Abstract
There is a possibility that crack fields form in large forgings, if the chemical composition and the manufacturing conditions interact in an unfavorable way and lead to hydrogen flaking. Comparable crack fields were found for example during ultrasonic inspections in reactor pressure vessels of two Belgian nuclear power plants in 2012. In an ongoing research project, new approaches for the assessment of crack fields are developed. The investigation of the reliability of ultrasonic testing techniques for crack fields is also a part of this project. Ultrasonic testing (UT) took place at a test block containing a crack field. The test block was later cut into plates and test specimen for destructive material tests were manufactured. In addition to the ultrasonic testing, magnetic particle testing (MT) was applied at the cutting surfaces of the plates and radiographic testing (RT) was done at the plates. The sum of all nondestructive examinations lead to a data set, that is in general suitable for the calculation of probability of detection curves (PoD). MT and RT deliver crack locations and crack sizes that are compared to the UT results.
With the results, PoD curves are calculated for UT testing at the crack field. Due to shadowing and material damping, the PoD curves should become poorer for areas deeper in the crack field. The paper shows the results from a PoD calculation using a Hit/Miss-Analysis from experimental data. The limits of the technique are discussed as well. Additionally, the interaction for the detected flaws will be investigated as far as possible according to actual codes.
