 Welcome to IIT Bombay and welcome to this course on Atrocious Corrosion and Control. Here the courses are most likely to be more interactive and object oriented course. So, you are not going to have too much of you know routine and factual information. So, other than you focus on the fundamentals of the subject. And this course all of you know is an Atrocious Corrosion and its control. It is a postgraduate course mainly taken for MM4 we call it Corrosion Science and Engineering, but the students from other disciplines within the department outside the department they do take this course. To briefly introduce myself I work in the area of Corrosion Science and Engineering. I give quite a bit of focus on electrochemistry and corrosion. You will see later how important it is to understand electrochemistry and corrosion there is quite a bit of interrelation between these two. Then I also look at corrosion mechanisms at the atomic level, microscopic level related to materials of course. I have wide range of interest in materials mostly metals and alloys. And we do some work reporting off late we have been focusing quite a bit on stress corrosion cracking. You will see later that stress corrosion cracking is a very important subject for any materials integrity ok. Yeah. So, this course today lecture is basically to introduce you to subject of corrosion. And to give an outline about what we are going to cover in this particular course. We are also going to discuss an outline what are the evaluation method that you do for grading the students. So, that you get a clear idea about how to proceed how to prepare for the course. However, I would like to say that do not prepare for the course for the sake of grades I think that is not going to help you in the long run ok. What is going to help you in the long run is what you have understood. So, that you can apply them in the field. And for that you need to understand the science and you need to understand the technology. You need to understand the relation between the science and technology. And how many of you have seen corrosion problems or failures? How many of you have seen one or two? I thought everybody raise the hand you know not seen at least you see the newspaper that the bridges collapse and so and probably it attributed to corrosion ok. They may or may not. And rustling is quite common right. I think rustling is quite common you might have seen steels being used for various purposes. It is a very very extensively used material for various applications like be it a fence, be it a reactor pressure results or be it a transportation sector, pipelines steel is very common. And steel of course, all of you know that is rust ok. But then if you rub it off and you see that everything looks fine you know it is not really a problem. But it is not really that problem it is much more. The corrosion is just not confined only to steels it is confined to all kind of materials which are made by own being you see that rustling. So, before we start discussing about corrosion probably you should know what is corrosion? And why does the corrosion occur? These are the primary question that haunts everyone's mind and you like to know the answer for that. And this not the answer a clarity is required actually. What exactly mean by corrosion? What is the clarity in that ok? Now corrosion why it becomes important because you have seen wherever that is a material that you have ok materials without material there is no civilization right. It is used for you take a mobile to take a laptop or ok how do you go to anywhere I think ok. Material of construction is the important one for human civilization. So, these materials are used for various engineering applications when they come in contact with that we call environment here ok. And they start interacting with each other leading to what is called as corrosion process. But these materials are just not freely hanging you know it is not like I have a beaker I have put soaring chloride in that I have hang a sample it is not. These materials are for structural applications right they may carry carry a load could be a tensile could be a fatigue or it might be a container to store a sulphuric acid for example, still it is applying certain pressure. So, the materials are designed for certain function that the very design itself alter the course of corrosion. So, there is a change in the way the corrosion occurs that is why we always worry about design and try to relate the corrosion of a reactor or a system to the material the design and the environment. This actually is a failure it is just fails it does not function. Can you then say whatever component that you see is failed for example, can you say it is due to corrosion? What are the failures that you are aware of? Can you tell me and talk about the structural failures right what are the failure yeah. Yeah it could be a simple overload failure you know I simply apply a load beyond the ultimate tensile strength the metal deforms and it fails not necessarily corrosion it is not necessary or you heat the material beyond the melting point or whatever it fails ok or you have simply wear and tear it fails. So, not all the failures are related to corrosion no it is not. So, it is it is not it is not correct to control that corrosion is the only the mode of failure. Corrosion is one of the modes of failures, but of course, it is a predominant failure that happens in various industrial components that you see that. Now, then how do I really define that? The way to define here I made it very simple you can have your own way of defining things. I just told you you need to rewrite the way you think this definition is the I have written my way and way of writing it actually. So, when I say corrosion you need to have a material and you should have a chemical environment coming in contact with the only when the metal fails we call them a corrosion failure. I can have a plastic failure taking place because of gamma radiation right, but it is not a corrosion failure a physical failure. So, I