Dye Penetrant Testing – 1

Hello and welcome back to this lecture series on non-destructive trying out which is being supplied underneath NPTEL on-line certificate and course so within the final lecture we discussed one of the crucial topics which was on visual optical approach and as I advised you you are able to do few matters by using utilizing this method however it has its own problem within the experience you could possibly be equipped to do simplest precise external inspection tunnel surface of the element and if you need to imagine whatever which is below the surface or which lies beneath you then need to use this sort of NDT ways that we now have listed as you would see in the first slide ok so we’ve mentioned this one as I mentioned the primary one visible optical in the final lecture and as I mentioned if you want to see and inspect what lies underneath then you definitely need to use the sort of entity methods which can be listed here some of these will come underneath the class of surface energy system and some of these will fall below the class of bulk or volume and DT ways tactics like liquid penetrant inspection magnetic particle inspection and eddy present trying out they are going to come beneath the skin approach and ways like ultrasonic checking out and radiographic trying out they’ll fall beneath the bulk class and there are specified techniques like for instance ultrasonic which will do each I imply it will probably do each floor entity as well as bulk entity so what we’re going to do in this series of lectures is to take each of these approaches every of those in detail methods separately after which first gain knowledge of concerning the basic precept at the back of the process as i’d have stated before additionally after which go on to be trained in regards to the system itself as to how the method is completed how the procedure is applied and what are the approach parameters and many others so in opt for one at a time after which we will speak about in more important points so in the ultra-modern lecture we are going to decide upon up the first matter on this record which is on liquid penetrant trying out k so this can be our first lecture as far as the entity methods are involved so this will likely be on liquid penetrant testing or typically it’s going to also name it as a dye penetrant trying out on account that a liquid dye is used and in brief someday they also decide upon to call it as effectively PT which stands for penitent trying out there’s an additional name to it which is liquid the or liquid penetrant inspection or LPI briefly k so these are the names of the same system which is the liquid penetrant trying out or penitent trying out okay in order I said we will first be trained concerning the normal precept at the back of this we will be able to see on what scientific principle this unique method is based on and then after we be taught that we will be able to go on to look the procedure and then see what are the method parameters how it’s accomplished etc so as I stated all you could have right here you could have a liquid and you ought to investigate cross-check a element so you’ve gotten an exceptional floor okay so that you observe this liquid on the stable surface and then permit it to spread over it and then if in case you have defects or flaws that you may inspect it depending on what this liquid does how these liquid interacts with the stable floor so that suggests you have to talk about strong liquid the interplay that implies allow us to say if i have a superior floor ok after which I put a liquid over this k now depending on the interplay or the skin energies two matters can happen one is the liquid will unfold over the strong surface or in other words the liquid will weight the strong surface k and the second possibility would be the liquid will not unfold or it’ll no longer moist so there shall be no waiting okay so two circumstances one is ready and the second is not any waiting okay so whether or not the liquid will put on the solid floor or no longer that might depend on a parameter which is known as a contact angle let us name this as theta k so allow us to say that is my strong floor and over this i’ve a liquid droplet like this ok in order I stated whether ready will occur or no longer this is determined by the skin energies and with a purpose to subsequently come again to this contact perspective so this is the outside power between the liquid and the vapor so if we call the skin energy as gamma so this will likely be gamma liquid vapor k so this is the surface anxiety of the liquid then you could have this specified interface over right here k so this is your strong liquid interface so right here you’ve gotten gamma SL which stands for strong liquid and then over here you’ve an additional interface another surface and one other surface power which is the interface between the strong and the vapor so you right here you’ve gotten gamma strong vapor okay and that is the perspective that I mentioned which is often called the contact attitude ok now in case you take the stability of forces what you could have here you will have this gamma is V is being balanced by way of gamma SL plus gamma can be cos theta okay so this is the recognized younger’s equation or young Duprey equation which talks about contact attitude between a superior surface and liquid and relying on this so that you may derive the contact perspective from this equation as k now