Turbine 360 ° Strength boundary conditions and loads of low pressure inner casing with volute inlet

1. Strength analysis

The comparison between the strain caused by temperature (including preload and gravity) and that under all loads proves that most of the strain comes from thermal deformation, and the pressure is not the main cause of strain.

It can be seen from Figure 1 that the maximum plastic deformation is located in the extraction pipe area, and the maximum is about 2.3%; The average strain of flange, the root of spiral case inner support plate, stiffener and the whole wall thickness range are less than the plastic deformation check standard of thermal power manual.

2. Sealing analysis of horizontal split

1) Contact stress of horizontal split. From the contact stress of horizontal split in Fig. 2, it can be seen that the contact stress of axial split is 0 MPa, and there is steam leakage in some parts; The contact stress of low pressure inner cylinder from inside to outside is greater than 0 MPa, and the sealing performance of inner and outer sides is good.

2) Contact clearance of horizontal split. The gap value of horizontal split is shown in Figure 3, and the area beyond 0.02mm decreases. For the area with large clearance, the sealing key is commonly used in the low-pressure inner cylinder in engineering, and the compression is about 0.96mm, which greatly reduces the clearance of the horizontal split, so as to play the role of sealing.

4.3 axial displacement analysis

The stiffness (deformation) of low pressure inner cylinder is an important aspect in analysis and calculation. The lower the stiffness is, the greater the deformation will be, which will directly cause the steam leakage of the split, the uneven axial and radial clearance of the flow passage, the dynamic and static friction or the reduction of the unit efficiency. The axial displacement of the inlet volute section is listed below, as shown in Figure 3, which can be used as a reference when designing the axial clearance of the flow passage.

4.4 ultimate pressure analysis

The purpose of this analysis is to determine the maximum pressure that causes the structure to rupture. In this analysis, the elastic and fully plastic material without hardening is used for the inner cylinder, and the bolt is also fully elastic, which is carried out under the temperature of steady-state operation. During the calculation, the pressure at all positions will be increased to determine the maximum pressure that the low pressure inner cylinder can bear.

The ultimate pressure load factor reached in the current analysis is 9.306. After loading the required loads (axial force of stator blade), the limit load coefficient will decrease, but it is still very high. The value of 9.306 indicates that the cylinder block can withstand the maximum (9.306 × 443) = 4.13 MPa.