New Insights into the Nondestructive Evaluation of Thermally Aged at 475 °C Duplex Stainless Steels: A Comparative Study Between 2507 and 2101 Duplex Stainless Steels

In the oil, gas, and thermal power plant industries, it is highly desirable to assess the integrity of components manufactured with duplex stainless steel (DSS) while in service. One problem is the detection the 475 °C embrittlement; the phenomenon is composition and temperature dependent and is usually evaluated by some special laboratory techniques such as low-angle neutron scattering and Mössbauer spectroscopy. This constraint motivated the search for in-field methods as an alternative and literature research shows that nondestructive evaluation (NDE) methods are capable of measuring microstructural transformations in different metallic alloys; therefore, they are good candidates for in-field 475 °C embrittlement assessment. Although considerable evidence is reported, it is still not clear how the chemical composition affects the NDE variables. In this study, three NDE methods, namely ultrasonic shear wave birefringence (SWB), thermoelectric power (TEP) coefficient, and electric conductivity (EC) measurements, were conducted to track the effects of thermal aging at 475 °C in two different chemical composition DSS alloys. The experimental results were compared to Vickers microhardness measurements and scanning electron microscopy (SEM) and Electron Back-Scattering Diffraction (EBSD). EC and TEP techniques appear to be the most promising to track nondestructively the embrittlement phenomenon in the field.