depending on whether theta is lower than ninety degree or theta is greater than ninety degree the liquid will both spread or not unfold so if theta is less than ninety degree then the liquid will price the stable floor okay and if theta is greater than ninety measure then the liquid will not spread or will not wet the stable surface ok so that is the parameter contact perspective theta it decides whether a liquid will unfold over a solid floor or whether it’s going to not okay now how does this hook up with liquid penetrant trying out let us go forward and see that in order I said you employ a liquid dye which is normally a colored dye more often than not a pink colour is used and you take this liquid dye and then you definately unfold it you practice it on the solid floor so for this dye to be spread over the stable floor of the factor that you are inspecting this contact perspective theta between the aspect being the skin of the component being examined and this liquid dyes should be less than 90 degree okay and for that to occur the skin should be easy so for this reason step one in this special procedure is surface cleansing so that you must easy the outside of the entire contaminants and remove them so these contaminants might be some thing like grease oil or scale which could have shaped on the surface okay so all these will tend to increase the contact attitude so first you need to easy all this so that you can have a smooth surface and the contact perspective will likely be lower than ninety measure so this will make sure that the liquid dye that you’re making use of on the surface we can unfold over the strong surface k so now as soon as that occurs as soon as the liquid spreads over the skin now relying on whether or not you could have an excellent surface with defect or with out defect this liquid to start with as I stated will spread over the outside now allow us to say you might have some variety of discontinuity let us say crack or another discontinuity over here k on the skin so this crack has a crack floor so here you’ve gotten a floor on both the edges of the crack you’ve got a surface so that implies you have a surface energy worried over there ok so due to the fact of that this liquid will be drawn inside of this so the drive which pulls a liquid inside an opening or any fissure on a superior floor is often called the capillary force which develops due to the outside anxiety of the liquid okay so that means for those who spread a liquid on a pretty good surface and if that surface has some style of opening some form of small opening or fissure then a capillary force will strengthen seeing that of the surface tension of the liquid and that capillary drive will draw the liquid inside that discontinuity or that opening ok so the capillary drive due to floor anxiety gamma ellby if you want to see it for a crack so allow us to say it is a solid surface and i’ve a gap a discontinuity allow us to say it is a crack okay and we will be able to provide a size to this crack so let us say the crack dimension is r so crack radius is r so this diameter is 2r ok so a crack of measurement R or radius R these capillary drive due to the skin anxiety would be 2 PI R gamma L V in which gamma L V is the skin anxiety of the liquid ok now which you could observe the liquid either by way of prime like this okay and if the liquid is spread if the solid floor is fettered by the liquid then because of this opening and the capillary force which develops this liquid will go inside the crack in this trend and this would be the contact perspective ok so this is the capillary which is drawing the liquid inside in targeted instances the dye is also applied from bottom that implies you’re taking the aspect and immerse it in a tank which involves the dye okay so that is your strong surface after which you might be immersing it right into a tank which contains the dye so in this case the liquid will penetrate from backside so it’ll go up however once more this is the same capillary force which is using this liquid throughout the crack so there once more you have got this contact perspective theta so this is the capillary to PI R gamma L V okay so what you might have within this crack is a liquid head so that implies the burden of the liquid is being supported with the aid of this capillary force so for those who take the factor of the capillary drive along this axis vertically then that is the element which is helping the liquid head or the burden of the liquid so the burden of the liquid is given the crack measurement as R or the radius of the crack as R and allow us to say this peak or this depth is H so this is the quantity then the density elevated by means of the gravity G ok so R is the crack size Rho is the density of the dye or density of the liquid and G is acceleration due to gravity or gravity and H is the depth of penetration so from right here you could be capable to derive that as much as what depth the liquid can ache it penetrate relying on the size of the crack and the density of the dye k so in case you see from here this will be your H so H is equal to ok so as you would see it in particular depends on the residences of the liquid dye that’s the floor anxiety of the liquid gamma LV and the density of the liquid and apart from that it additionally depends inversely with the crack measurement so when you’ve got a bigger crack the penetration depth will be minimize and vice versa so this offers you an notion