Technique for shortening the term of periodic inspection of a steam turbine utilizing 3D shape measurement and FEA

抄録

In a conventional periodic inspection of a steam turbine, the amount of clearance change during turbine assembly is obtained by temporary assembly and used in alignment adjustment. Because this temporary assembly takes several days to a week, this paper proposed a virtual assembly method using 3D shape measurement and finite element analysis (FEA) as an alternative to the temporary assembly for the purpose of skipping it and extending the plant operation term. In the virtual assembly, the shape of the horizontal flange surface of the turbine casing is firstly measured by high-precision laser measurement, and the continuous surface of Non-Uniform Rational B-Spline (NURBS) is automatically generated from the measured shape. Then, the horizontal flange surface of analysis mesh is adjusted to the generated NURBS surface to reflect the actual distorted shape. Finally, the FEA simulates the casing assembly and estimates the amount of clearance change during turbine assembly. The effectiveness of the proposed method was confirmed by evaluating the prediction accuracy in actual turbines. The proposed method makes it possible to shorten the total term of the periodic inspection by omitting the temporary assembly with maintaining the appropriate clearance.