Ultrasonic Inspection is one of the NDT methods to find out the condition of elastic materials (metals and few non – metals) by means of injecting mechanical vibrations into the materials. This method is capable of detecting surface, subsurface and internal discontinuities on materials. Ultrasonic waves are the sound waves having the frequency of above 20,000 C/S which is inaudible to the human ears. Ultrasonic waves are sent through materials by means of transducers and if there is any discontinuity in the path of its propagation, the material would change or modify the waves that can be viewed in the form of indication, through testing system. The theory of ultrasonic propagation is exactly the same as that of audible sound. It obeys the principle of optics. The ultrasonic method is used on processed materials, finished components and for in-service inspection on parts and assemblies. Ultrasonic waves can penetrate through several meters in to the material. The waves can be propagated through liquids, solids and gases.
Pulse-echo instrument capable of exciting a piezoelectric material and generating ultrasonic energy within a weld, and a suitable cathode ray tube scope capable of displaying the magnitudes of receiving sound energy. Calibration standards, liquid couplant.
Most weld discontinuities including cracks, slag, and incomplete fusion. Can also be used to verify weld thickness.
Most sensitive to planar type discontinuities. Test results known immediately. Portable. Most ultrasonic flaw detectors do not require an electrical power outlet. High penetration capability.
Surface condition must be suitable for coupling of transducer. Couplant (liquid) required. Small, thin welds may be difficult to inspect. Reference standards are required. Requires a relatively skilled operator or inspector.
Source: American Welding Society Inc., The McGraw-Hill Companies Inc.