For the aging and plant life management the integrity of the mechanical component and structure is one of the key objectives. In most cases, only a small percentage of mechanical components are subject to significant degradation, e.g. flow-accelerated corrosion which may affect this integrity or the function of the component. Flow-accelerated corrosion (FAC) is a degradation process resulting in wall thinning of piping, vessels, heat exchanger and further equipment made of carbon and low alloy steel. The FAC degradation mechanism occurs only locally under specific condition of flow, water chemistry, temperature and materials applied. The establishment and implementation of a long term strategy is essential to the success of a plant’s FAC program. Effective measures to reduce FAC effects are e.g.: • Optimizing the water chemical treatment (e.g. high-AVT); • Apply improved material concepts for replaced components or lines and/or sufficient wall thickness margins; • Apply qualified repair technologies (e.g. METCO spraying, sheet metal cladding). In case of changes in system operation conditions (e.g. power uprate) the effect on FAC degradation rates should be analyzed before implementation and appropriate precautions should be initiated. For this purpose AREVA NP GmbH has developed the computer code COMSY, which utilities more than 30 years of experience resulting from operational experience and research activities. The COMSY code provides the capability to establish a program guided technical documentation by utilizing a virtual plant model which includes information regarding thermal hydraulic operation, water chemical conditions and materials applied for mechanical components. It provides the option to perform a plant-wide screening for identifying system areas, which are sensitive for degradation mechanisms like FAC. If a system area is identified as being susceptible to degradation, a detailed analysis function enables the condition-oriented service life evaluation of vessels and piping systems in order to localize and conservatively quantify the effect of degradation. Based on these forecasts with COMSY, specific strategies can be developed to mitigate the effect of degradation and inspection activities can be focused on degradation sensitive areas.

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