 In this module, we will talk about again the construction material in fermented design. As we have seen over a previous module while talking about the glass as a construction material, but the limitation is that cannot be utilized for industrial scale. That can only be utilized on a laboratory scale or to some extent on a pilot scale. But when we talk about the construction material on a pilot scale or on an industrial scale, we have to think over and other choices. So as concerned the other choices, so there is normally there is a choice to use the stainless steel or at least that stainless steel which have cladding to limit the corrosion. So as concerned there are different varieties of the stainless steel. So as concerned the American Iron and Steel Institute AISI that state that the steel that have define that what will be at what concentration and what will be the composition of the steel and what in what condition and what composition that can be referred to as a stainless steel. So in this slide you can easily see that as concerned AISI reporting that if the steel have less than 4 percent chromium then that can be only called as the steel alloy. But when the chromium percentage is more than 4 then that can be classified as stainless steel. When we talk about the mild steel in mild steel cases that can only be coated with the glass or phenolic epoxy material but that is occasionally used in fermentation as a construction material. But that is such material is reported by different fermentation scientist and you can see that biochemical engineers by reporting the construction material of the fermenters. But in this slide as I have written here that wood, plastic and concrete bricks mean have been used but the limitation for such material in case of wood, plastic and concrete when there is no risk we can say that there is no any care about the contamination and we know that in case of very normal we can say that ordinary fermentation that concerned the biogas fermentation in which some solid state fermentation in some oriental food fermentation where there is no risk of we can say that if there will be a contamination that is no more problem for that. So, in such cases we can utilize these materials wood, plastic and concrete. The golden example of these material that is mostly used in biogas fermenters either on household level or on industrial level or a large scale levels. You can see in this slide that different fermenters and this so in this you can see that mostly the stainless steel material is in these fermenters. But that is why we are preferred as using the stainless steel that is mostly that stainless steel is a collision resistant that depend upon the existence of a very thin hydroxide film on the surface of the metal. So, that is why that can withstand the collision properties so that is the basic property of the stainless material. While selecting the construction material we have to be focused upon rolling, pickling and heat treatment to that material. So, either that withstand either we can have in general speaking because when we have to construct the fermenter vessel we have to need the joint or a welding sometime we have to select such material which we can have a very smooth surface and we can easily fix the weld joints by welding. So, we have to use that material that should be non porous, insoluble and self healing because sometime when there is a corrosion some materials have self healing process if that is damaged and then the film is repaired by even that exposed to the air with oxidizing is end. So, as concerned the minimum amount of the chromium needed to resist the corrosion that will depend upon the corroding agent in a particular environment such as acids, alkali, gases, oil, salt and fresh water. So, by increase the chromium content enhance the resistant to the corrosion, but only the grade of the steel containing at least 10 to 13 percent chromium develop an effective film. So when we talk about the different grades of the stainless steel, so then apart from the chromium there is also the supplementation of the nickel and other metals to increase the properties of the stainless steel as in case that the inclusion of the nickel in high percent chromium steel enhance their resistant and improve their engineering properties. So, apart from the chromium, nickel and then there is another addition that is the molybdenum. So, if you add the molybdenum that improve the resistance of stainless steel to the solution of halogen salt and pitting by chloride ions in a brine or a sea water like materials. So, the corrosion resistance can also be improved by adding of tungsten and silicon and with other elements. So, if you talk about, if we will talk about the actual composition of the different steel, stainless steel materials, then we can consult with the different parameters discussed by different research institute working on the improvement of stainless steel qualities.