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A beginner Guide to NDT

NDT is a buzz word for mechanical engineers and QA, QC engineers. Just like Information technology IT and Bio technology BT, NDT is also a technology expanded as nondestructive testing. NDT is useful in industries to performing testing of materials and components to analyze quality. Also, useful technology for testing quality of installed engineering structures and machines.

What is NDT? Easiest way to know the meaning

NDT involves testing for analyzing quality of products without adversely affecting the use of component under inspection. For example, we know what does it mean by a ‘Good Coffee’, ‘Good Biryani’, ‘Good shirt’, ‘Good music’ or ‘for QA QC engineer a quality weld’.

In all the above examples, what does it mean by ‘good’? how can you say something as ‘good’ or ‘excellent’? In the sense, ‘good’ means a product meeting or exceeding the expectation of the buyer. Then, what makes something to be judged as ‘good’ or excellent. Of course, it’s characteristics and serving intended purpose.

Let us understand a bit deeper. We all have a habit of having coffee or tea or any hot beverage the moment we wake up from bed. Certainly, we know what does it mean by ‘A Good Coffee/Tea’. Try to analyse the term a little more.

NDT for Coffee? Understanding Nondestructive testing using analogy

Good or the best coffee has predefined characteristics. For instance, it should have ‘rich aroma’. You might have observed a beautiful aroma when passing a coffee shop. It may attract your senses. You have an important tool fitted in your body to sense aroma. That is using your ‘nose’. Now, did you damaged or destroyed any thing while testing for aroma? obviously not. Then, can you call it as a type of NDT? Yes of course it is.

By smelling, you can judge whether your surroundings are neat and clean. Smelling can say the perfume you are about to buy matches to your interest. In our day to day life, we do use this to judge whether the food is fresh or stale. Just by smelling, we can decide the coffee may be good.

Let us see the second test, that is colour. Sometime when you are so tired you may order ‘Strong Coffee’. What does it mean by strong coffee?. It means, coffee having extra dum, that is to say extra coffee power/seeds. Then, how do you say it is strong? Simple, look at the colour of coffee. If the colour is dark, we can say it is strong and less the colour less stronger it is.

What is the instrument used here? Eyes. As we did not damaged for conducting color test can we call it as NDT? Yes of course based on simple definition, you can.

The third test, if aroma is good and color is strong does it mean coffee is good. May not be always. Now, we need to test whether the coffee is hot or not. Will you carry a thermometer to do temperature measurements. Of course NO. Your skin is sensitive enough to measure the temperature approximately. There are instances if you find coffee is not hot you may reject or request for reheat the same. Again, did you damaged or destroyed something here? No. Can we call it as NDT? Yes of course, using your skin as sensor, can measure approximate temperature.

The next test is ‘Taste’. This is a combination of quality and density of milk and quantity of sugar served. How will you estimate the density of milk here. Do you need a lactometer to mearsure? No, not necessary. Your tongue is capable to say if there is enough thick milk or not. Again a sense organ for judging the taste.

In conclusion, we used nose, eyes, skin, tongue. What are these? simple, sense organs you might have learned in your elementary school. One is mission out of five you learned, that is ear. You may also use ear to check if the coconut is of good quality or has it got spoiled?. A simple tap test can do wonder. This simple tap test is being used since our ancestors and we continue to use the same today.

Finally, we can say, NDT is a valuable technology not only for testing engineering materials, it is quite useful in our day to day life as well. In fact NDT is part of our every day life. Probably we can not live without doing NDT.

History of NDT

Since when are we using NDT? Answer is ‘Since unknown times’. That is to say, since man kind has come into existence on this plant earth. According to Christian mythology, indicated in Zensis, when the God Created the earth, oceans, birds, animals and virtually everything before human is created, HE found each of them seems to be ‘good’. How can HE say it is good? Because HE observed its characteristics found to be inline with HIS expectations. A simple test is observing each creation and judging it a good.

For example, if a baby is born. It is common for the mother to check for the baby’s body, activeness, skin tone, body parts for deficiencies if any. Also, a doctor can say the baby is healthy by its ‘First Cry’. A sound of cry say the baby is alive. Which means, just by listening the first cry sound. A simple visual testing of listening to sound.

Importance of NDT

Ancient times, energy is primarily generated by steam engines. These engines, generate power using steam boilers which in turn burns tonnes of coal. As there was not technology to ‘see’ inside of welds, rivets, pipes, plates, tubes and other critical boiler components, there NO assurance on quality of parts manufactured. Therefore, it is quite common to have boiler explosions leading to death of hundreds of people.

This has caused a major worry for manufacturers and especially insurance companies. To over come the economic losses companies used to insure almost everything. At the end, insurance companies are the sufferers.

Then, it is understood that majority of these failure are attributed to flaws in components and welds. And also observed that there was no major NDT method that detects flaws on surface or internally. Thus this it has been debated and found that there should be some type of check needed for each boiler, pressure vessel component that ensures defect free.

Then the word, nondestructive testing has been coined. With this, today this technology is millions of lives on this planet. NDT is ensuring not just quality of products, infact it even ensures safety and reliability. This leads to ultimately boosting the Sales of products.

Early NDT methods

It is understood that, initially railways are considered critical application because of less safety tolerance. Early days, in railways, invisible cracks are major cause of failures. To detect these cracks, there was no method. In the beginning, the first application said to be like this.

Where ever there is a possibility of crack, workers used to apply wasted oil generated from engines on those areas. Allow them to seep into surface cracks. Clean using wiping. Finally, applying the surface with chalk power. This enables the dirty oil to come of cracks and stain the white chalk powder which also acts as contrasting background. The method is most popularly known as ‘Oil and Whiting method’ famous in Europe. This method has later evolved as Dye penetrant testing. Now called as DPT Testing or in aerospace known as FPI testing due to usage of fluorescent dye for better sensitivity and detectability.