1.26 strategy
TRANSCRIPT
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Module 1.26
Testing Strategy 1
Frequency regime and bandwidth
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Before Data Collection Check presence and condition ofequipment and tools;
Select location and prepare pipe
surface if necessary;
Check probe orientation, attach ring
with correct orientation and check
that transducers contact the pipe;
Connect leads, turn on instrument,
start software, check ring and
instrument are detected;
Check capacitance and coupling; Complete collection screen inputs,
set range and choose protocol;
Collect.
After Data Collection Check status and raw data. Rectify anyproblems;
Measure visible features and mark on
results;
Classify other features using:
amplitude, shape, symmetry, frequency
behaviour, and orientation;
Auto fit DACs, adjust if necessary;
Check suspicious echoes and/or reverb
(move ring position if required);
Classify unidentified signals and confirmwith other techniques;
Write comments for reporting;
Attach photos and print/export report.
Wavemaker G3 usage checklist
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Toneburst excitation
Instead of a large pulse to excite the waves, we use tonebursts:
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Toneburst excitation
This allows us to chose the frequency and bandwidth of the signal:
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Time traces
The raw time traces are processed to show only the envelopeover distance
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Excitation signal parameters
Frequency used just like in standard UT, except that our transducers
work over a frequency range and not just at a single
frequency
Bandwidth
like choosing a narrow or wide band probe in standard UT
We use frequency regime instead of frequency: a number which normalises the wavelength to pipe diameter
a high number corresponds to high frequency, and a low
number to low frequencies
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Frequency regime
High frequency regime (>6) gives higher sensitivity
shorter propagation distances
Low frequency regime (
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Automatic collection
By default, the software always samples a range offrequencies
Results are presented at interpolated frequency
Frequency regime and the bandwidth of the displayed datacan be changed dynamically after data collection
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Frequency regime
Sweep function:
Use the Frequency regime slider and Animate
buttons to quickly sweep through a range of interpolated
frequency regimes
Animate buttonFrequency slider
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Frequency regime
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Frequency regime
Limits:
Transducer spacing sets an optimum frequency
regime (can be seen from status screen)
Limits are automatically set by the software
Level 1 operators are recommended to work within
the positive frequency regime (fr > 0) only.
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Frequency regime
Recommended frequency regimes:
Recommendations can be found in G3 manual (Table
3.2)
Practice using this and tables 3.3 and 3.5 to determinethe optimum spacing for the following cases:
16 pipe with welded supports
2 pipe with welded supports
Discuss the implications
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Frequency regime
Compromise between range and sensitivity:
Higher frequency regimes give higher sensitivity but
shorter propagation range Lower frequency regimes give lower sensitivity but
longer propagation range
Desired balance depends on the required sensitivity for
a specific application
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Bandwidth
Narrow frequency bandwidth meansMore power
Long time signal (many cycles)
Broad frequency bandwidth means
Better resolution
Short time signal (few cycles)
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Bandwidth
The number of cycles (in time) determines the bandwidth
broad band narrow band
Time
Amp
litu
de
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Dead zone
The transducers cannot receive any signals while theyare transmitting.
This creates the dead zone close to the ring that
cannot be inspected Exact length of dead zone depends on the excitation
signal bandwidth and frequency during collection
When planning ring location always consider the
worst case (the lowest frequency of the test)
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When the frequency regime is lower, the transmissiontime and the dead zone are larger
Dead zone
Low frequency regime High frequency regime
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Broad Band Narrow Band
Dead zone
When the bandwidth is narrower, the transmission timeand the dead zone are larger
Broad band Narrow band
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Dead zone
Display in software automatically activated
Green area is dead zone
Grey area is near field (more later)
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Collection protocols
There are times when it is beneficial to optimise the system forthe pipe that is being screened
Special collection protocols can be selected from the Collect
Screen
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Collection protocol
Short range screening Designed for use on short sections
Frequency is set as high as possible for current ringspacing
Bandwidth is increased to maximise resolution andminimise dead zone
High noise filter Designed for use on pipes that vibrate wildly
Increased averaging is selected Additional hardware filtering is engaged
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Summary
Ability to change the frequency regime and bandwidth isimportant:
We want to achieve a balance between High Sensitivity
Good Axial Resolution
Short Dead ZoneVersus
Range
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Frequency regime for thick pipes
Depending on frequency regime of excitation andthickness of pipe the second torsional mode T(0,2) can
appear
Generally the pipe wall thickness would have to beover 50mm for this to become important
Level 1 operators can only work in the frequency
regime where only T(0,1) is present
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-4.0 -2.0 0.0 2.0 4.0 6.0
0.0
2.0
4.0
6.0
8.0
10.0
12.0
Distance (m)
Amp(mV)
+
F1
-
F1
Frequeny regime for thick pipes
Example of test when T(0,2) IS NOT present
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-4.0 -2.0 0.0 2.0 4.0 6.0
0.0
2.0
4.0
6.0
8.0
10.0
12.0
Distance (m)
Amp(mV)
+F
1
-F
1
Frequeny regime for thick pipes
Example of test when T(0,2) IS present.