The Experts below are selected from a list of 21 Experts worldwide ranked by ideXlab platform
Li Ming - One of the best experts on this subject based on the ideXlab platform.
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Cyclic plasticity of welded P91 material for simple and complex power plant Connections
Elsevier, 2019Co-Authors: Li Ming, Arrett, Richard A., Scully Stephe, Harrison, Noel M., Sea . Lee, O’donoghue, Padraic E.Abstract:This paper focuses on with the cyclic plasticity modelling of welded, ex-service P91 material. A multi material model is developed for high temperature cyclic plasticity, including the effects of the three different material zones in the vicinity of the weld: parent metal, weld metal and heat-affected zone. The cyclic plasticity behaviour of the three zones is identified from previously-published high temperature, low cycle fatigue experimental tests on uniaxial parent metal, weld metal and cross-weld (repair weld) specimens on ex-service P91 material. The heat-affected zone is shown to be significantly softer than the parent and weld metals and to act as a focus for concentration of plastic strain, leading to significantly inhomogeneous distributions of stress and strain in the weldment. The multi-material cyclic plasticity model is applied, via a three-dimensional finite element analysis of a welded T-piece header-Branch Connection, to predict the effects of cyclic internal pressure and small amplitude thermal fluctuations. (C) 2016 Elsevier Ltd. All rights reserved.This publication has emanated from research conducted with the financial support of Science Foundation Ireland under Grant Number SFI/2010/IN.1/I3015 and Grant Number 14/IA/2604. The modelling work was supported by the Irish Center for High-End Computing (ICHEC). The Authors also acknowledg the contributions made by the collaborators in this project, including Mr David Joyce and Dr Dongfeng Li (formerly NUI Galway), Prof. Noel P. O’Dowd, Dr. Peter Tiernan, and Mr. Brian J. Golden of the University of Limerick, Ms Adelina Adams of ESB Energy International and Prof. Tom H. Hyde, Prof. Wei Sun and Dr Christopher J. Hyde of the University of Nottingham
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Macro- and micro-scale modelling of material inhomogeneity for the premature failure of welded 9Cr steels in power plants
NUI Galway, 2019Co-Authors: Li MingAbstract:Chromium-molybdenum steel pipe (9Cr-1Mo steel) is an important high temperature construction material for welded steam piping networks in gas-fired power plants. A major global problem of such materials is the premature failure which commonly occurs in the weld regions at elevated temperature. The primary objective of this thesis is the development of a macro- and micro-mechanical framework to predict this premature failure in the 9Cr-1Mo weldments. At the macro-scale level, a computational methodology for cyclic plasticity in multi-material welded components including laboratory scale test specimens and real plant is developed. At the micro-scale level, mixed-phase crystal plasticity models are developed to evaluate the mechanical performance of welding-induced micro-structure textures providing guidance into optimised heat treatments for welded components and material design for welded 9Cr-1Mo steel. For the work at the macro-scale level, a cyclic plasticity model including non-linear kinematic and isotropic hardening was adopted for the finite element analysis of welded 9Cr-1Mo steel in both cross-weld uniaxial test specimens and a welded T-piece power plant Connection. The identified parameters are successfully calibrated and validated against uniaxial high temperature low cycle fatigue data from test data and the finite-element modelling of the cross-weld configuration, including three different material zones: parent metal, weld metal and heat-affected zone (HAZ). The predicted plastic strain in the cross-weld test is shown to concentrate in the HAZ at the interface region with parent metal, where the premature failure location is observed. The predicted critical location of the 9Cr-1Mo welded T-piece header-Branch Connection, as predicted by a three-dimensional finite element model under combined thermo-mechanical fatigue loading histories from Aghada power plant, is consistent with the location of observed premature cracking for in-service conditions. The results highlight the significant importance of incorporating multi-material cyclic plasticity parameters for prediction of plasticity and stress evolution in such welded Connections. A key contribution of the present thesis is the development of a physically-based micro-mechanical framework for the modelling the ferrite-martensite inhomogeneity in the premature failure region of 9Cr-1Mo weldments. Previously-published monotonic tensile test data of IC-HAZ at 20 °C and 625 °C are adopted to calibrate the crystal plasticity finite element model of IC-HAZ. This demonstrated the importance of crystallographic orientation for localized stress and strain distributions, micro-crack initiation and subsequent damage evolution. Small volume fractions of ferrite are shown to have a clear detrimental effect on the mechanical behaviour of strength and ductility. The effect is significantly larger on both ductility and strength at 625 °C than at 20 °C. The micro-mechanical methodology demonstrates the key role of a small amount of ferrite on micro-crack nucleation and accelerated material degradation in IC-HAZ at 625 °C, leading to reduced life of 9Cr-1Mo welded joints at high temperature. The methodology for the macro-scale will specifically allow assessment of the impact of more flexible plant operation to allow for renewable energy uptake and energy cost fluctuations and provides a framework for extension to future ultra-supercritical operation scenarios. The micro-structure sensitive material model developed in this thesis will allow for more detailed consideration of the constitutive behaviour of welded 9Cr-1Mo material in power plant components. This will, in turn, enable power plant designers to carry out more reliable material design from a micro-structural perspective. The macro and micro computational methodologies, in direct collaboration with a power plant operator, provideguidance for life assessment and material optimization of existing, retrofitted and proposed new plant
D Elmakis - One of the best experts on this subject based on the ideXlab platform.
