Non-Destructive Testing

Thursday, April 2, 2015

Nondestructive testing, also called NDT, offers manufacturers a cost-effective quality control solution. NDT is used to determine the integrity of products and their components without damaging or disassembling them. Much of the technology used in non-destructive testing is similar to that used is medicine – such as x-ray and ultrasounds – detecting flaws that aren’t always visible on the surface.

NDT ultimately save companies money and time in product analysis because it does not require the disabling or sacrifice of the product or system being examined.

The following are some of the more common nondestructive testing methods:

Visual and Optical Testing: this includes visually inspecting with the naked eye or using a computer-controlled camera to identify surface imperfections on a part or product.

Radiography: An x-ray machine or radioactive isotope is used to penetrate a material’s surface with gamma- or x-rays to create an image that reveals defects

Magnetic Particle Testing: a magnetic field is induced in a ferromagnetic material. The surface of the material is dusted with iron particles. The particles concentrate over surface and near surface flaws.

Ultrasonic Testing: High frequency sound waves are transmitted into a material to detect imperfections or changes in material properties.

Penetrant Testing: In this nondestructive testing technique a test object is coated with a solution that contains a visible or fluorescent dye. Excess solution is removed from the surface. However the solution conforms to surface defects. When a fluorescent dye is used, an ultraviolet light is shown on the test object to clearly reveal the imperfections. When a fluorescent dye is used a contrast in colors between the penetrant and developer make the imperfections easy to see.

Electromagnetic Testing: Electrical currents or magnetic fields are induced inside a test object. Material defects inside the test object will interrupt the flow of the currents.
Leak Testing: Methods for this include electronic listening devices, pressure gauges, liquid and gas penetrant techniques and a simple soap-bubble test.


Acoustic Emission Testing: When stresses are applied to a solid material, imperfections in the material emit short bursts of acoustic energy. Special receivers can detect and monitor these waves of acoustic energy. Valuable information can be obtained from analyzing the emissions. For instance, the emissions can indicate the material’s structural integrity, can be sued to determine weld quality and can detect leaks.



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