NDT Technical Definition

Topics: Nondestructive testing, X-ray, Materials science Pages: 6 (1072 words) Published: April 18, 2015
NON-DESTRUCTIVE TESTING1

NON-DESTRUCTIVE TESTING:
A TECHNICAL DEFINITION

NON-DESTRUCTIVE TESTING2

INTRODUCTION
Non-destructive Testing (NDT) is a method of examining the strength of an object without rendering the object useless. Professionals use NDT in order to locate problems in materials which could possibly cause large accidents or failures. The benefits of NDT are an inexpensive form of effective quality control that will not affect the future ability of the object to function. There are many forms of NDT, including visual, penetrant, magnetic particle, electromagnetic, ultrasonic, acoustic emission, and leak testing. Non-Destructive Testing is similar to Non-Destructive Evaluation (NDE), however NDE does more than just find flaws in parts, it also measures and quantifies them. Compared to the traditional crash test, NDT is a rather inexpensive form of testing machines made up of expensive components, such as Formula 1 race cars. Formula One racing teams would rather not spend millions of dollars building a highly specialized race car only to destroy it in a crash test. The more efficient way to test the car’s strength would be to examine individual pieces of the car with NDT and learn how they can make the car stronger or lighter. HISTORY

The earliest forms of non-destructive testing were used on railcar components, specifically wheels and axles. A component to be examined would be dipped in brightly colored dye so that the dye could be absorbed into miniscule cracks in the part. After the surface dye was removed, the component would be powdered, and dye from the cracks would seep out to reveal defects in the material. This method is now known as dye penetrant testing. Early testing methods were crude, but as NDT technology became better, testing methods were able to detect more and more part defects. Even though the defects had always been there and the parts were just as strong, the NON-DESTRUCTIVE TESTING3

discovery of smaller cracks led to more manufactured parts being thrown out of the inspection tests. Soon, technology advanced again, bringing with it the ability to identify whether or not cracks of certain size would compromise the structural integrity of a part. This required examination to determine the size of cracks in material and the extent of the cracking. Tolerances in mechanical design now applied to stress fractures as well as part sizes. Parts could be acceptable with flaws, as long as the number and size of those flaws were known. The need to know more than just that parts contained fractures lead to the development of the technology known as NDE. NDE methods have given engineers the ability to understand the breaking point of materials, and determine the exact point at which crack sizes will become large enough to cause a critical failure. EXAMPLES

Acoustic Emission (AE) is a type of NDT with records and studies the miniscule sound waves produced by extremely small stress fractures. These stress fractures can be caused by external forces such as pressure or temperature. AE technology uses advanced microphones to listen for minor changes in materials which are undergoing stress tests. AE Testing is very flexible, which leads to its use in a variety of applications, such as structural strength or weld strength testing. AE Testing is unique in the world of NDT because of the type of data it collects. Typical NDT looks for previous flaws in materials, while AE specifically stresses the material and looks for cracks that form as a result of the test. This is useful in determining how fast fractures in

NON-DESTRUCTIVE TESTING4

components are growing. AE provides immediate results which can tell the user how far at risk a part is of reaching a critical breaking point. Because of the portability of AE instruments, it is relatively easy to test components while they are in use in the field. Numerous AE sensors...
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