EXTENDE

Generalities

In all cases, the tests are usually performed with probes radiating SV45° or P45° waves upon planar blocks containing vertical backwall breaking flaws. A scanning along X and Y axes is applied in these inspections.

The maximum amplitude of the rectified echoes and the C-scan are stored. Only the maximum amplitude from the corner echo will be extracted.

Back to the UT Module Validation menu
Back to the Validation menu

Several planar specimens are used in the followings experiments. The aim is to evaluate the influence of different parameters.

• Analysis of the echoes from a single notch inspected with P waves generated by a contact probe
• Notches of different heights inspected with SV45° waves generated by contact probes(1 extension)
• Notches of different heights inspected with SV45° waves generated by contact probes (2 extensions)
• Notches of different extensions inspected with SV45° waves generated by immersion probes
• Notches of different extensions inspected with P45° waves generated by immersion probes
• Notches of different extensions inspected with P60° waves generated by immersion probes
• Notches of different dimensions inspected with SV45° waves generated by immersion probes

Back to the top
Back to the UT Module Validation menu
Back to the Validation menu

Analysis of the echoes from a single notch inspected with P waves generated by a contact probe

Configuration

In order to evaluate all the echoes reflecting from a backwall breaking notch with a contact probe radiating P waves, this experiment is performed on a 37mm high planar stainless steel specimen containing a 10mm high and 20mm width backwall breaking notch.

The experiments involve a contact probe. For this Ø12.7mm circular contact probe, the P45° mode is used for inspection. The input signal frequency is 2.25MHz, with 50% bandwidth and 280° phase.

Results

The Bscan are recorded from simulated and experimental data:

The corner echoes from P waves, from SV waves and from converted waves are observed. Sometimes, conversion mode corner echoes are also called mixed corner echoes. Direct and indirect edge diffraction echoes are also identified.

The Bscan can be reconstructed along the P or SV mode ray pathes:

The results are calibrated versus a Ø2mm SDH at 37mm depth.

A good experiment/simulation agreement is obtained for the P, SV and conversion mode corner echoes amplitudes.

The SV mode corner echo is a little bit overestimated and shows two main contributions in the B-scan. It has been further investigated.

Click here for more information.

The main contribution is the P-defect-P-backwall-SV corner echo, as expected with a very favourable path and a strong SV-backwall-P field amplitude.
The SV-defect-SV-backwall-P corner echo contributes with 8dB lesser than the main contribution.


The paths of the contributions are shown here:





The beam corresponding to each mode have been individually computed including one reflection on the backwall (bw):





The simulated SV corner echo is divided into 2 contributions, the second one being not observed experimentally. The SV beam splitting is due to limitations of the model that occur in this case. The strong variation of the transmission coefficient close to the critical angle splits the SV incident beam and consequently the SV reflected beam, which gives rise to a non realistic secondary SV corner echo. However it can be noticed that it has no effect on the main SV corner echo as it can be seen that the discrepancy is only 2dB and the echo is well located.


The Civa development team is working on this specific problem that occurs around the critical angle in order to improve the models already implemented in CIVA.

Back to the top
Back to the UT Module Validation menu
Back to the Validation menu

Notches of different heights inspected with SV45° waves generated by contact probes (1 extension)

Configuration

Then, the case of notches of different heights with the same extension and depth is carried out. The specimens are 30mm high planar blocks containing a backwall breaking notch with a 40mm extension. In the first block the notch is 10mm high, and it is 3.2mm high in the second block.

A Ø6.35mm circular mono-element contact probe is used. The SV45° mode is used for inspection. The input signal frequency is 2.25MHz, with 44% bandwidth and 147° phase.

Results

The results are calibrated versus a Ø2mm SDH of 40mm extension at 28mm depth.

The comparison shows a good agreement, the maximum discrepancy being 1.5dB.


