Non-Destructive Tests

You might have heard and rather used many times, the word EUREKA (means 'I found it'). You might also be familiar with the Archimedes' principle, and the story behind it. When his king asked him to find out without destroying, whether the crown is made up of pure gold or any impurity is present, he really took the hardships, but finally made it possible to find the purity without destroying. Perhaps, that might be the first Non Destructive Test (NDT) in the modern science or it might be the root for development of NDT techniques if not the first. And then onwards, a variety of competitive NDT techniques for fault detection have long been established, and many more are being added to the list every day. A few are explained in this section.

 The NDT methods have gained popularity in the modern high-tech environment, as these are more reliable, safe and economical. In some cases, no other way than the NDT is to be employed for example, the bomb testing, Brick strength-testing, etc. In the present context, NDT has two important roles to play in diagnostic maintenance. These are:

• From these investigations, the presence of defects is established. It is also useful in estimating the nature and the extent of defects and arriving at a conclusion to run or shut down the machine.
• NDT also helps in measuring the defect size and distribution, which plays a crucial role in taking the final decision to continue or replace the spares or even the machine also in few cases.

A number of such tests are available to detect the defects in metallic components. The most popularly used NDT techniques are:

• Liquid Penetration Inspection
• Magnetic particle testing
• Eddy current inspection
• Ultrasonic Inspection
• Radiography (X-ray and gamma ray)