.
Hello everyone, today we will start our first
lecture on this course corrosion. This is
a MOOC course a 20 hour course and ah 8 week
ah this course will be this course lectures
should be floated. And I will be giving the
lecturers and in addition to that there will
be three t s teaching assistants available
to respond to your queries as well as ah the
problems what will be given to you, they will
be the first interface ah with whom you will
be interacting for those solutions as well
as ah if you have any queries table respond
and then of course, I will be also be available
all the time .
This three t s are mister P K Rai mister N
K Prasad and mister B Bhushan and interestingly
this all three t s are in their advance stage
of PSD and they are all doing in corrosion
related topics .
Now, as I have mentioned in in my introduction
that corrosion is a very very important subject.
And it is to be understood carefully and we
need to spend little time on this and also
we mentioned that there are scientific aspects
of corrosion, were electrochemistry is is
to be known is to be understood. But there
are many engineering aspects to this materials
corrosion, where you would be seeing that
many other factors like compositions of metals
and alloys ah design of components then environmental
factors like oxygen concentrations and H 2
O presence; that means, moisture presence
as well as sometimes you would see that the
stress also plays major role .
We will go gradually one by one two different
aspects of corrosion , but today we will have
a kind of ah history ah that why we should
study corrosion. And also you would find that
ah there are some aspects which lead to kind
of catastrophe and if we do not understand
corrosion properly, ah we would not be able
to protect our structures, which are made
out of metals and alloys from corrosion and
finally, from premature failure .
Now, ah before we got into the subject, I
would like to ah put up some of the corrosion
books with are good books, and of course,
other books are available thousands of books
are available, there are materials available
in internet you can Google anytime, and try
to get as much as you want from the literature
as well as from internet .
So, this books are just for reference, you
can find any other books because the aspects
of corrosion is same whether you follow this
book or that book. It depends on how it is
a presented in that particular book , but
still I have put some books. In addition to
that you would find ah some of the lectures
in YouTube ah as well as ah as I mentioned
that in this course we will also explain some
of the intricate matters related to corrosion.
Now, coming to the subject directly. ah This
slide is actually if you see this slide this
slide is ah related to some of those is basically
showing some the common features of corrosion.
Now ah in day to day life, every direction
if you look at you would find examples of
corrosion. I start with ah let us say ah our
utensils our a household goods, you will find
that ah many a times ah household goods like
ah scrubber or kind of a this spatulas those
are corroded heavily .
Even ah for example, the first picture if
you see the first picture this picture if
you see, this picture is related to the corrosion
of bolt, ok you see this entire part is so,
heavily corroded. This is the bolt part and
this is the nut part nut is also corroded,
this is commonly observed feature .
Now, another commonly observed feature is
ah if you consider ah overhead structures
beams, this is the overhead structures and
beams ah they are also heavily corroded. And
corrosion always it comes with the different
colour ah most of the cases and many a cases
you do not find any signature of corrosion,
but still it happens and those cases are more
deadly than ah any other cases, where you
have a kind of signature in the form of colour
change .
Here you have ah the basically red rust which
is forming, which is a typical feature of
iron corrosion. These are either a hydrated
ferric oxide ah the ferrous ah ferrous of
ferric ions are containing over there, and
this is this happens because of the presence
reaction with oxygen and moisture ah in the
environment, this is basically a atmospheric
corrosion . Again if you see this kind of
ah structure, which is a basically a kind
of beams as well as a kind of bridge also
you will find this kind of corrosion .
If you can see that ah the entire material
is out, ah and the kind of thickness what
it had this being physical initially it it
was basically this much thickness and now
it has reduced this parti ah this particular
section has reduced. That means, ah initially
it is to ah it it was designed ah to carry
some load, now since the cross section has
reduced of course, it will not be able to
follow that particular load it will not be
able to carry that load at some point of time
it will definitely fail. And when this metallic
structure fails it fails catastrophically
without giving any signal that it is failing
.
Now, a typical ah corrosion features like
this, if you see this this is a kind of pipeline.
ah I also ah relates to the ah safety safety
of ah people walking around that . Now, if
it is a pipeline, now if it carries oil and
if suddenly this kind of failure happens,
it might catch fire or any other things and
then it there could be explosions. Now kind
of ah a failure here if you see, this is a
kind of pipeline which carries water. And
then with the pipeline corrodes and finally,
it leaks ah before one could rectify and then
finally, stop that leak ah you lose lot of
water.
