POWER July 2020 - 18

FOCUS ON O&M
beams that are focused at a specific
depth in the part.
PA automated scanning can provide:
■ High productivity
■ Large-area coverage in one acquisition
■ High point density
■ Slow mechanical movements
■ Full volumetric representation
■ Data archiving
■ Usable offline data, even by non-NDT
engineers
■ Compatibility with any mechanical properties
and stress analysis tools
Corrosion inspection with a phased
array probe is performed using what is
called a linear scan, which helps increase
the overall efficiency by exploiting the
full width of the probe. Safety is less of
a concern with an automated inspection
configuration that uses phased array
probes because the scanner can move at
a slower speed while still increasing productivity.
For example, a 406-millimeter
(mm, 16-inch) outside diameter pipe with
a wall thickness of 9.5 mm was scanned
with 100% coverage and a resolution of
1 mm × 1 mm at a scanning speed of
100 mm/second (4 in./sec.). The scan
took a total of three minutes.
To help optimize the automated PA
11. The dual linear array probe provides advantages for corrosion inspection, including a larger
beam coverage. Courtesy: Olympus
solution, the data acquisition instrument
must meet the following requirements:
■ Phased array capability
■ Two-axis encoding enabled
■ Easy to operate to increase the pool
of operators and not be limited to one
expert
■ Multiple visualizations of the acquisition
to boost the probability of detection
■ Ability to save, store, and recall acquisition
files to monitor the evolution of
corrosion over time and for audits
9. Standard phased array probes utilize a
pulse-echo approach. Courtesy: Olympus
Combining the Advantages of
Dual Element UT and Phased
Array in One Probe
While standard phased array proposes a
pulse-echo approach (Figure 9), the signal
can be improved, and you can achieve
a near-surface resolution that is similar to
that of UT pitch-catch (Figure 10) transducers,
if you apply the same technology
that separates the transmitter and the
receiver to phased array probes.
The dual linear array (DLA) design incorporates
two arrays of elements yet
separates them with an acoustic barrier,
so they can be used in pitch-catch mode
like a UT dual-element transducer. There
are five main advantages of the DLA
probe (Figure 11) for corrosion inspection.
Larger Beam Coverage. Inspectors
10. The signal in a standard phased array design
can be improved by applying the same
technology that separates the transmitter
and the receiver in pitch-catch transducers.
Courtesy: Olympus
18
can increase productivity and the probability
of detection with the DLA probe's
wider beam coverage. While the width
of a typical UT probe's inspection beam
is 4.7 mm (0.19 in.), making it useful for
spot checks only when used manually,
DLA probes have a beam width of 30
mm (1.18 in.), so a large area can be inspected
quickly. It is, therefore, possible
to generate a C-scan with a higher likelihood
of detecting small flaws.
Locate Smaller Defects. When using
the conventional UT method to monitor
corrosion, inspectors take manual point
thickness measurements on the pipe
(spot checks), typically using a 1-squarewww.powermag.com
inch
grid. However, this can cause inspectors
to miss smaller defects that fall
between the point measurements.
The smaller elements used in DLA
probes help inspectors perform high data-point
density inspections faster than
what can be accomplished using conventional
dual UT probes. With a higher
point density, you can reduce the chances
of missing small defects.
Better Near-Surface Resolution.
DLA probes employ the pitch-catch technique
for increased near-surface resolution
as compared to phased array probes
that use pulse-echo mode. DLA probes
have a minimal interface echo, enabling
inspectors to locate flaws as close as
1 mm (0.046 in.) from the surface. This
feature is essential for locating critical
defects such as wall thinning and pitting.
Corrosion Scanning Made Easy. The
probe can be used for encoded data acquisition
using the mini-wheel encoder
or any Olympus scanner and comes supplied
with OmniScan setup files, so you
can start your inspections quickly with
minimal setup time.
Thanks to enhanced features, such as
built-in irrigation and a replaceable delay
line that can be contoured to better
adapt to pipe curvature, the DLA corrosion
probe can also be used to perform
semi-automated inspection using the
MapSCANNER or automated inspection
using the MapROVER with improved
sound transmission and no headaches
having to deal with couplant.
Reliable and Versatile. On top of a
replaceable delay line, DLA corrosion
probes feature a carbide wear plate for
extra protection. The probe also features
an integrated stabilization system
with a quick radius adjustment for
increased stability on curved surfaces
with a 4-inch outside diameter all the
way up to flat surfaces. ■
-Simon Alain is product manager, Scanners
and Inspection Solutions,
for Olympus.
POWER | July 2020

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POWER July 2020

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