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    Influence of Geometric Factors on Results of Ultrasonic Testing of Heavy Forgings


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    The problem of ultrasonic testing of heavy forgings has been treated most extensively both in the United States and in Europe, but the opinions of American and European experts apparently differ considerably. Since the identification of large, extended faults is not a problem and is not discussed in this paper, the interpretation of smaller indications merits an extensive discussion. Rankin and Moriarty (1) consider the ratio between indications of defects and hole echo as a criterion for the disturbing effect. They have developed an evaluation scheme for the specification of rotors based on the number of flaw echos in proportion to the hole echo. This scheme does not account for any determination of the site of the flaw echo within the forging. At first, the ratio between the flaw echo and the bottom echo, regardless of the geometry of the disturbance, was used as a reference basis for evaluation. However, this procedure soon proved unsatisfactory, and therefore the absorption of sound was next considered; later it was observed that the absorption of sound proved inadequate for interpretation in many cases. For this reason numerous tests were carried out with steel specimens furnished with artificial defects, as only such tests appeared promising to enable proper and safe interpretation of these correlations. Kloth (2) has carried out similar tests, principally on aluminum test pieces. At first the reproducibility of the ratio between the flaw echo and the back echo was explored. Specimens 500 mm long and furnished with bore holes of 2-mm diameter at a distance of 150 mm from the front wall were used. The deflection of the back echo was adjusted to 35 mm on the cathode-ray trace and the quartz was coupled with this system by means of oil, whereby 2 Mc per sec and 24-mm diameter were applied. Recording was done principally photographically. Photographic recording is not as convenient as visual observation, since the latter method enables adjustment of a flaw-echo to back-echo ratio. For this very reason, however, the less convenient photographic recording was preferred. Figure 1 illustrates the result. The average height of the recorded defect indication was 8.5 mm, the standard deviation being 2.1 mm or 25 per cent; the average back echo was 34.4 mm, with a standard deviation of not more than 2.1 mm, or 6 per cent. The resulting ratio between the flaw echo and the back echo was 0.249, whereby s = 0.061, or 25 per cent, as was to be expected from the fluctuations of the flaw echos.

    Author Information:

    Krainer, Helmut
    Gebr. Böhler & Co., A. G., Kapfenberg,

    Krainer, Ekkehardt
    Gebr. Böhler & Co., A. G., Kapfenberg,

    Committee/Subcommittee: A01.06

    DOI: 10.1520/STP47752S