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Home - About NDT

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What is NDT?-The field of Nondestructive Testing (NDT) is a verybroad, interdisciplinary field that plays a critical rolein assuring that structural components and systemsperform their function in a reliable and cost effectivefashion. NDT technicians and engineers define andimplement tests that locate and characterize materialconditions and flaws that might otherwise causeplanes to crash, reactors to fail, trains to derail,pipelines to burst, and a variety of less visible, butequally troubling events. These tests are performed ina manner that does not affect the future usefulness ofthe object or material. In other words, NDT allows parts and material to be inspectedand measured without damaging them. Because it allows inspection withoutinterfering with a product's final use, NDT provides an excellent balance betweenquality control and cost-effectiveness. Generally speaking, NDT applies to industrialinspections. Technology that is used in NDT is similar to those used in the medicalindustry; yet, typically nonliving objects are the subjects of the inspections.

What is NDE?

Nondestructive evaluation (NDE) is a term that is often used interchangeably withNDT. However, technically, NDE is used to describe measurements that are morequantitative in nature. For example, an NDE method would not only locate a defect,but it would also be used to measure something about that defect such as its size,shape, and orientation. NDE may be used to determine material properties, such asfracture toughness, formability, and other physical characteristics.

Some NDT/NDE Technologies:

Many people are already familiar with some of the technologies that are used in NDTand NDE from their uses in the medical industry. Most people have also had an X-raytaken and many mothers have had ultrasound used by doctors to give their baby acheckup while still in the womb. X-rays and ultrasound are only a few of thetechnologies used in the field of NDT/NDE. The number of inspection methods seemsto grow daily, but a quick summary of the most commonly used methods is providedbelow.

Visual and Optical Testing (VT)The most basic NDT method is visual examination. Visual examinersfollow procedures that range from simply looking at a part to see ifsurface imperfections are visible, to using computer controlled camerasystems to automatically recognize and measure features of a component.

Radiography (RT)

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Rail Inspectio

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Bridge Inspec

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Pipeline Insp

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RT involves the use of penetrating gamma- or X-radiation to examinematerial's and product's defects and internal features. An X-ray machineor radioactive isotope is used as a source of radiation. Radiation isdirected through a part and onto film or other media. The resultingshadowgraph shows the internal features and soundness of the part.Material thickness and density changes are indicated as lighter or darkerareas on the film. The darker areas in the radiograph below representinternal voids in the component.

Magnetic Particle Testing (MT)

This NDT method isaccomplished by inducing amagnetic field in aferromagnetic material andthen dusting the surfacewith iron particles (eitherdry or suspended in liquid).Surface and near-surfaceflaws produce magneticpoles or distort the magneticfield in such a way that the iron particles are attracted and concentrated.

This produces a visible indication of defect on the surface of thematerial. The images below demonstrate a component before and afterinspection using dry magnetic particles.

Ultrasonic Testing (UT)In ultrasonic testing, high-frequencysound waves are transmitted into amaterial to detect imperfections or tolocate changes in material properties.The most commonly used ultrasonictesting technique is pulse echo, whereby

sound is introduced into a test objectand reflections (echoes) from internalimperfections or the part's geometricalsurfaces are returned to areceiver . Below is an example of shearwave weld inspection. Notice the indication extending to the upper limitsof the screen. This indication is produced by sound reflected from adefect within the weld.

Penetrant Testing (PT)The test object is coated with a solutionthat contains a visible or fluorescentdye. Excess solution is then removedfrom the surface of the object butleaving it in surface breaking defects. A

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developer is then applied to draw thepenetrant out of the defects. With fluorescent dyes, ultraviolet light isused to make the bleedout fluoresce brightly, thus allowing imperfectionsto be readily seen . With visible dyes, vivid color contrasts between thepenetrant and developer make "bleedout" easy to see. The red indicationsbelow represent a number of defects in this component.

Electromagnetic Testing (ET)Electrical currents (eddy currents) aregenerated in a conductive material by achanging magnetic field. The strengthof these eddy currents can be measured.Material defects cause interruptions inthe flow of the eddy currents whichalert the inspector to the presence of adefect. Eddy currents are also affectedby the electrical conductivity andmagnetic permeability of a material,

which makes it possible to sort some materials based on these properties.The technician below is inspecting an aircraft wing for defects.

Leak Testing (LT)Several techniques are used to detect and locate leaks in pressurecontainment parts, pressure vessels, and structures. Leaks can be detectedby using electronic listening devices, pressure gauge measurements,liquid and gas penetrant techniques, and/or a simple soap-bubble test.

Acoustic Emission Testing (AE)When a solid material is stressed, imperfections within the material emit

short bursts of acoustic energy called "emissions." As in ultrasonictesting, acoustic emissions can be detected by special receivers. Emissionsources can be evaluated through the study of their intensity and arrivaltime to collect information about the sources of the energy, such as theirlocation.-

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