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Conference/SeminarConference/Seminar

May 2007May 2007

Presentation by Presentation by

KAP KAP Corrosion Control & ServicingCorrosion Control & Servicing

Danis Pang, Application EngineerDanis Pang, Application Engineer

The latest quote on corrosionThe latest quote on corrosion

33rdrd China International Corrosion Control China International Corrosion Control

Conference and ExhibitionConference and Exhibition

�� “Corrosion is harmful for human beings, the “Corrosion is harmful for human beings, the �� “Corrosion is harmful for human beings, the “Corrosion is harmful for human beings, the

environmentenvironment and life.” and life.”

�� We need to enhance the consciousness of safe We need to enhance the consciousness of safe

protection and strictly manage combustibles protection and strictly manage combustibles

,, explosive substanceexplosive substance

Presentation ContentPresentation Content

�� Introduction to Corrosion. Introduction to Corrosion.

�� Types of Corrosion.Types of Corrosion.

�� Consequences of Corrosion.Consequences of Corrosion.

�� Corrosion Stages/Scales.Corrosion Stages/Scales.

�� Surface PreparationsSurface Preparations

�� Application Methods for Coating.Application Methods for Coating.

�� Coating Failures and CausesCoating Failures and Causes

�� ConclusionConclusion

What is CorrosionWhat is Corrosion

�� Corrosion is Corrosion is the deterioration of materials by the deterioration of materials by chemical interaction with their environment.chemical interaction with their environment.

�� Most metals corrode on contact with water (and Most metals corrode on contact with water (and moisture in the air), acids, bases, salts, oils, moisture in the air), acids, bases, salts, oils, aggressive metal polishes, and other solid and liquid aggressive metal polishes, and other solid and liquid chemicals.chemicals.aggressive metal polishes, and other solid and liquid aggressive metal polishes, and other solid and liquid chemicals.chemicals.

�� Metals will also corrode when exposed to gaseous Metals will also corrode when exposed to gaseous materials like acid vapors, formaldehyde gas, materials like acid vapors, formaldehyde gas, ammonia gas, and sulfur containing gases.ammonia gas, and sulfur containing gases.

�� The term corrosion is sometimes also applied to the The term corrosion is sometimes also applied to the degradation of plastics, concrete and wood, but degradation of plastics, concrete and wood, but generally refers to metals.generally refers to metals.

Introduction to Corrosion

How does Corrosion happenHow does Corrosion happen

�� Corrosion is an electrochemical reaction.Corrosion is an electrochemical reaction.

�� The reaction require four prerequisites:The reaction require four prerequisites:

•• An anodeAn anode

•• An cathodeAn cathode•• An cathodeAn cathode

•• An electron pathwayAn electron pathway

•• An electrolyte (ionic pathway)An electrolyte (ionic pathway)

Introduction to Corrosion

Electrochemistry of CorrosionElectrochemistry of Corrosion

�� The corrosion process (anodic The corrosion process (anodic

reaction) of the metal dissolving reaction) of the metal dissolving

as ions generates some as ions generates some

electrons, as shown here, that electrons, as shown here, that

are consumed by a secondary are consumed by a secondary are consumed by a secondary are consumed by a secondary

process (cathodic reaction). process (cathodic reaction).

�� These two processes have to These two processes have to

balance their charges.balance their charges.

Introduction to Corrosion

�� The sites hosting these The sites hosting these

two processes can be two processes can be

located close to each other located close to each other

on the metal's surface, or on the metal's surface, or

far apart depending on the far apart depending on the

circumstances. circumstances.

�� The electrons (eThe electrons (e-- in this in this

figure) produced by the figure) produced by the figure) produced by the figure) produced by the

corrosion reaction will corrosion reaction will

need to be consumed by a need to be consumed by a

cathodic reaction in close cathodic reaction in close

proximity to the corrosion proximity to the corrosion

reaction itselfreaction itself..

