CORROSION resistance in construction ppt
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Sep 01, 2025
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About This Presentation
CORROSION resistance in construction ppt
Slide Content
CORROSIONCORROSION
Dr.G.S.ThirugnanamDr.G.S.Thirugnanam
Dr.G.S.ThirugnanamDr.G.S.Thirugnanam
PRINCIPLES OF CORROSIONNPRINCIPLES OF CORROSIONN
Concrete is a high alkalinity material. The pH Concrete is a high alkalinity material. The pH
of new concrete is 12 to 13.In this range of of new concrete is 12 to 13.In this range of
alkalinity, embedded steel is protected from alkalinity, embedded steel is protected from
corrosion by a passivating film bonded to the corrosion by a passivating film bonded to the
reinforcement surface.reinforcement surface.
However when the passivating film is However when the passivating film is
disrupted, corrosion may take place.disrupted, corrosion may take place.
Reinforcement corrosion can get initiated Reinforcement corrosion can get initiated
through one or more effects from the through one or more effects from the
environment.environment.
Concrete is a high alkalinity material. The pH Concrete is a high alkalinity material. The pH
of new concrete is 12 to 13.In this range of of new concrete is 12 to 13.In this range of
alkalinity, embedded steel is protected from alkalinity, embedded steel is protected from
corrosion by a passivating film bonded to the corrosion by a passivating film bonded to the
reinforcement surface.reinforcement surface.
However when the passivating film is However when the passivating film is
disrupted, corrosion may take place.disrupted, corrosion may take place.
Reinforcement corrosion can get initiated Reinforcement corrosion can get initiated
through one or more effects from the through one or more effects from the
environment.environment.
Corrosion mechanismCorrosion mechanism
The nature of reinforcement corrosion The nature of reinforcement corrosion
mechanism can be attributed to 3 mechanism can be attributed to 3
predominant process, namely chemical, predominant process, namely chemical,
electro-chemical and physical.electro-chemical and physical.
The alkalinity of concrete can get reduced to a The alkalinity of concrete can get reduced to a
pH level less than 10 by the ingress of COpH level less than 10 by the ingress of CO
2 2 or or
the passivity of steel can be destroyed by the the passivity of steel can be destroyed by the
ingress of chloride thereby initiating ingress of chloride thereby initiating
corrosion in both cases.corrosion in both cases.
The nature of reinforcement corrosion The nature of reinforcement corrosion
mechanism can be attributed to 3 mechanism can be attributed to 3
predominant process, namely chemical, predominant process, namely chemical,
electro-chemical and physical.electro-chemical and physical.
The alkalinity of concrete can get reduced to a The alkalinity of concrete can get reduced to a
pH level less than 10 by the ingress of COpH level less than 10 by the ingress of CO
2 2 or or
the passivity of steel can be destroyed by the the passivity of steel can be destroyed by the
ingress of chloride thereby initiating ingress of chloride thereby initiating
corrosion in both cases.corrosion in both cases.
The galvanic cells get established by forming locally The galvanic cells get established by forming locally
cathodic and anodic sites resulting in a flow of current cathodic and anodic sites resulting in a flow of current
with moist concrete serving as the electrolyte. Rate of with moist concrete serving as the electrolyte. Rate of
corrosion is influenced by the oxygen supply.corrosion is influenced by the oxygen supply.
The corrosion product experiences a volume growth as The corrosion product experiences a volume growth as
high as 6 times the original corroding metal. This high as 6 times the original corroding metal. This
volume growth exerts physical expansive forces to the volume growth exerts physical expansive forces to the
concrete surrounding the steel. These forces exceed the concrete surrounding the steel. These forces exceed the
tensile strength of concrete, cracking of concrete occurs tensile strength of concrete, cracking of concrete occurs
and as further corrosion takes place, spalling of and as further corrosion takes place, spalling of
concrete occurs resulting in exposure of reinforcement. concrete occurs resulting in exposure of reinforcement.
The galvanic cells get established by forming locally The galvanic cells get established by forming locally
cathodic and anodic sites resulting in a flow of current cathodic and anodic sites resulting in a flow of current
with moist concrete serving as the electrolyte. Rate of with moist concrete serving as the electrolyte. Rate of
corrosion is influenced by the oxygen supply.corrosion is influenced by the oxygen supply.
The corrosion product experiences a volume growth as The corrosion product experiences a volume growth as
high as 6 times the original corroding metal. This high as 6 times the original corroding metal. This
volume growth exerts physical expansive forces to the volume growth exerts physical expansive forces to the
concrete surrounding the steel. These forces exceed the concrete surrounding the steel. These forces exceed the
tensile strength of concrete, cracking of concrete occurs tensile strength of concrete, cracking of concrete occurs
and as further corrosion takes place, spalling of and as further corrosion takes place, spalling of
concrete occurs resulting in exposure of reinforcement. concrete occurs resulting in exposure of reinforcement.
Factors influencing corrosionFactors influencing corrosion
Cover thicknessCover thickness
Quality of concrete in the cover regionQuality of concrete in the cover region
Environmental conditionsEnvironmental conditions
pH value of concrete pH value of concrete
Chloride level in concreteChloride level in concrete
Presence of cracksPresence of cracks
Cover thicknessCover thickness
Quality of concrete in the cover regionQuality of concrete in the cover region
Environmental conditionsEnvironmental conditions
pH value of concrete pH value of concrete
Chloride level in concreteChloride level in concrete
Presence of cracksPresence of cracks
Corrosion mechanism of Corrosion mechanism of
embedded steelembedded steel
Under most circumstances, cement concrete Under most circumstances, cement concrete
provides good protection to the embedded provides good protection to the embedded
reinforcing steel.reinforcing steel.
This protection is generally attributed to the This protection is generally attributed to the
high alkalinity of the concrete adjacent to the high alkalinity of the concrete adjacent to the
steel and relatively high electrical resistance of steel and relatively high electrical resistance of
the concrete.the concrete.
Still, corrosion of the reinforcing steel is among Still, corrosion of the reinforcing steel is among
the most frequent damages to concrete. the most frequent damages to concrete.
embedded steelembedded steel
Under most circumstances, cement concrete Under most circumstances, cement concrete
provides good protection to the embedded provides good protection to the embedded
reinforcing steel.reinforcing steel.
This protection is generally attributed to the This protection is generally attributed to the
high alkalinity of the concrete adjacent to the high alkalinity of the concrete adjacent to the
steel and relatively high electrical resistance of steel and relatively high electrical resistance of
the concrete.the concrete.
Still, corrosion of the reinforcing steel is among Still, corrosion of the reinforcing steel is among
the most frequent damages to concrete. the most frequent damages to concrete.
The high alkalinity of the concrete pore The high alkalinity of the concrete pore
solution can be reduced over a long solution can be reduced over a long
period of time by carbonation.period of time by carbonation.
The electrical resistivity can be decreased The electrical resistivity can be decreased
by the presence of chemicals in the by the presence of chemicals in the
concrete. concrete.
The chemical most applied to concrete is The chemical most applied to concrete is
chloride salt in the form of deicers.chloride salt in the form of deicers.
The high alkalinity of the concrete pore The high alkalinity of the concrete pore
solution can be reduced over a long solution can be reduced over a long
period of time by carbonation.period of time by carbonation.
The electrical resistivity can be decreased The electrical resistivity can be decreased
by the presence of chemicals in the by the presence of chemicals in the
concrete. concrete.
The chemical most applied to concrete is The chemical most applied to concrete is
chloride salt in the form of deicers.chloride salt in the form of deicers.
As the chloride ions penetrate the concrete, the As the chloride ions penetrate the concrete, the
capability of the concrete to carry an electrical capability of the concrete to carry an electrical
current is increased significantly.current is increased significantly.
If there are differences within the concrete such as If there are differences within the concrete such as
moisture content, chloride content, oxygen content moisture content, chloride content, oxygen content
electrical potential differences will occur and a electrical potential differences will occur and a
corrosion cell may be established.corrosion cell may be established.
