Reinforced rubber has found broad application as a construction material for expansion joints in heat exchanger inlet and outlet piping. Traditionally, the products have been replaced based on age, regardless of the service time or conditions. The fundamental reason for this has been the absence of a suitable nondestructive examination (NDE) method which characterizes the true health of the component. Until recently, the primary tools for condition assessment of such rubber products have been:

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• Visual examination of surface condition

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•  Durometer inspection in accordance with ASTM D-2240 (also a determination of surface condition).

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Microwave Interferometric inspection represents a method for characterizing the condition of such an industrial rubber product volumetrically. This paper will provide technical information on this new NDE technology as well as present inspection results of cooling water system expansion joints installed in US commercial nuclear power plants.