Back to the top
Back to the UT Module Validation menu
Back to the Validation menu

Notches of different heights inspected with SV45° waves generated by contact probes (2 extensions)

Configuration

In this case, the notches of several heights are inspected for 2 different extensions. The mock-up is a planar stainless steel block containing backwall breaking notches of height 2mm, 5mm, 10mm and 20mm for extension 40mm and 5mm. An additional Ø2mm SDH with an extension of 60mm is located at 30mm depth for calibration.

Two mono-element contact probes are used:

The results corresponding to each probe are available by clicking on the size of the probe.

Results

For the 20*22mm rectangular contact probe at 2.0MHz, the SV45° mode is used for inspection. The input signal frequency is 2.0MHz, with 41% bandwidth and 75° phase. The results are calibrated versus the Ø2mm SDH at 30mm depth.

There is a good agreement.

For the Ø6.35mm circular contact probe at 2.25MHz, the SV45° mode is used for inspection. The input signal frequency is 2.25MHz, with 44% bandwidth and 147° phase. The results are calibrated versus the Ø2mm SDH at 30mm depth.

There is an overall good agreement.

The curves show a good agreement with discrepencies lower than 2dB, except for the small notch with the circular probe. In this case the maximum discrepancy is 4dB. As the flaw size (2mm) is close to the wavelength (λ = 1.6mm), this is coherent with well known limitations of the Kirchhoff approximation used in the CIVA response which is a high frequency approximation.


Back to the top
Back to the UT Module Validation menu
Back to the Validation menu

Notches of different extensions inspected with SV45° waves generated by immersion probes

Configuration

In the following experiment, the mock-up is a 20mm high planar steel block with 4 backwall breaking notches: 3 notches of height 2mm and extension 2mm, 5mm and 15mm, and a notch of height 6mm and extension 15mm.

Two immersion probes are used:

Results

The notches are associated with a number in order to display the results:

For the Ø6.35mm circular immersion probe at 2.25MHz with 20mm water path, the SV45° mode is used for inspection. The input signal frequency is 2.25MHz, with 64% bandwidth and 290° phase.
The results are calibrated versus a Ø2mm SDH of 40mm extension at 20mm depth.

There is a good agreement with less than 2dB discrepancy.

For the Ø12.7mm circular immersion probe at 4.5MHz with 20mm water path, the SV45° mode is used for inspection. The input signal frequency is 4.5MHz, with 73% bandwidth and 270° phase.
The results are calibrated versus a Ø2mm SDH of 40mm extension at 15mm depth.

There is a very good agreement with less than 0.5dB discrepancy.

Back to the top
Back to the UT Module Validation menu
Back to the Validation menu

Notches of different extensions inspected with P45° waves generated by immersion probes

Configuration

In order to evaluate the echoes reflecting from a backwall breaking notch with an immersion probe radiating P45° waves, this experiment is performed on a 20mm high planar steel block with 4 backwall breaking notches: 3 notches of height 2mm and extension 2mm, 5mm and 15mm, and a notch of height 6mm and extension 15mm.

The experiments involve an immersion probe. For this Ø6.35mm circular immersion probe with 25mm water path, the P45° mode is used for inspection. The input signal frequency is 4.7MHz, with 56% bandwidth and 255° phase.

Results

The Bscan are recorded from simulated and experimental data. They are also reconstructed using P or SV mode ray paths. This example comes from the inspection of the 6mm high and 15mm width vertical backwall breaking flaw.

The corner echoes from P45° waves, from SV waves and from converted waves are observed. Direct and indirect edge diffraction echoes are also identified.

The notches are associated with a number in order to display the results:

The results are calibrated versus a Ø2mm SDH at 5mm depth.

A good experiment/simulation agreement is obtained for the P and SV corner echoes amplitudes.

The observation of a split simulated SV corner echo made for the analysis of corner echoes regarding the division in two contributions is still valid. This splitting of the SV corner echo in simulation is observed for all the notches. As for the previous probe, the splitting is present in the SV direct beam and in the SV beam reflected beam on backwall (bw).

Back to the top
Back to the UT Module Validation menu
Back to the Validation menu

Notches of different extensions inspected with P60° waves generated by immersion probes

Configuration

In order to evaluate all the echoes reflecting from a backwall breaking notch with an immersion probe radiating P60° waves, this experiment is performed on a 20mm high planar steel block with 4 backwall breaking notches: 3 notches of height 2mm and extension 2mm, 5mm and 15mm, and a notch of height 6mm and extension 15mm.