Introduction to Corrosion

Iron in a deaerated neutral solutionIron in a deaerated neutral solution

Anodic reactionAnodic reaction

�� surface area = 1 cmsurface area = 1 cm22

�� Fe Fe ----> Fe> Fe2+2+ + 2 e+ 2 e--

�� EE00 = = --0.44 V vs. SHE 0.44 V vs. SHE

�� for a corroding metal one can assume that Efor a corroding metal one can assume that Eeqeq

= E= E00 · i· i00 = 10= 10--66 A cmA cm--22

�� II00 = 1x10= 1x10--66 A A

�� bbaa = 0.120 V decade= 0.120 V decade--11

Introduction to Corrosion

Cathodic reactionCathodic reaction

�� surface area = 1 cmsurface area = 1 cm22

�� [H[H++] = 10] = 10--55 (pH = 5) (pH = 5)

�� 2 H2 H++ + 2 e+ 2 e-- ----> H> H22

�� EEeqeq = E= E00 + 0.059 log+ 0.059 log1010 [H[H++] = 0.0 ] = 0.0 -- 0.059x(0.059x(--5) = 5) = --�� EEeqeq = E= E00 + 0.059 log+ 0.059 log1010 [H[H++] = 0.0 ] = 0.0 -- 0.059x(0.059x(--5) = 5) = --

0.295 V vs. SHE 0.295 V vs. SHE

�� ii00 = 10= 10--66 A cmA cm--22

�� II00 = 1x10= 1x10--66 A A

�� bbcc = = --0.120 V decade0.120 V decade--11

Introduction to Corrosion

Sequence of Corrosion (Pitting)Sequence of Corrosion (Pitting)

Introduction to Corrosion

Types of CorrosionTypes of Corrosion

�� Group 1.Group 1.

�� Group 2.Group 2.

�� Group 3. Group 3.

•• *Atmospheric Corrosion* *Atmospheric Corrosion* •• *Atmospheric Corrosion* *Atmospheric Corrosion*

•• *High Temperature Corrosion*High Temperature Corrosion**

Group 1 Group 1 -- readily identifiable by readily identifiable by

ordinary visual examinationordinary visual examination

�� Uniform corrosion Uniform corrosion

�� Pitting Pitting

�� Crevice corrosion Crevice corrosion Crevice corrosion Crevice corrosion

•• crevice model crevice model

•• filiform corrosion filiform corrosion

•• pack rust pack rust

�� Galvanic corrosion Galvanic corrosion

�� Lamellar corrosion Lamellar corrosion

Group 2 Group 2 -- may require supplementary may require supplementary

means of examinationmeans of examination

�� Erosion corrosion Erosion corrosion

�� Cavitation Cavitation

�� Fretting corrosion Fretting corrosion �� Fretting corrosion Fretting corrosion

�� Intergranular corrosion Intergranular corrosion

�� Exfoliation Exfoliation

�� Dealloying (selective leaching or Selective Attack)) Dealloying (selective leaching or Selective Attack))

Group 3 Group 3 -- verification is usually verification is usually

required by microscopy (optical, required by microscopy (optical,

electron microscopy etc.)electron microscopy etc.)

�� Environmental cracking Environmental cracking

�� Stress Corrosion Cracking (SCC) Stress Corrosion Cracking (SCC)

�� Corrosion fatigue Corrosion fatigue

�� Hydrogen embrittlementHydrogen embrittlement

Uniform CorrosionUniform Corrosion

�� occurs over the majority of occurs over the majority of the surface of a metal at a the surface of a metal at a steady and often predictable steady and often predictable rate.rate.

�� the most common form of the most common form of corrosion.corrosion.corrosion.corrosion.

�� normally characterized by a normally characterized by a chemical or electrochemical chemical or electrochemical reaction, which proceeds reaction, which proceeds uniformly over the entire uniformly over the entire exposed surface or over a exposed surface or over a large area.large area.

