Experimental Research and Assessment for Thermal Fatigue in T-Junction with Mixing Flows
Erlangen, Germany 6 July 2016
Technical Meeting on Fatigue Assessment in Light Water Reactors for Long Term Operation: Good Practice and Lessons Learned
Contents
1
2
3
Introduction
Tests for the pipe tee with mixing flows
Analysis of experimental results
4 Conclusions
1. Introduction
Fatigue is the major aging mechanism for aging management in nuclear power plants. In PSR, LR, fatigue has been taken as a special review topic in China. Within the part where hot and cold water are mixed, thermal stratification, turbulence penetration, thermal striping, and thermal cycling may occur in piping line in NPPs. The experimental facility was built to allow the study on the thermal fatigue in mixing tee more closely in RINPO under National Project and the NPP project support .
2. Tests for the pipe tee with mixing flows
Cold water was supplied to the main pipe and hot water was supplied to the branch pipe by pump Fluid in branch pipe was heated by automatic control electric-heater Flow rate which controlled by electric valve was measured with high-precision mass flowmeter Pressure in test loop was stabilized using pressurizer
Thermocouples was placed in fifteen measuring positions along the length of branch pipe. In each cross-section, 5 to 10 thermocouples were used for monitoring. To measure the pipe ID wall temperature without disturbing the flow , thermocouples were installed within the pipe wall at a distance of 1.5mm from the inner surface of pipe. 153 thermocouples were used to measure metal temperature. The maximum frequencies of monitoring temperature were 90 Hz.
2. Tests for the pipe tee with mixing flows
The purpose of strain measurement is to verify the stress calculation results by FEM and simplified methods. 4 groups strain gage were installed in 4 sections of branch pipe, each group includes 3 strain gages with 45°arrangement.
2. Tests for the pipe tee with mixing flows
Test results in steady states Inlet temperature of main pipe Flow rates of main pipe
Inlet temperature of branch pipe Flow rates of branch pipe
Temperature fluctuation and temperature stratification
2. Tests for the pipe tee with mixing flows
Test results in transient conditions
Tmax=210℃ Tmin=28℃
Qmin=60Kg/h
2. Tests for the pipe tee with mixing flows
In L=360mm section, the maximum temperature difference between top and bottom point is just 5.5℃. By the end of the condition, all temperature in the plane were accompanied by high frequency fluctuation with variational amplitude.
In L=1020mm section, the temperature difference was 61.8℃, it is about 90.3 percent of the total temperature difference of the hot and cold fluid.
2. Tests for the pipe tee with mixing flows
The results comparison of the temperature within wall of top point and bottom point between two sections reveal that the temperature of pipe wall are affected by wall thickness and distance along branch pipe. The temperature fluctuations arising due to mixing flow are of a relatively high frequency, as compared to the hysteretic temperature of outside surface because of heat capacity of pipe wall.
2. Tests for the pipe tee with mixing flows
3.Analysis of experimental results
3.Analysis of experimental results
3.Analysis of experimental results Mean Temp
Linear Temp
Nonlinear Temp
To proof the reasonability of the simplified method. the calculation results obtained by inverse transfer method compare with simplified method, and the stresses from simplified method is slightly larger than the stresses from inverse transfer method.
Transforming the strains into stresses under considering the thermal output and gage factor variation with temperature, null drift, and so on. the stress results from simplified method are somewhat conservative when compared with measured results. The cause of the conservatism is plane assumption that may lead to larger axial stress in considered section.
3.Analysis of experimental results
Turbulence penetration zone
The temperature display complicated and random behavior closer to the centre of the mixing zone, and gradually transit to regular and steady state. Away from T-junction to a certain degree, the distribution of temperature presents thermal stratification condition.
LES method in this study has better accuracy and calculating process can be used to predict the temperature gradient in pipe wall efficiently.
3.Analysis of experimental results
4.Conclusions
The projected model can be used to determine the turbulence penetration length conservatively was developed according to existing experimental data. Based on the thermal stratification tests, the profiles of stratified temperature from the top to bottom point in the cross-section somewhat present quadratic function relationship. The stress results from the simplified method related to temperature profile function in this study show encouraging agreement with those by using detailed analysis based on inverse transfer method. Combining the tests data, analysis of measured temperature in-site, and LES, the methods provide an acceptable approach to take into account stress distribution of turbulence penetration zone for fatigue life assessment.
The experimental study related to thermal stratification and turbulence penetration in mixing tee with hot and cold water were carried out in this work, valuable information has been obtained by analysis the tests results
THANK YOU .
Chen Yinqiang Research Institute of Nuclear Power Operation Tel: 86-27-81735249 Email: [email protected]
