The high temperature and large pressure of inlet steam lead to large thermal stress and large thermal deformation in high pressure casing of turbine, it has an apparent effect on the reliability of casing and may lead to steamtight problem of the casing. Based on the temperature filed analysis and elastic contact theory, a three dimensional Finite Element model to analyze the deformation and stress of casing has been developed. And then the high pressure casing of a 100 MW steam turbine is analyzed, some numerical results such as temperature distribution, stress and deformation are obtained. It is shown that with higher temperature and larger pressure, larger prestressing of bolt is necessary to guarantee the steamtightness of casing, the operation experience of real casing shows the numerical analysis can provide usable data for casing design and improve its reliability.

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