Final instalment of personal overview

Ultrasonic testing (UT) has been practised now for seven decades. Initial rapid developments in instrumentation spurred by the technological advances from the 1950s continue today. Through the 1980s and continuing through to the present, computers have provided technicians with smaller and more rugged instruments with more capabilities.

Thickness gauging is an example of an application in which instruments have been refined to improve data collection and make it easier. Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a ‘scribe’. Some instruments are able to capture waveforms as well as thickness readings. The waveform option allows an operator to view or review the A-scan signal of thickness measurement long after the completion of an inspection.

Some instruments are also capable of modifying the measurement based on the surface condition of the material. For example, the signal from a pitted or eroded inner surface of a pipe would be treated differently to that of a smooth surface. This has led to more accurate and repeatable field measurements.

Many ultrasonic flaw detectors have a trigonometric function that allows for the fast and accurate determination of the location of flaws when performing shear wave angle-beam inspections. Cathode ray tubes, for the most part, have been replaced with LED or LCD screens. These screens, in most cases, are extremely easy to view in a wide range of ambient lighting. Bright or low-light working conditions encountered by technicians have little effect on the technician’s ability to view the screen. Screens can be adjusted for brightness and contrast and, on some instruments, even the colour of the screen and signal can be selected. Transducers can be programmed with predetermined instrument settings. The operator only has to connect the transducer and the instrument will set variables such as frequency and probe drive.

Transducers have also contributed to improvements in ultrasonic examination. The materials from the early days of ultrasonic technology, such as quartz (SiO²), lithium sulphate (Li²SO⁴) or barium titanate (BaTiO³), are almost never used today. Instead, powerful new piezoelectric materials are available.

Permanently polarised material, such as quartz or barium titanate, will produce an electric field when the material changes dimensions as a result of an imposed mechanical force. This phenomenon is known as the piezoelectric effect. Lithium sulphate was long recognised as the best receiver material. Preceding the advent of piezoelectric ceramics, piezoelectric crystals made from quartz crystals and magnetostrictive materials were primarily used. The active element is still sometimes referred to as the crystal by us old-timers in the NDT field. When piezoelectric ceramics were introduced, they soon became the dominant material for transducers due to their beneficial piezoelectric properties and the ease of manufacturing into a variety of shapes and sizes. They also operate at low voltages and are usable up to approximately 300°C. The first piezoceramic in general use was barium titanate; this was followed during the 1960s by lead zirconate titanate compositions, which are now the most commonly employed ceramic for making transducers.

Transducers are now available in contact, immersion, paintbrush, roller, focused, delay line, compression, shear wave, phased array and many other forms, shapes and sizes, reflecting the inevitable flow of innovation and progress.

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