The anodes will experience corrosion while the The anodes will experience corrosion while the
cathodes will be undamaged.cathodes will be undamaged.
On an individual reinforcing bar there may be many On an individual reinforcing bar there may be many
anodes and cathodes , some adjacent and some anodes and cathodes , some adjacent and some
widely spaced. widely spaced.
As the chloride ions penetrate the concrete, the As the chloride ions penetrate the concrete, the
capability of the concrete to carry an electrical capability of the concrete to carry an electrical
current is increased significantly.current is increased significantly.
If there are differences within the concrete such as If there are differences within the concrete such as
moisture content, chloride content, oxygen content moisture content, chloride content, oxygen content
electrical potential differences will occur and a electrical potential differences will occur and a
corrosion cell may be established.corrosion cell may be established.
The anodes will experience corrosion while the The anodes will experience corrosion while the
cathodes will be undamaged.cathodes will be undamaged.
On an individual reinforcing bar there may be many On an individual reinforcing bar there may be many
anodes and cathodes , some adjacent and some anodes and cathodes , some adjacent and some
widely spaced. widely spaced.
As the corrosion progresses, two things occur: As the corrosion progresses, two things occur:
First, the cross sectional area of the First, the cross sectional area of the
reinforcement is reduced, which in turn reinforcement is reduced, which in turn
reduces the load carrying capacity of the steelreduces the load carrying capacity of the steel
Second, the products of the corrosion, iron Second, the products of the corrosion, iron
oxide (rust), expand since they occupy about 8 oxide (rust), expand since they occupy about 8
times the volume of the original material.times the volume of the original material.
This increase in volume leads to cracking and This increase in volume leads to cracking and
ultimately spalling of the concrete. ultimately spalling of the concrete.
As the corrosion progresses, two things occur: As the corrosion progresses, two things occur:
First, the cross sectional area of the First, the cross sectional area of the
reinforcement is reduced, which in turn reinforcement is reduced, which in turn
reduces the load carrying capacity of the steelreduces the load carrying capacity of the steel
Second, the products of the corrosion, iron Second, the products of the corrosion, iron
oxide (rust), expand since they occupy about 8 oxide (rust), expand since they occupy about 8
times the volume of the original material.times the volume of the original material.
This increase in volume leads to cracking and This increase in volume leads to cracking and
ultimately spalling of the concrete. ultimately spalling of the concrete.
For mild steel reinforcing ,the damage For mild steel reinforcing ,the damage
to the concrete will become evident to the concrete will become evident
long before the capacity of the steel is long before the capacity of the steel is
reduced enough to affect its load reduced enough to affect its load
carrying capacity.carrying capacity.
For prestressing steel, slight reduction For prestressing steel, slight reduction
in section can lead to catastrophic in section can lead to catastrophic
failurefailure
For mild steel reinforcing ,the damage For mild steel reinforcing ,the damage
to the concrete will become evident to the concrete will become evident
long before the capacity of the steel is long before the capacity of the steel is
reduced enough to affect its load reduced enough to affect its load
carrying capacity.carrying capacity.
For prestressing steel, slight reduction For prestressing steel, slight reduction
in section can lead to catastrophic in section can lead to catastrophic
failurefailure
In addition to the development of an In addition to the development of an
electrolytic cell, corrosion may be developed electrolytic cell, corrosion may be developed
under several other situations.under several other situations.
The first of these is corrosion produced by the The first of these is corrosion produced by the
presence of a stray electrical current. In this presence of a stray electrical current. In this
case, the current necessary for the corrosion case, the current necessary for the corrosion
reaction is provided from an outside source.reaction is provided from an outside source.
A second additional source of corrosion is A second additional source of corrosion is
that produced by chemicals that may be able that produced by chemicals that may be able
to act directly on the reinforcing steel. to act directly on the reinforcing steel.
In addition to the development of an In addition to the development of an
electrolytic cell, corrosion may be developed electrolytic cell, corrosion may be developed
under several other situations.under several other situations.
The first of these is corrosion produced by the The first of these is corrosion produced by the
presence of a stray electrical current. In this presence of a stray electrical current. In this
case, the current necessary for the corrosion case, the current necessary for the corrosion
reaction is provided from an outside source.reaction is provided from an outside source.
A second additional source of corrosion is A second additional source of corrosion is
that produced by chemicals that may be able that produced by chemicals that may be able
to act directly on the reinforcing steel. to act directly on the reinforcing steel.
Visual examination will typically reveal rust Visual examination will typically reveal rust
staining of the concrete. This staining will be staining of the concrete. This staining will be
followed by cracking. followed by cracking.
Cracking produced by corrosion generally run Cracking produced by corrosion generally run
in straight, parallel lines at uniform intervals in straight, parallel lines at uniform intervals
corresponding to the spacing of the corresponding to the spacing of the
reinforcement.reinforcement.
As deterioration continues, spalling of the As deterioration continues, spalling of the
concrete over the reinforcing steel will occur concrete over the reinforcing steel will occur
with the reinforcing bars becoming visible. with the reinforcing bars becoming visible.
Visual examination will typically reveal rust Visual examination will typically reveal rust
staining of the concrete. This staining will be staining of the concrete. This staining will be
followed by cracking. followed by cracking.
Cracking produced by corrosion generally run Cracking produced by corrosion generally run
in straight, parallel lines at uniform intervals in straight, parallel lines at uniform intervals
corresponding to the spacing of the corresponding to the spacing of the
reinforcement.reinforcement.
As deterioration continues, spalling of the As deterioration continues, spalling of the
concrete over the reinforcing steel will occur concrete over the reinforcing steel will occur
with the reinforcing bars becoming visible. with the reinforcing bars becoming visible.
Prevention of metal corrosionPrevention of metal corrosion
Use of concrete with low permeabilityUse of concrete with low permeability
Use of properly proportioned concrete having Use of properly proportioned concrete having
low W/C ratiolow W/C ratio
Use of good workmanship in placing the Use of good workmanship in placing the
concreteconcrete
Curing the concrete properlyCuring the concrete properly
Providing adequate cover to the steel Providing adequate cover to the steel
reinforcementreinforcement
Limiting chlorides in the concrete mixLimiting chlorides in the concrete mix
Providing good drainage to prevent water from Providing good drainage to prevent water from
standing on the concretestanding on the concrete
Use of concrete with low permeabilityUse of concrete with low permeability
Use of properly proportioned concrete having Use of properly proportioned concrete having
low W/C ratiolow W/C ratio
Use of good workmanship in placing the Use of good workmanship in placing the
concreteconcrete
Curing the concrete properlyCuring the concrete properly
Providing adequate cover to the steel Providing adequate cover to the steel
reinforcementreinforcement
Limiting chlorides in the concrete mixLimiting chlorides in the concrete mix
Providing good drainage to prevent water from Providing good drainage to prevent water from
standing on the concretestanding on the concrete
Reinforcing steel rebar corrosion is one of the Reinforcing steel rebar corrosion is one of the
most common causes of reinforced concrete most common causes of reinforced concrete
structures deterioration structures deterioration
Chloride existing in the marine environment is Chloride existing in the marine environment is
the main source of aggressivity for reinforced the main source of aggressivity for reinforced
concrete and main cause for its deterioration concrete and main cause for its deterioration
The resistivity of concrete is related to micro The resistivity of concrete is related to micro
structure of concrete, porosity and structure of concrete, porosity and
impermeability of concreteimpermeability of concrete
CORROSION PROCESSCORROSION PROCESS
Corrosion occurs by electro – chemical process.Corrosion occurs by electro – chemical process.
When steel is embedded in concrete some When steel is embedded in concrete some
difference in electrical potential is created in the rod.difference in electrical potential is created in the rod.
Due to this difference in electrical potential an electro Due to this difference in electrical potential an electro
– chemical cell is set up.– chemical cell is set up.
The volume of steel increases about six times the The volume of steel increases about six times the
original volume of steel.original volume of steel.
