– Effects on CorrosionEffects on Corrosion



•• Alkalinity provides buffering capacity in water systemsAlkalinity provides buffering capacity in water systems

COCO33

22-- + H+ H++ HCOHCO33

--

HCOHCO -- + H+ H++ HH COCO

•• Buffering is the ability to minimize pH fluctuationsBuffering is the ability to minimize pH fluctuationsresulting from introduction of acids or basesresulting from introduction of acids or bases

•• Certain types of bacteria in the distribution system canCertain types of bacteria in the distribution system canproduce organic and inorganic acids as byproducts of produce organic and inorganic acids as byproducts of

e r me a o sme r me a o sm ee. u ur x z ng ac er a. u ur x z ng ac er a

•• Some corrosion byproducts can hydrolyze producingSome corrosion byproducts can hydrolyze producingfree acid byproducts (free acid byproducts (ieie.. FeFe ++ + 2H+ 2H22O Fe(OH)O Fe(OH)22 + 2H+ 2H++))

Alkalinity Alkalinity – – Effects on CorrosionEffects on CorrosionIronIron




IronIronIronIron

• At pH 7 – 9, tuberculation and precipitation rate• At pH 7 – 9, tuberculation and precipitation rate

decreases

decreases

taken from a Boston distribution system showed

h r in lk lini fr m m L 1

taken from a Boston distribution system showed

h r in lk lini fr m m L 1 mg/L as CaCO3 at a constant pH resulted in animmediate increase of 1.5 - 3.5X in iron release.

mg/L as CaCO3 at a constant pH resulted in animmediate increase of 1.5 - 3.5X in iron release.

• Corrosion of cast iron and mild steel areminimized when alkalinit reater than 60 m L

• Corrosion of cast iron and mild steel areminimized when alkalinit reater than 60 m Las CaCO3as CaCO3



IronIronIronIron

Alkalinity Alkalinity – – Effects on CorrosionEffects on Corrosion Alkalinity Alkalinity – – Effects on CorrosionEffects on Corrosion



• Lead release is significantly lower whenalkalinit is between 30 and 74 m L as CaCO

• Lead release is significantly lower whenalkalinit is between 30 and 74 m L as CaCO than when alkalinity is <30 mg/L as CaCO3

•• rr i n f L l r r m inlrr i n f L l r r m inl

than when alkalinity is <30 mg/L as CaCO3

•• rr i n f L l r r m inlrr i n f L l r r m inl galvanic corrosiongalvanic corrosion – – alkalinity >74ppm doesalkalinity >74ppm doesnot reduce lead release into drinking water.not reduce lead release into drinking water.

galvanic corrosiongalvanic corrosion – – alkalinity >74ppm doesalkalinity >74ppm doesnot reduce lead release into drinking water.not reduce lead release into drinking water.

• A pH of at least 8 is required to minimize leadcorrosion to acceptable levels

• A pH of at least 8 is required to minimize leadcorrosion to acceptable levels

• pH of >9.2 is optimal for reduced leadconcentrations in drinking water• pH of >9.2 is optimal for reduced leadconcentrations in drinking water




a s

e

a s

e

R e l

R e l

L e a

L e a

15 30 45 60 74

Alkalinity

pHpH – – Effects on CorrosionEffects on CorrosionpHpH – – Effects on CorrosionEffects on Corrosion



0.20 L )

0.1280.15 l v e

d

( m

g /

0.10 D i s s

r

o s i o

0.0350.05 L e a d

m C

o

. 0.004

0.00 f r

o

6.7 8.5 9.2 10.5

pH




• Alkalinit <25 m L as CaCO increases• Alkalinit <25 m L as CaCO increasesuniform corrosion of copper.

•

uniform corrosion of copper.

