Time-of-flight diffraction (TOFD) technique for accurate sizing of cracks embedded in sub-cladding

Baby, Sony; Balasubramanian, T.; Pardikar, R. J.; Palaniappan, M.; Subbaratnam, R.

doi:10.1784/insi.45.9.600.52932

Cited by 15 publications

(5 citation statements)

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“…Time of Flight Diffraction is a well established technique in ultrasonic NDT working on the principle of diffraction from the tips of the cracks [6][7][8][9][10][11][12][13]. Fig.…”

Section: Time Of Flight Diffractionmentioning

confidence: 99%

Interval Dependant Thresholding based De-noising of Ultrasonic TOFD Signals from Austenitic Stainless Steel Welds

Praveen¹,

Vijayarekha²,

Venkatraman³

2013

IJCA

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Austenitic stainless steel has structural values in almost all industries. It is one of the most widely used materials. Qualitative assessment of such important components is of greater importance in very sensitive applications such as nuclear reactor vessels. Ultrasonic based Time of Flight diffraction is a reliable technique in testing the materials for many types of defects in welds. Echo signals obtained by the receiver are also accompanied by ambient scattering noise due to the signal interaction with the grains of the material. This noise degrades the quality of the defect echo signal and at times completely deteriorates the shape of the defect signal there by making it unsuitable for characterization. Signal processing is a necessary aspect in restoring the defect signal"s shape, size etc for proper detection and positioning of the defect in the material. Wavelet Transform is one such popular technique for denoising of the signals in which thresholding of high frequency components removes the unwanted noise. Conventional global thresholding gives good improvement in SNR values. This paper implements an Interval dependant thresholding method and it is found that it has very good improvement in SNR values compared to conventional techniques.

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“…Time of Flight Diffraction is a well established technique in ultrasonic NDT working on the principle of diffraction from the tips of the cracks [6][7][8][9][10][11][12][13]. Fig.…”

Section: Time Of Flight Diffractionmentioning

confidence: 99%

Interval Dependant Thresholding based De-noising of Ultrasonic TOFD Signals from Austenitic Stainless Steel Welds

Praveen¹,

Vijayarekha²,

Venkatraman³

2013

IJCA

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“…The experimental observations with respect to through thickness height of the simulated cracks obtained by radiography, SAFT and TOFD are shown in Table 4. The TOFD measurements carried out on the same blocks, in a separate study have been used for comparison (8) . Comparing the results of SAFT and TOFD, it was found that defects smaller than 2mm in height have been oversized by TOFD.…”

Section: Figure 5: Experimental Set Up Of Saftmentioning

confidence: 99%

Sizing of cracks embedded in sub-cladding using the ultrasonic synthetic aperture focusing technique (SAFT)

Baby¹,

Balasubramanian²,

Pardikar³

et al. 2004

Insight - Non-Destructive Testing and Condition Monitoring

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This paper deals with the experimental work carried out to demonstrate the feasibility of ultrasonic Synthetic Aperture Focusing Technique (SAFT) to obtain improved detection and sizing of vertical/inclined (10° and 15°) simulated cracks underneath different claddings. Crack heights ranging from 1.68mm to 19.04mm underneath stainless steel, Inconel and ferritic steel cladding could be sized with an accuracy of ±0.1 to ±0.3 mm. The problems encountered in TOFD with regard to sizing of near surface cracks was successfully overcome by SAFT. Mis-oriented (inclined) defects embedded below the cladding suffer added disadvantage due to loss of reflected energy due to mis-orientation. Using SAFT even these defects could be sized accurately. Introduction:Pressure vessels heat exchangers and many other components used in many applications such as nuclear reactors, petrochemical, power plants and paper mills are typically fabricated from thick carbon steel covered with austenitic stainless steel cladding. The purpose of the clad is to protect the carbon steel from the environment in the vessel; typically, the clad is not considered a structural part of the vessel. Clad is applied by welding using either an automated or manual process. These clads pose problem for the ultrasonic inspection during the routine inservice inspection. Inspection procedures based on NDE play an important role in structural integrity assessment and this involves the knowledge of the defects present in the structure in the areas particularly subjected to stresses induced by the pressurized thermal shock (PTS). These defects include sub-clad defects of the planar type generally perpendicular to the surface such as under clad cracks; weld cracks, lack of fusion and defects in the cladding. The most commonly used NDE method for these applications is ultrasonic testing. Evaluation of the acceptability of detected flaws according to ASME Section XI requires measurement of the depth of the flaw extending into the base metal. Accurate crack depth or size determination and cracks growth monitoring are essential for safe operation of critical components in industrial plants (1) . To obtain accurate defect sizes using conventional ultrasonic NDT equipment, considerable skill is required because; there are many factors, which affect the accuracy and sizing ability of the ultrasonic inspection. Two main factors that affect ultrasonic inspection of cladded components are: (a) the effect of clad, and (b) the beam spread of ultrasonic beam at longer range. The presence of a welded cladding layer particularly austenitic type, seriously affects the ultrasonic inspection due to its coarse grained anisotropic structure and the surface irregularities this leading to beam skewing, scattering and mode conversion of ultrasonic waves. The heavy scattering of ultrasonic waves in coarse grain structure of the clad results in poor signal to noise (S/N) ratio, in turn resulting in poor detection sensitivity. This problem is minimized to some extent by utilization of...

