Liquid Penetrant Inspection

Liquid pentrant inspection is probably the most widely used NDT method. The surface to be inspected is coated with a visible or fluorescent dye solution. The excess dye is removed from the surface, and then a developer is applied. The developer acts like a blotter and draws penetrant out of imperfections which are open to the surface. With visible dyes, the vivid color contrast between the penetrant and the developer makes the "bleedout" easy to see. With fluorescent dyes, a ultraviolet lamp is used to make the "bleedout" fluoresce brightly, thus allowing the imperfection to be readily visible.

Magnetic Particle Inspection

Magnetic particle testing is performed by inducing a magnetic field in a ferro-magnetic material and dusting the surface with iron particles (either dry or suspended in a liquid). Surface imperfections distort the magnetic field and concentrate the iron particles near the imperfections, which indicating the presence of defects.

Ultrasonic Inspection

Ultrasonic testing uses the transmission of high frequency sound waves into a material to detect imperfections within the material or changes in material properties. The most commonly used ultrasonic testing technique is pulse echo. Sound is induced into the material being inspected and reflections (echoes) from internal imperfections or geometrical surfaces are returned to receiver.

Eddy Current Inspection

In Eddy Current examination electrical currents are generated in a conductive material by an induced magnetic field. Interruptions or changes in the flow of the electric currents (Eddy Currents) are caused by imperfections or defects in the material being inspected.

Radiographic Inspection

Radiography involves the use of penetrating X or Gamma radiation to examine parts and products for imperfections. An isotope or X-ray tube is used as a source of radiation. Radiation is directed through a part and onto film. When the film is developed, a shadow image is obtained that shows the internal soundness of the examined area. Possible imperfections show up as density changes in the film.