• when alkalinity is >74 ppm due to theformation of soluble cupric bicarbonate andwhen alkalinity is >74 ppm due to theformation of soluble cupric bicarbonate andcar ona e comp exes – s e ec s ma eworse if the pH is also < 7.8car ona e comp exes – s e ec s ma eworse if the pH is also < 7.8

• p > copper corros on a occurs wbe non-uniform or pitting corrosion.• p > copper corros on a occurs wbe non-uniform or pitting corrosion.




e a s

e

r

e

r R e l

W a t e

C o p p i

15 25 35 45 55 65 75 85 95

Alkalinity




• Co er is least soluble at H>9. Chlorine• Co er is least soluble at H>9. Chlorinein water oxidizes copper surfaces to form arotective assive la er that revents

in water oxidizes copper surfaces to form arotective assive la er that revents

further corrosion. This passive film will

dissolve if pH<9.

further corrosion. This passive film will

dissolve if pH<9.



3030 4545a n ya n y

Iron

Copper

Lead

Alkalinity

Corrosion InhibitorsCorrosion InhibitorsCorrosion InhibitorsCorrosion Inhibitors



Two types of corrosion inhibitors:Two types of corrosion inhibitors:Two types of corrosion inhibitors:Two types of corrosion inhibitors:

1.1. Anodic Inhibitors Anodic Inhibitors: Form a film on the anode: Form a film on the anode

to prevent water from directly contacting theto prevent water from directly contacting the

1.1. Anodic Inhibitors Anodic Inhibitors: Form a film on the anode: Form a film on the anode

to prevent water from directly contacting theto prevent water from directly contacting themetal surfacemetal surface

2.2. h i Inhi i rh i Inhi i r : F rm r i i: F rm r i i

metal surfacemetal surface

2.2. h i Inhi i rh i Inhi i r : F rm r i i: F rm r i i barrier at the cathode to reduce the flow of barrier at the cathode to reduce the flow of electrons.electrons.barrier at the cathode to reduce the flow of barrier at the cathode to reduce the flow of electrons.electrons.

Anodic Corrosion Inhibitors Anodic Corrosion Inhibitors Anodic Corrosion Inhibitors Anodic Corrosion Inhibitors



•• Anodic Inhibitors work by passivation. Anodic Inhibitors work by passivation.•• Anodic Inhibitors work by passivation. Anodic Inhibitors work by passivation.

•• The Corrosion Inhibitor precipitates on the metalThe Corrosion Inhibitor precipitates on the metal

surface, filling in any gaps in the existing oxidesurface, filling in any gaps in the existing oxide

•• The Corrosion Inhibitor precipitates on the metalThe Corrosion Inhibitor precipitates on the metal

surface, filling in any gaps in the existing oxidesurface, filling in any gaps in the existing oxide..

•• The precipitated Corrosion inhibitor forms a thinThe precipitated Corrosion inhibitor forms a thin

..

•• The precipitated Corrosion inhibitor forms a thinThe precipitated Corrosion inhibitor forms a thin

the metal and the water, preventing migration of the metal and the water, preventing migration of ions from the solid state to the solution state.ions from the solid state to the solution state.

the metal and the water, preventing migration of the metal and the water, preventing migration of ions from the solid state to the solution state.ions from the solid state to the solution state.

•• As long as the reaction at the anode is prevented, As long as the reaction at the anode is prevented,electrons will not flow to the cathode.electrons will not flow to the cathode.•• As long as the reaction at the anode is prevented, As long as the reaction at the anode is prevented,electrons will not flow to the cathode.electrons will not flow to the cathode.



Problems Associated with UnderdosingProblems Associated with UnderdosingProblems Associated with UnderdosingProblems Associated with Underdosing

•• Underdosing orthophosphates will only coat someUnderdosing orthophosphates will only coat some•• Underdosing orthophosphates will only coat someUnderdosing orthophosphates will only coat some

•• Severe pitting corrosion will occur as the oxidationSevere pitting corrosion will occur as the oxidation•• Severe pitting corrosion will occur as the oxidationSevere pitting corrosion will occur as the oxidationconcentrates at t e unprotecte ano c s tes.concentrates at t e unprotecte ano c s tes.