need to have a chemical environment that is the primary requirement to call the failure as corrosion. So, that is very important you need to understand. Why does it important? Because the failure leads to loss of materials there are several definitions the loss of materials if it fails there could be casualties can happen. Primarily if you look at from operational point of view there is a loss in the function of the component. When I say the function of the component it is very important to realize that it is not necessarily it leads to leak it is not necessarily should I have a crack still there can be loss of function. I give two examples anybody for mechanically getting back around here ok. You know about the heat exchanger right. The heat exchanger it exchanges heat between two fluids to be a gas or to be a liquid and you have a cell side you want liquid and the tube side is another liquid and you transfer the heat. Assume that there is a corrosion very small amount of corrosion leads to scale formation. Scale is a thermal insulator. Structure it takes all the load no problem, but the exchanger is not functioning because of corrosion leading to loss in the thermal conductivity of the component. I give an example other one which you are more familiar with right. You have seen lot of electronic gadgets right you have pins connectors you have and if there is a small rust and you put the connector what will happen the current will not pass so easily there will be resistance it is ok, but it losses function. So, corrosion when you talk about is not necessarily a structural failure any loss in the function efficiency of the unit that you talk about that is a concern for us. But that problem should be as a result of corrosion and the corrosion is coming because of what? Because of the material interacting with the environment. So, the definition of a corrosion should be should encompass all this whatever way you write it whatever way you want to convey it ok. The chemical environment is key material is other key and the loss of function is the other important key the definition of what corrosion means is. Now, why would the metal corro? It is a question that happens to us most of us. It is not equilibrium with the nature it is a very very nice question nice answer I would say it is not equilibrium with the nature. Now, most of the metals and alloys that you deal with you know can you tell me example of what are the alloys used for structural applications yeah. Right. Be a little louder. Steel is one, aluminum is other one, magnesium titanium. What is common to all this material? The common because it is a man who made them or who makes them from the ore into metal right. To take platinum gold what is common there? It is naturally available. So, how do you make this material? How do you make this metals? Is the origin is the ore that you have here talk about the ore is is in the earth crust you have and the ore is nothing, but oxide, chloride, sulfates all this compounds. You convert this into metal how do you convert it? You convert by providing energy right you provide energy you reduce this the energy of this is increased because of the conversion form things ok. So, the energy of the metal is higher than the energy of the ore what is natural is that what goes up is to fall down that is nature's law the physics says that. So, when you interact with the environment what happens? It goes back this is what has stayed here. So, what drives the corrosion? The free energy change that drives corrosion. So, engineering materials that we deal with more specifically the metals I would say if they do not corrode you may get surprised ok not surprised that most of them will undergo corrosion process. Corrosion is a very very common thing. Now, what is what is then corrosion means ok? What is this corrosion means? Corrosion means that you have metal it comes in contact with the environment. Now, what is happening now? See there is an oxidation process I have given an example as iron here in the process the electrons are deposited on the metal surface the iron goes in the solution. Now, look at this the reaction is not going to continue right it does not continue at all why does not continue? Why the iron cannot continue to oxidize? It stops here why does it not why does it stop? Yes because the surface is enriched with electrons negative charges it loses its neutrality the reaction does not continue. So, for corrosion to occur what happens you need to remove these electrons from the surface. How do you remove that? You remove it by when one you see now here what happens it releases two electrons it is accepted by these pieces in the solution here the example I have given is H plus the H plus takes the electrons and the reaction continues. So, it is a chemical reaction occurring on the metallic surface there are two sub reactions two partial reactions you want to call it one is an oxidation the other is reduction process. Both of them have to occur only one occurs the corrosion will not proceed it might happen first two steps three steps, but corrosion does not continue to occur. It is a very important thing to understand this becomes a key to understand not only to understand corrosion to control corrosion also right. Suppose you are not an engineer you are a common man sitting on there somebody gives a lecture now which has please tell me from this how do I control corrosion? Can you tell me how do you control corrosion? I have to use steel, but I need control corrosion how do you do that? How do I do this? Do it there are of course, but I of course I can give a coating on all, but I cannot I have for example, pipelines carrying water how do I do that? It would be electrons. So, in fact, the answer comes from that. You have given one of the examples you are coating you put electrons to that you said actually one person will say what you will say please remove S plus from the electrolyte. In a boiler can you give a coating? If you give a coating what happens? Thermal conductivity is a problem you cannot do