ASSESSMENT OF MICROSTRUCTURE CHANGES OF STEEL IN STEAM PIPING BY CONVENTIONAL ULTRASONIC TESTING PROBES

摘要

Creep is one of the main phenomena responsible for degradation of material on in-service equipment operated at high temperatures and pressures e.g. steam pipings and superheaters. Process is accompanied by microstructure changes as well as plastic deformation of the equipment that is difficult to measure via conventional NDT. Ultrasonic waves velocity is able to react on changes created due to microstructure changes and due to change of stress-strain conditions. Measurements performed as a part of this article monitors deformation on a cross-section of a steam piping from heat-resistant steel via area scan of ultrasonic waves velocity ratio. Experiments also confirmed that the trend of the velocity ratio along the part's circumference corresponds to the cross-section measurements and is in correlation with hardness development.