Continuous on-line monitoring of active and passive systems, structures and components in nuclear power plants will be critical to extending the lifetimes of nuclear power plants in the US beyond 60 years. Acoustic emission and guided ultrasonic waves are two tools for continuously monitoring passive systems, structures and components within nuclear power plants and are the focus of this study. These tools are used to monitor fatigue damage induced in a SA 312 TP304 stainless steel pipe specimen. The results of acoustic emission monitoring indicate that crack propagation signals were not directly detected. However, acoustic emission monitoring revealed crack formation prior to visual confirmation through the detection of signals caused by crack closure friction. The results of guided ultrasonic wave monitoring indicate that this technology is sensitive to the presence and size of cracks. The sensitivity and complexity of guided ultrasonic wave (GUW) signals is observed to vary with respect to signal frequency and path traveled by the GUW relative to the crack orientation.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.