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1. INTRODUCTION
Corrosion is the destruction of metals and alloys by the chemical reaction with the
environment. During corrosion the metals are converted to metallic compounds at the surface
and these compounds wears away as corrosion product. Hence corrosion may be regarded as the
reverse process of extraction of metals from ore. Corrosion and in particular corrosion of metal
structures, is a problem that must regularly be addressed in a wide variety of areas, for example,
in the automotive industry, metal parts are often plated or coated to protect them from road salt
and moisture in hopes of increasing their longevity. Indeed, many traditional metal parts are
currently being used with polymeric components, which are not only lighter but also more cost
effective to produce. But these are generally impervious to electrochemical corrosion often
experienced by metals. Even with the proper selection of base metals and well-designed systems
or structures, there is no absolute way to eliminate all corrosion. Therefore, corrosion protection
methods are used to additionally mitigate and control the effects of corrosion. Corrosion
protection can be in a number of different forms/strategies with perhaps multiple methods
applied in severe environments. Forms of corrosion protection include the use of inhibitors,
surface treatments, coatings and sealants, cathodic protection and anodic protection.

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2. CORROSION
Corrosion is the destruction of metals and alloys by the chemical reaction with the
environment. During corrosion the metals are converted to metallic compounds at the surface
and these compounds wears away as corrosion product. Hence corrosion may be regarded as the
reverse process of extraction of metals from ore. It changes the properties of the metal and may
lead to loss of the metal and its mechanical properties such as strength, ductility and impact
strength. The rate of incident is highest as a result of deterioration of the underwater structure.
The economy, the environment, and the human beings will be seriously affected and also an
interruption of working as a result of the collapse of even one pile. Usually, the “chip and patch”
method (whereby all loose material is removed and the section re-formed with new material to
cover the affected areas) is used for repairing corrosion damage pile but due to its negative
efficiency, there has been alternative methods such as cathodic protection, fiber reinforced
polymer (FRP) wraps and fiber reinforced polymer incorporating cathodic protection are used for
corrosion repair of piles. The costly repair and maintenance works might have additionally to be
undertaken if timely remedial action is not taken. Hence, finally the repair of corrosion pile and
cyclic inspection is essential before the collapse of the structure because demolition is intolerable
and replacement is not feasible. Corrosion protection methods are used to additionally mitigate
and control the effects of corrosion.
2.1 Corrosion Management
Corrosion management can be divided into three major phases.
2.1.1 Phase 1
It is the programmatic assessment of the project. This phase is the planning stage for a
corrosion management program to take place. It initiates the program to be implemented on
structures that are found to be under the threat of corrosion. For the planning stage, three main
requirements are sought, namely the strategy, budget and schedule needed overcome the problem
raised from corrosion of reinforcement. This is seen as an important part for an effective

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management program as feasibility studies are normally conducted to determine the
serviceability of the structure after treatment.
Fig.1:-Phase 1
Source: [4]
2.1.2 Phase 2
It involves physical assessment and actual damages. Inspections for severity of corrosion
are conducted during this section to see what strategy or ways are best suited to be applied.
Development of corrosion management strategy would give a lot of choice to the management
program. Remedial work would be allotted once the right strategy has been recognized.
Fig.2:-Phase 2
Source: [4]

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2.1.3 Phase 3
It primarily deals with future observance of the repaired structure. Presently and
traditionally, most of the corrosion management programs are driven by response to incident or
pressing, instead of consistently distinctive and managing the prevailing resources. This could be
overcome by implementing internal or external observance system oppression of the current
technology practiced in oil and gas industries.
Fig.3:-Phase 3
Source: [4]

