Evaluation of the Precipitation Process of a Clad Pipe by the Thermoelectric Potential Technique

Abstract

The article reports a study carried out on metallic samples extracted from a metallurgically bonded clad pipe (API 5L X65 steel-Inconel 825 alloy) subjected to a solution heat treatment at 1200 °C and a subsequent aging treatment at 650 °C for different times in order to promote microstructural changes in thermo-metallurgical bonded materials. The non-destructive thermoelectric potential (TEP) technique was used to monitor microstructure changes due to the artificial aging process. In addition, micro-hardness tests were carried out on the metallic materials and micrographs were obtained by means of an optical and scanning electron microscope (SEM). The TEP value changed with solution treatment temperature and reached a maximum value for solution treatment at 1200 °C. The changes in TEP during solution treatment were caused by changes in the solubility of the alloying elements. In the artificial aging process, the TEP value decreased with increasing aging time due to the precipitation process, but exhibited distinct characteristics for the different zones at the clad pipe samples.