7. CONCLUSIONS
The general goals
of this study were to: (1) test and evaluate the AUT method of inspection in
parallel with both RT and manual UT to determine possible differences in inspection
results, (2) identify possible operational challenges in the fabrication shop
environment, and (3) develop the appropriate procedures for implementing AUT as
a replacement for RT. The following conclusions are based on the work performed
as part of this project:
-
AUT is a viable inspection technique for fabrication
inspection of butt welded steel plates.
-
AUT creates projection images of the defects in the weld along
three axes. One of the three images (i.e., the C-scan) is analogous to a
two-dimensional radiographic film. The other two images provide spatial
information about the defect that RT does not provide. AUT images, like RT
radiographic films, can be archived permanently as a hard copy or in an
electronic format.
- AUT images provide more complete information than manual UT
about the characteristics of the defects in the weld, including defect
position, length, depth, and orientation. Note that RT only provides the x-position,
y-position, and length of the defect.
-
AUT findings were in full agreement with the RT laboratory
results.
-
AUT findings generally agreed with the RT field testing
results. The slight lack of agreement is caused, in part, by the basic physics
behind each inspection method. AUT operates based on an ultrasonic wave theory,
while RT is based on differential absorption of penetrating radiation. The
threshold levels prescribed by the code for UT and RT do not yield identical
results. Therefore, certain defects that are rejectable by RT may be acceptable
under the UT provisions. In this testing, it was found that AUT and UT could
detect RT discontinuities; however, some of these discontinuities were
acceptable according to the UT and AUT code requirements.
-
AUT provides a relatively objective method of analysis. The
decibel ratings yielded by AUT are determined directly from electronic
measurements, without human interaction. With manual UT, the inspector must
determine the decibel rating while simultaneously applying the transducer to
the surface of the test specimen. This process includes maximizing the signals
on the instrument screen and identifying the decibel level and transducer
orientation when the signal matches the threshold value. For RT, the contrast
observed on the radiographic film is subjectively analyzed by the inspector to identify
discontinuities.
-
The time required for setting up, calibrating, and performing
an AUT inspection was generally greater than the time required by either RT or manual
UT. However, AUT took less time than RT and manual UT combined.
-
The P-scan system was not manufactured for use in a bridge
fabrication shop environment. The system currently consists of seven separate
modules with about eight interface cables. These modules should be
interconnected using interface cables prior to performing an inspection at a
fabrication shop. Assembling and transporting the P-scan system from one area
of the shop to another was time-consuming and cumbersome. Thus, improved
packaging by integrating the various modules and interface cables is
recommended.
-
Implementation of a fully automated (robotic) scanner instead
of a manual scanner is recommended. This will improve the inspection rate and
reduce human interaction.
-
Currently, there are defects that can be accepted by RT and
rejected by AUT or vice versa. Further research is recommended to explore the
defect sensitivity of AUT in comparison to RT. This should provide a clearer
understanding of the differences that exist in the acceptance‑rejection
criteria between AUT/UT and RT.
