Non-Destructive Testing: Ultrasonic Testing

Inspection of welds using ultrasound is a leading-edge technique for finding in weld flaws. Those involved with welding fabrication must have the necessary knowledge and training of the method and its application, often provided in the NDT technician course.

The basic ultrasonic equipment consists of a power source with CRT screen, probes, and calibration blocks. Ultrasonic waves are generated by applying an electric current from the power source to a probe, which contains piezoelectric crystals, such as quartz. The piezoelectric effect allows the conversion of electrical energy to mechanical energy, which is then transmitted through the material under test. Any energy that is reflected is returned to the probe converts back to electrical energy and is then transmitted to the ultrasonic equipment.

To transmit the sound energy into the material, the air gap between probe and metal must be eliminated and the task is performed by using a couplet, usually oil, grease or water. The calibrated CRT screen displays the history of the transmitted ultrasonic waves. Principally, these are the distance that sound travels of time-base shown on the horizontal axis and the amplitude of any reflector given on the vertical axis.

Prior to testing a weld, all other components which are casting the equipment must be calibrated on a block, which is of the same material and contains known dimensions and whole sizes.

Types of Ultrasonic Beam Modes

There are two types of ultrasonic beam modes usually employed in the testing of welds — longitudinal or normal waves and shear or angle waves. The direction of the longitudinal wave is normal to the surface being inspected and that of a shear wave at an angle. When a change occurs in a material, such as a void caused by a flaw, an acoustic mismatch occurs and some of the sound energy is reflected in the ultrasonic probe, converted into an electrical signal, and this is then electronically displayed on the CRT screen. It is usual to investigate a weld using a shear wave probe as the angle allows the operator to stand off to the side of the world, avoids the good buildup and allows the operator to select a probe angle that will strike the fusion line of the weld preparation at approximately 90 degrees. By reference to the calibration carried out on the test block, the position length and depth of the weld can be analyzed.

Accurate sizing and positioning of flaws are one of the greatest advantages of non-destructive testing. If you are planning to take NDT as a career, register yourself for the NDT technician training program in a reputable school for better learning of Ultrasonic testing and other non-destructive testing techniques.

About This Author

NDT Consulting Services Inc. https://www.ndtcs.com/ Joined: February 24th, 2019