Corrosion occurs by electro – chemical process.Corrosion occurs by electro – chemical process.
When steel is embedded in concrete some When steel is embedded in concrete some
difference in electrical potential is created in the rod.difference in electrical potential is created in the rod.
Due to this difference in electrical potential an electro Due to this difference in electrical potential an electro
– chemical cell is set up.– chemical cell is set up.
The volume of steel increases about six times the The volume of steel increases about six times the
original volume of steel.original volume of steel.
Corrosion damage to the reinforcing steel results
in the build-up of voluminous corrosion products,
generating internal stresses and subsequent
cracking and spalling of the concrete as shown
schematically in the diagram
in the build-up of voluminous corrosion products,
generating internal stresses and subsequent
cracking and spalling of the concrete as shown
schematically in the diagram
Effect of Corrosion of rebar on Effect of Corrosion of rebar on
RC structuresRC structures
Reduction in diameter of the Reduction in diameter of the
rebarrebar
Loss in strengthLoss in strength
Spalling of cover concrete Spalling of cover concrete
Reduction in structural strength Reduction in structural strength
and stiffnessand stiffness
Repair- possible if the extent of Repair- possible if the extent of
corrosion is within the tolerable corrosion is within the tolerable
limit.limit.
RC structuresRC structures
Reduction in diameter of the Reduction in diameter of the
rebarrebar
Loss in strengthLoss in strength
Spalling of cover concrete Spalling of cover concrete
Reduction in structural strength Reduction in structural strength
and stiffnessand stiffness
Repair- possible if the extent of Repair- possible if the extent of
corrosion is within the tolerable corrosion is within the tolerable
limit.limit.
STAGES OF CORROSIONSTAGES OF CORROSION
LIME LEACHING LIME LEACHING
RUST STAININGRUST STAINING
BULGING OF COVER (BULGING OF COVER ( COLLECTION OF RUST PRODUCTS)COLLECTION OF RUST PRODUCTS)
MICRO CRACKSMICRO CRACKS
MACRO CRACKSMACRO CRACKS
SPALLING OF COVER CONCRETESPALLING OF COVER CONCRETE
LIME LEACHING LIME LEACHING
RUST STAININGRUST STAINING
BULGING OF COVER (BULGING OF COVER ( COLLECTION OF RUST PRODUCTS)COLLECTION OF RUST PRODUCTS)
MICRO CRACKSMICRO CRACKS
MACRO CRACKSMACRO CRACKS
SPALLING OF COVER CONCRETESPALLING OF COVER CONCRETE
CO2
O 2
Cl2
SO4
H2O
COVER CONC
REINFORCEMENT
T1 T2
INITIATION
PERIOD
PROPOGATION
PERIOD
CRITICAL LEVEL
ENVIRONMENT
DEGREE OF CORROSION
O 2
Cl2
SO4
H2O
COVER CONC
REINFORCEMENT
T1 T2
INITIATION
PERIOD
PROPOGATION
PERIOD
CRITICAL LEVEL
ENVIRONMENT
DEGREE OF CORROSION
CORROSION PREVENTIONCORROSION PREVENTION
STEEL SHOULD BE PROTECTED FROM STEEL SHOULD BE PROTECTED FROM
VAROIUS ENVIRONMENTVAROIUS ENVIRONMENT
SEA ENVIRONMENTSEA ENVIRONMENT
INDUSTRIAL ENVIRONMENTINDUSTRIAL ENVIRONMENT
MILD, MODERATE,SEVERE,MILD, MODERATE,SEVERE,
VERY SEVERE AND EXTREMELY SEVERE VERY SEVERE AND EXTREMELY SEVERE
(IS 456-2000)(IS 456-2000)
STEEL SHOULD BE PROTECTED FROM STEEL SHOULD BE PROTECTED FROM
VAROIUS ENVIRONMENTVAROIUS ENVIRONMENT
SEA ENVIRONMENTSEA ENVIRONMENT
INDUSTRIAL ENVIRONMENTINDUSTRIAL ENVIRONMENT
MILD, MODERATE,SEVERE,MILD, MODERATE,SEVERE,
VERY SEVERE AND EXTREMELY SEVERE VERY SEVERE AND EXTREMELY SEVERE
(IS 456-2000)(IS 456-2000)
Factors affecting corrosion and Factors affecting corrosion and
resistanceresistance
resistanceresistance
PREVENTIVE METHODSPREVENTIVE METHODS
To Prevent Corrosion Following methods areTo Prevent Corrosion Following methods are
adoptedadopted
Metallurgical method –adding chromium and copperMetallurgical method –adding chromium and copper
Corrosion inhibitors –calcium nitrate extends the time Corrosion inhibitors –calcium nitrate extends the time
to corrosion initiationto corrosion initiation
Coatings to reinforcement –to provide a durable Coatings to reinforcement –to provide a durable
barrier to aggressive materialsbarrier to aggressive materials
Cathodic protectionCathodic protection
Design & DetailingDesign & Detailing
Coatings to concreteCoatings to concrete
To Prevent Corrosion Following methods areTo Prevent Corrosion Following methods are
adoptedadopted
Metallurgical method –adding chromium and copperMetallurgical method –adding chromium and copper
Corrosion inhibitors –calcium nitrate extends the time Corrosion inhibitors –calcium nitrate extends the time
to corrosion initiationto corrosion initiation
Coatings to reinforcement –to provide a durable Coatings to reinforcement –to provide a durable
barrier to aggressive materialsbarrier to aggressive materials
Cathodic protectionCathodic protection
Design & DetailingDesign & Detailing
Coatings to concreteCoatings to concrete
CATHODIC PROTECTIONCATHODIC PROTECTION
The principle involved in the cathodic protection is to force the The principle involved in the cathodic protection is to force the
metal to behave like a cathode.metal to behave like a cathode.
The corrosion of reinforcement in concrete is an The corrosion of reinforcement in concrete is an
electrochemical process.electrochemical process.
Cathodic protection is a technique by which the electrical Cathodic protection is a technique by which the electrical
potential of the steel is increased to a level at which corrosion potential of the steel is increased to a level at which corrosion
cannot take place.cannot take place.
It is widely used for both steel and concrete off shore It is widely used for both steel and concrete off shore
structures, while on the land it has been used for protection of structures, while on the land it has been used for protection of
pipe lines and similar structurespipe lines and similar structures
Two different methods are employed, an impressed current Two different methods are employed, an impressed current
and the use of sacrificial anodes.and the use of sacrificial anodes.
In the first the structure is connected to the negativeIn the first the structure is connected to the negative
The principle involved in the cathodic protection is to force the The principle involved in the cathodic protection is to force the
metal to behave like a cathode.metal to behave like a cathode.
The corrosion of reinforcement in concrete is an The corrosion of reinforcement in concrete is an
electrochemical process.electrochemical process.
Cathodic protection is a technique by which the electrical Cathodic protection is a technique by which the electrical
potential of the steel is increased to a level at which corrosion potential of the steel is increased to a level at which corrosion
cannot take place.cannot take place.
It is widely used for both steel and concrete off shore It is widely used for both steel and concrete off shore
structures, while on the land it has been used for protection of structures, while on the land it has been used for protection of
pipe lines and similar structurespipe lines and similar structures
Two different methods are employed, an impressed current Two different methods are employed, an impressed current
and the use of sacrificial anodes.and the use of sacrificial anodes.
In the first the structure is connected to the negativeIn the first the structure is connected to the negative
Contd..,Contd..,
terminal of a DC power source ,ideally using an terminal of a DC power source ,ideally using an
anode, which does not corrodeanode, which does not corrode
In the second reinforcement is connected to anodes In the second reinforcement is connected to anodes
with more negative corrosion potential than steel, with more negative corrosion potential than steel,
such as zinc or aluminium.such as zinc or aluminium.
