To achieve the quality and safety in industrial applications, the damaged products must be detected. To do that NDT is used. In NDT, Ultrasonic Time-of-Flight Diffraction is a well-known technique for detecting the size and location of the defects. Nowadays the Time of Flight Diffraction (ToFD) is used for inspecting the materials during production than that of radiography and other ultrasonic NDT procedures. ToFD technique can be used into many different ways. This study gives a review of various ultrasonic ToFD techniques for welding defects and aims at the usage of it.

Ultrasonic Time of Flight Diffraction Technique for Weld Defects: A Review

Time Of Flight Diffraction (TOFD) is a non destructive testing (ndt) technique which use the diffraction of the ultrasonic waves on the tips of discontinuities. In this technique, the data are displayed in the form of images and processing algorithms can be applied, allowing thus automatic detection and characterisation of defects.

The work we present here is an image processing algorithm which permits to detect and locate automatically several cracks present in a structure by analysing a TOFD image. This algorithm consists of two phases: In the first one, a pre-processing reduces the image to a sparse matrix containing only significant pixels, and separates the different groups by a graph-partioning. The second phase (the decision one) is an application of the Randomized Hough Transform on each population of pixels in order to detect and locate parabola characterising each crack defect.

http://www.wseas.us/e-library/conferences/2006elounda1/papers/537-202.pdf

Detection of cracks in materials using the randomized Hough transform on ultrasonic images

In service inspection (ISI) of aged power plant parts has a delicate task to provide information on presence, position, orientation and size of defects in material. As far as results of ISI are just a starting point for elaborate procedure of life assessment or risk analyses, the accuracy and reliability of these results are particularly important. Time of Flight Diffraction (TOFD) technique is regarded as one of ultrasonic techniques capable to fulfil required precision, being approved in nowadays routine inspection of retaining rings or LP turbine rotor discs. Apart from these, usually highly automated inspections, a manual TOFD testing designed for particular plant component reveals reliable and useful defect information as well. In this work, results of TOFD inspection of turbine inlet casing are presented. The component was inspected subsequently during several years up to the point of substitution by a new one. Gained TOFD results are compared with results of visual and metallographic examination of samples cut out from the casing. Key words: NDT, power plant industry, castings, TOFD

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Papers

Advantages and Limitations of TOFD Technique in Casting Inspection