a cathodic protection what you do there is simply remove S plus. How do you remove S plus? By turning the solution into a alkaline solution the pH of the water is increased. So, what I am trying to say if you know the principle it is easy for you to devise new methods you do not have to read what I am saying, do not have to read what Fontana says, you can devise your own method. It basically is very important in advancing the technology I think you should do that. Now, one way you have seen again in the day to day life right you have seen how how do people store sodium kerosene right reputant kerosene right. How does the corrosion is stopped? In kerosene why no corrosion occurs? There is no interaction the air is gone. Secondly, there is no free H plus in water in in in this particular environment no corrosion very simple ok. So, it is for us to understand what the corrosion how need to be tackled at all actually. Now, to summarize what you have seen so far you have metal it comes in contact with the environment here. You have an oxidation of the metal taking place right releasing electrons on the surface and from the environment you have a species it comes and accept the electron here and gets reduced and these species can be H plus, metal ions, oxygen and so on. So, do not understand what are these electron acceptor reduced species do not worry the course is meant for that ok to to make you understand. I am trying to only trying to tell you how the course is going to evolve what we are going to address in understanding the corrosion process. Now, as you have seen before thermodynamically most of the engineering alloys the structural materials are bound to corrode right. Why? Because the energy of the metal is higher and any time it can form it can corrode can you ever completely stop from corrosion you cannot forever you cannot forever cannot stop it. What we can do is you can slow down the corrosion process right I take long time I take more time for it to corrosion here ok take long time right. So, we have a steel pipeline the pipeline can last for let us say 25 years engineering it has served the purpose for a section. So, how do you how do you study what is this science called what is this science called this science is called the kinetics. So, first one we talked about the thermodynamics the free energy change and this is called the kinetics. So, this course will devote time in understanding the kinetics. In fact, the kinetics are the most important thing in controlling corrosion because thermodynamics says I am helpless you are using materials which are supposed to be corroding ok. So, this kinetics we are going to spend quite a lot of time. So, that we can understand the mechanisms that gives us a way to control corrosion of metals. One of the ways to control corrosion we are talking about coating the metallurgists do right. How do I control corrosion of a steel from metallurgy point of view? Yeah it forms corrosion oxide ok I form a film in the surface you have seen metals there outside you have saw lot of things there right. See how they prevent corrosion you apply a paint coating barrier coating. Metal can develop its own barrier oxide coating right and how does it happen? You have metal here it comes in contact with the environment here what it has to do it form a film on the surface and this film is a barrier for the environment to come in contact with this. This is corrosion stainless steel all of us know. Can you give another example of a reactive material? I mean high corrosion resistance yeah aluminum to certain extent. Other one anybody? Anybody can I give an answer? Have you heard of titanium? An example of that titanium is very reactive ok. It gives you in fact titanium titanium is more reactive than aluminum, but it gives you better corrosion resistance ok it forms its oxide resistance. So, you can develop a voice just like that. So, all this we talk about a kinetics ok. So, the course ok will spend about 10 to 15 lectures on the electrochemical corrosion, thermodynamics and kinetics, but 10 to 15 lectures will be there. We will see some examples and there will be some problems to solve so that you can understand how the kinetics are happening or the metal solution interface. Please see all happening of the metal solution interface we do not talk about what happens in the electrolyte it is on the interface ok. So, we talk about that actually. Things are not that simple right. If we have to simply talk about electron transfer it is so simple to corrosion control you do not need a big subject, you do not need lot of consultants, you do not need you do not need a specialized you know engineers to tackle the problems. The reason is very simple the metals are fabricated into different design you know one of the slides I told you have a material that the environment design come into pictures illustration here right. What is this? This is a heat exchanger right, a heat exchanger for a power plant you call a core generation done in one of the petrochemical industries. You do not want to waste the heat, you extract the heat and convert the steam and use for various purposes. These heat exchangers right if the shell you call it what do you call this call the cubes right. Now, look at this this is tube and tube sheets these tubes are welded to sheet here these are welded now that means now you start welding. What is the welding? Joining right of course. How do you people join Tic welding? What happens during Tic welding? No metal is melted joined together metallurgically there are changes. The location where you joined it has a different electro chemical properties compared to surroundings corrosion there same thing electron transfer takes place all, but the solution there is different ok. I am not saying that electron transfer does not take place, relation does not take place, but the engineering solution to the problem is different the mechanism of corrosion different. So, you have to look at corrosion from a different perspective of what you call as a different forms of corrosion