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Geotechnical Engineering
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CONTROL OF
CORROSION OF
UNDERWATER PILES
Presented by:Avinash Shaw
Roll no. 11/CE/45
Department of Civil Engineering
NIT Durgapur
Corrosion is the destruction of metals andalloys by the chemical reaction with theenvironment.
Generally many traditional metal parts areused with lighter polymeric components butthese are impervious to electrochemicalcorrosion so even with the proper selectionof base metals, there is no absolute way toeliminate corrosion.
Introduction
On steel piling in seawater, the more chemically active surface areas (anodes) are metallically coupled through the piling itself to the less chemically active surface areas (cathodes) resulting flow of electricity and corrosion of anodic areas.
Generally corrosion occurs when local anodic and cathodic areas continually shift about randomly but sometimes they do not shift position end, therefore the metal suffers localized attack and pitting occurs.
In general smaller the anode area relative to the cathode area, the deeper the pitting
Corrosion Caused By The Difference Of The Dissolved Oxygen
Concentration
ZONES
SPLASH
ZONE
ATMOSPHERIC
ZONE
SUBMERGED
ZONE
TIDAL
ZONE
Depending upon
time of wetness,
temperature,
pollutants etc.
Atmospheric
corrosion is
responsible for a
large fraction of the
total corrosion in
the world.
CORROSION
RATE(without
protection)
< 0.1 mm/year
ZONES
SPLASH
ZONE
ATMOSPHERIC
ZONE
SUBMERGED
ZONE
TIDAL
ZONE
The
splash/spray
zone can be
characterized by
as an aerated
sea water
environment
where exposed
material are
almost
continually wet
and biofouling
do not attach.
CORROSION
RATE(without
protection)
0.3 mm/year
ZONES
SPLASH
ZONE
ATMOSPHERIC
ZONE
SUBMERGED
ZONE
TIDAL
ZONE
The tidal zone is an
environment where
metals are
alternately
submerged in
seawater and
exposed to the
splash zone as the
tide fluctuates.
CORROSION RATE (without protection)
0.1-0.3 mm/year
ZONES
SPLASH
ZONE
ATMOSPHERIC
ZONE
SUBMERGED
ZONE
TIDAL
ZONE
The submerged/
shallow ocean
environment
zone usually
characterized by
well aerated
water combined
with marine
biofouling
organism of both
the plant and
animal variety.
CORROSION
RATE(without
protection)
0.1-0.2 mm/year
Phase 1 of the
program is the
programmatic
assessment or
planning stage of the
project.
For the planning
stage, three main
requirements sought,
budget and schedule
needed to overcome
the problem raised
from corrosion of
PHASE 1
PHASE 2
PHASE 3
Phase 2 of the
program involves
physical assessment
and actual
remediation.
Inspections for
severity of corrosion
are conducted in this
phase to determine
what strategy or
methods are most
suitable to be
applied.
PHASE 1
PHASE 2
PHASE 3
Phase 3 of the
program mainly deals
with future monitoring
of the repaired
structure.
Systematically
identifying and
managing the
existing resources
can be done by
implementing internal
or external
monitoring system
using current
technology.
PHASE 1
PHASE 2
PHASE 3
PROTECTIVE
COATING
CATHODIC
PROTECTION
ANODE DELIVERY SYSTEM
Application of FRP
composites
Protective CoatingIn order to protect metals from corrosion, the
contact between the metal and the corrosive
environment is to be cut off. This is done by
coating the surface of metals with a
continuous non-porous material inert to the
corrosive atmosphere.
Surface coatings are broadly classified into
three
Metallic coatings
Inorganic Coatings
Organic Coatings
Protective Coatings
1.• Inorganic Zinc Sillicates Primers
2.• High Build Epoxy Coatings
3.• Aliphatic Polyurethane Topcoats
4.• Zinc Rich Epoxy Primers
5.• Non-Skid Deck Coatings
• arrest rust creep, or undercutting of the coatings surrounding the damaged area
• high degree of resistance to heat and chemical spills
Inorganic Zinc
Silicates Primers
• Epoxies are generally more abrasion and chemical resistant than primers
• These are poor resistance of ultra violet from sunlight and most will chalk and fade rapidly.
High Build Epoxy
Coatings
• optimum resistance to UV and high degrees of flexibility and chemical resistance.
• maintain a very high level of cosmetic gloss and color retention and can be cleaned very easily with low pH detergents and fresh water pressure washing.
Aliphatic Polyuret
hane Topcoats
• high level of service and are more tolerant to compromised surface preparation and ambient weather conditions
• maintaining damaged areas and breakdown of the coatings systems
Zinc Rich Epoxy
Primers
• normally incorporate very course aggregates for an exaggerated profile.
• They are applied in very high film builds and normally without a zinc rich primer.
Non-Skid Deck
Coatings
CATHODIC PROTECTIONCathodic protection is an electrochemical process which halts the corrosion of metals in a particular environment by superimposing an electrochemical cell more powerful than the corrosion cell.
Sacrifical Anodes are fitted or bonded to the metal to be protected.
The implementation is simple, all you need is an anode, a power supply and engineering talent.
• These are similar to the cathodic
protection method in philosophy.
• These are designed on the design basis
of maximum current distribution for the
lowest possible cost, with the most long-
term reliability.
Anode delivery system
Pile Mounted
Anode
Retractable Anode
Sled Anode Suspension Anode
Application of FRP composites
The poor durability of conventional corrosion repairs has led to increased interest for its replacement by fiber reinforced polymers.
Although dry conditions are favorable but availability of resins that can cure in water has made it possible.
Saturating FRP with resin and installing is complex but benificial in costly repairs and rapid deterioration.
Fibre reinforced polymers
have long been used for the
repair and retrofit of concrete
structural elements.
Lightweight, high strength
and resistance to chemicals.
Unparallel flexibility, multi-
directional.
Twofold role: first to restore
lost flexural capacity and
second to provide resistance
to withstand expansive
forces.
• Figure shows impact
damage that led to both
cross-section and
breakage of the spiral
ties.
• Using FRP there is only
need to re-form the cross-
section and apply bi-
directional layers to
restore lost tensile
capacity.
• Bonding agents may be
required to assure
capillary suction of the
epoxy and to ensure
Though there is no absolute way to eliminate all corrosion on underwater piles, there are some effective measures to control them.
Cathodic protection is quit simple and protective coatings are used in vast and expensive structures.
The FRP composites have many advantages viz. lightweight, posses high strength and chemical resistance and moreover have incomparable flexibility.
Of the various ways of wrapping of FRP composites , transverse wrapping is found to be the easiest.
Bi-directional material is the best option. Scaffolding measures during the application of materials ensures safety and simplifies