that for a certain crack size and for a targeted dye what would be the depth as much as which that you would be able to go and check up on ok so this is the basis for this detailed process of dye penetrant checking out k so the basis for that is the capillary force which develops as a result of the outside tension now the query is the way to use this to make visible signs of the crack that you just could have on a aspect that you’re examining ok so now as you could have visible so allow us to magnify a little so you might have utilized this dye as I said it is more commonly purple in color and it has long past within inside the crack k and it is far and wide the situation for the reason that what you do on this case you’ve got a sprig can which includes the dye and also you spray it over the outside okay so the entire floor will probably be protected via this dye crimson colored dye and if there is any discontinuity any flaw or defect this dye will likely be sucked within by using the capillary force k so in case you see the system as such now that we’ve understood the fundamental principle we are able to go to the procedure and see how exactly it’s achieved so the first step as I instructed is surface cleaning or floor coaching k this is to ensure that your floor is easy and the contact angle is less than 90 measure so that the liquid dye can spread over nicely over this over the surface second you apply the dye k so that is what is being shown in the diagram so you take this die and it goes within ok so on this case as i’ve mentioned earlier than additionally you would either apply it by means of spray so that you would be able to have a small spray can and that you would be able to spray it or it’s also possible to use via immersing it in a tank which involves the dye ok so both manner depending on the size of the part or the convenience of the examiner both the procedure can be utilized ok now the next factor is you need to enable some dwell time seeing that this this liquid dye may have a designated viscosity although it does not come into that equation which we simply now talked about however this viscosity seeing that because of the viscosity it is going to make the effort for the liquid to head within the crack if there are discontinuities and crack on the outside so that you have got to permit designated time so that the liquid dye can go within the flaws and defects and this dwell time as to how so much time you must enable that is determined by comprehend what kind of section you could have what’s the measurement of that section and what kind of defects and what sort of size you expect in the what variety of defect measurement you expect in the part ok so this at good time will be certain that you’ve got ample time for the liquid to move within the flaws okay now as I mentioned this liquid will be now unfold over the stable floor so the whole surface the liquid can be all over the place the surface ok however before that allow us see what type of penitence are used and what houses this penitent should have k so the primary characteristics or property of this liquid is that it must be chemically stable okay chemical stability and it will have to also have uniform bodily consistency that suggests it is not have one density in a single section and any other density within the different materials okay then it must have a flash point we will have to no longer be scale down than ninety five measure Celsius so it is close to a hundred measure that means it it’s not be a flammable liquid you should be competent to handle it properly without the dangers of you realize hearth and all that and it must provide a excessive degree of weight skills as I advised before this weight potential is the primary requirement for this dye penetrant testing so that you must have a liquid so one can provide a higher degree of variability provided your surface is smooth and it must even have low viscosity in order that you don’t fairly ought to allow a very long well time so this may occasionally allow higher protection and in addition shop a while as I informed in terms of the dwell time and it will additionally furnish you a minimal drag-out then it should also be in a position to penetrate the discontinuity speedily and wholly then it should have enough brightness so that you just get that contrast for the visual inspection on the finish of the approach you need to investigate cross-check it so we should have sufficient brightness brightness so as to get that contrast for the inspection and permeance of color next it must be chemically inert it isn’t react with the outside that you are examining it should additionally it must now not be poisonous it has not evaporate rapidly so it should have sluggish drying property then it must be effortless to dispose of and it to no longer have any offensive smell so it will have to be as far as viable order less and for the sake of economics it will have to be low fee and so these are the most important specifications for a liquid for use as a penitent on this process ok so I suppose on this category i will discontinue right here today ok and within the next type we will be able to see the other steps of this approach after which ultimately we can see how the defects and discontinuities are made noticeable and you get viable signs by using this designated procedure okay so i will stop here today thanks for your awareness

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