The current is reversed and corrosion now takes The current is reversed and corrosion now takes
place at the anode which is gradually used upplace at the anode which is gradually used up
In both cases electrical continuity of the In both cases electrical continuity of the
reinforcement is requiredreinforcement is required
In addition the principles of cathodic protection have been In addition the principles of cathodic protection have been
used to remove chlorides from contaminated concreteused to remove chlorides from contaminated concrete
terminal of a DC power source ,ideally using an terminal of a DC power source ,ideally using an
anode, which does not corrodeanode, which does not corrode
In the second reinforcement is connected to anodes In the second reinforcement is connected to anodes
with more negative corrosion potential than steel, with more negative corrosion potential than steel,
such as zinc or aluminium.such as zinc or aluminium.
The current is reversed and corrosion now takes The current is reversed and corrosion now takes
place at the anode which is gradually used upplace at the anode which is gradually used up
In both cases electrical continuity of the In both cases electrical continuity of the
reinforcement is requiredreinforcement is required
In addition the principles of cathodic protection have been In addition the principles of cathodic protection have been
used to remove chlorides from contaminated concreteused to remove chlorides from contaminated concrete
APPLICATIONS OF CATHODIC APPLICATIONS OF CATHODIC
PROTECTIONPROTECTION
Cathodic protection is used to protect :Cathodic protection is used to protect :
PipelinesPipelines
Storage tank basesStorage tank bases
Harbour structuresHarbour structures
Steel sheet, tubular and foundation pilingsSteel sheet, tubular and foundation pilings
Offshore platforms, floating and sub sea structuresOffshore platforms, floating and sub sea structures
Ship’s tanks Ship’s tanks
Water-circulating systems.Water-circulating systems.
PROTECTIONPROTECTION
Cathodic protection is used to protect :Cathodic protection is used to protect :
PipelinesPipelines
Storage tank basesStorage tank bases
Harbour structuresHarbour structures
Steel sheet, tubular and foundation pilingsSteel sheet, tubular and foundation pilings
Offshore platforms, floating and sub sea structuresOffshore platforms, floating and sub sea structures
Ship’s tanks Ship’s tanks
Water-circulating systems.Water-circulating systems.
POLARIZATION TEST SET-UP
All the specimens cast were set to polarization
Current is being monitored with time up to the end of
propagation period
All the specimens cast were set to polarization
Current is being monitored with time up to the end of
propagation period
Specimens are ready for polarization test
Polarization Test Setup
Specimens shows after crack initiation and
propagation under polarization test
propagation under polarization test
EXPERIMENTAL SET UPEXPERIMENTAL SET UP
Regulated DC supply
Fibre reinforced tub
RCC Beam
Salt solution
Stainless steel plate
Steel bar
Regulated DC supply
Fibre reinforced tub
RCC Beam
Salt solution
Stainless steel plate
Steel bar
Half cell potential (HCP)Half cell potential (HCP)
Schematic
showing the half cell potential
measurement
technique
Schematic
showing the half cell potential
measurement
technique
Half cell reading being taken Half cell reading being taken
on corroded specimenon corroded specimen
on corroded specimenon corroded specimen
TRANSMISSION LINE TOWERS TRANSMISSION LINE TOWERS
The power transmission system consists of equipment, The power transmission system consists of equipment,
which has been built up since the turn of the century.which has been built up since the turn of the century.
Although, the design of individual components has Although, the design of individual components has
changed, the materials of construction remained changed, the materials of construction remained
virtually the same: steel and cast iron (bare, painted or virtually the same: steel and cast iron (bare, painted or
galvanised), aluminium alloys and copper alloys, galvanised), aluminium alloys and copper alloys,
porcelain, glass and wood. porcelain, glass and wood.
To enhance the corrosion resistance of these materials To enhance the corrosion resistance of these materials
various treatments, coatings and inhibitors are various treatments, coatings and inhibitors are
applied. applied.
The power transmission system consists of equipment, The power transmission system consists of equipment,
which has been built up since the turn of the century.which has been built up since the turn of the century.
Although, the design of individual components has Although, the design of individual components has
changed, the materials of construction remained changed, the materials of construction remained
virtually the same: steel and cast iron (bare, painted or virtually the same: steel and cast iron (bare, painted or
galvanised), aluminium alloys and copper alloys, galvanised), aluminium alloys and copper alloys,
porcelain, glass and wood. porcelain, glass and wood.
To enhance the corrosion resistance of these materials To enhance the corrosion resistance of these materials
various treatments, coatings and inhibitors are various treatments, coatings and inhibitors are
applied. applied.
The continued integrity and soundness of the power The continued integrity and soundness of the power
system components depend mainly on the control of system components depend mainly on the control of
corrosioncorrosion
The severity of this metal wastage and ageing process The severity of this metal wastage and ageing process
is governed by the aggressivity of the environment.is governed by the aggressivity of the environment.
The continued integrity and soundness of the power The continued integrity and soundness of the power
system components depend mainly on the control of system components depend mainly on the control of
corrosion. corrosion.
The severity of this metal wastage and ageing process The severity of this metal wastage and ageing process
is governed by the aggressivity of the environment. is governed by the aggressivity of the environment.
The continued integrity and soundness of the power The continued integrity and soundness of the power
system components depend mainly on the control of system components depend mainly on the control of
corrosioncorrosion
The severity of this metal wastage and ageing process The severity of this metal wastage and ageing process
is governed by the aggressivity of the environment.is governed by the aggressivity of the environment.
The continued integrity and soundness of the power The continued integrity and soundness of the power
system components depend mainly on the control of system components depend mainly on the control of
corrosion. corrosion.
The severity of this metal wastage and ageing process The severity of this metal wastage and ageing process
is governed by the aggressivity of the environment. is governed by the aggressivity of the environment.
Corrosion of buried power line components is Corrosion of buried power line components is
governed by diffusion of dissolved oxygen in governed by diffusion of dissolved oxygen in
the water entrapped in the soil resulting in the the water entrapped in the soil resulting in the
average corrosion rate of zinc and steel being average corrosion rate of zinc and steel being
about the same. Copper and lead, which form about the same. Copper and lead, which form
corrosion barrier films, show lower corrosion corrosion barrier films, show lower corrosion
rates. In marshy and swampy areas, anaerobic rates. In marshy and swampy areas, anaerobic
sulphate-reducing bacteria (SRB) enhance the sulphate-reducing bacteria (SRB) enhance the
corrosion rate of steel significantly. corrosion rate of steel significantly.
Corrosion of buried power line components is Corrosion of buried power line components is
governed by diffusion of dissolved oxygen in governed by diffusion of dissolved oxygen in
the water entrapped in the soil resulting in the the water entrapped in the soil resulting in the
average corrosion rate of zinc and steel being average corrosion rate of zinc and steel being
about the same. Copper and lead, which form about the same. Copper and lead, which form
corrosion barrier films, show lower corrosion corrosion barrier films, show lower corrosion
rates. In marshy and swampy areas, anaerobic rates. In marshy and swampy areas, anaerobic
sulphate-reducing bacteria (SRB) enhance the sulphate-reducing bacteria (SRB) enhance the
corrosion rate of steel significantly. corrosion rate of steel significantly.
Soils are classified into five classes, Soils are classified into five classes,
which have been found to correlate which have been found to correlate
with soil resistivity as measured by the with soil resistivity as measured by the
Wenner 4-pin method. These classes Wenner 4-pin method. These classes
range from very low corrosivity range from very low corrosivity
(Resistivity >10,000 Ωcm) to very high (Resistivity >10,000 Ωcm) to very high
corrosivity (Resistivity <1000 Ωcm). corrosivity (Resistivity <1000 Ωcm).
Soils are classified into five classes, Soils are classified into five classes,
which have been found to correlate which have been found to correlate
with soil resistivity as measured by the with soil resistivity as measured by the
Wenner 4-pin method. These classes Wenner 4-pin method. These classes
range from very low corrosivity range from very low corrosivity
(Resistivity >10,000 Ωcm) to very high (Resistivity >10,000 Ωcm) to very high
corrosivity (Resistivity <1000 Ωcm). corrosivity (Resistivity <1000 Ωcm).