Pitting CorrosionPitting Corrosion

�� occurs in materials that occurs in materials that have a protective film have a protective film such as a corrosion such as a corrosion product or when a product or when a coating breaks down. coating breaks down. coating breaks down. coating breaks down.

�� Pitting corrosion is a Pitting corrosion is a localized form of localized form of corrosion by which corrosion by which cavities or "holes" are cavities or "holes" are produced in the produced in the material. material.

Trough PitsTrough Pits

•�arrow, deep•�arrow, deep

•Elliptical•Vertical grain attack

•Shallow, wide

Sideway PitsSideway Pits

•Subsurface

•Horizontal grain attack

•Undercutting

Crevice CorrosionCrevice Corrosion

�� Crevice corrosion is a localized Crevice corrosion is a localized form of corrosion usually form of corrosion usually associated with a stagnant associated with a stagnant solution on the microsolution on the micro--environmental level. environmental level.

�� Crevice corrosion is initiated by Crevice corrosion is initiated by changes in local chemistry within changes in local chemistry within the crevice: the crevice: the crevice: the crevice:

•• Depletion of inhibitor in the Depletion of inhibitor in the crevice crevice

•• Depletion of oxygen in the Depletion of oxygen in the crevice crevice

•• A shift to acid conditions in the A shift to acid conditions in the crevice crevice

•• BuildBuild--up of aggressive ion up of aggressive ion species (e.g. chloride) in the species (e.g. chloride) in the crevice crevice

Filiform CorrosionFiliform Corrosion

�� A special form of A special form of

crevice corrosioncrevice corrosion in in

which the aggressive which the aggressive

chemistry buildchemistry build--up up

occurs under a occurs under a occurs under a occurs under a

protective film that has protective film that has

been breachedbeen breached. .

Filiform corrosionFiliform corrosion

�� normally starts at small, sometimes microscopic, normally starts at small, sometimes microscopic,

defects in the coating. Lacquers and "quickdefects in the coating. Lacquers and "quick--dry" dry"

paints are most susceptible to the problem. Their use paints are most susceptible to the problem. Their use

should be avoided unless absence of an adverse effect should be avoided unless absence of an adverse effect

has been proven by field experience. Where a coating has been proven by field experience. Where a coating has been proven by field experience. Where a coating has been proven by field experience. Where a coating

is required, it should exhibit low water vapor is required, it should exhibit low water vapor

transmission characteristics and excellent adhesion. transmission characteristics and excellent adhesion.

ZincZinc--rich coatings should also be considered for rich coatings should also be considered for

coating carbon steel because of their cathodic coating carbon steel because of their cathodic

protection quality.protection quality.

Pack RustPack Rust

�� Pack rust is a form a Pack rust is a form a localized corrosion typical localized corrosion typical of steel components that of steel components that develop a crevice into an develop a crevice into an open atmospheric open atmospheric environment. This environment. This environment. This environment. This expression is often used in expression is often used in relation to bridge inspection relation to bridge inspection to describe builtto describe built--up up members of steel bridges members of steel bridges which are showing signs of which are showing signs of rust packing between steel rust packing between steel plates.plates.

GALVANIC CORROSIONGALVANIC CORROSION

�� occurs when two different occurs when two different metals are placed in contact metals are placed in contact with each other and is with each other and is caused by the greater caused by the greater willingness of one to give willingness of one to give up electrons than the other.up electrons than the other.

This is one of the most This is one of the most �� This is one of the most This is one of the most common forms of corrosion common forms of corrosion as well as one of the most as well as one of the most destructive. Here’s a classic destructive. Here’s a classic example of galvanic example of galvanic corrosion; a stainless screw corrosion; a stainless screw in contact with a cadmium in contact with a cadmium plated steel washerplated steel washer

The Statue of Liberty CaseThe Statue of Liberty Case

�� The galvanic reaction The galvanic reaction between iron and copper between iron and copper was originally mitigated by was originally mitigated by insulating copper from the insulating copper from the iron framework using an iron framework using an asbestos cloth soaked in asbestos cloth soaked in asbestos cloth soaked in asbestos cloth soaked in shellac. However, the shellac. However, the integrity and sealing integrity and sealing property of this improvised property of this improvised insulator broke down over insulator broke down over the many years of exposure the many years of exposure to high levels of humidity to high levels of humidity normal in a marinenormal in a marineenvironment.environment.

