UT-TOFD (Time of Flight Diffraction)

The use of TOFD enabled crack sizes to be measured more accurately , so that expensive
components could be kept in operation as long as possible with minimal risk of failure . The TOFD technique is a fully computerized system able to scan , store , and evaluate indications in terms of  height , length , and position with a grade of accuracy never achieved by other ultrasonic techniques . Measuring the amplitude of reflected signal is a relatively unreliable method of sizing defects because the amplitude strongly depends on the orientation of the crack , instead of amplitude , TOFD uses the time of flight of an ultrasonic pulse to determine the position of a reflector .The more accuracy guaranteed by TOFD in sizing thruwall extention of flaws allows more reliable fracture mechanic calculation for residual life evaluation .



 

UT-Guided Waves (Long Range Ultrasonic)

Long-range ultrasonic inspection or guided wave ultrasonic testing was commercially introduced in early 1998 for in-service monitoring of pipes and pipelines. The oil, gas and chemical process industries now use it for detection of corrosion and other metal loss defects and it has gained acceptance as a valid means of assessing the condition of pipes and pipelines where inspection preparation or access is difficult or expensive. The use of the technology is especially significant in view of the high percentage of unpiggable gas pipelines in the world industries. The technique has been extensively used in the field for evaluating the condition of pipes in the range of 2 to 48 inches in diameter and has performed well in identifying corrosion in pipes in a variety of situations.

 

 

UT-Phased array

Conventional ultrasonic transducers for NDT commonly consist of either a single active element that both generates and receives high frequency sound waves, or two paired elements, one for transmitting and one for receiving. Phased array probes, on the other hand, typically consist of a transducer assembly with from 16 to as many as 256 small individual elements that can each be pulsed separately. These may be arranged in a strip (linear array), a ring (annular array), a circular matrix (circular array), or a more complex shape. As is the case with conventional transducers, phased array probes may be designed for direct contact use, as part of an angle beam assembly with a wedge, or for immersion use with sound coupling through a water path. Transducer frequencies are most commonly in the range from 2 MHz to 10 MHz. A phased array system will also include a sophisticated computer-based instrument that is capable of driving the multi-element probe, receiving and digitizing the returning echoes, and plotting that echo information in various standard formats. Unlike conventional flaw detectors, phased array systems can sweep a sound beam through a range of refracted angles or along a linear path, or dynamically focus at a number of different depths, thus increasing both flexibility and capability in inspection setups.

 

Acoustic Emission Testing (AE)

Acoustic Emission (AE) refers to the generation of transient elastic waves produced by a sudden redistribution of stress in a material. When a structure is subjected to an external stimulus (change in pressure, load, or temperature), localized sources trigger the release of energy, in the form of stress waves, which propagate to the surface and are recorded by sensors. With the right equipment and setup, motions on the order of picometers (10 -12 m) can be identified. Sources of AE vary from natural events like earthquakes and rockbursts to the initiation and growth of cracks, slip and dislocation movements, melting, twinning, and phase transformations in metals. In composites, matrix cracking and fiber breakage and debonding contribute to acoustic emissions. AE’s have also been measured and recorded in polymers, wood, and concrete, among other materials.
Detection and analysis of AE signals can supply valuable information regarding the origin and importance of a discontinuity in a material. Because of the versatility of Acoustic Emission Testing (AET), it has many industrial applications (e.g. assessing structural integrity, detecting flaws, testing for leaks, or monitoring weld quality) and is used extensively as a research tool.