RILEM Week 2023
Vancouver, BC, Canada
September 4-8, 2023
MARINE CORROSION AND ITS MITIGATION
Balkrishna Jadhav,
Dy. General Manager-Mechanical, Finolex Industries Ltd, Ratnagiri, India, bnj@finolexind.com.
ABSTRACT
Refineries and petrochemical plants located on seashore for obvious reasons generally face
marine corrosion as a major form of damage mechanism. It is aqueous environmental
corrosion involving presence of chlorides. The corrosion is aggressive in nature and affects
differently in submerged zone, tidal zone, splash zone and atmospheric zone. The present
paper tries to describe the different corrosion mechanisms directly associated with the marine
environments like pitting corrosion, crevice corrosion, galvanic corrosion, corrosion
concentration cells, microbial corrosion, etc. It will also discuss the factors affecting the
corrosion rates like water chemistry, temperature, turbidity, marine life, other pollution.
It will address the mitigation methods for arresting and limiting the marine corrosion like
selection of materials, design criteria, protective coatings, cathodic protection, sacrificial
anodic protection, inspections and NDTs.
The paper tries to explain the practical marine corrosion experienced and the mitigation
actions exercised on a shore facility for dock civil construction, storage tanks, and surface
condenser tube corrosion. Under deposit MIC of 70-30 Cu-Ni tubes of a sea water cooled
surface condenser identified with metallurgical investigation of failed tube and appropriate
remedial actions ensured with enhanced MTBF. For dock jetty piles and slabs corrosion and
structural strength assessment was carried out by using NDT techniques like USPV, Rebound
hammer, Surface carbonation, pH and Chloride profile test, ROV, PECT. Rehabilitation was
carried out with pouring micro-concrete and applying carbon fibre wrap.
Keywords: Marine corrosion, Galvanic corrosion, Material selection, Life extension, nondestructive testing, MIC, SRB, TBC, MTBF
Balkrishna N. Jadhav, BE-Mechanical
Finolex Industries Ltd., Ranpar-Golap, Pawas Road, Ratnagiri, Maharashtra, India, 415616
Email: bnj@finolexind.com | Tel: +91 2352-2238027 | Web: www.finolexwater.com
1.
INTRODUCTION
Corrosion is called as the “Great Destroyer”. The cost of corrosion worldwide is over 2% of
the world GDP. These are only direct costs involved with repair, maintenance, & replacement
and do not include the environmental damage, waste of resources, loss of production,
resulting from corrosion.
All metals and alloys when exposed to marine environment undergo corrosion. It is generally
accepted that the marine environment that combines the effects of saline sea water, salt laden
air, rain, dew, condensation, localised high temperature and the corrosive effects of
combustion gases is the most corrosive of naturally occurring environments.
Refineries and petrochemical plants located on seashore for obvious reasons generally face
marine corrosion as a major form of damage mechanism. This paper will address the damage
mechanisms associated with the marine corrosion and the available mitigation methods. Three
specific case studies will be discussed to explain how marine corrosion could be managed.
2.1. Marine corrosion – How is it different than usual rusting?
Marine corrosion is aqueous environmental corrosion (electrochemical process) involving
presence of chlorides.