Lamellar Corrosion or ExfoliationLamellar Corrosion or Exfoliation

�� Exfoliation corrosion is a Exfoliation corrosion is a particular form of particular form of intergranular corrosion intergranular corrosion associated with high associated with high strength aluminum alloys. strength aluminum alloys. Alloys that have been Alloys that have been Alloys that have been Alloys that have been extruded or otherwise extruded or otherwise worked heavily, with a worked heavily, with a microstructure of elongated, microstructure of elongated, flattened grains, are flattened grains, are particularly prone to this particularly prone to this damage.damage.

�� In ferrous alloys, exfoliation is In ferrous alloys, exfoliation is characterized by excessive characterized by excessive internal growth of oxide, which internal growth of oxide, which has a volume some seven times has a volume some seven times that of the steel. Excessive that of the steel. Excessive internal growth of oxide can internal growth of oxide can elevate temperature and the elevate temperature and the exfoliated material damage exfoliated material damage turbines. Exfoliation occurs in turbines. Exfoliation occurs in ferritic materials when ferritic materials when multilayer growth occurs. multilayer growth occurs. multilayer growth occurs. multilayer growth occurs.

�� Stresses are induced by Stresses are induced by temperature cycles and by the temperature cycles and by the difference in thermal expansion difference in thermal expansion between the scale and tube. between the scale and tube. Exfoliation can also occur in Exfoliation can also occur in austenitic stainless steels, again austenitic stainless steels, again because of the difference in because of the difference in thermal expansion between the thermal expansion between the metal and the oxide. metal and the oxide.

Erosion CorrosionErosion Corrosion�� Erosion corrosion is an Erosion corrosion is an

acceleration in the rate of acceleration in the rate of corrosion attack in metal corrosion attack in metal due to the relative motion due to the relative motion of a corrosive fluid and a of a corrosive fluid and a metal surface.metal surface.

�� The increased turbulence The increased turbulence caused by pitting on the caused by pitting on the caused by pitting on the caused by pitting on the internal surfaces of a tube internal surfaces of a tube can result in rapidly can result in rapidly increasing erosion rates increasing erosion rates and eventually a leak. and eventually a leak.

�� Erosion corrosion can also Erosion corrosion can also be aggravated by faulty be aggravated by faulty workmanship.workmanship.

Cavitation ErosionCavitation Erosion

�� Cavitation occurs when a Cavitation occurs when a fluid's operational pressure fluid's operational pressure drops below it's vapor drops below it's vapor pressure causing gas pockets pressure causing gas pockets and bubbles to form and and bubbles to form and collapse.collapse.

This form of corrosion will This form of corrosion will �� This form of corrosion will This form of corrosion will eat out the volutes and eat out the volutes and impellers of centrifugal impellers of centrifugal pumps with ultra pure water pumps with ultra pure water as the fluid. as the fluid.

�� will eat valve seats.will eat valve seats.

�� It will contribute to other It will contribute to other forms of erosion corrosion, forms of erosion corrosion, such as found in elbows and such as found in elbows and tees.tees.

Fretting corrosionFretting corrosion

�� Fretting corrosion refers to Fretting corrosion refers to corrosion damage at the asperities corrosion damage at the asperities of contact surfaces.of contact surfaces.

�� This damage is induced under This damage is induced under load and in the presence of load and in the presence of repeated relative surface motion, repeated relative surface motion, as induced for example by as induced for example by as induced for example by as induced for example by vibration.vibration.

�� Pits or grooves and oxide debris Pits or grooves and oxide debris characterize this damage, characterize this damage, typically found in machinery, typically found in machinery, bolted assemblies and ball or bolted assemblies and ball or roller bearingsroller bearings..

