On the creep fatigue and creep rupture behaviours of 9-12% Cr steam turbine rotor

This paper presents the study of creep-fatigue interaction damage and creep rupture limit for 9-12% Cr steam turbine rotor under coupled cyclic thermal-mechanical loadings that alter in phase and out of phase. The investigation is implemented using the Linear Matching Method (LMM) and based on the newly developed creep-fatigue and creep rupture evaluation procedures. Latest experimental creep data of FB2 which belongs to 9-12% Cr heat-resistant steel family is employed to calculate creep-related damage and creep rupture bearing capacity of steam turbine rotor. Various factors that affect creep and fatigue damage of steam turbine rotor are analyzed and discussed, including dwell period and rotating speed of rotor. From the parametric studies, the damage locations and cycles to failure induced by creep and fatigue mechanism are presented respectively. Moreover, through creep rupture analyses for varying desired fracture time, the novel creep rupture curves under multi-type double-cyclic-loading conditions are given and further compared with cyclic plasticity failure curve. These surrogate-model analyses offer a deep understanding of structural responses of steam turbine rotor under long-term high temperature operation and provide critical loading conditions to be referenced for smooth running

Coupling crystal plasticity and continuum damage mechanics for creep assessment in Cr-based power-plant steel

To improve the design and safety of power plant components, long-term hightemperature creep behaviour of a power-plant material, such as Cr-based alloy, should be assessed. Prior studies indicate that power-plant components undergo material degradation and premature failure by nucleation, growth and coalescence of microvoids as a result of creep damage. In classical crystal-plasticity-based models, a flow rule and a hardening law do not account for global stiffness degradation of materials due to evolving microvoids, having a significant influence on material behaviour, especially under large deformations. In this study, a crystal-plasticity scheme coupled with an appropriate continuum damage model is developed to capture the anisotropic creep-damage effect on the overall deformation behaviour of Cr-based power-plant steel. Numerical simulations show that the developed approach can characterize creep deformation of the material exposed to a range of stress levels and temperatures under consideration of stiffness degradation under large deformation

Numerical Analysis of a Steam Turbine Rotor subjected to Thermo-Mechanical Cyclic Loads

The contribution at hand discusses the thermo-mechanical analysis of a steam turbine rotor, made of a heat-resistant steel. Thereby, the analysis accounts for the complicated geometry of a real steam turbine rotor, subjected to practical and complex thermo-mechanical boundary conditions. Various thermo-mechanical loading cycles are taken into account, including different starting procedures (cold and warm starts). Within the thermal analysis using the FE code ABAQUS, instationary steam temperatures as well as heat transfer coefficients are prescribed, and the resulting temperature field serves as input for the subsequent structural analysis. In order to describe the mechanical behavior of the heat-resistant steel, which exhibits significant rate-dependent inelasticity combined with hardening and softening phenomena, a robust nonlinear constitutive approach, the binary mixture model, is employed and implemented in ABAQUS in two different ways, i.e. using explicit as well as implicit  methods for the time integration of the governing evolution equations. The numerical performance, the required computational effort, and the obtained accuracy of both integration methods are examined with reference to the thermo-mechanical analysis of a steam turbine rotor, as a typical practical example for the numerical analysis of a complex component. In addition, the obtained temperature, stress, and strain fields in the steam turbine rotor are discussed in detail, and the influence of the different starting procedures is examined closely

A Framework for Remaining Useful Life Prediction of Steam Turbines Applicable to Various Data Types

