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