Eddyfi Technologies Guided Wave Testing Now Finding a Needle in a Haystack Instructions
- June 9, 2024
- Eddyfi Technologies
Table of Contents
GUIDED WAVE TESTING: NOW FINDING A NEEDLE IN A HAYSTACK
Guided wave testing, or GWT, uses low-frequency ultrasound operating between 20-150kHz compared to the MHz frequency range for conventional ultrasonics used for thickness checks. This allows the ultrasound to be broadcast away from the tool and axially along the pipe in GWT. When this broadcast ultrasound encounters a change in cross-section, the change in acoustic impedance of this region causes an echo of sound to return to the tool for detection. Using the welds on a pipe for calibration and comparing amplitudes of other signals to these welds, it is possible to indicate the severity of any corrosion detected. Moreover, using additional advanced methods such as C-scan imaging techniques and, in Eddyfi Technologies’ case, a unique secondary focusing method, it is possible to give angular positioning and circumferential extent. Most experience and use of guided waves have been for LongRange Ultrasonic Testing (LRUT). Lower frequencies (20-50kHz) are used for screening pipelines with ranges greater than tens of meters achieved. These methods and the procedures for this type of inspection are well established and implemented within industry with global standards published, including international standards such as ISO 18211. However, guided waves are for more than just LRUT, as demonstrated in this application for drill riser inspection.
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THE CHALLENGE
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Explore the applicability of a long-range ultrasonic testing solution for shorter ranges such as weld to weld or flange tflange inspection. -
THE SOLUTION
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An improved tool and signal-to-noise enables improved sensitivity, detectability, and positioning of defects, making assessment over a shorter range possible. -
THE BENEFITS
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The principle and sensitivity are transferable to other pipe sizes and materials as a potential solution for consideration to other important inspection challenges within other industries.
The Challenge
This application explores the use of guided waves for MediumRange Ultrasonic Testing, or MRUT, where frequencies in excess of 100kHz are employed. At these frequencies, there is improved resolution due to the shorter pulse length of the ultrasound 1 transmitted. An improved tool and signal to noise allows for improved sensitivity, detectability, and positioning of defects, making inspection over a defined shorter range possible, for example, weld to weld or flange to flange inspection where test lengths are up to 15 meters (50 feet) depending on conditions. A client provided a calibration pipe used for the pretesting of NDT inspection equipment for drill riser testing. The pipe was 114-millimeter (4.5-inch) diameter schedule 80 wall thickness (8.56mm/0.337in). The length of the pipe was 1.83 meters (6 feet) and had eight 1.5-millimeter (1/16-inch) drilled holes at 45° different angular positions and 76-millimeter (3-inch) separation along the pipe. There was a thinned area of pipe where thickness had been reduced by a maximum 1.5 millimeters (1/16 inches) gradually over a 76-millimeter (3-inch) length. A schematic and photograph of the test pipe are shown in Figure 1. A close-up of the defects included in the pipe is given in Figure 2, showing the diameter of the holes and the thinned area.
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The Solution
The Sonyks™ guided wave system (Figure 3) is the first equipment on the market
to use both piezoelectric and magnetostrictive transduction methods for
generating guided waves. Both methods have pros and cons, with the
piezoelectric transducers being most suitable and optimal for the LRUT type
inspection and larger diameter pipes. In comparison, the magnetostrictive
transducers are optimal for small diameter pipes and expand into high
frequencies such as MRUT.
The magnetostrictive collars are comprised of a magnetic strip and an Electro
Magnetic Acoustic Transducer (EMAT) coil housed in a clamp. Torque is used to
provide mechanical coupling when inducing the ultrasound into the pipe. There
have been several limitations to using magnetostrictive guided waves in the
past, particularly the need for bonding the foil to the pipe and the
difficulty in extracting the flexural information from the collected data.
These issues have been overcome with the Sonyks Magnetotools resulting in a
low-profile simple collar, as shown in Figure 4.
The signal-to-noise ratio improvements at higher frequencies and its low
profile make this tool ideal for inspection of small diameter pipes (40-200
millimeters/1.5-8 inches) with limited radial clearance.
