Effect of Focal Law Parameters on Probability of
Detection in Phased Array Ultrasonic Testing Using a
Simulation and Case Study Approach
Publication: Publication Date: 1 November 2016Testing Method:
The growing energy industry has demands for
high-quality, cost-effective solutions in design,
fabrication, and inspection. Nondestructive testing
(NDT) has always played a crucial role in the
overall product integrity. Phased array ultrasonic
testing (PAUT) is one of the advanced inspection
technologies that promises to become the primary
inspection technique for most applications in the
industry. PAUT has immense inherent capabilities
but, as a system, possesses controllable and
uncontrollable variables, which influence its reproducibility,
repeatability, and detection capability. In
general, the challenge of NDT system capability is
further compounded by the latest advancements in
material and product diversities, which demand
system validation. Validation using simulation
software is likely to be a promising alternative to
conventional validation techniques that utilize
specimens with known reflectors. Simulation
software takes into account most of the influential
parameters involved during an inspection
regarding the transducer, geometry, and material
inspected. This paper provides outcomes on the
effects of focal law parameters of PAUT on probability
of detection in the aspects of detectability,
resolution, and sizing of flaws. Several S-scan
plans were formulated using focal parameters,
including element quantity, pitch, focal depth,
range of angle, and angle resolution. All of the
scan plans were analyzed using simulation and
practical trials to derive the best scan plan in
terms of detectability, resolution, and sizing.
Factors affecting the PAUT signal response due to
the NDT system (probe configuration and scan
plan), part (geometry and material properties), and
flaw (size and orientation) were accounted for.
However, other factors, including psychological
and physiological human factors, were not considered.
The study infers that for an effective PAUT
examination, focal law parameters must be
validated either through practical or simulation
approach. In addition to proving the necessity of
validating the focal law parameters, a simulation
approach to evaluate the smallest detectable
discontinuity based on effective scan plan was also
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