Ultrasonic Testing uses sound waves to determine the quality of the internal structure of weld joints, castings as well as other materials.  It is also used to determine the remaining material thickness when access it limited to only one side. Using specially designed probes, sound waves are sent through the item being tested. Once these sound waves hit a defect or discontinuity within the material, the sound waves then bounces back and the technician interprets the results on an Ultrasonic Testing machine’s screen.  Ultrasonic Testing Machines are designed so the technician is able to size up the defect or discontinuity that has been detected. If the item being tested is free of defects, the sound waves pass right through without any interruptions. Following Ultrasonic Inspection & Testing techniques are carried out by ARL technicians: When caring out Ultrasonic Thickness surveys, the technician uses a calibrated step wedge to set his machine up against know material and material thickness.  Once the machine is calibrated and set, the technician is then able to carry out detailed material thickness checks.  This is usually carried out on such things as in-service pipe lines, in-service pressure vessels and storage tanks.  This is explained in detail below.