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life assessment evaluation of piping Branch Connection under creep and fatigue
International Journal of Pressure Vessels and Piping, 1997Co-Authors: R Miroshnik, Y Shaked, D ElmakisAbstract:The comparative results of fatigue life assessment analyses are presented for piping Branch Connection of Tee type (Tee) of power station main steam piping. The results are derived using the German Standard TRD approach with and without usage of modified finite element analyses of transient thermal stresses, occurring during power station startup or shutdown. The traditional TRD approach for Tee stress analyses is conservative due to the use of formulas which are the upper estimate of transient thermal stresses. The TRD assumption about the coincidence of creep and fatigue maximum stress areas is very conservative as well. The analyses results enable us to extend the power station piping components life assessment.
O’donoghue, Padraic E. - One of the best experts on this subject based on the ideXlab platform.
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Cyclic plasticity of welded P91 material for simple and complex power plant Connections
Elsevier, 2019Co-Authors: Li Ming, Arrett, Richard A., Scully Stephe, Harrison, Noel M., Sea . Lee, O’donoghue, Padraic E.Abstract:This paper focuses on with the cyclic plasticity modelling of welded, ex-service P91 material. A multi material model is developed for high temperature cyclic plasticity, including the effects of the three different material zones in the vicinity of the weld: parent metal, weld metal and heat-affected zone. The cyclic plasticity behaviour of the three zones is identified from previously-published high temperature, low cycle fatigue experimental tests on uniaxial parent metal, weld metal and cross-weld (repair weld) specimens on ex-service P91 material. The heat-affected zone is shown to be significantly softer than the parent and weld metals and to act as a focus for concentration of plastic strain, leading to significantly inhomogeneous distributions of stress and strain in the weldment. The multi-material cyclic plasticity model is applied, via a three-dimensional finite element analysis of a welded T-piece header-Branch Connection, to predict the effects of cyclic internal pressure and small amplitude thermal fluctuations. (C) 2016 Elsevier Ltd. All rights reserved.This publication has emanated from research conducted with the financial support of Science Foundation Ireland under Grant Number SFI/2010/IN.1/I3015 and Grant Number 14/IA/2604. The modelling work was supported by the Irish Center for High-End Computing (ICHEC). The Authors also acknowledg the contributions made by the collaborators in this project, including Mr David Joyce and Dr Dongfeng Li (formerly NUI Galway), Prof. Noel P. O’Dowd, Dr. Peter Tiernan, and Mr. Brian J. Golden of the University of Limerick, Ms Adelina Adams of ESB Energy International and Prof. Tom H. Hyde, Prof. Wei Sun and Dr Christopher J. Hyde of the University of Nottingham
R Miroshnik - One of the best experts on this subject based on the ideXlab platform.
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life assessment evaluation of piping Branch Connection under creep and fatigue
International Journal of Pressure Vessels and Piping, 1997Co-Authors: R Miroshnik, Y Shaked, D ElmakisAbstract:The comparative results of fatigue life assessment analyses are presented for piping Branch Connection of Tee type (Tee) of power station main steam piping. The results are derived using the German Standard TRD approach with and without usage of modified finite element analyses of transient thermal stresses, occurring during power station startup or shutdown. The traditional TRD approach for Tee stress analyses is conservative due to the use of formulas which are the upper estimate of transient thermal stresses. The TRD assumption about the coincidence of creep and fatigue maximum stress areas is very conservative as well. The analyses results enable us to extend the power station piping components life assessment.
V. Luzin - One of the best experts on this subject based on the ideXlab platform.
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Effect of residual stress on the integrity of a Branch Connection
International Journal of Pressure Vessels and Piping, 2012Co-Authors: O. Kirstein, V. LuzinAbstract:Abstract A new Connection to an existing gas pipeline was made by hot-tapping, welding directly onto a pressurised pipeline. The welds were not post-weld heat treated, causing significant residual stresses. The critical weld had residual stresses determined by neutron diffraction using ANSTO's residual stress diffractometer, Kowari. The maximum measured residual stress (290 MPa) was 60% of the yield strength. The magnitudes of errors from a number of sources were estimated. An integrity assessment of the welded Branch Connection was performed with the measured residual stress values and with residual stress distributions from the BS 7910 and API 579 analysis codes. Analysis using estimates of residual stress from API 579 overestimated the critical crack size.