Expanding the applicable duration for shrink fitting of the ultrathin-walled reactor coolant pump rotor-can

doi:10.1016/j.anucene.2017.08.029

Annals of Nuclear Energy

Volume 110, December 2017, Pages 1217-1223

https://doi.org/10.1016/j.anucene.2017.08.029 Get rights and content

Highlights

•
A thermal-mechanical coupled finite element model was developed to simulate the whole process.
•
Heat capacity added layer was used to extend the limited time for the process.
•
Shrink-fitted experiments were performed to verify the simulation results.

Abstract

The rotor-can of reactor coolant pump (RCP) is generally assembled on the rotor using shrink fitting technique. The rotor-can is characterized by large height and ultrathin-walled cylinder, thus, its rigidity is weak and heat capacity is quite limited. The shrink fitting process has to be completed within a short limited-time, which makes it difficult for rotor to insert in the rotor-can completely. In order to solve this problem, a new method was proposed to extend the limited time by using a heat capacity added layer (HCAL) during the shrink fitting process. A thermal-mechanical coupled finite element (FE) model was developed to simulate the whole process. The transient heat exchange with a narrow gap between rotor and rotor-can during the shrink fitting process was taken into consideration. The limited time was predicted by calculating and analyzing the evolutions of temperature field and radial displacement field of the rotor-can. The simulation results indicate that the limited time of the shrink fitting process can be significantly extended with the increase of HCAL in thickness. Then, shrink fitting experiments were performed to confirm the extending effect of the HCAL. The experimental results of limited time show good agreement with the predicted values. The current results will certainly help the designer to improve the shrink fitting technique.

Introduction

The reactor coolant pump (RCP) in the advanced passive pressurized water reactor is a kind of nuclear canned-motor pump. The rotor is a rotating component in RCP to safely running for 60 years (Cheng et al., 2014, Hu and Wang, 2012, Fetterman, 2009), and would be probably damaged due to the corrosion. The rotor-can is assembled on rotor by shrink fitting process to protect rotor from rotor-can as shown in Fig. 1. The rotor-can is usually made of Hastelloy C-276 and the inner diameter is more than 550 mm, the height is more than 3000 mm and the thickness is about 0.50 mm.

Due to this large height and ultrathin-walled geometric feature, the rigidity of the rotor-can is weak, and its heat capacity is quite small. When the rotor is inserting in rotor-can, since transient heat exchange with a narrow gap occurs and the temperature of rotor-can is decreased, the top end of rotor-can quickly shrinks on rotor firstly, as presented in Fig. 1(b). Thus, applicable duration for shrink fitting process of rotor-can is defined as before the top end of rotor-can contacts with rotor and the whole process has to be completed within this limited time. The whole process is carried out in pit furnace and the rotor inserts in the rotor-can with the help of lifting crane. During the whole hot shrink fitting process, the axis alignment between rotor and rotor-can is required and the speed of lifting crane couldn’t be too high. In order to increase the success ratio, it is necessary to accurately predict and efficiently extend the limited time.

For the shrink-fitted thin-walled parts, Karami and Ghazanfari Oskooei, 1994, Singh, 1994, Gamer and Lance, 1983 have analyzed the longitudinal and circumferential stresses and deformations based on the thermo-elastic theory in thin cylinders. Ozel et al. (2005) analyzed various fit forms for the shrink-fitted hub-shaft joint using finite element method. Abdelsalam and Sedaghat (2013) proposed the fully coupled thermo-elastic analysis of a hollow multilayer cylinder to illustrate the fatigue life of the shrink-fitted compound cylindrical shells. Sun et al. (2010) simulated and optimized the shrink fitting process for a large marine crankshaft by three-dimensional finite element method. It can be seen that previous studies were mainly concentrated on the elastic-plastic deformation and residual stresses for shrink fitting process. Unfortunately, according to our best knowledge, because the applicable duration for shrink fitting is usually enough for previous shrink-fitted parts, the illustration about shrink fitting time was ignored.

In current research, the limited time of the shrink fitting process was predicted by establishing a thermal-mechanical coupled FE model. In order to extend the limited time, a kind of heat capacity added layer (HCAL) was proposed and the effect of the HCAL on extending the limited time was illustrated. Then, experiments of shrink fitting process for the RCP rotor-can was performed in lab to verify the validity and effectiveness of the proposed method.

Section snippets

Boundary conditions of thermal computation

The boundary conditions are shown in Fig. 2. The rotor is assumed to be at 20 °C before contacting with rotor-can. The boundary conditions contain the heat and radiation exchange between the rotor-can and the hot air. Specially, the transient heat exchange between rotor-can and the rotor with a narrow gap is considered.

The heat exchange process between the external surface of the rotor-can and hot air is considered as follows: $- k \frac{\partial T}{\partial n} = h_{c} (T - T_{a})$ $h_{c} = 35 w / (m^{2} ° C)$ $k = f (T)$ where k is the thermal conductivity

The prediction of limited time

The external radius of the rotor is manufactured with radial interference respect to the inner radius of the rotor-can. The rotor-can expands freely in the heating process, during which the radial interference disappears and the narrow gap appears. The narrow gap relates to the shrink fitting temperature and radial interference, and it increases with the decreasing of radial interference and the increasing of temperature, as illustrated in Fig. 5.