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3. CORRECTIONMECHANISM OF STEELIN SEA WATER
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 in a flow of electricity and corrosion of the anodic areas. General surface
roughening occurs when these local anodic and cathodic areas continually shift about randomly
during the corrosion process. Sometimes these active local areas do not shift position end,
therefore, the metal suffers localized attack and pitting occurs. In general, the depth of pitting is
related to the ratio of the anodic sites to the area of cathodic site in contact with the electrolyte
(seawater). The smaller the anode area relative to the cathode area, the deeper the pitting
corrosion occurs.
A general corrosion mechanism and initiation of corrosion in a pipe surface in the
presence of salt water are given in Fig. 4. It can be seen from the Fig. 4 that the hydroxide and
chloride ions are contributing to the accelerated corrosion in submerged and sea water
conditions. Fig.5 shows degradation of the protective coating and formation of hydroxide of iron
as a result of the corrosion.
Fig.4. Corrosion of Steel in seawater
Source: [4]

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Fig.5. Corrosion on steel surface
Source: [4]
3.1 Corrosion Zones of Steel Pipes
Fig. 6 Corrosion Zones of Steel Pipes
Source: [5]

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3.1.1Tidal
It is an environment where the metals are submerged in the seawater and then exposed to
the splash zone alternately as the tide fluctuates.
3.1.2 Submerged
This environment zone is usually characterized by well-aerated water in combination
with the marine bio fouling organism of animal and the plant.
3.1.3 Atmospheric
It depends upon the temperature, pollutants, time of wetness. It is also largely responsible
for large fraction of corrosion. Splash – It is characterized as an aerated environment of seawater
where the exposed material continually wet and there is no attachment of bio fouling.
Fig: 7 Zones of corrosion
(Source: http://4.bp.blogspot.com)

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3.2 Corrosion Measuring Methods
Corrosion measurement is necessary to assess the severity or rate of corrosion. It is
required for durability, safety of structure, and confirming repair or maintenance methods .The
methods can also be used for checking the efficiency of corrosion methods i.e. to check whether
the adequate corrosion control has been achieved or not by the corrosion methods. The corrosion
can be measure using any one of the following technique:
3.2.1 Half-cell potential test
This test was developed in the 1960s for corrosion measurement and comprised by
ASTM standard C876.It is an electrochemical technique used to evaluate the rate of corrosion
and classify the chloride infected boundaries. This test comprises high impedance voltmeter and
a standard reference electrode such as copper-copper sulfate electrode. The reference electrode is
placed by drilling a hole into the structure. The holes should be cleaned with fresh water and
compressed air for removing the deleterious substance. Before placing reference electrode, holes
should prefill with low resistivity grout then after reference electrode inserted in holes. The
reference electrode is connected to the copper wire and the wire will fix into the grooves made in
concrete and covered with grout. This copper wire for reference electrode was routed into the
junction box where they were connected to the reinforcement and protected from the
environment. The test is conducted by connecting the negative and positive end of the voltmeter
to the reference electrode and steel bars respectively. After arrangement, half-cell potential
readings are taken and can be plotted on equipotential contour map. For illustration, the more
positive reading of potential is generally indicates the less corrosion.
Table 1 Half-cell potential readings
Source: [1]

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3.2.2 Linear polarization test
Linear polarization is the best method for measuring the corrosion rate of metal
embedded in concrete and also known as polarization resistance. The PR-Monitor (Cortest
Columbus tech.), the NSC Device, the Gecor Device, and the 3LP Device etc. are used to
measure the corrosion rate. Linear polarization relies on the linear relationship between the
corrosion current and its potential when the equilibrium potential is disturbed by the application
of an incremental current or incremental voltage. The slope of linear polarization curve as
follows:
The measurement of the corrosion rate requires;
 A working electrode, the element whose corrosion rate is to be determined.
 A reference electrode, to measure the electrical potential of the working
electrode.
 An auxiliary or counter electrode, to apply a current and complete the circuit.
Fig. 8 Setup for linear
polarization measurements
Source: [1]