There are ten broad classes of significant corrosion damage, which There are ten broad classes of significant corrosion damage, which
lead to loss of component function and/or integrity if not lead to loss of component function and/or integrity if not
remedied. These are: remedied. These are:
General Corrosion General Corrosion
Pitting Corrosion Pitting Corrosion
Crevice Corrosion Crevice Corrosion
Exfoliation Corrosion Exfoliation Corrosion
Stress Corrosion Stress Corrosion
Corrosion Fatigue Corrosion Fatigue
Hydrogen Embrittlement Hydrogen Embrittlement
Galvanic Corrosion (dissimilar metal, differential aeration) Galvanic Corrosion (dissimilar metal, differential aeration)
Stray-Current Corrosion Stray-Current Corrosion
Coating Damage and Deterioration Coating Damage and Deterioration
Microbial Induced Corrosion Microbial Induced Corrosion
Rotting of WoodRotting of Wood
There are ten broad classes of significant corrosion damage, which There are ten broad classes of significant corrosion damage, which
lead to loss of component function and/or integrity if not lead to loss of component function and/or integrity if not
remedied. These are: remedied. These are:
General Corrosion General Corrosion
Pitting Corrosion Pitting Corrosion
Crevice Corrosion Crevice Corrosion
Exfoliation Corrosion Exfoliation Corrosion
Stress Corrosion Stress Corrosion
Corrosion Fatigue Corrosion Fatigue
Hydrogen Embrittlement Hydrogen Embrittlement
Galvanic Corrosion (dissimilar metal, differential aeration) Galvanic Corrosion (dissimilar metal, differential aeration)
Stray-Current Corrosion Stray-Current Corrosion
Coating Damage and Deterioration Coating Damage and Deterioration
Microbial Induced Corrosion Microbial Induced Corrosion
Rotting of WoodRotting of Wood
The most common method of power line The most common method of power line
inspection is visual assessment, performed inspection is visual assessment, performed
from the ground by foot-patrol or from the from the ground by foot-patrol or from the
air during routine helicopter surveillance. air during routine helicopter surveillance.
This is a very efficient method, but must be This is a very efficient method, but must be
used in conjunction with instrumental, used in conjunction with instrumental,
chemical, biological, electrical and chemical, biological, electrical and
electrochemical methods followed by electrochemical methods followed by
laboratory failure analysis to obtain a true laboratory failure analysis to obtain a true
picture of future maintenance or picture of future maintenance or
refurbishment work required.refurbishment work required.
The most common method of power line The most common method of power line
inspection is visual assessment, performed inspection is visual assessment, performed
from the ground by foot-patrol or from the from the ground by foot-patrol or from the
air during routine helicopter surveillance. air during routine helicopter surveillance.
This is a very efficient method, but must be This is a very efficient method, but must be
used in conjunction with instrumental, used in conjunction with instrumental,
chemical, biological, electrical and chemical, biological, electrical and
electrochemical methods followed by electrochemical methods followed by
laboratory failure analysis to obtain a true laboratory failure analysis to obtain a true
picture of future maintenance or picture of future maintenance or
refurbishment work required.refurbishment work required.
Degradation of foundations enclosed in Degradation of foundations enclosed in
concrete or grillage-type can be best concrete or grillage-type can be best
assessed by excavation. This is the most assessed by excavation. This is the most
rigorous method since it allows rigorous method since it allows
determination of the extent and type of determination of the extent and type of
corrosion attack, including possible corrosion attack, including possible
involvement of microbial induced involvement of microbial induced
corrosion. To minimize excavation at every corrosion. To minimize excavation at every
footing, tests to indicate the presence of footing, tests to indicate the presence of
stray current and/or galvanic corrosion can stray current and/or galvanic corrosion can
be used. be used.
Degradation of foundations enclosed in Degradation of foundations enclosed in
concrete or grillage-type can be best concrete or grillage-type can be best
assessed by excavation. This is the most assessed by excavation. This is the most
rigorous method since it allows rigorous method since it allows
determination of the extent and type of determination of the extent and type of
corrosion attack, including possible corrosion attack, including possible
involvement of microbial induced involvement of microbial induced
corrosion. To minimize excavation at every corrosion. To minimize excavation at every
footing, tests to indicate the presence of footing, tests to indicate the presence of
stray current and/or galvanic corrosion can stray current and/or galvanic corrosion can
be used. be used.
Stray current and galvanic corrosion Stray current and galvanic corrosion
can be identified by potential surveys can be identified by potential surveys
of the footings with a Cu/CuSO4 half-of the footings with a Cu/CuSO4 half-
cell reference electrode.cell reference electrode.
Stray current and galvanic corrosion Stray current and galvanic corrosion
can be identified by potential surveys can be identified by potential surveys
of the footings with a Cu/CuSO4 half-of the footings with a Cu/CuSO4 half-
cell reference electrode.cell reference electrode.
New galvanized steel footings, when New galvanized steel footings, when
buried will exhibit a potential of -0.85 to buried will exhibit a potential of -0.85 to
-1.1 V. After the galvanizing is lost, the -1.1 V. After the galvanizing is lost, the
newly exposed bare steel surface will newly exposed bare steel surface will
have a potential between -0.5 V and -0.7 have a potential between -0.5 V and -0.7
V. Corroded steel with a heavy scale will V. Corroded steel with a heavy scale will
have a potential between -0.3V andhave a potential between -0.3V and
-0.5 V. -0.5 V.
New galvanized steel footings, when New galvanized steel footings, when
buried will exhibit a potential of -0.85 to buried will exhibit a potential of -0.85 to
-1.1 V. After the galvanizing is lost, the -1.1 V. After the galvanizing is lost, the
newly exposed bare steel surface will newly exposed bare steel surface will
have a potential between -0.5 V and -0.7 have a potential between -0.5 V and -0.7
V. Corroded steel with a heavy scale will V. Corroded steel with a heavy scale will
have a potential between -0.3V andhave a potential between -0.3V and
-0.5 V. -0.5 V.
In addition to the potential survey, an electrochemical In addition to the potential survey, an electrochemical
polarization technique was developed to determine polarization technique was developed to determine
the rate of galvanic corrosion.the rate of galvanic corrosion.
The device operates by passing a small current between The device operates by passing a small current between
the tower footing and a probe inserted into the ground the tower footing and a probe inserted into the ground
nearby.nearby.
These currents perturb the electrochemical processes at These currents perturb the electrochemical processes at
any active corrosion site and the resulting changes in any active corrosion site and the resulting changes in
potential are measured with reference to a Cu/CuSo4 half potential are measured with reference to a Cu/CuSo4 half
cell in contact with the ground close to the footing.cell in contact with the ground close to the footing.
The level of current required to displace the corrosion The level of current required to displace the corrosion
potential indicates the severity of the corrosion process in potential indicates the severity of the corrosion process in
progress. progress.
In addition to the potential survey, an electrochemical In addition to the potential survey, an electrochemical
polarization technique was developed to determine polarization technique was developed to determine
the rate of galvanic corrosion.the rate of galvanic corrosion.
The device operates by passing a small current between The device operates by passing a small current between
the tower footing and a probe inserted into the ground the tower footing and a probe inserted into the ground
nearby.nearby.
These currents perturb the electrochemical processes at These currents perturb the electrochemical processes at
any active corrosion site and the resulting changes in any active corrosion site and the resulting changes in
potential are measured with reference to a Cu/CuSo4 half potential are measured with reference to a Cu/CuSo4 half
cell in contact with the ground close to the footing.cell in contact with the ground close to the footing.
The level of current required to displace the corrosion The level of current required to displace the corrosion
potential indicates the severity of the corrosion process in potential indicates the severity of the corrosion process in
progress. progress.
