Review and discussion of the development of synthetic aperture focusing technique for ultrasonic testing (SAFT-UT)

Busse, L.J.; Collins, H. D.; Doctor, Steven R.

doi:10.2172/6977775

Cited by 25 publications

(13 citation statements)

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“…Thus, a highly divergent beam is used to keep a discontinuity in view over as large an aperture as possible. The principle of SAFT is schematically shown in Figure 1 (3) . When the transducer is located directly above the discontinuity, the time delay to receive the defect echo is minimum and as the transducer moves away from this position, the time delay increases in a non-linear fashion.…”

Section: Principle 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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Section: Principle 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

View full text Add to dashboard Cite

show abstract

“…These conditions are satisfied by the following facts: According to the SAFT theory [9], the optimal transducer position shift ( spatial sampling rate) in the aperture for forrning a SAFT image is equal to one half of the transducer diameter( lateral resolution); and it was also found in ultrasonic NDE [2] [3] that the grain noise pattern in an A-line signal is significantly changed when the transducer position is shifted much less than the one half transducer diameter. So we can use the interlaced array method as we described before to reduce the speckle in SAFT images.…”

Section: Saft Image Speckle Reductionmentioning

confidence: 99%

“…This algorithm involves the summation of the raw RF data shifted by predicted time delay. SAFT has been used for the fine grained materials ultrasonic evaluation with excellent results [9] [10]. However, use of SAFT in coarse grained material results in an image which suffers from ultrasonic speckle.…”

mentioning

confidence: 99%

Speckle Reduction in Ultrasonic SAFT Images in Coarse Grained Material Through Split Spectrum Processing

Newhouse

Shankar

et al. 1989

Review of Progress in Quantitative Nondestructive Evaluation

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“…The conventional synthetic aperture focusing technique (SAFr) experiment typically involves a single transmitter with a diverging beam and a single receiver which are scanned to cover the desired aperture. In order to create a correctly focused image, it is necessary to know the transducer location accurately and the appropriate speed of sound [8][9]. The time delay !…”

Section: Synthetic Aperture Imaging and Laser Ultrasoundmentioning

confidence: 99%

High Resolution Laser Ultrasound Detection of Metal Defects

Lorraine

Hewes

Drolet³

1997

Review of Progress in Quantitative Nondestructive Evaluation

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Review and discussion of the development of synthetic aperture focusing technique for ultrasonic testing (SAFT-UT)

Cited by 25 publications

References 0 publications

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

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

Speckle Reduction in Ultrasonic SAFT Images in Coarse Grained Material Through Split Spectrum Processing

High Resolution Laser Ultrasound Detection of Metal Defects

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