Intergranular CorrosionIntergranular Corrosion

�� Intergranular corrosion Intergranular corrosion

is localized attack along is localized attack along

the grain boundaries, or the grain boundaries, or

immediately adjacent to immediately adjacent to

grain boundaries, while grain boundaries, while grain boundaries, while grain boundaries, while

the bulk of the grains the bulk of the grains

remain largely remain largely

unaffected.unaffected.

Dealloying (selective leaching)Dealloying (selective leaching)

Selected AttackSelected Attack�� occurs in alloys such as occurs in alloys such as

brass when one component brass when one component or phase is more susceptible or phase is more susceptible to attack than another and to attack than another and corrodes preferentially corrodes preferentially leaving a porous material leaving a porous material leaving a porous material leaving a porous material that crumbles. that crumbles.

�� Dealloying or selective Dealloying or selective leaching refers to the leaching refers to the selective removal of one selective removal of one element from an alloy by element from an alloy by corrosion processes. corrosion processes.

Environmental CrackingEnvironmental Cracking

�� Environmental cracking refers to a corrosion Environmental cracking refers to a corrosion

cracking caused by a combination of cracking caused by a combination of

conditions that can specifically result in one of conditions that can specifically result in one of

the following form of corrosion damage:the following form of corrosion damage:the following form of corrosion damage:the following form of corrosion damage:

•• Stress Corrosion CrackingStress Corrosion Cracking

•• Corrosion fatigueCorrosion fatigue

•• Hydrogen EmbrittlementHydrogen Embrittlement

Stress Corrosion CrackingStress Corrosion Cracking

�� ((SCC) is the cracking SCC) is the cracking

induced from the induced from the

combined influence of combined influence of

tensile stress and a tensile stress and a

corrosive environment.corrosive environment.corrosive environment.corrosive environment.

Corrosion Corrosion

FatigueFatigue

�� CorrosionCorrosion--fatigue is the fatigue is the result of the combined result of the combined action of an alternating or action of an alternating or cycling stresses and a cycling stresses and a corrosive environment.corrosive environment.

�� The fatigue process is The fatigue process is thought to cause rupture of thought to cause rupture of the protective passive the protective passive film, upon which film, upon which film, upon which film, upon which corrosion is accelerated.corrosion is accelerated.

�� If the metal is If the metal is simultaneously exposed to simultaneously exposed to a corrosive environment, a corrosive environment, the failure can take place the failure can take place at even lower loads and at even lower loads and after shorter time.after shorter time.

Hydrogen EmbrittlementHydrogen Embrittlement

�� It involves the ingress It involves the ingress of hydrogen into a of hydrogen into a component, an event component, an event that can seriously that can seriously reduce the ductility and reduce the ductility and reduce the ductility and reduce the ductility and loadload--bearing capacity, bearing capacity, cause cracking and cause cracking and catastrophic brittle catastrophic brittle failures at stresses failures at stresses below the yield stress of below the yield stress of susceptible materials.susceptible materials.

Atmospheric CorrosionAtmospheric Corrosion

�� Metals can corrode when exposed to the Metals can corrode when exposed to the

outdoor atmosphere as a consequence of wet outdoor atmosphere as a consequence of wet

and dry cycles induced by rainfall and and dry cycles induced by rainfall and

condensation. condensation. condensation. condensation.

�� Corrosion is more significant when pollutants Corrosion is more significant when pollutants

such as sulphur dioxide or chloride are present such as sulphur dioxide or chloride are present

in the atmosphere. in the atmosphere.

