 Hi friends. My name is Mahirubali. I am an assistant engineer in WIT-Solabor. Today we are going to talk about a topic, corrosion in metal pipes. So what are the learning outcomes? Learning outcomes are students will be able to understand the concept of corrosion phenomenon in only metal pipes. Before going to the details of the corrosion in metal pipes, let's understand how the corrosion is done. And what is basically the corrosion? Corrosion is the natural process that converts the refined metal into a more chemically stable form such as oxides, hydroxides or sulphides. It is basically a gradual destruction of metals and it is done by chemical or electrochemical reaction with their environment. What is basically a redox reaction? Redox reaction means there are two materials. One is oxidant and another one is reductant. What is oxidant? Oxidant means it is an agent which gives out, it means gives out in the sense it oxidizes the electrons to become reductant. Here reductant is a stable form. It is in the stable form. And what does reductant do? Reductant basically takes the electron which has been thrown out by oxidant to become oxidant. But here the formed oxidant is a stable material. It means after the reactions or after the oxidation and reduction both the materials become stable and the corrosion happens. So this redox reaction is happening both ways. It is in the form of oxidation and reduction simultaneously. So let's talk about the metal pipes. In the metal pipes basically water is continuously adhered to the metal pipe. Here it is a metal pipe. And on which a paint has been given just to protect the metal from corrosion. But you have to understand one that water is continuously touched with the or what we can say adhered to the metal pipe. Here for the example I had taken iron because most of the time in the distribution network iron pipes are mostly used. Nowadays steel pipes or steel alloy pipes are typically used. But now for the example I am just taking only one metal that is iron. After a long duration or suppose 10 years or 15 years the paint will get deducted continuously. So there will be an area where the pipe is directly coming to the contact with water. Similarly here it is happening. And what will happen after that? This metal it will try to come mostly in the water in the form of ions. Now here as we are using iron. So iron will come into the water with the help of oxygen which is present in the pipe. Because fully pipe is not fully covered with water it is also having some kind of oxygen content in it. We call it as dissolved oxygen. So oxygen will try to react with the iron and this iron will become this reaction will form Fe2+. Now as it has been oxidized it is giving out electron. It means that electron has to be passing through as we are seeing the only iron is coming into the water. So electron will be passing through the pipe. So this form will always continue. So electron is continuously moving throughout the pipe. It is not inside the pipe, within the pipe. So what we can say? We can say that iron is getting oxidized in the form of Fe2+, and 2electron-. So as this is oxidizing the iron is getting oxidizing. So it means we can say this site is anodic site. What does it mean? What is mean by anod? Anod is the one which is continuously giving out electrons. So here also the electron is getting out from the pipe. So we are calling it as anodic site. Now as the electron is passing through the pipe, this electron will capture the area where the pent is very much negligible. And it will join with oxygen which is present in the water and this water and it will form 2OH-. So how we can write the reaction? As half of the oxygen which is present in the form of gases and water plus the electron which is flowing through the pipe will form 2OH-. Now as here there is an addition of electron which is happening at this site. We can also call it as cathodic site. Because at the cathode the electron is always captured. So here you can see it is oxidation happening. Here it is reduction is happening. Simultaneously we call it as a redox reaction. We had seen in the earlier site. Now what will happen further? This Fe2 plus and this OH- will form the rest. What they will form? How it is going to happen? What is the proper precipitate? We call it in the technical form. We call it as FeOH-. That is ferric hydroxide. It is mostly insoluble impermeable precipitate. But at the initial stage when the rusting is continuously going on it will form on the layer of pipe. But at that time automatically this cathodic site is also getting covered with the rust. So there are chances then redox reaction is going to dampen. But this rust, the initial rust is not too much impermeable. It is mostly permeable. So it will give out lot of cathodic sites. Therefore the redox reaction is not going to stop. So here the continuously rusting going on for a longer, longer period and the pipe going to