2.1.1. Usual rusting in benign atmosphere generates ferrous and ferric hydroxide:
Solid iron oxidises under water droplet containing a little dissolved oxygen and Dissolved
oxygen undergoes reduction process to produce water:
𝐹𝑒(𝑠𝑜𝑙𝑖𝑑) → 𝐹𝑒 2+ (𝑎𝑞𝑢𝑒𝑜𝑢𝑠) + 2𝑒 −
𝑂2 (𝑎𝑞𝑢𝑒𝑜𝑢𝑠) + 4𝑒 − + 4𝐻 + (𝑎𝑞𝑢𝑒𝑜𝑢𝑠) → 2𝐻2 𝑂(𝑙𝑖𝑞𝑢𝑖𝑑)
The Fe2+ ions also react with hydrogen ions and oxygen to produce Fe3+ ions:
4𝐹𝑒 2+ (𝑎𝑞𝑢𝑒𝑜𝑢𝑠) + 4𝐻 + (𝑎𝑞𝑢𝑒𝑜𝑢𝑠) + 𝑂2 (𝑎𝑞𝑢𝑒𝑜𝑢𝑠) → 4𝐹𝑒 3+ (𝑎𝑞𝑢𝑒𝑜𝑢𝑠) + 2𝐻2 𝑂 (𝑙𝑖𝑞𝑢𝑖𝑑)
Hydrogen ions are consumed by the process and its concentration drops (pH rises). With
further oxidation of iron, hydroxide ions (OH-) appear in water. They react with the Fe2+ and
Fe3+ ions to produce insoluble ferrous hydroxides (green rust) and ferric hydroxide:
𝐹𝑒 2+ (𝑎𝑞𝑢𝑒𝑜𝑢𝑠) + 2𝑂𝐻 − (𝑎𝑞𝑢𝑒𝑜𝑢𝑠) → 𝐹𝑒(𝑂𝐻)2 (𝑠𝑜𝑙𝑖𝑑)
𝐹𝑒 3+ (𝑎𝑞𝑢𝑒𝑜𝑢𝑠) + 3𝑂𝐻 − (𝑎𝑞𝑢𝑒𝑜𝑢𝑠) → 𝐹𝑒(𝑂𝐻)3 (𝑠𝑜𝑙𝑖𝑑)
The loose porous rust or Fe(OH)3 can slowly transform into a crystallized form written as
Fe2O3.H2O the familiar red-brown rust forming tubercles. This rust has limited solubility in
sea water.
2.1.2. Marine corrosion generates ferrous chloride
The deposition of salt particles on a metallic surface accelerates its corrosion, especially, as in
the case of chlorides, if they can give rise to soluble corrosion products rather than the only
slightly soluble products formed in pure water.
Cl− ions are abundant in marine atmospheres, Salt particles and droplets of more than 10 µm
cause corrosion when deposited on a metallic surface. For salt to accelerate corrosion the
metallic surface needs to be wet. The RH level that marks the point at which salt starts to
absorb water from the atmosphere (hygroscopicity) seems to be critical from the point of view
of corrosion. A high Cl− concentration in the aqueous adlayer on the metal and high moisture
retention in much deteriorated areas of the rust gives rise to the formation of ferrous chloride.
𝐹𝑒 2+ (𝑎𝑞𝑢𝑒𝑜𝑢𝑠) + 4𝐶𝑙 − (𝑎𝑞𝑢𝑒𝑜𝑢𝑠) → 𝐹𝑒(𝐶𝑙)2 (𝑠𝑜𝑙𝑖𝑑)
This is highly soluble in water than ferrous hydroxides leading to a higher corrosion rates.
Ferrous chloride hydrolyses the water and raises acidity of the electrolyte. This reaction feeds
for itself further corroding the metal.
𝐹𝑒(𝐶𝑙)2 (𝑠𝑜𝑙𝑖𝑑) + 𝐻2 𝑂 (𝑙𝑖𝑞𝑢𝑖𝑑) → 𝐹𝑒𝑂 + 2𝐻𝐶𝑙 (𝑙𝑖𝑞𝑢𝑖𝑑)
2.
CORROSION MECHANISMS ASSOCIATED WITH MARINE CORROSION
The different corrosion mechanisms that are directly associated with the marine environments
are Uniform or General corrosion, Pitting corrosion, Crevice corrosion, Galvanic corrosion,
Microbiological corrosion, Erosion corrosion, Fatigue corrosion cracking, Stray current
corrosion, Waterline corrosion, Weld corrosion, Coating related corrosion.
2.1. General corrosion
General corrosion is a uniform process and hence allowances can be given to the products by
proper calculation based on the amount of material being corroded during a particular period
of time. The environment to which the metal is exposed is also important. Uniform or general
corrosion usually occurs in stagnant or low flow seawater.
