Critical sections of steam plants and heat-recovery steam generators require materials with enhanced properties such as 9Cr-1Mo steel. Ensuring compliance with specifications for heat treatment, chemical composition, contamination limits, and joint design is crucial to prevent premature failures. This study describes the development of a user-friendly, multi-property nondestructive sensor arrangement to qualify heat-treated 9Cr-1Mo steel. Experimental results demonstrate that correlations between thermal heat treatment and electronic, magnetic, and elastic measurements can determine if T91 steel achieves the necessary microstructure and properties for service. Additionally, rejected parts can be assessed for microstructural issues causing unacceptable properties. The techniques utilize a common electronic setup with different sensors, requiring calibration for specific NDE systems and sensor setups, high-speed data acquisition, and frequency analysis (FFT). Further development on crept and welded samples is recommended to enhance NDE practices for in-service T91 steel conditions.

In the late 1980s, the domestic utility industry experienced failures in dissimilar metal welds (DMWs) between low-alloy ferritic tubing and austenitic tubing in superheaters and reheaters. Extensive research by EPRI found that nickel-based filler metals provided significant service life improvements over 309 stainless steel filler metals. Improved joint geometries and additional weld metal reinforcement were determined to extend service life further. A new nickel-based filler metal was also developed, exhibiting thermal expansion properties similar to the low-alloy base metal and a low chromium content that would result in a smaller carbon-depleted zone than currently available fillers. However, this new filler metal was never commercialized due to a tendency for microfissuring, resulting in less than desired service life. This paper discusses further investigation into the filler metal microfissuring issue and examines long-term testing to determine the filler's suitability for high-temperature applications.