Mcdermott Technology, Inc.

Electric Power Research Institute Incorporated

Garry W Roman

John W Berthold

Thomas O Passell

A fiber optic acoustic emission (FOAE) sensor particularly suitable for vibration sensing in a hostile environment has a pair of optical fibers each having an end face. In one embodiment, a hollow tube or core having opposite open ends receives the end faces of the optical fibers. Means are provided for fixing the optical fibers in the hollow core with the end faces facing each other and spaced by a distance from each other in the core. A signal processing unit is connected to the optical fibers for supplying light to, and for receiving light from, the optical fibers and for measuring variations in optical phase which result in changes in the light intensity due to vibrations of the hollow core. The hollow core is fixed in a resonant cylinder, and the resonant cylinder is fixed in a housing to complete the sensor. Other embodiments dispense with the need for the hollow tube or core and employ means for fixing the optical fibers within a precision hole, advantageously produced by electrical discharge machining (EDM) or similar processes, provided in the resonant cylinder. A system employing these embodiments of the FOAE sensor is also disclosed.

Fiber optic acoustic emission sensor

An autoclave-enclosed sidestream model boiler is used to predict the onset of intergranular attack ('IGA') and stress corrosion cracking ('SCC') within tubing associated with a power generator. Power generator final feed water is fluid coupled to a pipe within the model boiler, which pipe is strain-gage monitored, preferably using welded fiber optic strain gage devices. The monitored pipe includes a crevice region that produces a water-starved region in which chemical impurities in the feed water become concentrated. A cylindrical heater, located within a portion of the monitored pipe, promotes the water-starved region. A cylindrical portion of the pipe wall preferably is thinned, generally in the region bounding the crevice. Thinning promotes the onset of IGA/SCC within the monitored pipe and also passively amplifies the effects of IGA/SCC to promote easier strain detection. To further promote stress, the monitored pipe is subjected to loading and unloading from an axial load. Drift in the strain gage measurement can be substantially eliminated by taking measurements under axial load and no load conditions, as these two conditions may be attained within a short time of each other, e.g., a few minutes. Long term monitoring of the strain gages provides a measure of onset and progression of IGA and SCC within the autoclave model. These measurements can provide a prediction of the onset of IGA and SCC within the actual power generator, allowing corrective action to be taken before a pipe fails.

Growing community of inventors

Alliance, OH, United States of America

Garry W Roman