Table 1: General corrosion rates in marine environment
Material
Corrosion rate
Mild and low alloy steel (< 8% alloying elements)
10 microns per year
Stainless steels
less than 1 micron per year
Copper and its alloys
less than 0.01 microns per year
2.2. Pitting corrosion
Pitting corrosion is a form of extremely localized corrosion that leads to the creation of small
holes in the metal. The driving power for pitting corrosion is the lack of oxygen around a
small area. This area becomes anodic while the area with excess of oxygen becomes cathodic;
leading to very localized galvanic corrosion. The corrosion area tends to burrow into the mass
of the metal, with limited diffusion of ions, further pronouncing the localized lack of oxygen.
Addition of about 2% of molybdenum increases pitting resistance of stainless steels. The
presence of chlorides in sea water, significantly aggravate pit formation through an auto
catalytic process. Stagnant water conditions also favour pitting.
2.3. Crevice corrosion
Crevice corrosion refers to localized attack due to the contact with a corrosive environment.
It can occur between narrow spaces between metals or between metal and other non-metal
parts like gaskets. A concentration cell forms with the crevice being depleted of oxygen. This
differential oxygen content between the crevice and the external surface gives the crevice an
anodic character. This can contribute to a highly corrosive condition in the crevice. This type
corrosion always occurs in components where gaskets, washers, o-rings, fasteners and lap
joints are used.
2.4. Erosion corrosion
Erosion corrosion deals with the corrosion taking place on metal surface due to the removal of
the coating from the surface of the metal. Typically, erosion corrosion is greater with metals
that are exposed to seawater with higher salinity than to those that are in a brackish (lower
salinity) or fresh water. A more specific form of erosion corrosion that typically occurs on the
propellers of ships, impellers of pumps is caused by cavitation. The formation and immediate
collapse of vapour bubbles (cavitation) repeatedly hitting a particular location will often result
in surface damage on the propeller / impeller.
2.5. Microbial assisted corrosion
Microscopic bacteria can cause corrosion in marine environments in many ways. In some
cases a layer of slime can contain bacterial colonies which will consume oxygen and cause
low oxygen concentration area (anodic) on a metal corroding it rapidly. These bacteria may
also produce corrosive substances such as hydrogen sulphide, carbon dioxide, ammonia or
acids as part of their metabolic cycle. Such substances enter into direct chemical reactions
corroding most metals.
A special class of bacteria called anaerobic bacteria can exist in regions completely free of
oxygen. These anaerobic bacteria live by reducing available sulphate ions to sulphites, a
reaction in which iron can directly participate:
4𝐹𝑒 + 4𝐻2 𝑂 + 𝑆𝑂42− → 3𝐹𝑒(𝑂𝐻)2 + 𝐹𝑒𝑆 + 2(𝑂𝐻)−
2.6. Fatigue corrosion cracking
In many practical cases such as anchor chains and cables, the stress on metal surfaces is
cyclic, causing a gradual change in microstructure of materials over millions of cycles. Metal
fatigue cracking occurs regardless of corrosion. However when corrosion is present, it can
reduce the expected useful life of equipment by a factor of 10 to 1,000 depending on the
metal, stress and corrosion rates oinvolved
3.
FACTORS AFFECTING THE MARINE CORROSION RATE (BS-6349-1:2000)
3.1. Turbidity
Turbidity is usually caused by suspended clay or silt particles, dispersed organics and microorganisms. A lower water temperature increases the amount of sediment that can be
transported in suspension due to the viscosity change. The most rapid changes in turbidity
usually occur during dredging operations. Dredging operations can also cause the release of
harmful substances that are locked into fine sediment particles.
3.2. Marine life:
Many forms of marine organisms including algae, mussels, bacteria, barnacles and others
attach themselves to a maritime structure. The organisms can cause blockage of intake and
discharge pipes, impose or increase mechanical stresses, accelerate degradation, retard flow or
simply obstruct inspections for maintenance purposes. Methods of controlling marine growth
include the use of anti-fouling paints, scraping with the hand or mechanical removal by wateror air-jetting.
