Ultrasonic testing is expected to account for the largest market share in 2021. It is presently the most popular ultrasonic testing technique owing to its ability to identify defects and determine their severity accurately. Some advanced techniques such as ultrasonic immersion testing and guided-wave ultrasonic testing can also be used for critical applications in the oil & gas and aerospace industries. Ultrasonic testing has evolved considerably over the last few decades and is the most important NDT technique for identifying and quantifying surface and subsurface defects. Ultrasonic testing and inspection can be conducted by using a wide range of methods, a few of which are manual and cost-effective, while others need advanced automated equipment for determining faults in critical applications. This technique can also be deployed to inspect objects that are not easily accessible through direct contact, such as inspecting the piping system buried under the earth's surface.