And of course, if you see this kind of situation,
where ah those corroded products even if the
if it is carrying some kind of a liquid which
contains ah heavy metals and other stuffs
like what we have in chemical factories. If
it leaks if that wall leaks it will leave
that particular liquid into the ah environment
in the into the soil and that soil is contaminated
ok ah.
For example ah if some sections some in if
ah for example, in Kanpur specially, ah in
ah it is basically a belt where lot of ah
ah this ah tanneries are there ok . So, the
tannery ah the this particular this particular
ah kind of liquids, it it lead to the environment
those liquid contains lot of ah hm not so
good metals . So, its also leads to environmental
hazards . So, ah this kind of corrosion ah
we can see these are all ah visible ah naked
eyes .
Now, if you consider this kind of corrosion,
which is basically related to a corrosion
of ah tooth fooling. Tooth filling ah this
is also corroding, ah ah this is also not
good ah if some metal is put up and then ah
if it goes out again it leads to a health
hazard .
Now, this is a typical ah corrosion failure
for example, in this zone, ah this is a kind
of broken bone which is ah locked which is
connected by screwing and putting a rod. And
now if a this corrosion product is accumulating;
and when this kind of attachment is fixed
to the bone to the broken bone finally, its
function is to carry load. Now if there is
a corrosion product, it becomes weak now it
will no longer hold the load and it will fail.
And when it fails, again if the person has
to go and sleep on the operation table ok.
So, in other ah invasive surgery and a kind
of trauma and other things other pains ah
those that person has to be here ah for another
time .
So,. So, corrosion see these are actually
some of the pictures are taken from internet
, but in the internet you just put this particular
buzz word corrosion and damage or corrosion
accidents, you will find thousands of example
.
Now, ah let me put up some ah small small
examples like you might find in the ah though
it looks a little awkward, in the urinal you
will find that a ah some ah kind of water
connections, there you will find that ah the
top this nuts are little shiny , but ah the
base of that particular metal with the connector
ah is corroded heavily. Now the question is
ah people always put nuts in the form of a
kind of a better metal, which has little bit
of extra corrosion resistance. And that particular
connector the small rod connector connects
this particular nut to the ah main pipeline
source. Is of a a poorer great metal I would
say compared to that ah nut material ah .
Now, this I am telling poorer great means
ah with reference to the corrosion resistance
of those metals. Now that case a kind of corrosion
happens which is called galvanic corrosion,
and there the connector which actually takes
water pipeline to the ah to the pipeline ah
inside the ah bathroom ah that gets corroded
and leakage happens . So, this kind of stuff
many a times happen in our day to day life
.
And for example, another example I can sight
ah let us say ah water ah sink ah this ah
kitchen sink. Kitchen sink sometimes we find
that ah at the corners we do get little bit
of a kind of small small ah dots like ah appearance,
which are nothing, but pits and over the time
this pit grows and then there is a leakage
.
Another example ah water storage tank. Now
water storage tank the typical ah failure
point is ah in the corner positions, at the
at the bottom corner you would find that leakage
is taking place from there . So, that actually
relates to another kind of corrosion which
is ah called crevice corrosion . So, those
everywhere you will find corrosion .
Now, some of the cases you would see if some
construction is taking place. Sometimes people
ah do construction and then they form the
beam and that beam is half cooked beam, I
would say that half is made the half is ah
exposed; that means, all those reinforce birds
are ah exposed to the environment. And you
would find that ah that beam during the rainy
season that beam will become a kind of reddish
appearance, because that red rust what is
forming on the expose reinforce spurs those
are trickle down and then it will make the
beam colour reddish ok. This particular nature
is always ah visible ah if you look around
Now, ah coming to your house, ah sometimes
ah if it is old house and if there is a problem
of seepage. You would see after ah little
ah if you if you if you see a for a longer
duration of time, the corners or say where
the seepage is more you would see that the
cement is that particular concrete structure
as if its solemn ok and you will see the peel
off of that particular a concrete ah ah pots.
