Comparison of electromagnetic inspection methods for creep-degraded high chromium ferritic steels

Abstract

Nondestructive testing (NDT) techniques are used to evaluate the material degradation of ferromagnetic materials, for example, in sensitive environments, such as thermal power plants, where the materials are subjected to creep damage. There is no consensus on the use of an electromagnetic NDT technique to characterize the evolution of creep damage in high-chromium ferritic steels. In this work, an overview and comparison of three different electromagnetic NDT techniques that were applied to high-chromium steels is provided to understand creep evolution in terms of microstructural changes, such as precipitation, dislocation and grain size. To quantify the empirical measurements, a modelling technique was proposed for each applied method. The model parameters were optimized for each NDT technique and tested material. Depending on the model parameters, the accuracy of the parameter determination depends strongly on the NDT technique, which indicates its correlation with the microstructural information.