you see later. Similar thing you seen right this is a reformer unit one of the refineries he served of course, about 14 to 20 I think about 14 years he served and they found that there are some bulging slide is not so clearly visible. So, there is a bulging they sectioned this and they saw you see that how looks like this sectioned plate you see looks like a fish mop and the different type of failure and this failure we call them as hydrogen damage, hydrogen blistering they call it. What does it happen? When you when you take a steel and put it in a environment hydrogen evolves there is a corrosion, but one more thing happens the hydrogen enters the steel and gets into the material it affects it. In this case the hydrogen got accumulated now you see now we are getting to a different dimension of the problem the primary cause is corrosion the secondary cause is a real reason for failure. If the hydrogen has not gone into this the corrosion was even minor have the guidance has not gone into it minor. Now, this is a different kind of problems how we solve it. So, this is called different mechanism we call hydrogen damage in the broader sense of that. You can see look you know this is a kind of a a kind of you know pipeline you see here in a refinery they are all insulated right with a lot of insulators it carries lot of lot of steam inside actually high temperatures very nearby here only this refinery was located and it is a nozzle there there is a nozzle here the nozzle is a crack you cannot see it is so clearly the things cracked. What are the material? The material was stained the steel um the material was stained the steel and see how the crack was the crack started like this started branching. They thought stainless steel is a better one unfortunately it is not actually and the cracking took place. You see this is a weldment if you are a metallurgist you know this is a different microstructure here different microstructure here there is a cracking taking place from the so called ethyl pressure zones takes place. You know what the solution for that was we are not using better material core simple core solution was using a steel not a stainless steel. How do I come to the conclusion? You need to understand the mechanism it is anywhere you stainless steel is better compared to carbon steel is not correct always. If you want to illustrate this further tell me how do I store how do I store chlorine gas? Human are gone to swimming pool the use is of bleaching right. What what kind of cylinders they use? They use simple carbon steel cylinder. What if if I use a titanium? So, titanium is prone to cracking but the same chlorine gas I add small amount of water in that I make it a wet chlorine the carbon steel cylinder will not work the titanium works there. The reason being in water the titanium forms mice oxygen. That is the reason why I said you need to understand the science otherwise you simply cannot go by intuition what really happens to the materials at all. So, that is what I think you will see in this course. So, different kind of failure we have seen one of the chemical manufacturing company it is in agitator arms you see this here because of the jet here impingement the corrosion occur velocity is one factor. The corrosion occur in a in a tank is different from corrosion occurring in a pipeline or a nozzle or or maybe an impeller things are different. Sometimes people misunderstand issues. It is an example of how people do not read the fine prints. What is the difference between a martensitic steel and a martensitic stainless steel are both the same or different? Composition. Composition right right. The martensitic what is the difference between a martensitic steel and a steel? What is the difference? Heat treatment? What is the property you get in a martensitic steel? High hardness, good erosion resistance right all this will happen. The martensitic steel will give you good wear and tear, erosion all this. But you have an environment corrosion environment the martensitic steel is no good at all because that is going to corrode very high. So, people use for pump applications martensitic stainless steel not martensitic steel. Here is a case somewhere in Siberia happened one of the company which is a friends company located in India who went for the overall plant over here they used in the pump a martensitic steel instead of martensitic stainless steel. They really notice oh this is really a problem why you know here what is the liquid? Here is simply it is not a really hazard you know very interesting actually it is called a condensate you know in a hydrocarbon what you do? Suppose you get a LPG gas right you may have water what happens you have to separate the water and then take the gas out that is called as condensate right. You condense and remove the water from the process liquid and that water is being pumped here you know very interesting thing that water is more corrosive than the water you have in the pipelines it is a pure water. You see why later and they got worried you know what they did they start using two pumps alternatively you want to call that right. Oh I said why do you use alternatively because anytime it will go if I order a new pump with the martensitic stainless steel you may take not less than 6 months. Now without this pump you need to hold unit cannot run what is the cost of this pump so small compared to shunting the whole plant for about 6 months. They thought ok there is a erosion corrosion let me work alternatively. I said so we did some lot of work and find out what happens and all. But at the first instance I told do not use two pumps alternatively why if you shut one pump down there is a water inside keep corroding all the time ok. Shunting pump does not mean that you do not have water inside. So, please do not do this at least if you keep it dry you have a problem you start running out after about one month ok. Then you shut the other one dry it start running because you know what will happen. So, we did of course, some calculations about the pH all this