When the rotor is inserting in the rotor-can,

Experimental procedure

The dimension deviation of the rotor-can was controlled by vacuum hot bulge forming technique (Zhu et al., 2014). The radial interference was precisely calculated by measuring the inner diameter of rotor-can and rotor using PI tape as shown. The inner diameter measurement results of rotor-can are presented in Table 2. To ensure the HCAL contact with the rotor, the hoop belt was installed on the outside of the HCAL with a small hoop stress. All the HCAL and the hoop belt were made of Hastelloy

Conclusions

(1)
A thermal-mechanical coupled FE model, which considering the heat and radiation exchange between the rotor-can and the hot air, and the transient heat exchange with a narrow gap between the rotor and the rotor-can, was developed to predict the limited time of shrink fitting process. The predicted values showed good agreement with the experimental results, which verified the reliability of the FE model.
(2)
A new method was proposed to extend the limited time by using the HCAL. The limited time of

Acknowledgment

Thanks for the sponsoring of the Major State Basic Research Development Program of China (973 Program) (No. 2015CB057305).

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Cited by (6)

Evaluation of service reliability of AP1000 nuclear reactor coolant pump rotor-can
2022, Annals of Nuclear Energy
Citation Excerpt :
In order to protect the rotor from the erosion of the coolant in primary loop, a rotor-can was canned out of the rotor. Rotor-can is one of the important parts in the RCP (Li et al., 2017), which is assembled on the outside of the rotor through shrink fitting process. During the service process, the rotor-can is in directly contact with the coolant in the primary loop.
This paper aims to provide a comprehensive scheme for verifying the service reliability of reactor coolant pump(RCP) rotor-can. The stress distribution on rotor-can during the service condition was calculated using finite element method. According to the calculation results, the maximum-stress position was located, and the load spectrum of the maximum-stress position was obtained. The tensile and fatigue experiments were done to study the mechanical properties of Hastelloy C276. Based on the simulation results and the experiment results, the service reliability of rotor-can was analyzed. The results show that during service condition, the maximum stress occurs at the position of the rotor-can corresponding to the position where the unbalance mass was added on rotor, and its value is less than the yield strength of Hastelloy C276. The rotor-can would undergo two alternating stresses during service condition. The values of both of them are smaller than the fatigue strength of Hastelloy C276.
Stress analysis of shrink fitting process of ultra-thin reactor coolant pump rotor-can
2021, Annals of Nuclear Energy
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Moreover, For the ultra-thin wall cylinder rotor-can, the shrink fitting process is quite different from the shrink fitting process of thick-wall workpiece. In our previous work, the shrink fitting process of ultra-thin wall rotor-can has been studied using finite element method, a new method was proposed in that work to extend the limited time (Li et al., 2017). However, that work focused on the limited time of shrink fitting process of rotor-can, the stress condition was not taken into account, and the rotor-can was considered as a perfect cylinder workpiece.
This paper aims to accurately predict the stress evolution and stress distribution during shrink fitting process. The hoop stress on rotor-can after shrink fitting process was calculated using Lame’s equation. Then finite element (FE) method was used to calculate the stress evolution on rotor-can during shrink fitting process. The effects of manufacture defects on stress distribution on rotor-can after shrink fitting process was analyzed. Finally, a shrink fitting experiment was carried out, and the residual stress on rotor-can after shrink fitting was measured by hole-drilling strain-gauge method. The results show that during shrink fitting process, thermal stress would occur on rotor-can along axial direction and hoop direction. After shrink fitting process, the fitting stress was along hoop direction. When there were ring-shaped defects on rotor-can, there would be axial stress in the defective area. The theoretical calculation results, simulation results and experimental results are in good agreement with each other.
Shape-righting capacity analysis of vacuum hot bulge forming process of reactor coolant pump rotor-can with ring-shaped defects
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Citation Excerpt :
It is a thin thickness cylinder with large diameter made by Hastelloy C276 through clipping, rolling circle and welding [2]. The manufacturing quality of rotor-can affects the performance of whole RCP significantly [3]. Due to its thin thickness and large radius/thickness ratio, the precision manufacture of rotor-can is difficult, and wrinkle may appear during welding process due to the uneven deformation in welding area.
Rotor-can is one of the key components of the canned reactor coolant pump(RCP) in nuclear industry and it can be used for protecting the rotor from corrosion damage. It demands high dimension precision, posing great challenges to the processing technology. Vacuum hot bulge forming(VHBF) process is thought as an optional technique to promote the manufacture precision. In this paper, a 2-D nonlinear thermo-mechanical coupled finite element model was established to simulate the VHBF process of rotor-can with ring-shaped defect. Based on this model, the radial displacement field and inner radius distribution of rotor-can after VHBF process were calculated. The shape of defect after VHBF process was predicted. And the shape righting capacity of VHBF process for RCP rotor-can with ring-shaped defect was analyzed. The results show that VHBF process can modify the dimension error and shape error of rotor-can with ring-shaped defect. With decreasing width and increasing height of the defect on rotor-can, the shape-righting difficulty is increasing.
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Finite Element Analysis of the Reduction in Stress Concentration Factors in Shrink Fits by Using Contact Rings
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Characterization of Static Recrystallization of a Ni-Cr-Mo-Based C276 Superalloy in Two-Stage Isothermal Compression
2018, Journal of Materials Engineering and Performance

View full text

Expanding the applicable duration for shrink fitting of the ultrathin-walled reactor coolant pump rotor-can

Highlights

Abstract

Introduction

Section snippets

Boundary conditions of thermal computation

The prediction of limited time

Experimental procedure

Conclusions

Acknowledgment

Mater. Sci. Eng. A

Ann. Nucl. Energy

Int. J. Mech. Sci.

Mater. Des.

Mater. Sci. Eng., A

Int. J. Press. Vessels Pip.

Mater. Des.