Online Creep and Fatigue Monitoring in Power Plants
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Voimakattilan virumisen ja väsymisen jatkuvatoiminen seuranta
Increasing wind and solar power production and deregulation of electricity market have significantly changed electricity market environment in many areas such as Germany, Ireland and parts of USA. Consequently, demand for electricity production using combustion boiler units has been experiencing increasing fluctuation. This has been causing increasing amount of variable load operation and on-off cycles for these boilers. Such operation has undesired effects on condition of boiler pressure part and therefore operability and economic efficiency of whole boiler unit. Objective of first part of this work is to study mechanisms of creep and fatigue occurring in pressure vessels. Then, problems arising from cyclical operation of power boiler pressure part are introduced. Steam turbines are also briefly covered. The latter part of the work discusses possibilities for computer-assisted real time monitoring of boiler condition. More detailed description of a computer application made as a part of this thesis work is also given. One part of the work was to study, if there is need for such applications at the market. Using information provided by a real time monitoring application, it is possible to reduce problems related to creep, thermal stresses and following fatigue. There are reports indicating that underestimating costs related to cyclical boiler operation may have considerable financial consequences. Therefore it would be beneficial to have estimations on such costs. Several available commercial software products include features that as-sist in making these estimations.