This instrument provides results, which This instrument provides results, which
are a useful guide to the relative condition are a useful guide to the relative condition
of the footings, but not an absolute of the footings, but not an absolute
measure of the metal wastage. For measure of the metal wastage. For
concrete footings, the scale of potential concrete footings, the scale of potential
readings is greatly affected by the high readings is greatly affected by the high
resistance of the concrete. Great care is resistance of the concrete. Great care is
required to interpret the readingsrequired to interpret the readings
This instrument provides results, which This instrument provides results, which
are a useful guide to the relative condition are a useful guide to the relative condition
of the footings, but not an absolute of the footings, but not an absolute
measure of the metal wastage. For measure of the metal wastage. For
concrete footings, the scale of potential concrete footings, the scale of potential
readings is greatly affected by the high readings is greatly affected by the high
resistance of the concrete. Great care is resistance of the concrete. Great care is
required to interpret the readingsrequired to interpret the readings
Towers and Tower Steel Towers and Tower Steel
Determining correctly the type and extent of Determining correctly the type and extent of
power line tower component damage is power line tower component damage is
essential for making proper assessments of essential for making proper assessments of
the structure condition and for the structure condition and for
recommending the specific place of action to recommending the specific place of action to
ensure safe and reliable operation. ensure safe and reliable operation.
Component damage is defined as degradation Component damage is defined as degradation
leading to loss of load bearing capacity, which leading to loss of load bearing capacity, which
would, if not remedied, lead to tower failure. would, if not remedied, lead to tower failure.
Towers and Tower Steel Towers and Tower Steel
Determining correctly the type and extent of Determining correctly the type and extent of
power line tower component damage is power line tower component damage is
essential for making proper assessments of essential for making proper assessments of
the structure condition and for the structure condition and for
recommending the specific place of action to recommending the specific place of action to
ensure safe and reliable operation. ensure safe and reliable operation.
Component damage is defined as degradation Component damage is defined as degradation
leading to loss of load bearing capacity, which leading to loss of load bearing capacity, which
would, if not remedied, lead to tower failure. would, if not remedied, lead to tower failure.
During visual inspection, the type of corrosion damage During visual inspection, the type of corrosion damage
is established at locations where the protective coating is established at locations where the protective coating
was lost.was lost.
The extent of the corrosion damage must be The extent of the corrosion damage must be
accurately determined to: assess structure's fitness for accurately determined to: assess structure's fitness for
service, estimate the remaining service life and service, estimate the remaining service life and
recommend maintenance, refurbishment or recommend maintenance, refurbishment or
replacement of the line.replacement of the line.
The techniques and methods used to gauge the The techniques and methods used to gauge the
corrosion attack are standard and excellent corrosion attack are standard and excellent
instruments for field and/or laboratory use are readily instruments for field and/or laboratory use are readily
available. available.
During visual inspection, the type of corrosion damage During visual inspection, the type of corrosion damage
is established at locations where the protective coating is established at locations where the protective coating
was lost.was lost.
The extent of the corrosion damage must be The extent of the corrosion damage must be
accurately determined to: assess structure's fitness for accurately determined to: assess structure's fitness for
service, estimate the remaining service life and service, estimate the remaining service life and
recommend maintenance, refurbishment or recommend maintenance, refurbishment or
replacement of the line.replacement of the line.
The techniques and methods used to gauge the The techniques and methods used to gauge the
corrosion attack are standard and excellent corrosion attack are standard and excellent
instruments for field and/or laboratory use are readily instruments for field and/or laboratory use are readily
available. available.
Breakdown of the protective coating occurs usually by a Breakdown of the protective coating occurs usually by a
combination of erosion and physical damage.combination of erosion and physical damage.
The extent of erosion (loss of thickness) of an intact The extent of erosion (loss of thickness) of an intact
coating can be measured by a variety of methods.coating can be measured by a variety of methods.
These include destructive (scribing), magnetic pull-off, These include destructive (scribing), magnetic pull-off,
magnetic flux, eddy current, ultrasonic, etc. magnetic flux, eddy current, ultrasonic, etc.
Breakdown of the protective coating occurs usually by a Breakdown of the protective coating occurs usually by a
combination of erosion and physical damage.combination of erosion and physical damage.
The extent of erosion (loss of thickness) of an intact The extent of erosion (loss of thickness) of an intact
coating can be measured by a variety of methods.coating can be measured by a variety of methods.
These include destructive (scribing), magnetic pull-off, These include destructive (scribing), magnetic pull-off,
magnetic flux, eddy current, ultrasonic, etc. gages. magnetic flux, eddy current, ultrasonic, etc. gages.
Breakdown of the protective coating occurs usually by a Breakdown of the protective coating occurs usually by a
combination of erosion and physical damage.combination of erosion and physical damage.
The extent of erosion (loss of thickness) of an intact The extent of erosion (loss of thickness) of an intact
coating can be measured by a variety of methods.coating can be measured by a variety of methods.
These include destructive (scribing), magnetic pull-off, These include destructive (scribing), magnetic pull-off,
magnetic flux, eddy current, ultrasonic, etc. magnetic flux, eddy current, ultrasonic, etc.
Breakdown of the protective coating occurs usually by a Breakdown of the protective coating occurs usually by a
combination of erosion and physical damage.combination of erosion and physical damage.
The extent of erosion (loss of thickness) of an intact The extent of erosion (loss of thickness) of an intact
coating can be measured by a variety of methods.coating can be measured by a variety of methods.
These include destructive (scribing), magnetic pull-off, These include destructive (scribing), magnetic pull-off,
magnetic flux, eddy current, ultrasonic, etc. gages. magnetic flux, eddy current, ultrasonic, etc. gages.
Change in colour is an indication of the galvanized Change in colour is an indication of the galvanized
coating condition.coating condition.
As galvanizing weathers, it loses its brightness and As galvanizing weathers, it loses its brightness and
turns dull grey and becomes progressively darker turns dull grey and becomes progressively darker
grey as it gradually corrodes.grey as it gradually corrodes.
The appearance of yellow and reddish-brown colour The appearance of yellow and reddish-brown colour
indicates that the pure zinc coating has been lost and indicates that the pure zinc coating has been lost and
corrosion has reddened the zinc-iron amalgam layer.corrosion has reddened the zinc-iron amalgam layer.
This is the optimal time to paint the structure. When This is the optimal time to paint the structure. When
the coating is lost, the surface of the bare steel the coating is lost, the surface of the bare steel
becomes covered with dark-brown corrosion scale. becomes covered with dark-brown corrosion scale.
Change in colour is an indication of the galvanized Change in colour is an indication of the galvanized
coating condition. coating condition.
Change in colour is an indication of the galvanized Change in colour is an indication of the galvanized
coating condition.coating condition.
As galvanizing weathers, it loses its brightness and As galvanizing weathers, it loses its brightness and
turns dull grey and becomes progressively darker turns dull grey and becomes progressively darker
grey as it gradually corrodes.grey as it gradually corrodes.
The appearance of yellow and reddish-brown colour The appearance of yellow and reddish-brown colour
indicates that the pure zinc coating has been lost and indicates that the pure zinc coating has been lost and
corrosion has reddened the zinc-iron amalgam layer.corrosion has reddened the zinc-iron amalgam layer.
This is the optimal time to paint the structure. When This is the optimal time to paint the structure. When
the coating is lost, the surface of the bare steel the coating is lost, the surface of the bare steel
becomes covered with dark-brown corrosion scale. becomes covered with dark-brown corrosion scale.
Change in colour is an indication of the galvanized Change in colour is an indication of the galvanized
coating condition. coating condition.
As galvanizing weathers, it loses its brightness As galvanizing weathers, it loses its brightness
and turns dull grey and becomes progressively and turns dull grey and becomes progressively
darker grey as it gradually corrodes. darker grey as it gradually corrodes.
The appearance of yellow and reddish-brown The appearance of yellow and reddish-brown
colour indicates that the pure zinc coating has colour indicates that the pure zinc coating has
been lost and corrosion has reddened the zinc-been lost and corrosion has reddened the zinc-
iron amalgam layer.iron amalgam layer.
This is the optimal time to paint the structure. This is the optimal time to paint the structure.