And after sometime you might find that the
reinforce bar is also exposed.
And the reinforce bar if you see carefully,
ah its a kind of a flect reinforce bar the
reinforce bar if you see in the raw condition
you will find that its nicely ripped a reinforce
bar ah with a little bit of red rust, but
otherwise its fine. But over the time inside
the concrete that red rust is forming and
that red rust has got a higher volume than
the metal so; that means, that particular
concrete ah reinfore rebar, which call reinforce
bar the rebar is confined in the concrete
structure .
So, when that corrosion is taking place in
the rebar, its getting solemn because of that
rust formation and rust has got higher volume
it gives huge pressure on the concrete. And
since concrete has got a very very small ah
elongation, so, at some point of time concrete
starts cracking and then it falls off. And
in fact, that makes the structure extremely
vulnerable to failure; even it happens in
bridges old bridges you will find that some
places the ah rebar is exposed. ah Though
it was initially confined in a concrete, but
over the time this concrete is getting spoiled
off and then finally, the rebar is exposed
. So, those are kind of examples I am putting
up .
So, these examples though you would not find
that significant , but if we if we see some
of the data you will see that yes it is a
significant and we need to see that how to
stop them. And in order to stop those we need
to know how corrosion takes place . So, I
when I know the reason then we can attack
some problem .
So, let us see a a kind of accidents that
can that have taken place due to corrosion.
So, these data I am I have put ah Aloha incident
Bhopal accident ah Carlsbad pipeline explosion
all sort of examples I am I I am putting . So,
this you can also find out in this particular
website, its basically called corrosion doctors
dot org, there you can get the history of
this particular ah failures there are other
failures also , but here its nicely ah recorded
.
Now, in those cases the accidents many a times
took life ok. Also ah if something breaks
something fails for example, a silver bridge
1967, it broke down and there are lot of ah
economy loss life loss finally, the connection
is lost and then again you have somebody has
to rebuild it so, those cost needs to be considered.
And in fact, these particular failures all
of though cases the corrosion is one of the
major causes major cause .
Now, if I see some of the pictures) for example,
this picture this is a kind of oil vessel
Erika, this failed due to corrosion. ah This
is a major reason ah that this failed this
broke into half actually. Now this is ah the
kind of failure I was talking about this is
a silver bridge silver bridge failure, ah
and ah I think ah its it happen in 1967. And
again if you come to see this part this particular
situation, ah this is high temperature oxidation
failure of aluminium steel heater tubes .
Now, here also since steel heater tubes, now
here also since it is mentioned as oxidation
later you will see that oxidation is also
a kind of corrosion ok . So, this kind of
failure I am just giving an example for sake
of understanding that yes it can lead to a
serious accident .
Now, a coming to cost ok ah we do see lot
of losses. For example, the USA its basically
I could find 1998 data, it says that the cost
of corrosion means at the loss of money loss
ah loss of money due to direct as well as
indirect ah loss. I will come to that direct
as well as indirect loss 260 billion dollar
its not a small money, its 3.1 percent of
ah g d p of that particular country .
Now, in India ah I have put two data, one
is a ah this data which is 2012 data 2 lakh
crore ah rupees and this is in the form in
in rupees. Then in 2016 data ok this is a
kind of a data what we have the 6 lakh crore
so; that means, 2012 to 2016, ah we have for
the increase in loss of money due to corrosion
is of the order of around ah 300 percent ok
its a quite a bit actually. Then its also
the 4 to 5 percent GDP of a our country, which
is almost two trillion dollar economy . So,
its a quite up quite a bit of loss .
Now, direct cost is basically us data infrastructure.
Infrastructure when I am talking about direct
cost, this will be the failure of infrastructure
bridge, buildings, utilities then transportation
of course, transportation railways. If you
have noticed railways and also you can find
some of the pictures in the internet, that
sometimes ah if you see the goods train ok.
In beach vizag I will show later some of the
pictures in vizag sometimes a one picture
I have I will show it later .
Ah One goods train ok was stranded for ah
almost two months there was waterfall. And
that entire bogie was full of with water and
it was looking like a small swimming pool
. So, now, you imagine, if it stays for longer
duration how much corrosion it can take place?
