The Basics of Non Destructive Testing Part 1

Non-destructive testing methods test mechanical and other properties without permanently altering the subject, which saves time and money in product evaluation.

There are many companies that sell non-destructive machines to test material properties but they rarely explain how their methods work. Eng-Tips Forums member “afronova” posted the question, “Are there any good sites that inform about destructive and non-destructive material testing techniques?”

Well, afronova, there is now.

And so begins a three-part series on nine methods of non-destructive material testing. In part one, we discuss radiographic testing, ultrasonic testing and magnetic particle inspection.

RT – Radiographic Testing

Radiographic testing is often used to inspect assembled components and to find flaws in complex structures. It uses short wavelength electromagnetic radiation in the form of high-energy photons to penetrate materials and inspect for hidden flaws. Neutron radiographic testing uses neutrons in the place of photons.

Neutron radiation can pass easily through lead or steel but is stopped by plastics, water and oils. When radiation directed through the material hits a defect, it scatters. Variations in the radiation exiting the opposite side of the material thus allow quality professionals to identify the location of defects as well as determine the thickness and composition of the material.

In magnetic particle inspection, a part is magnetized either directly or indirectly. Direct magnetization occurs when an electric current is passed through the test object and a magnetic field forms in the material. Indirect magnetization does not involve a current applied to the material but occurs when a magnetic field is applied from an outside source.

Since iron particles concentrate along magnetic field lines, when they are applied to the magnetized part they will cluster around a leakage.