Nondestructive Evaluation of Low Temperature Thermal Embrittlement in Duplex Stainless Steels: Review and Comparison of Multiple Techniques

This paper investigates nondestructive evaluation (NDE) for assessing low‑temperature thermal embrittlement (also known as the 475°C embrittlement) in duplex stainless steel (DSS) alloys. Current assessments rely primarily on destructive methods such as the Charpy test and double‑loop electrochemical potentiokinetic reactivation (DL-EPR). To date, no systematic comparative investigation has been conducted to identify reliable NDE methods for evaluating the 475°C thermal embrittlement in DSS alloys. This paper reviews and appraises several candidate NDE techniques, including thermoelectric power (TEP), alternating current potential drop (ACPD), and nonlinear ultrasound (NLU), as well as ultrasonic velocity and attenuation, with respect to their ability to characterize the mechanical and corrosion property degradation of a DSS alloy. Benchmark comparisons are conducted using a set of controlled UNS S32750 super DSS samples. The advantages and drawbacks of the investigated NDE techniques are discussed in terms of measurement sensitivity, correlation with impact energy loss, and suitability for field implementation. Among the techniques examined, TEP emerges as the most viable technique, not only because of its high sensitivity (up to a 130% change) but also because of its relatively simple experimental setup. ACPD technique shows promise for continuous monitoring with a reasonable level of sensitivity (up to a 6.25% change) to Cr content. While NLU techniques also exhibit high sensitivity (up to 44% and 25% changes), it is currently uncertain to which microstructural mechanism they are sensitive, lacking the ability to isolate the thermal embrittlement effects from other concurrent microstructural changes.