And then finally, what happens you have to
throw that particular bogie and its a loss
of money.
Then a production and manufacturing around
17.6 billion, government expenditure point
20.1 billion, total around 137.9 billion.
Indirect cost is a kind of cost of labour
attributed a corrosion management activities.
For example, ah let us say painting ok time
to time we have to paint the ah structures
in the factory ok . So, for that you need
to spend money on paint, you need to spend
money on the manpower because somebody is
to be there, to paint that particular structure
. Then cost of equipment required because
the corrosion related activities ok. Of course,
corrosion related for example, there is one
corrosion protection system which is called
cathodic protection or anodic protection you
need to monitor ok instruments that how good
is that particular corrosion protection . So,
that also needs money ah.
Loss of revenue due to disruption in supply
of product for example, the bridge is broken.
And once the bridge is broken then next at
least 2 3 months the supply chain is broken
. So, its also loss of money of course, the
loss of cost of loss of reliability and it
is not mentioned here, there is nothing important
other than life there will be life loss ok
. So, this is a kind of data what I am showing
. So, we have to study corrosion .
Now, coming to as we have mentioned about
all those losses, kind of accidents kind of
examples, what we have put for till now that
there are corrosion incidents everywhere every
direction. Now coming to material degradation,
material degradation something degrades and
every structure everything what we have to
do with the material ah.
Mechanisms of material degradation and the
characteristics of the economically significant
forms of damage to the material are discussed
in terms of the physically and chemical process
involved. Yes there will be physical features
there will be chemical process. For example,
one particular example of physical features,
let us say ah ah a kind of a a structure we
have built. Now if their for example, in a
stormy areas, where we have lot of storms.
If there are sand particles and if that sand
particles hits any structure it will always
erode its not corrosion, but it erodes ok
that is also a kind of loss of material is
a material degradation .
Now, ah coming to railways ok in the railways
ah there is one form of loss of material is
wear ok because wear happens when two bodies
are in contact, and due to friction ah some
part of the material is lost ok. So, there
will be a thickness reduction and finally,
you have to discard that particular product
particular particular material, and you have
to replace that material with a new one .
So, by direct mechanical action of course,
this wear; where you have ah kind of relative
action a between two bodies and which are
in contact. Heat or radiation of course, heat
does play a major role. Radiation of course,
for example, radiation damage one particular
radiation damage is in nuclear applications.
Radiation does lead to a kind of a a loss
of a material properties ok. We will come
to that it can lead to a a kind of void formation
in materials. By [preseme/presence] presence
of chemical reagents yes there are chemical
reactions there are electro chemical reactions
.
Now, we would concentrate on electrochemical
reactions not chemical reactions of course,
when we talk about electrochemical reactions,
we would also consider couple of things. ah
For example, if we try to see iron corrosion,
and that iron corrosion you will see that
iron is corroding in the form of electrochemical
reactions , but there there could be other
aspects other reactions, which will be coming
along with that electrochemical reactions
. So, our interest would be mainly in this
particular sections .
Now, if we see all three by direct mechanical
action, by heat or radiation, by presence
of chemical reagents, there could be combination
of two or more or all three could be present.
For example, erosion corrosion, this is a
classic example of combination of all three
. So, sometimes we for example, in heat exchanger.
Heat exchanger ah the hot air is being cooled
by water ok . So, this water when it is flowing
it takes the heat .
Now, when it flows, it could also lead to
erosion on the pipeline and at the same time
this water also contains little bit of ah
chemicals which can lead to chemical attack
on the surface in the form of chemical reaction
or electrochemical reaction so, there will
be material loss . So, those kind of situation
for example, mechanical action and chemical
reactions. Classic example is fritting action;
in the fritting also we have mechanical action
as well as corrosion action ok .
So, this combination can also lead to material
degradation fine . So, we would look at more
in a in a greater detail on this part electrochemical
reactions or rather electro chemical degradation
which is nothing, but corrosion .
So, as we understand till now that, first
of all we need to study corrosion and when
you need to study corrosion we have to also
see the features of corrosion, we also need
to see k the reasons of corrosion, we also
need to see how we can tackle corrosion . So,
if we have all three combined then we can
become the successful corrosion engineer.
Thank you .