and then found yes I think you run a pump for 3 months continuously one case and another case run for 3 months another case I think you can sustain the production for 6 months by the time you can buy when you want. So, sometime you have money, but you cannot do anything at all loss of productivity takes place ok is one of the issues. Very similar issue is the refinery is again close to us. Simple condensate tube in a refinery they were using sea water. Sea water you cannot use carbon seal you know because of high velocity a problem you cannot use stainless steels they start using copper nickel alloy it is called cupronic alloy right alloy in the form the inlet portion there is a erosion corrosion taking place very low velocity. I am not going to give answer for this please look for answers when I am teaching this code that means, you understood that I mean I am just raising the questions now ok. Now, this is the velocity it is called inlet corrosion taking place real problem. In fact, every you know fortnightly they used to pull the tube out in the prog it and keep doing actually shutting out and then it used to cost 10 million rupees per day because you cannot do anything at all one day finish one day means 1 core rupees is gone for that. So, cost of the tube is less, but the consequence productivity is quite quite a huge amount of loss you will see. Now, it is this not the structural thing it is not just function there is one more ok I do see a car right if I am talking about a car like this oh structural is very good I can drive no problem who will buy the car if it is frustrated it looks so bad nobody will buy the car really. Now, the GM or some of these companies you know they give guarantee of 12 years of how rust free coatings the technology has developed over a time period. So, aesthetics are important why do you quote nickel on some of these you know steel plates because you want to have good appearance you go to washroom you see color some of these you know fittings are extremely good looking actually right because appearance is also equally important ok and that can get damaged corrosion problems here corrosion is a real problem ok. This another aspect of why corrosion should be controlled and again if you see very interestingly you know you need to look at it you see what is this what is this why does the red color appear here it is chipping actually the stone hit and coating paint coating broke and you have rusting here to the color you see here also you know there are some blisters taking place there are blisters taking place it is called blisters ok and the blisters occurring because of the cathodic reaction or I would say a reduction reaction you are not told about what the cathodic is I think it is probably very appropriate for me to say a a reduction reaction because there is alkalization reduction reaction here the corrosion takes place corrosion problem not only associated with oxidation sometime the corrosion problem structural failure can occur if some cathodic reaction occurs reduction reaction occurs on surface this also will be a problem taking place ok this is another thing that really happened I have given this example pipeline I think some of you would have seen it see here this is internal this is external and very different the internal corrosion depends on what depends upon the water chemistry water it is going to be used in this case the corrosion occurred because of microbes we call microbial corrosion taking place but here the the outside they expose the soil the soil chemistry is a different entirely different solutions are different from that ok. So, corrosion can be very complex ok in in in a single single structure ok it can be different depending upon how the environment is really exposed to. There are so many reasons why corrosion should be seen and I have shown this here if this happened within India it has got larger impact in terms of you know in terms of problems that we face. The two accidents happened here right right side you see here the gas pipeline happened about a few years back ok and it caught the fire why did the leak occur the primary reason was corrosion or the pipeline and a lot of casualties you know you see 18 people were reportedly killed and 14 killed. So, these are the kind of problems that you can have actually. So, there are cases that we call penny wise palm foolish we do not really do things thinking that you can save the money the money is not really saved. In fact, the money is spent more to destroy the environment you know to destroy environment it also a matter of sustainability right you have a steal how long the war is going to last how long the natural gas is going to last ok or if you are going to pollute this environment how long is going to happen ok. The question of sustainability depleting resources sometimes as a metallurgist I will develop a better a voice as a mechanical engineer I design a very nice structures but corrosion does not tolerate. I say oh I want to use magnesium because he is one of the lightest engineering metals right he will still use it right but then magnesium is very highly corrosive isn't it. In automobiles or transportation sector people use magnesium, but if you know of any of the chemical industries magnesium is also used as a sacrificial anode corolls and used there how can you reconcile both that is the critical thing that we talk about. The technology sometimes cannot be advanced unless you take care of the corrosion control that is the important thing and of course, the process becomes less efficient loss of profit cannot have a production in the profitable levels. Now, as we have been talking about industrial things are very complicated materials are subjected to fabrication on the process side they are subjected to temperatures and pressures they are all contribute to various different forms of corrosion a complex forms of corrosion. An example here this is one which I went I have done a consultancy work for one of the industries right see this is all fabrication or I have done it