3.3. Pollution
The effects of water-borne pollution on the structure should be considered. Some trade
effluents, if insufficiently diluted, can accelerate the deterioration of concrete and steel. The
effect of oil spillages is usually benign with respect to structural condition, but the surface
coating makes inspection difficult. Pollution can act as nutrients or deterrents to bacteria,
significantly affecting microbial induced corrosion.
3.4. Salinity and Conductivity
The salinity of seawater is considerably higher than that of freshwater. The increased presence
of salts makes seawater an excellent conductor of electricity, and thus an ideal electrolyte for
electrochemical-driven corrosion. Increased conductivity means that corrosion rates in
seawater are considerably higher than those in other environments.
Furthermore, chlorides in seawater can also react with the passive films on metallic surfaces,
causing the film to break down.
3.5. Dissolved Oxygen
Corrosion rates are also directly linked to the dissolved oxygen content. Dissolved oxygen
destroys the protective hydrogen films on the metal's surface, leaving it open to corrosion
attack. The higher the concentration of dissolved oxygen, the faster the rate of corrosion. The
dissolved oxygen content in seawater is dependent on several factors, including seasonal
variations, biological activity, salinity and temperature.
3.6. pH Value
pH is indicative of the concentration of hydrogen ions in a solution. The lower the pH, the
more acidic the seawater, and the higher the concentration of hydrogen ions. Therefore, low
pH (acidic) waters accelerate corrosion by providing an abundant supply of hydrogen ions for
the electrochemical reaction. The pH in seawater is affected by several environmental factors,
including biological activity, respiratory behaviour of marine life, ocean depth, decomposition
of organic matter, etc.
4.
MITIGATION OF MARINE CORROSION
While seawater can be detrimental to metal metallic structures, piping, equipment; several
solutions can be implemented to control corrosion rates. These measures include, but are not
limited to:
4.1. Material Selection
The first measure that should be taken to minimize the effect of marine environments is
proper material selection. The ideal material should have the right balance between corrosion
resistance, mechanical strength and cost.
Additionally, the pairing of dissimilar metals should also be carefully assessed to ensure that
conditions for galvanic corrosion are not created.
4.2. Surface Treatment
Surface treatment, as its name implies, involves applying a medium on the surface of the
material to be protected to prevent corrosion or slow down the corrosion rate. Surface
treatment methods, such as coating or metal plating, form a protective barrier that prevents
corrosion-causing agents from coming into contact with the metal substrate.
4.3. Cathodic Protection
Galvanic corrosion can be intentionally induced in order to protect a more important metallic
component. It involves coupling a more active metal (lower on the galvanic series) to the
pipeline or structure to be protected. This active metal corrodes sacrificially and acts as a
sacrificial anode. Magnesium and zinc are most commonly used sacrificial anodes.
4.4. Insulate dissimilar metals
Electrically resistive non-metallic materials can be used to insulate two dissimilar metals.
This in turn breaks electrical connection or increase resistivity between dissimilar metals and
reduces potential galvanic corrosion.
4.5. Inspection and Preventive Maintenance
Scheduled inspection to remove microorganisms from structure surface extends life.
5.
CASE STUDIES
5.1. Failure of Cu-Ni 70/30 tubes of seawater cooled surface condenser
5.1.1. Preface and Failure Description
Surface condenser of a 43 MW captive power plant had a problem of repetitive failure of
90/10 Cu-Ni tubes. Seawater is used as cooling medium for condensing the turbine exhaust
steam. The condenser Mean Time between Failures (MTBF) was 3-4 weeks only and Mean
Time to Repair (MTTR) including leakage identification by helium leak detection, plugging
of leaky tubes, pneumatic testing and re-commissioning was @ 4 days. Plant disruption,
production loss, repair costs was annoying and frustrating. Eddy Current Testing (ECT) of
tubes was not effective as the required 85% fill factor for the ECT probe could not be ensured
due to internal fouling of the tubes. Chemical Cleaning of tubes was carried out with
Sulphamic Acid (H3NSO3) of 2.5 to 5 % w/w at a temperature of 45 to 60°C and time of 6 to
8 hours after achieving acid strength.