•• This type of problem is often found at sites whereThis type of problem is often found at sites where

concentrates at t e unprotecte ano c s tes.concentrates at t e unprotecte ano c s tes.

•• This type of problem is often found at sites whereThis type of problem is often found at sites where

phosphoric acid is used as a corrosion inhibitorphosphoric acid is used as a corrosion inhibitorphosphoric acid is used as a corrosion inhibitorphosphoric acid is used as a corrosion inhibitor



•• Orthophosphate:Orthophosphate: Effective in distributionEffective in distributionsystems at moderate dosagessystems at moderate dosages

•• Orthophosphate:Orthophosphate: Effective in distributionEffective in distributionsystems at moderate dosagessystems at moderate dosages

•• Silicate:Silicate: Very effective but require extremely Very effective but require extremely

high dosageshigh dosages

•• Silicate:Silicate: Very effective but require extremely Very effective but require extremely

high dosageshigh dosages•• Molybdate:Molybdate: he best of the anodic corrosionhe best of the anodic corrosion

inhibitors but high dosage and high costinhibitors but high dosage and high cost•• Molybdate:Molybdate: he best of the anodic corrosionhe best of the anodic corrosion

inhibitors but high dosage and high costinhibitors but high dosage and high cost

..•• Borate:Borate: Boron is a possible carcinogen so thisBoron is a possible carcinogen so this

..•• Borate:Borate: Boron is a possible carcinogen so thisBoron is a possible carcinogen so this

•• Nitrite:Nitrite: Nitrite is useful in oxygen free systemsNitrite is useful in oxygen free systemssuch as chillers but is not used in drinkinsuch as chillers but is not used in drinkin

•• Nitrite:Nitrite: Nitrite is useful in oxygen free systemsNitrite is useful in oxygen free systemssuch as chillers but is not used in drinkinsuch as chillers but is not used in drinkinwater systems.water systems.water systems.water systems.



Cathodic Corrosion InhibitorsCathodic Corrosion InhibitorsCathodic Corrosion InhibitorsCathodic Corrosion Inhibitors



•• Zinc:Zinc: Effective in distribution systems atEffective in distribution systems atmoderate dosagesmoderate dosages

•• Zinc:Zinc: Effective in distribution systems atEffective in distribution systems atmoderate dosagesmoderate dosages

•• Calcium:Calcium: Recent studies dispute effectivenessRecent studies dispute effectiveness

of calcium carbonate as corrosion inhibitorof calcium carbonate as corrosion inhibitor

•• Calcium:Calcium: Recent studies dispute effectivenessRecent studies dispute effectiveness

of calcium carbonate as corrosion inhibitorof calcium carbonate as corrosion inhibitor•• Magnesium:Magnesium: heoretically will provideheoretically will provide

corrosion inhibition when Magnesiumcorrosion inhibition when Magnesium•• Magnesium:Magnesium: heoretically will provideheoretically will provide

corrosion inhibition when Magnesiumcorrosion inhibition when Magnesium

•• Polyphosphate:Polyphosphate: Claimed to form a protectiveClaimed to form a protective – –

•• Polyphosphate:Polyphosphate: Claimed to form a protectiveClaimed to form a protective

– –

show it is ineffective in absence of calcium orshow it is ineffective in absence of calcium orzinc.zinc.

show it is ineffective in absence of calcium orshow it is ineffective in absence of calcium orzinc.zinc.




ZincZincZincZinc

u r r ru r r r

•• he zinc works by precipitating as a zinc hydroxidehe zinc works by precipitating as a zinc hydroxide

u r r ru r r r

•• he zinc works by precipitating as a zinc hydroxidehe zinc works by precipitating as a zinc hydroxide

(Zn(OH)(Zn(OH)22) on the cathodic surface, inhibiting the) on the cathodic surface, inhibiting the

reductions.reductions.