When the coating is lost, the surface of the When the coating is lost, the surface of the
bare steel becomes covered with dark-brown bare steel becomes covered with dark-brown
corrosion scale. corrosion scale.
As galvanizing weathers, it loses its brightness As galvanizing weathers, it loses its brightness
and turns dull grey and becomes progressively and turns dull grey and becomes progressively
darker grey as it gradually corrodes. darker grey as it gradually corrodes.
The appearance of yellow and reddish-brown The appearance of yellow and reddish-brown
colour indicates that the pure zinc coating has colour indicates that the pure zinc coating has
been lost and corrosion has reddened the zinc-been lost and corrosion has reddened the zinc-
iron amalgam layer.iron amalgam layer.
This is the optimal time to paint the structure. This is the optimal time to paint the structure.
When the coating is lost, the surface of the When the coating is lost, the surface of the
bare steel becomes covered with dark-brown bare steel becomes covered with dark-brown
corrosion scale. corrosion scale.
The contamination of tower surfaces with aggressive The contamination of tower surfaces with aggressive
chemicals can lead to enhanced corrosion and chemicals can lead to enhanced corrosion and
deterioration of protective coatings. Although, the deterioration of protective coatings. Although, the
methods of detection and determination are not methods of detection and determination are not
standardized, several test methods are accepted by the standardized, several test methods are accepted by the
industry. industry.
Surface contamination analysis kits are available to Surface contamination analysis kits are available to
measure pH, chlorides (detection limit 40 ppm) and measure pH, chlorides (detection limit 40 ppm) and
soluble ferrous ions (detection limit approximately 3 ppm). soluble ferrous ions (detection limit approximately 3 ppm).
In most cases these detection limits are sufficient to In most cases these detection limits are sufficient to
establish the aggressivity of the operating environment establish the aggressivity of the operating environment
and surface cleanliness before painting. and surface cleanliness before painting.
The contamination of tower surfaces with aggressive The contamination of tower surfaces with aggressive
chemicals can lead to enhanced corrosion and chemicals can lead to enhanced corrosion and
deterioration of protective coatings. Although, the deterioration of protective coatings. Although, the
methods of detection and determination are not methods of detection and determination are not
standardized, several test methods are accepted by the standardized, several test methods are accepted by the
industry. industry.
Surface contamination analysis kits are available to Surface contamination analysis kits are available to
measure pH, chlorides (detection limit 40 ppm) and measure pH, chlorides (detection limit 40 ppm) and
soluble ferrous ions (detection limit approximately 3 ppm). soluble ferrous ions (detection limit approximately 3 ppm).
In most cases these detection limits are sufficient to In most cases these detection limits are sufficient to
establish the aggressivity of the operating environment establish the aggressivity of the operating environment
and surface cleanliness before painting. and surface cleanliness before painting.
Polarization Resistance Polarization resistance is a Polarization Resistance Polarization resistance is a
simple, electro-chemical measurement that is an simple, electro-chemical measurement that is an
established and proven technique for monitoring established and proven technique for monitoring
corrosion rate insitu. In controlled circumstances, it can corrosion rate insitu. In controlled circumstances, it can
give an absolute value of corrosion rate and, therefore, give an absolute value of corrosion rate and, therefore,
metal loss. metal loss.
When applied to steel tower foundations, however, When applied to steel tower foundations, however,
results must be interpreted cautiously. Many unknowns results must be interpreted cautiously. Many unknowns
exist, namely the area of steelwork involved in the exist, namely the area of steelwork involved in the
corrosion, details of the environment, soil types and corrosion, details of the environment, soil types and
moisture levels. moisture levels.
The technique can indicate active corrosion situations The technique can indicate active corrosion situations
and can quickly and relatively inexpensively give a and can quickly and relatively inexpensively give a
measurement.measurement.
Polarization Resistance Polarization resistance is a Polarization Resistance Polarization resistance is a
simple, electro-chemical measurement that is an simple, electro-chemical measurement that is an
established and proven technique for monitoring established and proven technique for monitoring
corrosion rate insitu. In controlled circumstances, it can corrosion rate insitu. In controlled circumstances, it can
give an absolute value of corrosion rate and, therefore, give an absolute value of corrosion rate and, therefore,
metal loss. metal loss.
When applied to steel tower foundations, however, When applied to steel tower foundations, however,
results must be interpreted cautiously. Many unknowns results must be interpreted cautiously. Many unknowns
exist, namely the area of steelwork involved in the exist, namely the area of steelwork involved in the
corrosion, details of the environment, soil types and corrosion, details of the environment, soil types and
moisture levels. moisture levels.
The technique can indicate active corrosion situations The technique can indicate active corrosion situations
and can quickly and relatively inexpensively give a and can quickly and relatively inexpensively give a
measurement.measurement.
Polarization Resistance is a simple, electro-chemical Polarization Resistance is a simple, electro-chemical
measurement that is an established and proven measurement that is an established and proven
technique for monitoring corrosion rate insitu. technique for monitoring corrosion rate insitu.
In controlled circumstances, it can give an absolute In controlled circumstances, it can give an absolute
value of corrosion rate and, therefore, metal loss. value of corrosion rate and, therefore, metal loss.
When applied to steel tower foundations, however, When applied to steel tower foundations, however,
results must be interpreted cautiously.results must be interpreted cautiously.
Many unknowns exist, namely the area of steelwork Many unknowns exist, namely the area of steelwork
involved in the corrosion, details of the environment, involved in the corrosion, details of the environment,
soil types and moisture levels. soil types and moisture levels.
The technique can indicate active corrosion situations The technique can indicate active corrosion situations
and can quickly and relatively inexpensively give a and can quickly and relatively inexpensively give a
measurement. measurement.
Polarization Resistance is a simple, electro-chemical Polarization Resistance is a simple, electro-chemical
measurement that is an established and proven measurement that is an established and proven
technique for monitoring corrosion rate insitu. technique for monitoring corrosion rate insitu.
In controlled circumstances, it can give an absolute In controlled circumstances, it can give an absolute
value of corrosion rate and, therefore, metal loss. value of corrosion rate and, therefore, metal loss.
When applied to steel tower foundations, however, When applied to steel tower foundations, however,
results must be interpreted cautiously.results must be interpreted cautiously.
Many unknowns exist, namely the area of steelwork Many unknowns exist, namely the area of steelwork
involved in the corrosion, details of the environment, involved in the corrosion, details of the environment,
soil types and moisture levels. soil types and moisture levels.
The technique can indicate active corrosion situations The technique can indicate active corrosion situations
and can quickly and relatively inexpensively give a and can quickly and relatively inexpensively give a
measurement. measurement.
METHODS OF CORROSION PROTECTIONMETHODS OF CORROSION PROTECTION
To protect sections of buried steel from To protect sections of buried steel from
corrosion, a variety of methods have been corrosion, a variety of methods have been
tried and evaluated in Sweden. For a short tried and evaluated in Sweden. For a short
period, steel foundations were dipped in hot period, steel foundations were dipped in hot
tar. After five years, investigation of these tar. After five years, investigation of these
towers showed corrosion of the buried towers showed corrosion of the buried
sections and that method was abandoned.sections and that method was abandoned.
METHODS OF CORROSION PROTECTIONMETHODS OF CORROSION PROTECTION
To protect sections of buried steel from To protect sections of buried steel from
corrosion, a variety of methods have been corrosion, a variety of methods have been
tried and evaluated in Sweden. For a short tried and evaluated in Sweden. For a short
period, steel foundations were dipped in hot period, steel foundations were dipped in hot
tar. After five years, investigation of these tar. After five years, investigation of these
towers showed corrosion of the buried towers showed corrosion of the buried
sections and that method was abandoned.sections and that method was abandoned.