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The reference electrode and counter electrode embedded in concrete and connected to the
PR-monitor. The reading is taken by varying the voltage in steps from zero to 15 mV, with the
current adjusted accordingly. The slope of the change in potential and applied current gives the
polarization resistance.
Table 2 Interpretation of Linear Polarization Results
Source: [1]
3.2.2.1 Advantage
 This technique may be used for accurately measuring the very low
corrosion rate i.e. less than 0.1 miles per year
 This technique may also be used for rapid corrosion rate measurement.
3.2.2.2 Disadvantage
 This test causes error up to 50% because the approximation comprises by
this method in the calculation.
 Another disadvantage is that the test is sensitive to factors such as
humidity and temperature. Corrosion rate measurements will increase in warm
conditions.
 Since the resistivity of concrete decreases when the concrete is wet,
corrosion rate measurements increase in wet conditions.
3.2.3 Polarization decay test

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The performance and monitoring of the cathodic protection system are given by the
polarization decay test. This test is also known as an instant-off test as it conducted only in two
days. On the 1st day, an instant-off reading taken by temporarily cut off the connection between
steel reinforcement and anode. This instant off readings shows the more negative or polarized
potential against a reference electrode because taken immediately after the connection between
anode and steel cut off i.e. system provides an electron to steel as a result, the steel becomes
more .On the 2nd day i.e. after 24 hrs, once again the potential readings (i.e. stabilize readings)
taken. This reading shows the less negative or depolarized potential against a reference electrode,
because taken after 24 hrs i.e. temporarily cut off the connection between anode and steel, stops
the supply of electron .The difference between these two readings shows the polarization decay.
According to NACE SP0169 .when the polarization decay shows a minimum of 100mV potential
with respect to a reference electrode, and then the cathodic protection system shows full
protection.
3.2.4 Galvanic current test
The performance and monitoring of the FRP system are given by the current density.
Current density required the measured electric current and the surface area of protected steel. It
maintains the protection level of steel and provides rapid polarization. The data loggers are
utilized to automatically record the electric current and recorded data is regularly downloaded
from the site. The current density can be determined by dividing the measured electric current by
the surface area of protected steel. The measured electric current is not constant but influenced
by the water velocity and the concrete resistivity. Generally, dry concrete has a higher resistivity
compared to the wet concrete. The current density can be plotted on the graphs for a different
element. On the comparison, the system has less current density shows the reduced corrosion
rate.

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4. METHODS FOR CORROSIONPROTECTION
4.1 Protective Coating
For protection of metals from corrosion, the metal and the corrosive environment contact
is required to be cut off. The surface of metals is coated with a continuous non- porous material
inert to the corrosive atmosphere to prevent it from corrosion. The coatings are classified into
different categories
 Organic
 Metallic
 Inorganic
For Under Water Piles the types of coatings used are -
4.1.1 Inorganic Zinc Silicate Primers
Structures (Steel) that are immersed in seawater – jackets below the Splash Zone, are
usually not coated and protected solely by cathodic protection system. Many anti corrosive-
pigmented primers, some that passivates the steel. Inorganic zinc silicate primers are the most
effective as they essentially become anodic to the steel in a corrosion process. The advantage of
this coating - it will arrest rust creep, high degree of heat resistance and spills of chemical.
4.1.2 Epoxy Coatings (High Build)
Epoxies in comparison to primers and topcoats are more chemical and abrasion resistant.
It protects not only the substrate, but also the zinc primer and all other detrimental factors. One
disadvantage of epoxy coatings is that, it has very little resistance against ultra violet rays from
sunlight. This leads to the erosion of the coatings reducing the barrier protection.
4.1.3 Epoxy Primers (Zinc Rich)
Epoxy anti corrosives modified with Zinc will ensure a high level of service and are
tolerant to different weather conditions and compromised surface preparation provided that the
zinc loading is sufficient. It is also most effective in maintaining the damaged areas.
4.1.4 Aliphatic Polyurethane Topcoats