The experiments involve an immersion probe. For this Ø6.35mm circular immersion probe with 25mm water path, the P60° mode is used for inspection. The input signal frequency is 4.7MHz, with 56% bandwidth and 255° phase.

Results

The Bscan are recorded from simulated and experimental data. This example comes from the inspection of the 6mm high and 15mm width vertical backwall breaking flaw.

The corner echoes from P60° waves, from SV waves and from converted waves are observed as for the P45° radiating probe. Direct and indirect edge diffraction echoes are also identified.

The results are calibrated versus a Ø2mm SDH at 5mm depth.

For all notches, a very good experience/simulation agreement is obtained for the P corner echo amplitude. For the conversion mode corner echo there is also a good agreement with less than 3dB discrepancy.
But some important discrepancies (up to 12dB) are observed for the SV corner echo over all notches. This phenomenon is likely to be similar to the one for the P45° waves discussed above. This configuration is more sensitive since the SV beam angle is closer to the critical angle.

Back to the top
Back to the UT Module Validation menu
Back to the Validation menu

Notches of different dimensions inspected with SV45° waves generated by immersion probes

Configuration

The next experiment evaluates the influence of the notch height for several extensions. The 5mm high specimen contains backwall breaking notches of height 0.5mm, 1.5mm and 2.5mm for 2mm, 5mm and 15mm extensions.

The measurements are performed with two Ø6.35mm circular immersion probes.

Results

For the Ø6.35mm circular immersion probe at 2.25MHz with 20mm water path, the SV45° mode is used for inspection. The input signal frequency is 2.25MHz, with 64% bandwidth and 290° phase. The results are calibrated versus a Ø2mm SDH of 40mm extension at 4mm depth.

For the Ø6.35mm circular immersion probe at 4.7MHz with 10mm water path, the SV45° mode is used for inspection. The input signal frequency is 4.7MHz, with 56% bandwidth and 255° phase. The results are calibrated versus a Ø2mm SDH of 40mm extension at 15mm depth.

The agreement is very good for all cases with the 5Mhz probe and for the 2 higher flaws with the 2.25 Mhz probe (less than 2dB discrepancies).
For smaller notches at 2.25 MHz, we observe a stronger difference between measured and simulated amplitudes but this difference remains acceptable (less than 4dB difference). As the size of the flaw gets closer to the wavelength, it can be expected in these cases to obtain less precised results.


Back to the top
Back to the UT Module Validation menu
Back to the Validation menu

Conclusion for corner echoes

A very good agreement is obtained between measured and simulated results for corner echoes from SV45° waves: the gap between the measured and simulated corner echo maximum amplitudes is less than 2 dB for most of the configurations studied.

In few cases, some discrepancies (until 4 dB) are observed for small notches relatively to the probe center frequency. They occur for example in the following cases:

• Measured/simulated discrepancies between 2 and 4 dB are observed for the notches of 2 mm height with the contact probe at 2.25 Mhz (wave length λ = 1.4mm) but not for the notches of greater heights
• Measured/simulated discrepancies of about 4 dB are observed for the smallest notches (0.5 mm height) with the immersion probe at 2.25 MHz (wave length λ = 1.4mm). The discrepancy between simulation and experiment increases as the flaw size is smaller than the wavelength. This is coherent with well known limitations of the Kirchhoff approximation used in the CIVA response which is a high frequency approximation.

A very good agreement is also obtained between measured and simulated results for corner echoes from P waves: the gap between the measured and simulated corner echo maximum amplitudes is less than 2 dB for most of the configurations studied.

The corner echo from the SV waves associated with P waves is sometimes badly estimated by Civa when incidence is close to the critical angle. This is due to a splitting in the simulated SV beam as explained above.

Further studies will be carried out on this topic.


Back to the top
Back to the UT Module Validation menu
Back to the Validation menu