Non-destructive Evaluation
Non-destructive testing (NDT) methods are employed in the technical field as a precautionary to avoid accidence or emergency situations for the human and the environment. A risk situation in the technical field could happen if the load of a component is i
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Non-destructive Evaluation Anton Erhard
Nondestructive testing (NDT) methods are employed in the technical field as a precautionary to avoid accidence or emergency situations for the human and the environment. A risk situation in the technical field could happen if the load of a component is increasing and the wall thickness due to defect growth is decreasing until a critical defect situation. The result of such scenarios could be catastrophic breakdown of the component with sometimes severe aftermath for the human. For this reason, the detection of defects is an essential part of quality control of engineering systems and their safe use. Applications of NDT techniques, however, are much deeper and broader in scope than just the detection of defects, because for the estimation of the component integrity and the timely initiation of preventive accident management measures, the history and extension of the defects should be known for further safety evaluation of the component, e.g., with the help of fracture mechanic procedures. Of course the detection of defects and the knowledge about their position at the component into the volume or on the surface is important and is the first step in the direction to technical diagnostic, i.e., diagnostics is used to determine the causes for problems like material degradation, damages, or accidents.
A. Erhard (&) Bundesanstalt für Materialforschung und –prüfung, Unter den Eichen 87, 12205 Berlin, Germany e-mail: [email protected]
Within the meaning of diagnostics in the present chapter the definition is: identification of the defect size and defect character (if possible). Mostly, if the character is known, the defect growth velocities can be estimated using synergies of well-known mechanisms. Together with a-priori information an evaluation of the component safety is possible. Unfortunately, the determination of the real character of a defect employing NDT methods is difficult. It is often satisfactory to know the shape of the defect, i.e., more volumetric, that corresponds with pores or slag inclusion and more planar that corresponds with cracks or lack of fusion. From that information diagnostics about the generation of the flaws and about the safety is derivate. Further, the time of flaw geneses is important. In [1] there are mentioned three stages for flaw generation: – The first stage is during primary manufacturing, e.g., castings and forgings. – The second stage is fabrication into structures, in which welding is the most important process. – The third stage is the flaw generation during operation. As mentioned above, the knowledge of the flaw extensions is essential for the diagnostic of the component, i.e., the integrity assessment. Therefore, in the next chapter NDE methods which have a potential to measure these extensions (defect sizing) are described. The fundamentals of these NDE techniques are explained in some books and publications and are not part of this book.
H. Czichos (ed.), Handbook of Technical Diagnostics, DOI: 10.1007/978-3-642-25850-3_9, Ó Sprin
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