(Zn(OH)(Zn(OH)22) on the cathodic surface, inhibiting the) on the cathodic surface, inhibiting the

reductions.reductions.

•• If alkalinity in the water is sufficient, a moreIf alkalinity in the water is sufficient, a more•• If alkalinity in the water is sufficient, a moreIf alkalinity in the water is sufficient, a more

((hydrozincite), preventing oxygen from reaching, preventing oxygen from reaching((hydrozincite), preventing oxygen from reaching, preventing oxygen from reaching....




ZincZincZincZinc

nc corros on n tors prov e su stant a

protection of asbestos-cement pipe by

nc corros on n tors prov e su stant a

protection of asbestos-cement pipe by

fiber release and water attack.fiber release and water attack.




CalciumCalciumCalciumCalcium

Carbonate Film on the metal surface whenCarbonate Film on the metal surface whenCarbonate Film on the metal surface whenCarbonate Film on the metal surface when

sufficiently high. However, most studies showsufficiently high. However, most studies showsufficiently high. However, most studies showsufficiently high. However, most studies show

a protective scale on metals and is not ana protective scale on metals and is not an

ff iv rr i n inhi i r.ff iv rr i n inhi i r.

a protective scale on metals and is not ana protective scale on metals and is not an

ff iv rr i n inhi i r.ff iv rr i n inhi i r.

•• Under certain conditions calcium has beenUnder certain conditions calcium has been•• Under certain conditions calcium has beenUnder certain conditions calcium has been....




MagnesiumMagnesiumMagnesiumMagnesium

metal surface only when Magnesiummetal surface only when Magnesiumconcentration is sufficientl hi h Sea water .concentration is sufficientl hi h Sea water .metal surface only when Magnesiummetal surface only when Magnesiumconcentration is sufficientl hi h Sea water .concentration is sufficientl hi h Sea water .Magnesium hydroxide films are only stable atMagnesium hydroxide films are only stable atvery high pH.very high pH.Magnesium hydroxide films are only stable atMagnesium hydroxide films are only stable atvery high pH.very high pH.

Pol hos hatesPol hos hatesPol hos hatesPol hos hatesCathodic Corrosion InhibitorsCathodic Corrosion InhibitorsCathodic Corrosion InhibitorsCathodic Corrosion Inhibitors



•• Will produce a thin, amorphous salt filmWill produce a thin, amorphous salt film ONLY ONLY in thein thepresence of Zinc or high levels of Calcium.presence of Zinc or high levels of Calcium.

•• Will produce a thin, amorphous salt filmWill produce a thin, amorphous salt film ONLY ONLY in thein thepresence of Zinc or high levels of Calcium.presence of Zinc or high levels of Calcium.

• When used alone, polyphosphate does not act towards

iron as a corrosion inhibitor but as a sequestrant, causing

• When used alone, polyphosphate does not act towards

iron as a corrosion inhibitor but as a sequestrant, causingr v u rv r w r.

• If polyphosphate products are dosed in systems with

r v u rv r w r.

• If polyphosphate products are dosed in systems with

,increase the rate of corrosion of the steel pipe as theysequester iron from the surface. However, since

,increase the rate of corrosion of the steel pipe as theysequester iron from the surface. However, sincepo yp osp ates ecrease t e appearance o re water,

this corrosion goes unnoticed.

po yp osp ates ecrease t e appearance o re water,

this corrosion goes unnoticed.

increase corrosion of steel, copper and lead when used inincrease corrosion of steel, copper and lead when used in

absence of zinc.absence of zinc.

increase corrosion of steel, copper and lead when used inincrease corrosion of steel, copper and lead when used in

absence of zinc.absence of zinc.