After the chemical cleaning, tube failure rate got increased with now MTBF being approx. 2
weeks only. A major capital expenditure was planned and all the 6360 nos. tubes were
replaced with an upgraded 70/30 Cu-Ni material and tube thickness increased to 1.2 mm from
earlier 1.0 mm. After giving satisfactory service for 82 days only, first leakage was reported
and failure rate increased to MTBF of 18 days within a span of 1.5 years.
ECT of 70/30 Cu-Ni tubes carried out and based on % wall loss and earlier plugging history,
total 59 tubes replaced with identical tubes and 60 nos. more tubes were plugged.
5.1.2. Root Cause failure Analysis
Metallurgical investigation of most prominent leaky tube was carried out with various tests
like macroscopic and microscopic inspection, dimension and thickness measurement,
chemical and mechanical analysis, Scanning Electron Microscopy (SEM), Energy Dispersive
Spectroscopy (EDS), etc.
The MOC of the cupronickel condenser tube was in line with the requirement of 70:30 Cu:Ni
based alloy – B111 UNS 71500. The tensile and hardness values are normal. The dimensional
measurements indicated 0.5 mm wall loss without any change in outer diameter. Thus the
anomalous thickness reduction was evident from seawater side. Visually, greenish colour,
loose and porous nature of scale was seen on inner surface.
Figure 1: ID surface of leaky Cu-Ni 70/30 tube and low magnification views
Figure 2: Tube sample a) As mounted- thinning from inner surfce visible; b)As-polished- thinning from ID in
the form of pitting (100X); c) As-etched- microstructure is worked grains of Cu-Ni solid solution, with pitting
from ID (100X)
Figure 3: SEM image on ID surface at puncture reveals micro-level metal dissolution indicating metal wastage
by corrosion
Under the deposit, crevices would form where corrosion initiates when the available oxygen
is consumed in formation of the protective film (cuprous oxide-Cu2O, cuprous hydroxylchloride- Cu2(OH)3Cl, cupric oxide-CuO) Due to deficiency of oxygen the under-deposit
corrosion continues. During the primary corrosion reaction, a cuprous oxide-Cu2O film is
produced that is predominately responsible for the corrosion protection. The corrosion
resistance in seawater thereby depends on naturally occurring formation of protective scale.
4𝐶𝑢 + 2𝐻2 𝑂 → 2𝐶𝑢2 𝑂 + 4𝐻 + + 4𝑒 − (𝑎𝑛𝑜𝑑𝑒)
𝑂2 + 2𝐻2 𝑂 + 4𝑒 − → 4(𝑂𝐻)− (𝑐𝑎𝑡ℎ𝑜𝑑𝑒)
𝑁𝑒𝑡 𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛: 4𝐶𝑢 + 𝑂2 = 2𝐶𝑢2 𝑂
The evidences thereby indicate that tube failures are because of the combination of pitting
assisted by MIC due to under-deposit corrosion indicating inadequate seawater treatment.
5.1.3. Remedial actions and benefits obtained
The sea water treatment was Azol based corrosion inhibitor + anti-scalent + oxidizing and
micro biocides. After discussing with various water treatment vendors, it was concluded that
the Azole is getting consumed by the chlorine used as oxidizing biocide and hence the
treatment was not effective. The deposit analysis confirmed the MIC theory as the sample was
majorly LOI and corrosion products.
Sea water treatment changed with a new halogen resistant Azole for most effective Cupro
Nickel corrosion protection. A Ca-inhibitor for scale and deposit control and ClO2 as
oxidizing biocide for effective control of sulphate reducing bacteria (SRB) were also
introduced.
In addition to the changes in the water treatment, many other treatments / care / precautions /
changes in SOP were introduced before the actual treatment in cooling tower basin.
