State of Ultrasonics
testing (UT) has been practiced for many decades. Initial
rapid developments in instrumentation spurred by the technological
advances from the 1950's continue today. Through the 1980's and
continuing through the present, computers have provided technicians
with smaller and more rugged instruments with greater capabilities.
Thickness gauging is an example application where instruments have been
refined make data collection easier and better. Built-in data logging capabilities allow thousands of measurements to be recorded and eliminate the need for a "scribe." Some instruments have the capability
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.
Also, some instruments are capable of modifying the measurement based on the surface conditions of the material. For example, the signal from a pitted or eroded inner surface of a pipe would be treated differently than a smooth surface.
This has led to more accurate and repeatable field measurements.
Many ultrasonic flaw detectors have a trigonometric
function that allows for fast and accurate location determination of flaws when performing shear wave 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, contrast,
and on some instruments even the color 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.
Along with computers, motion control and robotics have contributed to the advancement
of ultrasonic inspections. Early on, the advantage of a stationary
platform was recognized and used in industry. Computers
can be programmed to inspect large, complex shaped components,
with one or multiple transducers collecting information. Automated systems typically consisted
of an immersion tank, scanning system, and recording system for a printout
of the scan. The immersion tank can be replaced with a squirter systems, which allows the sound to be transmitted through a water column. The resultant C-scan provides a plan or top view
of the component. Scanning of components is considerably faster
than contact hand scanning, the coupling is much more consistent. The scan
information is collected by a computer for evaluation, transmission
to a customer, and archiving.
quantitative theories have been developed to describe the interaction
of the interrogating fields with flaws. Models incorporating the
results have been integrated with solid model descriptions of
real-part geometries to simulate practical inspections. Related
tools allow NDE to be considered during the design process on
an equal footing with other failure-related engineering disciplines.
Quantitative descriptions of NDE performance, such as the probability
of detection (POD), have become an integral part of statistical
risk assessment. Measurement procedures initially developed for
metals have been extended to engineered materials such as composites,
where anisotropy and inhomogeneity have become important issues.
The rapid advances in digitization and computing capabilities
have totally changed the faces of many instruments and the type
of algorithms that are used in processing the resulting data.
High-resolution imaging systems and multiple measurement modalities
for characterizing a flaw have emerged. Interest is increasing
not only in detecting, characterizing, and sizing defects, but
also in characterizing the materials. Goals range
from the determination of fundamental microstructural characteristics
such as grain size, porosity,
and texture (preferred grain orientation), to material properties
related to such failure mechanisms as fatigue, creep, and fracture
toughness. As technology continues to advance, applications of
ultrasound also advance. The high-resolution imaging systems in the
laboratory today will be tools of the technician tomorrow.