The 128kHz, ASME 100-millimeter (4-inch) Magneto-tool with Sonyks software was
employed for this inspection. Due to the short length of the sample, the tool
was positioned at the very end of the pipe such that the pipe end would be in
the dead zone of the data making interpretation easier. In the field, the pipe
lengths would normally be longer. The tool would be situated at approximately
one third along the length. It was possible to inspect forwards and backwards
simultaneously.
Due to the new data collection methodology, a combination of Full Matrix
Capture (FMC) and broadband chirp was utilized. Data was collected using the
Sonyks instrument, and interpretation was carried out on the integrated screen
using the Sonyks softwarOnce the data collection is completed, all the data
ever nehas been captured even the secondary focusing.
On interpretation, the signal-to-noise ratio on this sample was excellent, and
it was possible to detect all the defects within the sample. The collection’s
pulse length was not quite short enough to resolve all eight defects
individually. The C-scan image shows six colour spots corresponding to the
location of the eight defects. However, it is evident that these six spots
rotate around the pipe in precisely the same pattern and position of the
defects in the pipe. It was also possible to detect the thinning of the pipe
between 1.29 and 1.37 meters (5 and 5 feet 3 inches) from the datum of the
pipe end. This area is a band in the C-scan that is fully circumferential
around the circumference. The data displayed in the software is displayed in
Figure 5.
Secondary focusing was used to see if further information and resolution of
the defects could be discerned, and by altering the focal length and focal
distance of the data, it was possible to view each defect in turn and map the
rotation of all eight defects around the pipe from 0° to 315°. These focus
plots are displayed in Figure 6.
In this example, the signal to noise of the tool was excellent, such that it
was possible to find a 1.5-millimeter (1/16-inch) hole on a 114-millimeter
(4.5-inch) diameter. This equates to 0.4% CSA.
The test shows that Sonyks with the high-frequency Magneto-tools has the
potential to find very small (1.5mm or 1/16in) localized defects over a
defined inspection range. From the results, it is anticipated for a clean pipe
that this sensitivity could be applicable along a pipe length of up to 12
meters (36 feet) inspecting weld to weld, flange to flange, or socket to
socket fittings the most appropriate application.
Figure 4:
Sonyks Magneto-tool for 100mm/4in diameter pipe and 128kHz test frequency. The
tool is lightweight, low profile and can be quickly installed.
Figure 5 : A-scan and colour map of the data showing the defects in the pipe. The coloured spots correspond with the defects. The rotation of these spots matches identically with the defects’ rotation on the pipe.
Figure 6 : Focusing shows the defects’ rotation with distance from 0° to 315°
The Benefits
Although this pipe was designed as a calibration test pipe for drill riser
inspection, the principle and sensitivity are transferable to other pipe sizes
and materials as a potential solution for consideration to other important
inspection challenges within the energy, chemical, food, and even
pharmaceutical industries.
For example, particularly interesting would be to inspect stainless steel pipe
where corrosion from chloride attack or microbiological induced corrosion can
lead to very localized corrosion. The MRUT methodology can detect this when
inspecting the pipe section by section.
In addition, a targeted inspection of U-bolt clamps by MRUT is another
highlighted area of interest by the industry. Small diameter pipe clamps are
difficult to inspect. Using MRUT would negate the need to interfere by lifting
or using radiography.
Finally, an inspection of air to soil interfaces where the first few inches of
inspection are important for detecting corrosion is another example of
utilizing the attributes of this technique.
Therefore, targeted inspection on any small diameter pipe 40 to 200
millimeters (1.5 to 8 inches) would be interesting for this technique.
For further discussion and information, please contact us.
The information in this document is accurate as of its publication. Actual
products may differ from those presented herein.
© 2022 EddyfiTechnologies. Sonyks, FOCUS+, Multi-Mode, Teletest, and their
associated logos are trademarks or registered trademarks of Eddyfi in the
United States and/or other countries. Eddyfi Technologies reserves the right
to change product offerings and specifications without notice.
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info@eddyfi.com
2022-04
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