1.1 General Introduction to Ultrasonic Testing
Ultrasonic test instruments have been used in industrial applications for more than sixty years. Since the 1940s, the laws of physics that govern the propagation of high frequency sound waves through solid materials have been used to detect hidden cracks, voids, porosity, and other internal discontinuities in metals, composites, plastics, and ceramics, as well as to measure thickness and analyze material properties. Ultrasonic testing is completely nondestructive and safe, and it is a well established test method in many basic manufacturing, process, and service industries, especially in applications involving welds and structural metals.
The growth of ultrasonic testing largely parallels developments in electronics, and later in computers. Early work in Europe and the United States in the 1930s demonstrated that high frequency sound waves would reflect from hidden flaws or material boundaries in predictable ways, producing distinctive echo patterns that could be displayed on oscilloscope screens. Sonar development during the Second World War provided further impetus for research in ultrasonics. In 1945, US researcher Floyd Firestone patented an instrument he called the Supersonic Reflectoscope, which is generally regarding as the first practical commercial ultrasonic flaw detector that used the pulse/echo technique commonly employed today. It would lead to the many commercial instruments that were introduced in the years that followed. Among the companies that were leaders in the development of ultrasonic flaw detectors, gages, and transducers in the 1960s and 1970s were Panametrics, Staveley, and Harisonic, all of which are now part of Olympus NDT.
In the late 1940s, researchers in Japan pioneered the use of ultrasonic testing in medical diagnostics using early B-scan equipment that provided a two-dimensional profile image of tissue layers. By the 1960s, early versions of medical scanners were being used to detect and outline tumors, gallstones, and similar conditions. In the 1970s, the introduction of precision thickness gages brought ultrasonic testing to a wide variety of manufacturing operations that required thickness measurement of parts in situations where there was access to only one side, and corrosion gages came into wide use for measurement of remaining wall thickness in metal pipes and tanks.
The latest advances in ultrasonic instruments have been based on the digital signal processing techniques and the inexpensive microprocessors that became available from the 1980s onward. This has led to the latest generation of miniaturized, highly reliable portable instruments and on-line inspection systems for flaw detection, thickness gaging, and acoustic imaging.