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Polyurethane coats provide optimum resistance to UV rays and
have high degree of flexibility and high chemical resistance. It also
helps to maintain a high degree (level) of cosmetic gloss, color
retention and it can be easily cleaned. Polyurethane finishes does
not provide any real anti-corrosive or barrier protection, they do
provide a high degree of protection to integrity of the coatings system.
4.1.5 Non-Skid Deck Coating
These coatings are that are designed and engineered with anti-
slip properties. These coatings incorporate course aggregates. The
coatings are applied in very high film builds and usually without a zinc rich primer.
4.2 Cathodic Protection (CP)
Most preferred technique for mitigating underwater or marine corrosion is cathodic
protection (CP) i.e. the practice or art of using electrochemical reactions for prevention of steel
structures from corrosion. The implementation of a Cathodic Protection system is quite simple.
Let us assume, there is corroding steel in seawater, all we require is an anode and power supply.
A protective circuit is achieved between the anode, steel (cathode), seawater (electrolyte) and
power supply.
4.2.1 Pile Mounted Anode
This method of anode delivery is used when the anode can be tied or attached to the piles
or cathode directly. These anodes are designed for efficient distribution of current into and
around the piling.

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Fig.9 Pile Mounted Anode
(Source: https://theconstructor.org)
4.2.2 Sled Anode
These anodes are designed and engineered for operation in either seawater (electrolyte) or
it can be buried in the mud. An anode mounted on the seabed ensures the best spread or
distribution of protection for a marine structure. The advantage of this anode is its low profile,
hence limiting the chances of damage by fishing nets, ships anchor, etc.
Fig.10 Sled Anode
(Source: https://theconstructor.org)
4.2.3 Retractable Mount

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This type of anode delivery system is used when the anode is to be replaced with new one
periodically. When the cathodic protection is needed only time to time but not continuously, this
type of system is used so that the anode can be replaced easily.
Fig.11 Retractable
Mount
(Source: https://theconstructor.org)
4.3 Fiber reinforced polymer (FRP) repair
Fiber reinforced polymers (FRP) are mostly used for the repair and rehabilitation of
concrete structural elements. The composites are very light in weight, are resistant to chemicals,
have high strength and in fabric form have high degree of flexibility. The FRP composite when
mixed with wet concrete makes it economical to conduct repairs on sub structure parts. When the
FRP is used, then the corroded part of the structure element is carefully removed and the FRP
composite induced concrete is applied. The FRP provides the lost tensile capacity and it also
provides the steel with lateral support. When the FRP is applied with concrete, the spreading of
corrosion to other piles is
protected and it also
ensures protection
from UV radiation.

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Fig. 12 Fiber reinforced polymer
(Source: https://theconstructor.org)
5. CONCLUSION
As there is no absolute way for elimination of all corrosion from under water piles, there
are some effective methods or ways to control them. Cathodic protection is found to be most
simple to understand and use and are largely used in marine conditions. The Fiber Reinforced
Polymer composites have many advantages in comparison to conventional methods - they are
lightweight, are chemical resistant and possess high strength and have high degree of flexibility.

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REFERENCE
[1] Abhishek Jain,Dr. Trilok Gupta And Dr. Ravi K. Sharma (2016)
“Measurement and Repair Techniques of Corroded Underwater Piles: An
Overview” Journal of Engineering Research and Application,Vol. 6, Issue 7,page
no:.19-27
[2] Rajan Sen ,Gray Mullins (2006) “Application of FRP composites for
underwater piles repair” Department of Civil and Environmental Engineering,
University of South Florida Tampa, FL 33620, USA
[3] Rajan Sen, Gray Mullins(2007) “Application of FRP composites for underwater
piles repair” Department of Civil and Environmental Engineering, University of
South Florida Tampa, FL 33620, USA,vol:38 page no:751–758
[4] Sahil Mehta, Rishabh Madhani, Abhishek Gurav and Divyesh Maiyani
(2018) “Investigative study on corrosion of piles due to seawater”, international
journal of advanced research. TCET, Mumbai.
[5] Sidhant Agarwala1 & Dr. O.M Prakash Netula (2017) “Study of Corrosion
Control of Underwater Piles” Imperial Journal of Interdisciplinary Research
(IJIR) Vol-3, Issue-4.
[6] Tahsin Tezdogan Yigit Kemal Demirel (2014) “An overview of marine
corrosion protection with a focus on cathodic protection and coatings”
Brodogradnja/Shipbuilding, Volume 65.

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