Nondestructive Testing: A Cost-effective Solution to Quality Control

Nondestructive testing (NDT) offers manufacturers a cost-effective quality control solution. An umbrella term for a variety of methods, NDT is used to determine the integrity of products and their components without damaging or disassembling them.

Much of the technology used in nondestructive testing is similar to that used in medicine—such as x-ray and ultrasound—detecting flaws that aren’t always visible on the surface.

Nondestructive testing saves companies money and time in product analysis because it does not require the disabling or sacrifice of the product or system being examined.

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 and internal features.

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, and a developer is applied to draw the penetrant out of the defects. When a fluorescent dye is used, an ultraviolet light is shown on the test object to clearly reveal the imperfections. When a visible 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 used to determine weld quality and can detect leaks.