right. You just cut open this and see the one weldment here another weldment here this is called as seam weld seam weld is getting corroded stainless steel ok here ok here the seam place will support corrosion. So, the corrosion is complex. So, there are different types of mechanisms that we have talked about and failures are different. Some examples of mechanisms are given and not all of them we have seen this before it is called hydrogen induced cracking hydrogen gets into the material and then builds pressure and cracks this is called stress corrosion cracking when you apply a stress and you have environment it cracks you know all cracks it is brittle. So, what is the ductility of a typical 3 1 6 L stainless steel anybody here can tell ductility this could be 60 percent ductility right that is why metals are used in the environment that ductility in terms of percentage elongation can draw from 60 percent to 10 percent 5 percent and moves acts like a ceramic now. So, it become brittle there are brittle failures you have what is called as a crevice corrosion right you have mechanical joints flange joints you have rivets right it undergoes a different forms of corrosion we call them as a crevice corrosion another mechanism that you have ok. You weld it the grain boundaries of the stainless steels become very reactive we call them as sensitization another form of corrosion called intergranular corrosion just now you have seen it you have microbes induced corrosion here there are microbes the different forms of corrosion mechanism ok and it is called a cavitation damage it is a it is actually what it is an engine block actually for ship ok and because of constant vibrations you know and bubbles form and then the impact leading to failure is called as a cavitation damage you can have a pitting look at this here a pitting corrosion taking place only localized form corrosion. So, we started with a simple concept of corrosion what is that metal exposed to the environment leads to two kind of reactions one in oxidation where the metal releases electrons and the environment picks up that electron here we call reduction process in all corrosion process is taking place. But the way this reaction occurs can be very complex the solution to these problems are different. So, we have different forms of corrosion in fontana book it calls it calls as eight forms of corrosion you may not agree with it I also may not agree with it you may call nine forms the 10 forms and 12 forms of corrosion when you say mechanism why you call a mechanism when I say mechanism that tells me how do I count of it is not it. If I know the mechanism I put an obstacle for the movement or the process. So, the mechanism is different ok and the solutions are different. So, that is what is this we see you should be seen in the light of the fact material selection when you talk about or any industries where you talk about aerospace or you talk about a car that the pipeline or a pressure vessels you go to a mechanical engineer or design engineer what does he first think? He first thinks about he or she will think about what thinks about oh what is the strength what is the toughness ductility is it wear resistance is it dimensionally stable all missionability all this. If you are going to a another kind of guys who are making devices like that oh what is thermal conductivity what are magnetic properties optical properties corrosion does not figure in material selection more often industries. Oh I have a very nice glass borosil glass does not corrode can you use it can I go and tell a mechanical engineer that oh is that your crazy guy. He will say oh I want to use magnesium kind of thing can you provide a solution for that. Say corrosion engineer you provide solution where the metal is or metals are expected to corrode. So, how do you prevent the corrosion? So, that is the science of engineering of corrosion look at that actually that is what does you do that. So, this code is to show that the corroding metals can be safely used at definite time without corrosion barriers. So, is it that trivial problem rare if there is some electron some welding and what is so big about is this is really a problem what is impact. You ask your question counter way can you tell me an industry system where you not find corrosion can you just tell me can you just find out one industry where oh there will be no corrosion glass industry. If you want how do you know how to make glasses glasses are melted right is melted in what melted in various steel retards corrode. In fact, one of the same thing you know I was giving one of the consultancy service to the company making glass for the thaws you know for thaw and you have that nice glass we cover it right. You start melting and it is just you know deteriorate over time period that corrosion of course, is called high temperature glass of course, it does not have. But the glass is not eternally correct if somebody is going to use hydrofluoric acid for his own purposes can you use a glass no people step on in fact, those industries which deals with HF you know what they use they use monolab it consists of copper and nickel the glass is not going to work. So, it is only safe to say that those industries which are not using materials metals will not have corrosion problem. But can you find a industry which is not using materials and metals or it like to happen where does the corrosion problem occurs? See it occurs almost all industries talk about all industries using metals and materials or won't have corrosion problem. The extent of corrosion changes a chemical process industry a petrochemical industries a fertilized industries for example, may have different aerospace industry may be somewhat different other transportation industry may be different nuclear industry may be different. But I do not see that there are any industry would not have any corrosion problem at all so long as they use metals and alloys I mean engineering metals the engineering alloys. It has a great impact I have shown this here I have taken this