Nondestructive Characterization of Neutron Induced Embrittlement in Nuclear Pressure Vessel Steel Microstructure by Using Electromagnetic Testing
By using nuclear power for energy generation the pr essure vessel wall is exposed to neutron fluences of different levels depending on the distance to th e core. Hence materials undergo a change in their microstructure in terms of embrittlement, to be mea sured as toughness reduction and shift of the Ductile-to-Brittle Transition Temperature (DBTT) to higher temperatures. Normally plant safety concerning this change in mic rostructure is assured by destructively testing surveillance samples. These are standard te nsile and ISO V-specimen which consist of exactly the same material as the pressure vessel and its we ld metal, being exposed to accelerated irradiation rates within special irradiation channels allowing a pronounced ageing. It is demonstrated that electromagnetic parameters allow to characterize the changes in the microstructure generated through neutron irradiatio n. After a defined calibration process a quantitative characterization of the embrittlement specially in terms of the shift of the DBTT is possible. This has been demonstrated for reactor pr essu e vessel steels used in nuclear power plants o f eastern and western designs. As testing methods 3MA ( icromagnetic, Multiparameter, Microstructure and stress A nalysis) [1] and the dynamic magnetostriction using EMAT (Electromagnetic Acoustic Transducers) have been applied in a nondestructive c ombination measurement system. Further experiments show the possibility to measure 3MA and dynamic magnetostriction quantities through an 8 mm thick austenitic stainle ss steel cladding.
Robust solutions of inverse problems in electromagnetic non-destructive evaluation
Non-destructive testing (NDT) is the application of physical measurement technology based on energy interaction with the material and its nonconformities. The material's response is sensed by transducers and sensors which?in most cases?scan the component and document the results in inspection images. However, NDT measures a physically defined quantity or even an intrinsic property. The difference between non-destructive evaluation (NDE) and NDT is in the interpretation of the inspection data. NDE has to discuss the inspection results in terms of quality elements and characteristics which are relevant to describe the fitness of the material for use. In the case of macroscopic defects these are the kind of defect (cracklike, globular) and its size and orientation to the main stress directions; in the case of material property determination the parameters are mainly mechanical properties. Therefore, in NDE one has to solve inverse problems. The solution of inverse problems based on mathematical procedures such as integral equations is a strong developing discipline and most of the articles prepared for this special issue of the journal have the objective of discussing the latest state of the art in that field. However, practical NDE needs robust and quick solutions which are to be applied mainly online. Therefore, we present here inversion procedures based on multiple linear regression algorithms applied to inspection data. We describe the calibration procedure to fit the free parameters of the model functions and give examples of practical applications in industry.
Finite Difference Modeling on the Temperature Field of Substrate in Friction Surfacing
Friction surfacing is an advanced process of great potential, especially in the field of repair and reclamation of worn and damaged components. As a kind of thermal processing technology, the temperature profile and changes of the substrate in friction surfacing are important factors to get coatings of high quality. In this paper, the temperature field of the substrate during the process is simulated by finite difference method. The results are consistent with experiments, reappearing the temperature change of the substrate during friction surfacing, allowing further study on figuration and quality of coatings.