Imagine you have an egg. You need to find out whether this egg is fresh, or perhaps not so fresh, or even definitely old. Easy, you say: break it on a plate and you'll know.
You're right. But suppose you have to arrange a couple scores eggs by freshness. You cannot surely break them all... what are you going to do?
Well, if you look in some old-fashioned recipe book, you'll discover a little smart trick: you can put all of the eggs in a large bucket of water. The fresher they are, the more they'll rest flat on the bottom: and an egg which bobs up and floats is definitely too old to eat it. And notice how you learned all of this without having to break a single egg.
Weird as it may seem, this example exposes the same principle we want to talk about today: that of non-destructive testing. And as we had Ecomag, a company that's been in this business for more than twenty years, explain to us, that of verifying the conditions an object is in without damaging it is not a problem that only occurs when you're cooking eggs.
In an Industrial setting, what often needs to be verified by the application of specific tools is a material's properties, or a product's integrity. And it is a matter of great importance, as emphasized, for example, in welding analysis. A badly executed welding may fail under the stress which is normal for the interested component, and this can translate to a pipe breaking, and perhaps starting to leak dangerous substances, or even worse in the collapse of a weight-bearing structure. Since it is of course completely impossible (and quite absurd, to tell the truth) to tear a welding apart to find out if it had been properly made, the need is born for non-destructive testing methods: in this case, metal radiography could be used to verify the absence of cracks in the weld, or a sound test could be made to check whether sound waves correctly propagate from one side of the weld to the other (which is a guarantee that the material is compact and uniform), or special paint layers are set on the object, which is afterwards washed: if a crack exists, even if it is too small and thin to be visible to the naked eye, color will penetrate it anyway, and a series of adequate chemical reactions will make it visible and evident, no matter how small it may be.
But, we asked, what happens if the defect is not outside, but under the surface? What if it's not a crack we're looking for, but, for example, an air bubble inside a metal beam?
Fortunately, a non-destructive test is also possible in this instance. This specific case requires exploiting the properties of the object's magnetic field: the presence o fan empty bubble inside will cause a distortion of the magnetic field itself. To make it visible, the object is bathed in a liquid, such as kerosene, containing small magnetized particles in suspension, like iron filings. The moment the object is magnetized itself, the particles will migrate along the force lines of the object's field, concentrating in the spot where, under the surface, a vacuum may be, since the magnetic field will bend and distort on that same spot.
Both of the methods we've described, such as the dozens of other techniques developed through decades of testing, allow manufacturers to verify, while maintaining costs acceptable, that the objects we use every day, the bridges we cross, the rails on which the train we take to go to work every morning travels, are safe and sound: an extremely important guarantee.
As for eggs, on the other hand, as we've already said... a simple old bucket of water can aptly suffice!
Ecomag strumentazione di misura has been in the business for measuring instruments for non-destructive testing for more than twenty years. Find out more at www.ecomagsrl.it