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“…A direct idea of sizing the surface-breaking crack in ultrasonic testing is to measure the flight time of the diffracted echoes and calculate the crack depth with the knowledge of the geometry of the component, this has led to the development of the Impulse-Echo-Technique (IET) and the Time of Flight Diffraction Technique (TOFD). Shiuh-Chuan Her et al [6], [7] applied the IET to conduct the through-wall detection of the surface-breaking cracks, while Baby et al [8] evaluated the depth of the surface-breaking crack on the far surface using the TOFD. The results of their work showed that these methods can achieve a good accuracy for a crack larger than one wavelength but have a poor performance for the cracks smaller than one wavelength [6], [8].…”

Section: Introductionmentioning

confidence: 99%

“…Shiuh-Chuan Her et al [6], [7] applied the IET to conduct the through-wall detection of the surface-breaking cracks, while Baby et al [8] evaluated the depth of the surface-breaking crack on the far surface using the TOFD. The results of their work showed that these methods can achieve a good accuracy for a crack larger than one wavelength but have a poor performance for the cracks smaller than one wavelength [6], [8].…”

Section: Introductionmentioning

confidence: 99%

The Application of the Factorization Method to the Subsurface Imaging of Surface-Breaking Cracks

Zhang

Huthwaite

Lowe

2018

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

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Abstract-A common location for cracks to appear is at the surface of a component; at the near surface, many nondestructive evaluation (NDE) techniques are available to inspect for these, but at the far surface this is much more challenging. Ultrasonic imaging is proposed to enable far surface defect detection, location and characterisation. One specific challenge here is the presence of a strong reflection from the backwall, which can often mask the relatively small response from a defect. In this paper, the Factorization Method (FM) is explored for the application of subsurface imaging of the surface-breaking cracks. In this application, the component has two parallel surfaces, the crack is initiated from the far side and the phased array is attached on the near side. Ideally, the pure scattered field from a defect is needed for the correct estimation of the scatterer through the FM algorithm. However, the presence of the backwall will introduce a strong specular reflection into the measured data which should be removed before applying the FM algorithm. A novel subtraction method was developed to remove the backwall reflection. The performance of the FM algorithm and this subtraction method were tested with the simulated and experimental data. The experimental results showed a good consistency with the simulated results. It is shown that the FM algorithm can generate high quality images to provide a good detection of the crack and an accurate sizing of the crack length. The subtraction method was able to provide a good backwall reflection removal in the case of small cracks (1-3 wavelengths).

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Time-of-flight diffraction (TOFD) technique for accurate sizing of cracks embedded in sub-cladding

Cited by 15 publications

References 1 publication

Interval Dependant Thresholding based De-noising of Ultrasonic TOFD Signals from Austenitic Stainless Steel Welds

Interval Dependant Thresholding based De-noising of Ultrasonic TOFD Signals from Austenitic Stainless Steel Welds

Sizing of cracks embedded in sub-cladding using the ultrasonic synthetic aperture focusing technique (SAFT)

The Application of the Factorization Method to the Subsurface Imaging of Surface-Breaking Cracks

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