Simplification of the evaluation of inservice inspections using the ALOK-techniques
The basic idea that led to the development of the ALOK-System was to combine both the search phase and the phase of defect analysis during the inservice inspection of pressurized components in nuclear power plants. Therefore, the system has to accomplish the following demands: high sensitivity and high resolution, reliability, reproductibility and comparability of successive investigations, on line presentation of the inspected volume, possibility of the analysis of flaw indications and hence minimization of the necessity of re-examination with more analytical systems, limitation of the expenditure of the evaluation corresponding to the number of flaws. Since the conventional evaluation of amplitude information practically gives no information on the defect geometry, the ALOK-system mainly uses other data that are directly combined with the characteristics of a flaw like position, size, orientation and shape: the time-of-flight of the ultrasonic signals as a function of the locus of th e beam incidence when moving the probe along a line parallel to the plane of incidence. Thus the reflector migrates through the widely spread sound beam. The resulting typical transit-time function is called time-of-flight locus curve, the corresponding amplitude values yield the so-called amplitude curve. The realization of the ALOK technique required the development of a hardware-equipment for fast data acquisition and of a software package for the evaluation of the stored data.