1. Guided waves Robert Ernst
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2. About Guided Ultrasonics Ltd.
Developer and manufacturer of the Wavemaker pipe screening system
NOT a service provider
Resource for support, training, and consultancy
Their mission is to innovate and develop Guided Waves NDT methods
Company formed in 1999 uniting world experts in guided waves
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3. Typical applications Pipe racks Insulated pipe
Pipe with restricted access
Road crossings
Submerged pipe
Buried pipe
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4. Guided Waves
Basics
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5. Propagation along, not through, a structure
Transducer
Structure
Region of inspected structure
Conventional
Guided waves
The pipe walls form a guide for ultrasonic waves, which directs them down the length of the pipe
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6. Reflection from a Feature (such as corrosion)
When the guided wave hits a change in cross section, it reflects back toward the transducer
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7. Standard UT vs Guided Waves
high frequency
short wavelength
sensitive to small defects at high frequencies
point measurement
Guided Waves
low frequency
long wavelength
sensitive to “small” defects even at low frequencies
rapid screening
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8. Key advantages In service inspection Rapid 100% coverage
Limited access required
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9. The torsional mode
Torsional (twisting of the pipe)
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10. At every change in cross section there is a reflection of the guided waves
The amplitude of the guided wave depends on
The cross section and the cross section al change
The distance from the transducer ring
The transducer ring used
The grey section represents the
cross-sectional area
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11. Change in cross-sectional area
Method is equally sensitive to defects at any depth and wall position
Method is sensitive to changes in cross section (increase or decrease)
Reflection from welds and flanges are used as a reference
Amplitude of reflection is scaled with distance
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12. For example: a weld Incoming wave (100% of energy) Reflected wave
Transmitted wave
(80 % of energy)
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13. At each reflection the transmitted energy gets weakened
Incoming wave (100 % of energy)
20%
80%
16%
64%
13%
51%
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14. These effects appear as an amplitude decay
The reflected amplitude from distant features will be smaller than for close features
DAC curves are used to compensate for attenuation
DAC curves are used as the references
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15. Symmectric reflectors
When they reflect from a symmetric feature (such as a weld), they are reflected as a symmetric wave which appears as a black trace
The reflected wave is presented as a black line on the screen
Pipe
Symmetric Reflector
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16. Asymmetric Reflectors
When the wave is reflected by a asymmetric reflector, then the reflected wave will have a symmetric fraction (torsional mode) and an asymmetric fraction (flexural mode)
The flexural mode is represented as a red line on the result graphic
The amplitude of the red line compared to the black line gives the degree of asymmetry
Pipe
Asymmetric Reflector
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17. Examples to the symmetry
Pure BLACK lines represent symmetric features - Uniform around the circumference
RED lines represent non-symmetric features - Varies around the circumference
Asymmetric feature
Symmetric feature (Weld)
#12403
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18. Determination of wall thickness reduction
The remaining wall thickness can never directly be measured by using guided waves. Guided waves should always be considered as a screening tool.
The relation of the red to the black curve gives a hint about the severityof the feature.
The features will be graded according to the amplitude of the black and red lines.
It is always necessary to follow up any features with complementary methods. Most often conventional UT or visual inspection is used.
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19. Wavemaker G3, System Components
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20. Guided waves
Typical Performance
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21. Detection Threshold
Typically minimum detectable defect is 5% cross sectional change
If pipe is in good general condition defects down to 1% have been detected
A change in the cross section of 1% in a 3” pipe corresponds to a defect with a width of 5 mm and a depth of about half the wall thickness
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22. Diagnostic Range
In ideal conditions 200m of pipe can be screened in each direction from a single test location
Typically range on above ground pipe is 50m in each direction
For buried pipes 20m in each direction is more typical unless the pipe is sleeved
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23. Unrolled Pipe Example Defect at 150° (close to bottom)
Defect at 50° (close to top)
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24. Limiting factors
The general condition of the pipe influences the detection threshold and the diagnostic range
Some coatings or coverings are reducing the diagnostic range, e.g. earth or bitumen wrapping
High external noise such as vibrations from compressors reduce the performance of the technique
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25. Effect of the pipe content
Gas – No effect
Liquids
No effect for low viscous media
Sludge or high viscous media
High viscous media can shorten the diagnostic range drastically by attenuating the signals
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26. References Bayernoil, Neustadt an der Donau, Germany
Statoil, Oslo, Norway
Neste Oil, Finland
Statoil, Norrköping, Sweden
ST1 Raffinerie, Göteborg, Sweden
DynaMate, Södertälje, Sweden
Umeå Hafen, Umeå, Sweden
E-on, Halmstad, Sweden
STS, Norrköping, Sweden
Luleå Energi, Luleå, Sweden
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27. Thanks!
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