Using either X-rays or gamma rays, the radiographic non-destructive testing method can provide information on several key areas within a structure. Radiographic NDI can determine the thickness of walls, internal corrosion and potential welding defects both above and below the welded surface. This method is often used to verify compliance to building codes.
Also used in the detection of potential welding defects, liquid penetrant non-destructive inspections often use dyes. An important step in ensuring building and building occupancy safety, this testing method involves applying a dye to the material being tested. The dye is then washed away, leaving clear "indications" of any defects. Some dyes are not visible to the eye and require special lighting to view the indications, while others can be used in normal lighting conditions.
In addition to locating surface cracks, the magnetic particle NDI method is also able to identify cracks and deformities below the surface of metals such as carbon steel and cast iron. A magnetic flux is discharged that goes through the material, and the imperfections then attract metal dust. This identifies the flawed area, and the dust is subsequently sprayed onto the flaw. While good for determining the location and length of a defect, this method does not provide inspectors with the depth.
Similar to the radiographic method of testing, ultrasonic non-destructive inspections can detect cracks above and below the surface. This method can also be used to locate corrosion and measure the thickness of the materials. When used to test steel, ultrasonic NDI inspectors can also check for welding flaws. The ultrasonic testing method uses short sound waves that are directed into the material, and then bounce back and provide the equipment operator with a picture showing any defects.
Positive materials testing uses either X-rays or spectrography to assist in the identification and confirmation of a material's composition and strength. Hardness non-destructive tests help inspectors determine the strength of welded joints, particularly the heat-affected areas. And finally, one of the most popular non-destructive inspections is completed using the trained eye of a professional during a visual inspection. The inspector may use a magnifying glass or other assistance such as cameras in completing this type of testing.