Ultrasonic Testing (UT) is a method of nondestructive examination that involves the use of high frequency sound waves to detect flaws in components and welds. UT can also be used to measure the thickness of materials, which is a common way of detecting metal losses from corrosion.
The process works by having a transducer generate an ultrasonic sound wave which travels through the material until it encounters a surface; this causes a part of the sound wave’s energy to be reflected back to the transducer. The time of flight of the reflected energy is measured based on a known material velocity and from this the thickness of the component can be detected. Flaws can be detected and sized based upon the amount of reflected energy and by physically scanning to determine the limits of the reflector.
UT has several advantages over other types of NDE:
- It is capable of detecting not only surface flaws, but sub-surface flaws as well;
- it has superior depth of penetration compared to other methods;
- it is very accurate at measuring discontinuity size and shape; and
- the results of the scan are instantaneous when using electronic equipment.
Of course, it has its disadvantages as well. To work, the method requires an accessible surface on the object being examined. A couplant is usually required to promote sound transfer and certain types of materials, such as those with complex geometries, rough surfaces, coarse grains, or thin materials, are difficult to inspect. Finally, linear defects that happen to be oriented parallel to the sound beam often tend to go undetected.
Hi-Tech Testing has dedicated staff and equipment to provide thickness, soundness, bond-inspection, angle beam examination, and weld inspections using either conventional UT methods, phased arrays, or TOFD. Ultrasonic testing has been and will continue to be one of Hi-Tech Testing’s key offerings. Corrosion investigation during API 653 examinations, ultrasonic recovery boiler thickness surveys and general soundness examination of forgings and castings are performed on a regular basis with special attention paid to the code and/or applicable specification requirements.