Study On Assembly Deviationfor The Low Pressure Cylinder Ofsupercritical 600MW Steam Turbine

As an important power equipment, the supercritical 600MW steam turbine occupies the main market share of the power industry now in China. The diameter of the low pressure (LP) outer cylinder of this turbine is 7000mm approximately. But the thickness of the LP outer cylinder wall is only 32mm. As mentioned above, the LP outer cylinder belongs to typical big thin-wall part. This kind of parts, due to their large volume and low rigidity, are apt to deformation under the force of fixture and the effect of assembly surface during machining and assembling processes. And the quality of the turbine will also be affected by the anormaly of contact among those assembled surfaces. According to the normal technical method based on the experience and qualitative analysis, the turbine must be adjusted and assembled repeatedly, and in some cases even its main part should be machined again. Thus the manufacturing period of the turbine becomes longer and the manufacturing cost is higher. Moreover, there is short of systemic study on the effect of assembly deviation on the steam turbine performance. And the effect on the flow gap and on the LP outer cylinder base contacting surface caused by assembly deviation should be analysed in great need in industry. Therefore, the study of this thesis is of great significance from both academic and practical perspectives for making qualified turbines according to the design standards.As proven by a lot of industrial practices, the assembly deviation of LP cylinder of steam turbine occurs finally on the vertical joint surfaces of LP upper outer cylinder in a form of wedging gap. Based on the finite element analysis method, in this thesis the effect on the turbine performance caused by the assembly deviation of supercritical 600MW steam turbine LP cylinder will be studied. The 3D UG models and finite element analysis models of main parts of LP cylinder are finished at first. And then the assembly deviation should be eliminated by the tighting force of screw bolts. Under this condition and based on the different assembly deviation values, the effect on the screw bolt intensity, the deformation of LP outer cylinder, the flow gap of LP cylinder, the contacting between the LP outer cylinder and base bedplates will be explored. According to the practice of the enterprise, several representative wedgeing gap values are selected and used for studying the alteration trend of LP cylinder flow gap, the affected range on LP outer cylinder base supporting surface and the strength of screw bolt on the LP outer upper cylinder vertical joint surfaces. It is shown with the FEA analysis that the maximum stress of screw bolt, the deformation of LP outer cylinder, the deformation of LP outer cylinder base supporting surface and the vertical deformation of the inlet opening of LP outer upper cylinder increase with the increasing of assembly deviation. But the deformation altering of the contacting surfaces between the LP outer cylinder and LP inner cylinder is very small based on different assembly deviation. Therefore, the LP cylinder flow gap is hardly affected by assembly deviation.The plentiful and comprehensive technical data obtained in the thesis is very useful and valuable for instructing the production. And the analysing method based on wedging gap deviation suggested in this thesis can be extended and applied in the assembly process of other kinds of steam turbines.