MICROBIOLOGICALLY

INFLUENCED CORROSION

(MIC)

Presented by

Nikhil Koshy Jacob

ME – Industrial Metallurgy

14MY33

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INTRODUCTION

Corrosion which takes place with the participation of some

special kinds of microorganism on a metal surface is called

microbiologically influenced (induced) corrosion (MIC)

MIC occurs on a metal surface in the presence of a suitable

environment and conditions which help special kinds of

microorganisms to participate in corrosion

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The bottom of a crude oil storage tank after a microbial attack

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EXISTENCE OF MICROORGANISMS

The various microorganisms include bacteria, fungus,

algae etc

Estimation of bacteria quantity on the Earth gives a

value of 5 million trillion of trillion (5 with 30 zeroes)

Today we are familiar with various microorganisms

which live and grow in the environment at pH = 0 to 13,

at temperatures between −15to +150◦ C, at pressures

up to 1,000 bar, in aqueous solutions with different salt

content (from pure water to the Dead Sea – 26% of

salts), in oils, in fuels etc4

STRUCTURE OF A BACTERIUM

A rigid cell wall completely surrounds the bacterium and lies

outside the membrane.

Flagellum is a long filamentous appendage that propels

bacteria.

Pili are thin protein tubes.

All bacteria need nutrients– the substances that bacteria

consume for their existence, growth, and reproduction. These

nutrients are carbon, nitrogen, sulphur, phosphorous,

inorganic salts, and trace metals. 5

STRUCTURE OF A BACTERIUM

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Motile bacteria can swim along a chemical concentration

gradient towards a higher concentration of a nutrient, and this

movement is called chemotaxis.

Bacteria usually reproduce through binary fission, budding,

chains of spores, and through the segmentation of elementary

units, shortly, in asexual processes, in periods lower than 20

minutes. A single cell and its descendants will grow

exponentially to more than 2 million cells in 8 hours

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CLASSIFICATION OF MICRO ORGANISMS

Usually they are classified into three groups: aerobic,

anaerobic, and heterotrophic

Aerobic microorganisms use oxygen in metabolic processes.

Anaerobic microorganisms grow in the environment without

oxygen

Heterotrophic microorganisms are those which can exist and

grow both with and without oxygen

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MECHANISM OF CORROSION

Here is a scenario how three major kinds of microorganisms

capture the surface of metal.

Probably, the trace of organic compounds and other nutrients are

the first substances adsorbing on the metal surface and form

“conditioning layer” for the attachment of microorganisms.

The heterotrophic microorganisms usually settle on the first.

Some of these cells adsorb to the surface for a finite time, and

then desorb. This is called reversible adsorption. Some of the

adsorbed cells form dense formation and become irreversibly

adsorbed.

There is no or only a low oxygen concentration underneath.

Conditions without oxygen are convenient for the growth of

anaerobic microorganisms under heterotrophic ones.

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Aerobic microorganisms settle above heterotrophic ones and are

close to the media (water, crude oil, fuel, etc.).

Thus, anaerobic microorganisms are arranged the closest to a

metal surface.

Certainly, aerobic and heterotrophic microorganisms can

separately settle on a metallic surface, form biofilm, and play, in

this particular case, an essential role in the corrosion of metals.

The development of a mature biofilm may take several hours to

several weeks, depending on the system

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Biofilm containing anaerobic, heterotrophic, and aerobic microorganisms

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A large quantity of microorganisms form bio fouling(biofilm)defined with the naked eye and they are slippery to the touch.

They choose metal surfaces as a place to live and form biofilm with thicknesses from several microns to several centimeters.

Biofilm consists of microorganisms and substances (mainly products) of their metabolism. The latter is the sum of chemical reactions that take place within each cell of a living organism and that provide energy for vital processes and for synthesizing new organic material.

Bacteria in biofilm excrete extracellular polymeric substances(EPS), or sticky polymers, which work as glue and hold the biofilm together and cement it to the metal surface.

BIO FOULING (BIOFILM)

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EPS is called glycocalyx, which serves for trapping and concentrating

nutrients from the water, and acts as a protective coating for the attached

cells.

Because the glycocalyx matrix holds a lot of water, a biofilm-covered

metal surface is gelatinous and slippery.

More than 99% of all microorganisms live in biofilm communities.

Microorganisms adhere to carbon steels, stainless steels, and polymers

(Teflon, PVC ) with almost equal “enthusiasm” within 30 seconds of

exposure

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Bio fouling in carbon steel pipes14

CLASSIFICATION OF CORROSIVE

MICROORGANISMS

It is convenient to divide all microorganisms taking part or influence corrosion into five groups:

Sulphate Reducing Bacteria(SRB). They are anaerobic and play an important role in corrosion of metals.

Microorganisms producing acids.

Microorganisms which oxidize ferrous (Fe2+) and manganese (Mn 2+) cations.

Slime-forming bacteria.

Methane (methanogens) and hydrogen producing bacteria.

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MICROORGANISMS CAUSING CORROSION

SRB

Desulphotomaculum

Desulphovibrio vulgaris

Microorganisms producing acids

Thiobacillus Thiooxidans

Bacteria oxidizing cations Fe2+(iron bacteria) and

Mn2+

Galionella,Sphaerotilus

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PREVENTION OF MIC

Changes of conditions in the system

Aeration, if anaerobic bacteria are responsible for MIC,

or agitation in order to prevent stagnation conditions.

Mechanical scrubbing or scraping, and high-pressure spraying

are also used

Use of coatings

Anti-fouling coatings of two types are mainly used. The

first one contains biocides [sodium hypochlorite (NaOCl),

calcium hypochlorite{Ca(ClO)2}, chlorine dioxide (ClO2)]

which are released during the lifetime of the coating and which

discourage the settlement and growth of microorganisms. The

second type presents a sufficiently smooth surface to which

microorganisms cannot attach.

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Boiling of water

It is one of the ancient disinfection measures. Many

bacteria may be killed at 100◦C

Use of ultraviolet (UV) light

The rays from the sun contain the UV spectrum used in

UV water treatment against microorganisms. In order to kill

microorganisms, the UV rays must strike the cell and the energy

penetrates the outer cell membrane, passes through the cell body,

and disrupts its nucleic acids, thus preventing reproduction.

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o Use of ultrasound

It consist of two mechanisms . The first mechanism produces

conditions of cavitation (hammer of water), which causes cell walls to

break resulting in cell death. Cavitation is the process of formation and

collapsing of Bubbles.

The second mechanism is based on the apoptosis, or “dance of

death”. As soon as the cells are exposed to the ultrasonic waves, they

loose their ability to reproduce and will slowly enter into a dying phase.

In other words, the ultrasonic waves induce microorganisms to commit

suicide through a cascade of biochemical, physiological and

morphological changes in the cell with membrane rupture

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REFERENCE

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THANK YOU

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