Non Destructive Evaluation by Time of Flight Diffraction Method Mechanical Applications

The TOFD (time of flight diffraction method) which consists in an ultrasonic method for detection and dimensioning the discontinuities in the mechanical components, is more and more present in the industry. In some cases, the question of opportunity of using TOFD instead of X ray testing is discussed. This paper gives information about the interest and the limitations of the method, and its position in relation with X ray testing. Finally, applications of this method for mechanical engineering are described. Method still often ignored, the TOFD is a new process of ultrasonic control. The recent studies concerning this technique showed its effectiveness and its speed, and its competitiveness compared to radiography, without the disadvantages of the ionizing radiations. It is applied today in fields of control of the welded joints, but not only. In NDT community, the method is not yet known of all, and yet, in a few seconds, it allows the inspection of one meter welding on 50 mm thickness! A rather significant data when one knows that between the installation and measurements, other NDE methods require until several hours. Moreover, measurements are given in millimetres, detection does not depend on the orientation of the defect, and one can use it at high temperatures (up to 250°C). This method: the T.O.F.D. an acronym for Time of flight diffraction. Control TOFD has been increasingly popular, in fact, for these last years, more particularly in the laboratories and companies having a high level of expertise and which seek an advantageous alternative to the methods of non destructive testing (NDT) already existing. The strong probability of detection and especially the measuring accuracy of depth of the indications are there obviously for much. When the limits of the TOFD are reached, the traditional method of ultrasonics inspection can come in complement. The applicability is already rich: nuclear power with petrochemistry while passing by boiler making: for forgings, rolled, or of the pipes; one can use it within the framework of the quality control during the manufacture of engines, die spherical tanks, or of periodic inspections for the maintenance actions. The precise determination of the size of the defects makes it possible to follow their evolution well. But before going further in the possibilities than does the technique offers, how does it work?