A computational approach to thermomechanical fatigue life predictions of dissimilarly welded superheater tubes

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GRIN Verlag, Sep 6, 2012 - Technology & Engineering - 126 pages
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Doctoral Thesis / Dissertation from the year 2012 in the subject Engineering - Mechanical Engineering, grade: cum laude (gut), Karlsruhe Institute of Technology (KIT), course: Mechanical Engineering, language: English, abstract: The primary focus of this work is to investigate the influence of residual stresses on thermomechanical fatigue (TMF) life predictions. Both experimental and numerical methods have been adapted in order to predict the lifetimes of dissimilarly welded superheater tubing in power plants. The fatigue behavior and lifetime predictions of such components are complicated at high temperatures since a complex interaction between thermally activated, time-dependent processes are involved. At the same time, components that operate at elevated temperatures are often subjected to transient temperatures due to start-up and shut-down where thermally induced cyclic stresses can occur. The superposition of thermal transients with mechanical load cycles along with unequal heating of parts of a component result in a complex evolution of damage, leading to TMF failure of the component. To add to the complexity, the degradation mechanisms relevant to welded power plant components can be accelerated by the presence of residual stresses.
 

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Contents

Introduction
4
Viscoplastic deformation and TMF life prediction model
19
Experimental program for material characterization
35
Parameter identification for deformation model
44
Parameter identification for lifetime model
59
Numerical simulation of welding and post weld heat treatment
65
Results of welding and PWHT simulations
74
Fatigue life prediction of welded superheater tubes
81
Discussion
96
Conclusion
104
A Classical life prediction models
112
Stresses in internally pressurized thickwalled tubes
119

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