Factors conducive to atmospheric Factors conducive to atmospheric

corrosioncorrosion�� Sensible moistureSensible moisture

�� High RH (above 70High RH (above 70--80%)80%)

�� Salt mistSalt mist

�� Surface contaminants (dust, sweat residues, Surface contaminants (dust, sweat residues, �� Surface contaminants (dust, sweat residues, Surface contaminants (dust, sweat residues, soldering fluxes, etc)soldering fluxes, etc)

�� Atmospheric contaminants (SO2, HCl, organic Atmospheric contaminants (SO2, HCl, organic acids)acids)

�� High temperatureHigh temperature

High Temperature CorrosionHigh Temperature Corrosion

�� is a form of corrosion that is a form of corrosion that

does not require the does not require the

presence of a liquid presence of a liquid

electrolyte. electrolyte.

�� this type of damage is called this type of damage is called �� this type of damage is called this type of damage is called

"dry corrosion" or "scaling"."dry corrosion" or "scaling".

�� oxidation of metal/Alloy oxidation of metal/Alloy

resulted from exposing to resulted from exposing to

high temperature.high temperature.

Corrosive High Temperature Corrosive High Temperature

EnvironmentsEnvironments

�� Corrosive gases Corrosive gases

�� AshAsh

�� Molten saltsMolten salts

�� Molten metalsMolten metals

Consequences of CorrosionConsequences of Corrosion

Reduction of metal thickness leading to loss of mechanical Reduction of metal thickness leading to loss of mechanical strength and structural failure or breakdown. When the strength and structural failure or breakdown. When the metal is lost in localized zones so as to give a crack like metal is lost in localized zones so as to give a crack like structure, very considerable weakening may result from structure, very considerable weakening may result from quite a small amount of metal loss.quite a small amount of metal loss.

Hazards or injuries to people arising from structural failure Hazards or injuries to people arising from structural failure �� Hazards or injuries to people arising from structural failure Hazards or injuries to people arising from structural failure or breakdown (e.g. bridges, cars, aircraft)or breakdown (e.g. bridges, cars, aircraft)

�� Loss of time in availability of profileLoss of time in availability of profile--making industrial making industrial equipment.equipment.

�� Reduced value of goods due to deterioration of appearance.Reduced value of goods due to deterioration of appearance.

�� Contamination of fluids in vessels and pipes (e.g. Contamination of fluids in vessels and pipes (e.g.

beer goes cloudy when small quantities of heavy beer goes cloudy when small quantities of heavy

metals are released by corrosion)metals are released by corrosion)

�� Perforation of vessels and pipes allowing escape Perforation of vessels and pipes allowing escape

of their contents and possible harm to the of their contents and possible harm to the

surroundings. For example a leaky domestic surroundings. For example a leaky domestic

radiator can cause expensive damage to carpets radiator can cause expensive damage to carpets radiator can cause expensive damage to carpets radiator can cause expensive damage to carpets

and decorations, while corrosive seawater may and decorations, while corrosive seawater may

enter the boilers of a power station if the enter the boilers of a power station if the

condenser tubes perforate.condenser tubes perforate.

Other Factors that accelerate Other Factors that accelerate

corrosionscorrosions

�� Acid RainAcid Rain

�� Coastal FactorCoastal Factor

�� DeDe--icing Agents icing Agents –– i.e Road salt, MgCli.e Road salt, MgCl

�� Green House EffectGreen House Effect

Acid Rain Impact on Paint SurfaceAcid Rain Impact on Paint Surface

CorrosionCorrosion rates for ingot iron (Coast distance and Salt rates for ingot iron (Coast distance and Salt

content)content)

Approx distanceApprox distance

from surffrom surf

(M)(M)

Salt content of airSalt content of air

(mg �aCl/dm2)(mg �aCl/dm2)

Rate of rustingRate of rusting

(mm/year)(mm/year)

5050 11.111.1 0.950.955050 11.111.1 0.950.95

200200 3.13.1 0.380.38

400400 0.80.8 0.0550.055

13001300 0.20.2 0.040.04

25 miles25 miles 0.0480.048

Green House EffectGreen House Effect

��75 Deg F + 75% Humidity =75 Deg F + 75% Humidity =

��Corrosion Acceleration.Corrosion Acceleration.

KAP KAP Corrosion Control & ServicingCorrosion Control & Servicing

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