from this you know there is a document called you know ok impact studies done by nation international this is very recent 2016 they have shown that the last nation is about 3.4 percent of the GDP ok. Now, if you look at the western countries like you know France or UK or even Japan what is the growth rate of these countries many of them less than 1 percent hard to get that. So, there is a significant impact in terms of corrosion if it happens at all because the cost that you can cost you know if you have to nation is quite quite significant it contributes and of course, India you have about 4.2 percent that that you see that. So, corrosion is not trivial is just not confined to only one industries it is just not see replacing materials oh I use a glass I use a titanium I use this you cannot find the solution at all. So, there is a science that is engineering very important in order to fix the problem and it is even more important in the technology evolve actually ok. The technology evolves what does it mean you know in India about few years back the thermal power plants were all subcritical thermal power plant they called subcritical boilers the mechanical engineers who know about it right the pressure of these boilers less than 25 mega Pascal's. Now, you want to raise the pressure more they called supercritical boilers. Now, they gone into ultra supercritical boilers why are we doing this the efficiency of these thermal power plants will increase significantly not only that the carbon could print the emission control this can significantly reduce if you increase this by the temperatures and pressures because the efficiency of of heat transfer becomes very high you cannot rise the temperature you cannot use the same steel the corrosion problems faced by these industries are different from the boilers the way you do water treatment is different. So, as the technology evolves at the time the same methods of corrosion control may not work the same understanding of corrosion of materials may not work it changes. So, corrosion control is evolving because the technologies are being grown you know the Apple Apple phone iPhone they use on the cover you know this is what use this is what is the magnesium right you mean use magnesium how do you think the magnesium can be used because you know how to have good coatings in that. So, as you develop new technologies you are under threshold we cannot afford to allow corrosion yesterday I was into one of the industry here I do not want to mention the industries it is supercritical within 3 months started failing heat exchanger in about 5 months they had 3000 tubes in heat exchanger tubes 1400 tubes are plugged because these are the start cracking they were very happy earlier now they are not very happy because the technologies have changed you cannot use same we have corrosion control taking place. So, there is a need to change how to do that we need to understand mechanisms the mechanisms are going to be there. So, the next part of my course we have about 25 lectures we deal with the mechanisms various forms of corrosion when you know the mechanisms it is for you you can figure out what are the parameters that affect corrosion under each cases right. If you know the parameters affecting corrosion you can devise control measures yourself do not have to read the book if you know the basics you can devise a test method yourself you do not have to again go to the book you can devise a test method ok. Of course, we also give illustrations to show how these failures occurred in industries between the states. So, this will be the second part of these course and do that and I have these books here I can share this slides with you we can you do not have to take this notes of this. As I told you in the beginning of the course I will use Fontana as the main line if you know of new lectures ok. It is it has got a lot of industrial component here I also refer these books actually ok. And Ulig book is a good book it spends quite a bit of the chapters on mechanisms the fundamental understanding the Fontana book is not really that one actually is not happening at all ok. And if this is Stansbury and Buchanan you are going to be interested too much on electrochemistry, thermodynamics and kinetics and all the stuffs this is a excellent book actually you can refer the book. Or you are going to do a project later more involving electrochemical experimentations that is a good book to refer to ok. And you want to go again stray into more and more deeper you can also look at book on Test Corrosion Cracking here in practices there are about 80 some 20 22 chapters by various experts across the globe industrial problems also. You want to go into more realistic problems and all I would recommend the book Corrosion Failures Theory, Case Studies and Solutions. You do not want to go anywhere I am want to put a little lazy. I think you can look this Eisenman book it is huge collection of you have fundamentals volume A, volume B on materials and volume C is on what on industrial problems. Of course, each of them may be 1500 pages ok. So, all put together probably about close to about 5000 pages should be there I think something like that. It is a nice book and you know anytime that you can refer it ok. And lots I do not know more than 600 authors or maybe more have contributed to this particular book actually volumes I would say ok good. So, these are the things I think you you can really do in addition to that and you are interested in some research there are journals available you know Corrosion is one journal Corrosion Sciences is another journal Corrosion Engineering Science and Technologies another journal we are getting these journals in our library. There are journals later to fuel the materials act on that and all you know act on material here where you have corrosion and it is available if you can read it you have very nice collection of books and journals in your in our library that that should help you a lot actually and I think we have now come to end of today's lectures ok.