Nondestructive Microstructure Characterization of Tempered Martensitic Steels Through Data Fusion

Abstract

Determination of the present condition of grade 91 steels commonly used in fossil plants presents an ongoing challenge for the industry. Current individual methods of nondestructive evaluations (NDEs) are challenged to reliably determine steel microstructures and are impractical for deployment over large areas such as piping systems. This work investigates the discriminatory potential of an integral assessment combining multiple NDE techniques: magnetic methods (including coercive field, incremental permeability, and Barkhausen noise), thermoelectric power, and ultrasonic methods (including attenuation, backscatter, and absorption). Using a sample inventory of manufactured representative microstructure conditions in thin-walled tubes, five of the eight microstructure conditions could be identified by data fusion. Combined magnetic methods appeared as a primary technique, as this can identify four out of the eight conditions, while the ultrasonic methods can be seen as complimentary tests to increase confidence in classification and identify a fifth condition.