Following the introduction in the 1930s of Following the introduction in the 1930s of
grillages, the main sections of the steel towers grillages, the main sections of the steel towers
were hot galvanized with 110 µm of zinc, a were hot galvanized with 110 µm of zinc, a
practice that continued until 1954. Analyses of practice that continued until 1954. Analyses of
soils and corrosivity measurements were taken soils and corrosivity measurements were taken
on each selected tower position. Additionally, the on each selected tower position. Additionally, the
conductivity (soil resistivity), pH value and type of conductivity (soil resistivity), pH value and type of
soil were determined on layers below ground soil were determined on layers below ground
level. Each tower was then considered level. Each tower was then considered
individually in terms of the corrosion protection individually in terms of the corrosion protection
to be employed.to be employed.
Following the introduction in the 1930s of Following the introduction in the 1930s of
grillages, the main sections of the steel towers grillages, the main sections of the steel towers
were hot galvanized with 110 µm of zinc, a were hot galvanized with 110 µm of zinc, a
practice that continued until 1954. Analyses of practice that continued until 1954. Analyses of
soils and corrosivity measurements were taken soils and corrosivity measurements were taken
on each selected tower position. Additionally, the on each selected tower position. Additionally, the
conductivity (soil resistivity), pH value and type of conductivity (soil resistivity), pH value and type of
soil were determined on layers below ground soil were determined on layers below ground
level. Each tower was then considered level. Each tower was then considered
individually in terms of the corrosion protection individually in terms of the corrosion protection
to be employed.to be employed.
Towers exposed to the most corrosive soils Towers exposed to the most corrosive soils
were protected with an extra rust allowance were protected with an extra rust allowance
of the steel, hot galvanizing and two layers of of the steel, hot galvanizing and two layers of
0.5-mm-thick zinc plate welded to the tower 0.5-mm-thick zinc plate welded to the tower
leg and wrapped around the sections buried leg and wrapped around the sections buried
in soil. Finally, the whole “package” was in soil. Finally, the whole “package” was
dipped in hot tar. The towers subjected to this dipped in hot tar. The towers subjected to this
protection would likely have a long life, but protection would likely have a long life, but
this method was expensive and intensive this method was expensive and intensive
development took place to increase the development took place to increase the
thickness of galvanized zinc.thickness of galvanized zinc.
Towers exposed to the most corrosive soils Towers exposed to the most corrosive soils
were protected with an extra rust allowance were protected with an extra rust allowance
of the steel, hot galvanizing and two layers of of the steel, hot galvanizing and two layers of
0.5-mm-thick zinc plate welded to the tower 0.5-mm-thick zinc plate welded to the tower
leg and wrapped around the sections buried leg and wrapped around the sections buried
in soil. Finally, the whole “package” was in soil. Finally, the whole “package” was
dipped in hot tar. The towers subjected to this dipped in hot tar. The towers subjected to this
protection would likely have a long life, but protection would likely have a long life, but
this method was expensive and intensive this method was expensive and intensive
development took place to increase the development took place to increase the
thickness of galvanized zinc.thickness of galvanized zinc.
CATHODIC PROTECTIONCATHODIC PROTECTION
One of the most promising methods of protecting the One of the most promising methods of protecting the
underground tower sections is cathodic protection. underground tower sections is cathodic protection.
This method has been used for many years in other This method has been used for many years in other
industries such as pipelines and harbors. industries such as pipelines and harbors.
The corroding object (the tower) is the cathode in an The corroding object (the tower) is the cathode in an
electrochemical cell. The electrode potential of the electrochemical cell. The electrode potential of the
metal is then displaced in negative direction to a value metal is then displaced in negative direction to a value
below its steady-state corrosion potential.below its steady-state corrosion potential.
This way, the dissolution is prevented (complete This way, the dissolution is prevented (complete
cathodic protection) or at least counteracted. Cathodic cathodic protection) or at least counteracted. Cathodic
protection is divided into galvanic and electrolytic protection is divided into galvanic and electrolytic
according to the following scheme:according to the following scheme:
CATHODIC PROTECTIONCATHODIC PROTECTION
One of the most promising methods of protecting the One of the most promising methods of protecting the
underground tower sections is cathodic protection. underground tower sections is cathodic protection.
This method has been used for many years in other This method has been used for many years in other
industries such as pipelines and harbors. industries such as pipelines and harbors.
The corroding object (the tower) is the cathode in an The corroding object (the tower) is the cathode in an
electrochemical cell. The electrode potential of the electrochemical cell. The electrode potential of the
metal is then displaced in negative direction to a value metal is then displaced in negative direction to a value
below its steady-state corrosion potential.below its steady-state corrosion potential.
This way, the dissolution is prevented (complete This way, the dissolution is prevented (complete
cathodic protection) or at least counteracted. Cathodic cathodic protection) or at least counteracted. Cathodic
protection is divided into galvanic and electrolytic protection is divided into galvanic and electrolytic
according to the following scheme:according to the following scheme:
Galvanic cathodic protection of steelGalvanic cathodic protection of steel
The corroding object is made the cathode of a The corroding object is made the cathode of a
galvanic cell, the anode of which is a base metal (for galvanic cell, the anode of which is a base metal (for
example, magnesium, zinc and aluminum) that is example, magnesium, zinc and aluminum) that is
sacrificed to protect valuable construction.sacrificed to protect valuable construction.
Electrolytic cathodic protection of steelElectrolytic cathodic protection of steel
The corroding object is made the cathode of an The corroding object is made the cathode of an
electrolytic cell, which is supplied with impressed electrolytic cell, which is supplied with impressed
direct current from an external current source. The direct current from an external current source. The
anode of this cell is usually insoluble (platinum, lead, anode of this cell is usually insoluble (platinum, lead,
carbon, nickel).carbon, nickel).
Galvanic cathodic protection of steelGalvanic cathodic protection of steel
The corroding object is made the cathode of a The corroding object is made the cathode of a
galvanic cell, the anode of which is a base metal (for galvanic cell, the anode of which is a base metal (for
example, magnesium, zinc and aluminum) that is example, magnesium, zinc and aluminum) that is
sacrificed to protect valuable construction.sacrificed to protect valuable construction.
Electrolytic cathodic protection of steelElectrolytic cathodic protection of steel
The corroding object is made the cathode of an The corroding object is made the cathode of an
electrolytic cell, which is supplied with impressed electrolytic cell, which is supplied with impressed
direct current from an external current source. The direct current from an external current source. The
anode of this cell is usually insoluble (platinum, lead, anode of this cell is usually insoluble (platinum, lead,
carbon, nickel).carbon, nickel).
Most of the corrosion problems in power transmission Most of the corrosion problems in power transmission
can be reliably detected and assessed using can be reliably detected and assessed using
conventional and well established corrosion testing conventional and well established corrosion testing
instruments, practices and methods.instruments, practices and methods.
Data, from both field and laboratory, are essential for Data, from both field and laboratory, are essential for
the implementation of ameliorative measures, and the implementation of ameliorative measures, and
must be interpreted in conjunction with a quantitative must be interpreted in conjunction with a quantitative
understanding of ageing processes before information understanding of ageing processes before information
can be provided for effective decision making.can be provided for effective decision making.
Corrosion control technology available today can, in a Corrosion control technology available today can, in a
cost-effective way, improve reliability, performance and cost-effective way, improve reliability, performance and
safety of transmission lines. safety of transmission lines.
Most of the corrosion problems in power transmission Most of the corrosion problems in power transmission
can be reliably detected and assessed using can be reliably detected and assessed using
conventional and well established corrosion testing conventional and well established corrosion testing
instruments, practices and methods.instruments, practices and methods.
Data, from both field and laboratory, are essential for Data, from both field and laboratory, are essential for
the implementation of ameliorative measures, and the implementation of ameliorative measures, and
must be interpreted in conjunction with a quantitative must be interpreted in conjunction with a quantitative
understanding of ageing processes before information understanding of ageing processes before information
can be provided for effective decision making.can be provided for effective decision making.
Corrosion control technology available today can, in a Corrosion control technology available today can, in a
cost-effective way, improve reliability, performance and cost-effective way, improve reliability, performance and
safety of transmission lines. safety of transmission lines.
THANK YOUTHANK YOU
THANK YOUTHANK YOU
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