Anodic/Cathodic Anodic/Cathodic Anodic/Cathodic Anodic/Cathodic



Products combining anodic and cathodic

corrosion inhibitors exhibit su erior


corrosion inhibitors exhibit su erior

corrosion inhibition.corrosion inhibition.

Anodic/Cathodic Anodic/Cathodic Anodic/Cathodic Anodic/Cathodic



• It was observed in an 18-month survey of 31 water• It was observed in an 18-month survey of 31 watersystems in North America that distribution systems using

zinc orthophosphate inhibitors had fewer coliform

systems in North America that distribution systems using

zinc orthophosphate inhibitors had fewer coliform

• Coliform bacteria counts are directly indicative of • Coliform bacteria counts are directly indicative of

.

• The Zinc Orthophosphate does not attack bacteria – but

.

• The Zinc Orthophosphate does not attack bacteria – but,

chlorine/chloramines) active in the water instead of beingconsumed by corrosion reactions (oxidation of ferrous to

,

chlorine/chloramines) active in the water instead of beingconsumed by corrosion reactions (oxidation of ferrous toferric ions)– this reduces biologically induced corrosion.ferric ions)– this reduces biologically induced corrosion.

Corrosion Coupon TestsCorrosion Coupon TestsCorrosion Coupon TestsCorrosion Coupon Tests



Port St. LuciePort St. Lucie -- JEA PlantJEA PlantRO WaterRO Water





4045

)

Blank

Poly/Ortho

30

35

e ( M P Y A-751

40.6120

25

i o n R a

24.96

1.73510

C o r

r o

0Mild Steel


P S L iP S L i JEA PlJEA Pl




5.13

5

6

Y )

Blank Poly/Ortho A-751

3.56

3.914

a t e ( M

2.73

1.682

3

s i o n

1.13

0.18 0.12

.

1 C o

r r

0Copper Brass Lead


P t St L iP t St L i P i ill Pl tP i ill Pl t



Port St. LuciePort St. Lucie -- Prineville PlantPrineville PlantRO Water Blended with Lime Softened WaterRO Water Blended with Lime Softened Water






25 )

Blank

Poly/Ortho

20

e ( M P Y A-751

23.82 23.62

10 i o n R a

5 C o r

r o

.0

Mild Steel






2.16

2.5

Y )

Blank Poly/Ortho A-751

1.75

1.5

.

a t e ( M

0.92

0.700.84

0.931.0 s i o n

0.39.

0.320.5 C o

r r

.Copper Brass Lead

Water Quality forWater Quality forO timal Corrosion InhibitionO timal Corrosion Inhibition

Water Quality forWater Quality forO timal Corrosion InhibitionO timal Corrosion Inhibition



–

Maintain a pH > 8.5


Reverse Osmosis Permeate.

er orm orros on oupon stu es to ensure

adequate corrosion control.



•• Metal Ion Cell: The metal surface ex osed toMetal Ion Cell: The metal surface ex osed to•• Metal Ion Cell: The metal surface ex osed toMetal Ion Cell: The metal surface ex osed towater with lower concentration of the metal’swater with lower concentration of the metal’s

ions will become the anode (oxidizes andions will become the anode (oxidizes and

water with lower concentration of the metal’swater with lower concentration of the metal’s

ions will become the anode (oxidizes andions will become the anode (oxidizes anddissolves), while the surface exposed to waterdissolves), while the surface exposed to waterwith higher concentration of the metal’s ionswith higher concentration of the metal’s ionsdissolves), while the surface exposed to waterdissolves), while the surface exposed to waterwith higher concentration of the metal’s ionswith higher concentration of the metal’s ions

..

•• (Diagram or Animation for Explanation)(Diagram or Animation for Explanation)

..

•• (Diagram or Animation for Explanation)(Diagram or Animation for Explanation)

•• Le Chatelier’s PrincipleLe Chatelier’s Principle•• Le Chatelier’s PrincipleLe Chatelier’s Principle

corrosion mechanisms and prevention rev8

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