NDT as a tool to optimize the maintenance planning of feedwater heaters in power plants
Mechanical features and the integration of feedwater heaters (FH) in the water steam-cycle is conceived in the assumption that their failures would be rare events; but normal operating experience shows that this is not always the case. On this background ENEL has developed during the years diagnostic procedures which significantly improved the knowledge of failure mechanisms and, consequently, the design of new equipment and also maintenance planning. The maintenance policy based on ``action after failure'' (possibly assisted by acoustic monitoring to avoid secondary failures) has been gradually replaced by preventive action, (defective tube plugging), based on the practice of reliable and low-cost inspection methods (e.g. remote field eddy current testing for ferromagnetic materials) performed during planned maintenance of the generation unit. In this paper the relative economic merit of several maintenance policies is evaluated, considering the prevalent failure mechanism (shell-side tube erosion-corrosion) through the development of a mathematical model which takes into account the probability and the unit cost of repair after failure and the cost of the efficiency reduction due to premature plugging. In this situation the economic optimization of preventive maintenance planning actually requires additional information on thickness reduction rate and the assessment of failure rates related to the several defect categories. To this end a systematic monitoring of the tube thickness and tube failures on a representative set of feedwater heaters must be performed, in order to acquire a better knowledge of the pattern of tube degradation in the various situations. Appropriate diagnostic techniques are also developed for other damage mechanisms.
- Research Organization:
- ENEL (IT)
- OSTI ID:
- 20018898
- Report Number(s):
- CONF-9806214--
- Country of Publication:
- United States
- Language:
- English
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