1. An Investigation into the use of FEA methods for the prediction of Thermal Stress Ratcheting
Huse, Stephen

2. Abstract Calculate heat transfer for given initial conditions
Calculate thermal gradients and stresses
Predict the onset of thermal stress ratcheting using FEA methods
Compare to ASME code prediction

3. Background (cont.)
Thermal gradients occur due to changes in temperature of fluid flowing through piping
T - Mean Temperature
V - Linear Temperature Gradient, ∆T1
Peak Temperature Gradient, ∆T2

4. Background Bree Diagram Regions σp – Primary Stress, PD/2t
E – Elastic
S – Shakedown
P - Plastic cyclic
R - Ratcheting
σp – Primary Stress, PD/2t
P – Pressure
D – diameter
t – thickness
σt – Secondary Stress, EαΔT1/2(1-v)
E – Young’s modulus
α – Mean coefficient of thermal expansion
∆T1 – Linear temperature gradient
v – Poisson’s ratio
σy – Yield Strength

5. Problem Description
Nuclear power plants have high thermal gradients and pressures resulting in sever primary and secondary stresses
Severe primary and secondary stresses result in accumulating plastic strains known as thermal ratcheting
Prevention of thermal ratcheting is performed by limiting the allowable stresses

6. Methodology
Convective heat transfer of turbulent flow inside a cylinder: Nu=0.023Re0.8Prn
Nu=hd/k
h – convective heat transfer coefficient
d – inner diameter
k – fluid thermal conductivity
Re=vd/ν
v – velocity
ν – kinematic viscosity
Pr – Prandtl number
ABAQUS for solving heat transfer analysis and structural analysis
Geometry
Material properties
Load conditions

7. Results
Stress Vs strain for iterated pressures of 1, 2, and 3 ksi

8. Results (cont)

9. Conclusion
Onset of Thermal Ratcheting is able to be predicted with ABAQUS.
ABAQUS predicted psi, whereas ASME code predicted to 1600 based on different yield stress

10. References
Bree, J. (1967). Elastic-plastic behaviour of thin tubes subject to internal pressure and intermittent high-heat fluxes with application to fast nuclear reactor fuel elements.Journal of Strain Analysis, (2),
2010 ASME boiler & pressure vessel code an international code. (2010). New York, NY: American Society of Mechanical Engineers.
ABAQUS (Version 6.13) [Software]. (2013). Providence, RI: Dassault Systèmes Simulia Corp.