disturb. Now let's see about the chemistry we had seen here. The Fe2 plus and 2 OH- is forming FeOH twice. Which is ferrous hydroxide. Now let's talk about the two conditions. This ferrous hydroxide is not the rust. It is not a proper rust. It has to go from the further reactions. Let's talk about two conditions. One is the condition where water is alkaline and it is free from carbon dioxide. At that time what will happen? This ferrous hydroxide which is formed around the perimeter of pipe will react with the oxygen which is present in the water. And then it will try to form FeOH thrice. It is 2 FeOH thrice and it is ferric hydroxide. What is this? This is our main rust and it will stick to the pipe. Here I had written anode. What is anode basically? Anode is the area around which the rust is going to form. It is not going to form at the cathodic site. Because at that point only the Fe2 plus is continuously going out. So we can also say that it will continuously stick to only anode part. Now what is the second condition? Second condition is the water is acidic and it is containing the free carbon dioxide. Now what will happen? This free carbon dioxide will react with the ferrous hydroxide and it is present in the water. And what will form? Ferrous bicarbonate. It will react with the oxygen which is present in the water and some H plus ions. The water is acidic. It means it is having a lot of H plus ions. So there are a lot of formation of H2 gas also. And all this combines to form FeOH thrice. And what will happen? It will stick to the anode. And it will throw out carbon dioxide. Now let's come to the point of technical words. Because rust is a very common word. Now let's understand. The first here, the deposit of insoluble red precipitate. That is our ferric hydroxide is formed in the interior pipe surface. We call it as tuberculates which is another name of rust. And this process is called as tuberculation. It will happen when there is a higher roughness in the pipe. To this roughness of the pipe. What will happen? The head loss will increase. And what will happen due to that? There will be a creation of pressure. And what will happen after that? The water carrying capacity of the water is going to decrease. So now after that, what are the physical significance of that? See here, if you see for the cast iron pipes which is normally present in the distribution systems, what it will do? For the lower diameter, it will try to decrease mostly 50% of the water carrying capacity in nearly 5 years. So it's a huge risk and you have to think about the corrosion or technically what we say, tuberculation in the pipes. So how we can do that? Normally it is cleaned and it is lined with other materials in the interior part. So that there will be a very, there will be a stoppage of corrosion or there will be a decrease in the formation of corrosion. So let's see about the wet electrochemical corrosion of iron. We are using alloy. So if in the alloy, how the corrosion is going to happen? There are electrochemical series in which different metals react with water to form compounds. So here if you see, I am using copper and steel alloy. And if I put in the water, because these both are adhered to the water, what will happen? As the steel or the iron is too much higher electrochemical than copper, what will happen? The iron will come into the water and it will take the OH- from this cathodic side or what we can say from the copper which is present in the form of alloy. And the first iron will try to decay or what we can say it is tried to form the tuberculates. What does it mean? It means that in the alloy whatever the metal which is higher electrochemical will rust but not the other one. So corrosion is going to happen in the alloys too. So what are the examples? If you see in the fittings, because in the fittings we are not using the same metal. If we are using the iron pipe, we are not using the caps or fittings of the iron but we are using the different. And these fittings are also adhered to the inside water. So this iron pipe is going to rest but the fittings or here you can say the fitting is not going to rust but the pipe is going to rust fast. This is one another example of fitting. Here you can see these fittings are also getting corroded by different questions on which we can resolve more. The first question is corrosion of steel is always relatively lesser than iron, true or false. Second one is corrosion dependent on leakage in the metal pipe or pH of water or conductivity of underground soil or all of the bow. And the third one is in the corrosion process metal pipe behaves as anode or cathode. So this is the answer for the first. It is always true. Second one is corrosion is dependent on pH of water, leakage and conductivity of underground soil. And the third one is in the corrosion process metal pipe behaves as anode. So these are the references I had studied and made this paper. Thank you.