The multi-skip TOFD technique has been developed initially for the inspection of inaccessible components such as pipe supports and clamps, for which the number of available proven techniques for in-service inspection in the oil and gas industry at least is currently very limited. The techniques such as CHIME which are currently used for this application only provide limited defect wall loss information. Also, the CHIME technique can be prone to false-calls and, for the application to pipe supports, it can be affected by poor surface condition which may lead to significant signal loss when large probe separations are used. Initial results from laboratory trials of the multi-skip TOFD technique have been highly encouraging on a range of specimens, including those containing both machined defects and natural areas of corrosion. Scans have been made with probe separations of up to 1 m, which is sufficient to allow inspection of wider pipe support assemblies and large pipe clamps. The method provides quantitative information in two conditions. Firstly, accurate measurements of average wall thickness along the line of sight between the probes can be obtained for approximately uniform thickness components. This can be used to measure the loss of wall for corroded/eroded areas which extend approximately uniformly between the probes. Also, and potentially of equal importance, the technique can verify that there are no extended areas of significant loss of wall under a pipe support or clamp. The results of the laboratory evaluation trials have shown that the CHIME and multiskip TOFD techniques are to some extent complimentary, and there would be benefit to applying both techniques in some circumstances. The CHIME method was shown to be capable of detecting reliably the deeper defects (some of which were missed or could not be sized using multi-skip TOFD). However the multi-skip TOFD method gave good detection and sizing results on many defects in the scanned specimens.


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    Title :

    Multi-skip TOFD. A quantitative technique for the measurement of wall loss in inaccessible components


    Additional title:

    Multi-Skip TOFD. Ein quantitatives Verfahren zur Messung von Wandverlusten in unzugänglichen Bauteilen


    Contributors:
    Burch, S.F. (author) / Collett, N.J. (author) / Terpstra, S. (author) / Hoekstra, M.V. (author)


    Publication date :

    2006


    Size :

    12 Seiten, 8 Bilder, 5 Quellen


    Type of media :

    Conference paper


    Type of material :

    Storage medium


    Language :

    English




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