Nuclear Plant Journal, May-June 2015 NuclearPlantJournal.com
21
tubing for new plant construction, and in
weld overlays applied to repair damaged
transition joints in the operating fleet.
Currently, detailed inspections for
fabrication flaws are conducted after field
DMWs are completed. Defects created
early in the process may require removal,
followed by weld repair, sometimes from
the inside diameter. Real-time NDE will
allow quality control immediately after a
weld pass, eliminating wait time for defect
mitigation and minimizing excavation
and rework. This will reduce welding
costs and avoid the residual stress that
can be created during post weld defect
mitigation, potentially decreasing the
future susceptibility of DMWs to stress
corrosion cracking.
EPRI began exploring real time
welding NDE in 2010, proceeding with
a literature review, innovation scouting,
and laboratory testing of technologies
that could enable real time NDE
without disrupting the welding process
(1025631). In 2013, EPRI selected high
temperature ultrasonic testing (UT) and
electromagnetic acoustic transducer
(EMAT)
technology
for
further
development at its laboratory in Charlotte,
NC. They were evaluated on test plates
engineered to incorporate representative
defects and then reheated to simulate real
time NDE under field conditions. Results
demonstrated that both technologies
offer significant potential for pass by
pass inspection at nuclear plant sites
(3002004436).
In 2015, developmental work
through EPRI’s Welding & Repair
Technology Center and the Advanced
Nuclear Technology Program will focus
on improving the NDE sensitivity and
stability of high temperature UT under
welding conditions and on optimizing
inspection parameters for typical DMW
configurations.
Demonstration
and
qualification testing for field welding
applications are planned in 2016-17.
To document stress corrosion cracking
mitigation benefits, residual stresses
from shallow repair of defects detected
during the welding process will be
compared to those of conventional inside
diameter repair performed after welding
is complete.
Contact: Dana Couch, telephone:
Guided Wave
Technology
Expanding the application of guided
wave technology to enable buried
pipe inspection around elbows could
help ensure pipe integrity and reduce
inspection costs.
Guided wave technology offers a
number of attractive features for buried
pipe inspection at nuclear plants. For
example, the technology can be used to
screen pipes for damage without taking
them out of service, and the technology
enables rapid inspection, as much as 10-
30 feet per hour.
Guided
wave
technology,
however, was originally developed
for examining straight runs of piping.
Signal interpretation is difficult for
waves that have traversed an elbow, and
contemporary inspection equipment
is unable to effectively control guided
wave energy beyond an elbow. EPRI is
investigating technical solutions to this
problem, with the ultimate goal being to
develop and demonstrate a methodology
for manipulating guided wave energy
past an elbow. Such technology could
enable inspection from inside a building
without requiring any excavation.
The first step is enhanced
understanding of how elbows affect
guided wave propagation. EPRI has
developed methods of approximation
that allow fundamental insights into how
wave energy will propagate beyond an
elbow. They have already proven useful
in predicting wave behavior, as shown in
the figure, where finite element modeling
(FEM) simulations were conducted to
validate the new approximation methods.
In the figure, the upper image shows
the energy profile of a guided wave
Electromagnetic acoustic transducer
technology (EMAT) undergoing testing
for real-time NDE.
simulation designed to focus guided
wave energy on a drilled hole beyond the
elbow. This image represents an instant
in time when the energy has focused on
the hole as designed. The lower image
shows a view of the energy field around
the circumference of the pipe at the axial
position of the drilled hole. Most of the
energy in the plot is concentrated at about
1.7 milliseconds, near the magenta line,
which indicates the position of the drilled
hole. This image shows that the quality of
the energy focus at the drilled hole is very
good, as the energy is tightly concentrated
near the hole.
The next stage of development
involves validation of these wave
propagation concepts using laboratory
experiments, which are scheduled for
2015. If results from those tests are
promising, work in 2016-2017 will
establish a technical basis for the use
of guided wave to inspect pipe elbows
and beyond. This will involve further
theoretical and numerical analysis,
experimental validation, and more
complete characterization of the
advantages and limitations of the new
tools. Additionally, EPRI will work
to integrate the methods into practical
hardware and software to transfer the
ideas into commercial guided wave
inspection of real piping systems.
Contact: Luke Breon, telephone:
Source: Electric Power Research
Institute’s (EPRI) Nuclear News, March
2015.
FEM simulation of focusing guided
wave energy past an elbow.