Sea water is pumped through a flocculator and a tube settler (FeCl3 and Polyelectrolyte) to
remove the fine suspended solids. After this sea water is introduced to an intake tank where it
settles further and overflowing water is taken into second intake tank which is further pumped
to CT basin as make up water. Side stream filters introduced in cooling tower (CT) make-up
water to remove turbidity. CT basins and seawater intake tanks cleaned thoroughly and
cleaning frequency introduced. Earlier turbidity was 15 to 18 Nephelometric Turbidity Units
(NTU) based on seasonal variations. It has improved to 4 to 6 NTU now due to above efforts.
This is definitely helping in reduction of scaling and growth of bacteria.
TBC and SRB monitoring started on regular basis which was not there earlier. This helps in
adjusting the biocide treatment as required.
Corrosion coupons of identical (Cu-Ni 70/30) material introduced in the CT basin and regular
monitoring of corrosion rates introduced to give early warning. Rate of corrosion reduced
from 10-12 micron/year to 1.5 microns per year with the changed water treatment as well as
effect of other changes.
A small dummy condenser with identical tube material and tube size was introduced in the
system for monitoring its corrosion and to relate the same with main surface condenser.
With all the improvements above, rate of failure of tubes got drastically reduced with MTBF
increased from 18 days to more than 180 days. With replacement of most affected tubes as
identified by ECT and initial passivation treatment, more improvement is expected in MTBF.
5.2. Marine corrosion of jetty structure and rehabilitation
5.2.1. Introduction and history of Jetty structures
This case study is about an “Open Sea” jetty constructed in 1992 without a protective break
water wall. It comprises of two breasting dolphins and four mooring dolphins. The jetty is
utilized for import of liquid and liquefied hydrocarbons like Ethylene Dichloride (EDC),
Ethylene, Vinyl Chloride Monomer (VCM), LPG, Methanol and it is designed to handle
tankers up to 20,000T dead weight tonnage (DWT). The jetty subjects to extremely
aggressive marine environments of extreme humidity and salinity, severe tidal and wave
action. During monsoon periods (15-May to 15-Sep) ships could not be berthed due to rough
sea conditions. This jetty had faced a severe cyclone in 1996 causing a substantial damage to
the jetty. The approach beams to the mooring dolphins got entirely washed away and main
approach got laterally shifted by 0.6 mm. During strengthening /repairs the width of the jetty
was increased by provision of extra piles below including an array of raker piles. Over the
years corrosion deterioration of the beams, deck slabs, and severe corrosion of sacrificial
liners on the jetty piles, cracks in slabs and columns of dolphins were observed and it was
decided to go for detailed corrosion assessment. Based on inspection findings, rehabilitation
and strengthening was undertaken to extend the working life of the jetty.
Figure 4: Jetty layout
5.2.2. Details of Inspection and nondestructive testing (NDT)
Initially visual survey was conducted to identify the location, extent and intensity of
•
•
•
•
Corrosion and stress induced cracking due to chemical attack on reinforcement from
various deterioration causing chlorides, sulphates, carbonates, etc. in solution
Exposed reinforcement
Bulged / depressed region of concrete
Concrete spalls and porosity
Following NDTs were carried out on pre-marked grid spot locations and on core samples –
Table 2: NDT Details
Sr
Test
Purpose
1
Rebound hammer
To verify the soundness of the structure and comparative strength assessment
To detect internal cracking, honeycombing and voids in concrete
2
Ultrasonic pulse velocity
(USPV)
3
Corrosion testing
4
pH gradient on drill dust
sample
5
Chloride profile test on
drill dust sample
6
Surface carbonation test
7
Carbonation depth test
on drill dust sample
To identify the depth of penetration of aggressive chemical based deterioration
8
Concrete core extraction
To obtain in-situ compressive strength of concrete and further check
permeability, chemical and physical analysis
9
Chemical Analysis of
core samples
To determine the active chemical ingredients present and ingressed in the
concrete such as sulphate, chlorides, admixtures, etc.
10
Physical Analysis of
core samples
To find out cement content
To identify the degree of existing corrosion in reinforcement
To ascertain degree of acidity / alkalinity in the concrete. Concrete
reinforcement loses its passivity occurs at pH of 10
To find out chloride content (cast-in and introduced from external environment)
To identify onset of carbonation based deterioration mechanism in the concrete
5.2.3. Findings and Recommendations
West dolphins face direct sea waves and cracks, surface porosity, delamination is observed in
visual inspection to a higher extent.
•
•
Mean strength of concrete predicted by rebound hammer test is more for piles on East
side than those on West side.
Concrete quality is generally good with a mean value of USPV 3.6±0.1 km/s. However
there is more variability in USPV for pillars on the West side dolphin.
Figure 5: West side dolphin-column C-2; a) Re-bound hammer test b) USPV test
•
•
Ingress of chloride ions on the surface concrete is higher than that observed at the depth
of steel reinforcement. The threshold limit can be considered as 0.2% Cl- by weight of
concrete. At the surface the values are exceeding 0.25% indicating continuous ingress of
chlorides from environment compared to insignificant locked in chlorides.
The core concrete is highly alkalined. It is observed that up to the depth of 25 mm, pH
value is below the threshold value of 10 to 11. The steel is passivated at pH of 12 to 13.
Figure 6: West side dolphin; a) Chloride profile, b) pH profile
•
•
Threshold limit for sulphate content is 0.4% by weight of concrete. The value exceeds in
few of the columns indicating definite ingress of sulphur up to 3 to 10 mm depth.
The value of percentage cements content in concrete lies between 13 to 18% and is
definitely above the requirement of 12%.
Figure 7: For different cores of the dolphins, value of a) Sulphate content and b) Cement content in concrete
Overall there was ingress of salts and carbonates in the RCC structure to a great extent
causing further acceleration in the corrosion deterioration in the reinforcement of the cracked
columns and slabs. The overall health was assessed to be at the Onset of Rapid rate of
corrosion. This threshold had arrived at 30% of the time of expected for it. It was decided to
go for rehabilitation and strengthening of the jetty structures in a phased manner to extend
useful life of the jetty.
5.2.4. Strengthening and Rehabilitation
Following procedure was followed for strengthening and rehabilitation of jetty structure
including main approach piles, breasting and mooring dolphin pillpilears, main beams and
cross beams, etc.
•
•
•
•
•
•
Chipping off damaged and loose concrete till reinforcement
Cleaning of reinforcement by water jet and buffing, application of Zn primer
Provide sacrificial anodes on the reinforcement steel to prevent further corrosion
Provide underwater micro-concrete to rebuild the affected area by shuttering
Application of glass fibre wrapping for the newly concreted surface.
Polyurethane coating above the glass fibre wrapping and application of protective coating
Figure 8: Marine corrosion of jetty beams; a) Spalling of concrete, b) Corroded reinforcement
Figure 9: Jetty beams treatment of the reinforcement; a) During treatment, b) After treatment
Figure 10: Glass fiber wrapping to the beams; a) During application, b) After completion
Figure 11: Jetty beams and piles after protective coating application
6.
CONCLUSION
The chemical reactions responsible for the corrosion of structures, equipment and piping in
marine environments are predominantly electrochemical in nature. The type and rate of the
resulting corrosion are dependent on several factors, including salinity, electric conductivity,
pH and dissolved oxygen levels. Seawater being particularly aggressive towards metals, a due
care need to be taken during the design stage like studying the various parameters of the
marine environment and their extreme condition, selecting proper materials, surface area,
surface treatments, coating, deciding on cathodic protection, inspection and preventive
maintenance program, etc. These specific measures if put in place can ensure that the
infrastructure functions safely and effectively in a given marine environment. It is always to
be kept in mind that in want of such considerations a huge maintenance and repairs costs to
the tune of 10 times the original protection costs need to be incurred.