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 기계항공공학부, 2018. 8. 윤병동.최근 발전사간 경쟁이 치열해짐에 따라 발전 산업에서는 운전 비용을 절감하고 핵심 설비의 수명을 연장하는데 많은 노력을 기울이고 있다. 한편 운전 시간이 설계 수명에 근접함에 따라 증기터빈과 같은 핵심 설비의 열화가 가속되고 크고 작은 고장이 많이 발생하고 있다. 가속화된 열화나 예기치 못한 손상으로 발전소가 정지되면 막대한 경제적 손실과 국가적인 재해를 야기할 수 있다. 이에 따라 안정적인 설비의 운전을 가능케 하는 다양한 기술들이 개발되고 있으며 최근 들어 더욱 많은 각광을 받고 있는 시스템 건전성 관리 기술은 효과적으로 시스템의 상태를 감지, 진단, 그리고 예지하여 관리자가 유지 보수에 있어 필요한 결정을 내릴 수 있도록 도와준다. 특히 최적 유지정비 관점에서 적합한 방법론을 통해 예측된 잔존유효수명은 설비 수명에 정확한 정보를 기반으로 효과적인 유지 정비를 가능하게 한다. 증기 터빈은 발전소 수명을 결정하는 핵심 설비이기 때문에 발전소의 최적 운영을 위해 활용 가능한 정보를 최대한 활용하여 운전 중인 증기터빈의 잔존유효수명을 정확하게 예측하는 방법론의 개발이 매우 중요하다. 이에 본 박사학위 논문에서는 (1) 증기 터빈에 대한 고장모드영향분석과 연계한 잔존유효수명 예측 프레임워크, 그리고 이를 바탕으로 한 (2) 손상 성장 모델 (데이터 기반 방법론), (3) 크리프-피로 손상 상호작용을 고려한 모드 의존 손상 모델 (모델 기반 방법론) 등의 연구를 제안한다. 첫 번째 연구에서는 고장모드영향분석에 기반하여 증기터빈의 잔존유효수명을 예측하는 프레임워크를 제안한다. 프레임워크는 측정된 데이터에 기반한 방법론과 손상 모델에 기반한 방법론으로 구성된다. 오프라인이나 온라인과 같이 다른 목적으로 잔존유효수명을 예측할 때 불확실도를 평가하고 감소시킬 수 있도록 불확실도를 정량화하는 절차를 포함하였다. 두 번째 연구에서는 데이터 기반 방법론을 이용해 증기터빈의 잔존유효수명을 평가할 수 있는 손상 성장 모델의 개발을 목적으로 한다. 잔존유효수명은 손상 인자로부터 손상 성장 모델을 연계하여 예측한다. 현장에서 측정된 경도값으로부터 손상인자의 확률분포를 추정하고 손상의 성장을 평가할 때 불확실도를 고려하기 위해 베이지안 방법을 사용하였다. 제안된 손상 성장 모델을 통해 기저부하나 첨두부하에 사용되는 증기터빈의 종류에 상관없이 정확한 잔존유효수명 예측이 가능하다는 것을 검증하였다. 마지막 연구에서는 모델 기반 방법론을 이용해 크리프와 피로 상호작용이 고려된 모드 기반 손상모델을 제안하였다. 손상기구에 따른 재료 데이터를 통계적 기법으로 분석하고 실 증기터빈의 형상 정보와 운전정보를 이용해 기저부하와 첨두부하 터빈을 대상으로 크리프 및 피로 손상율을 계산하였다. 각각 계산된 손상율 결과와 크리프-피로 상호작용 모델을 통해 운전모드 또는 손상모드에 따른 증기터빈에서의 크리프와 피로 상호작용 효과를 분석하였다. Abstract i List of Tables viii List of Figures x Nomenclatures xiv Chapter 1 Introduction 1 1.1 Motivation 1 1.2 Research Scope and Overview 4 1.3 Dissertation Layout 7 Chapter 2 Literature Review 8 2.1 Life Prediction Methodologies of Steam Turbine 8 2.1.1 Destructive Method 11 2.1.2 Non-destructive Method 11 2.1.3 Analytical Method 13 2.1.4 Summary and Discussion 13 2.2 Data-driven and Model-based Life Prediction 15 2.2.1 Data-driven Approach 21 2.2.2 Model-based Approach 21 2.3 Empirical Model-based Life Prediction 15 2.3.1 On-site Data Measurement 18 2.3.2 Bayesian Inference 19 2.3.3 Summary and Discussion 20 2.4 Damage Model-based Life Prediction 21 2.4.1 Creep or Fatigue Damage Model Analysis 22 2.4.2 Creep-Fatigue Damage Summation Model analysis 23 2.4.3 Summary and Discussion 27 Chapter 3 A Practical RUL Prediction Framework of Steam Turbine with FMEA Analysis 28 3.1 Overview of Steam Turbines 28 3.2 FMEA for Steam Turbines 31 3.3 A Framework for RUL Prediction of Steam Turbine 34 3.4 Summay and Discussion 38 Chapter 4 A Bayesian Approach for RUL Prediction of Steam Turbines with Damage Growth Model 39 4.1 Characteristics of On-site Measurement Data 40 4.2 Measured Data based Damage Indices 46 4.3 Damage Growth Model using Sporadically Measured and Heterogeneous On-site Data 51 4.3.1 Proposed Damage Growth Model 51 4.3.2 Bayesian Updating Scheme of the Damage Growth Model 58 4.3.3 Damage Growth Model Updating 60 4.4 Predicting the Remaining Useful Life(RUL) of Steam Turbines 68 4.4.1 Damage Threshold 68 4.4.2 Validation of the Proposed Damage Growth Model 72 4.4.3 RUL Prediction 74 4.5 Summary and Discussion 78 Chapter 5 Mode-Dependent Damage Assessment for Steam Turbines with Creep-Fatigue Interaction Model 80 5.1 Dominant Damage Mechanisms of Steam Turbine 82 5.2 Typical Opeation Data of Steam Turbine 83 5.3 Dominant Damage Model of Steam Turbine 86 5.3.1 Creep Damage Model 86 5.3.2 Fatigue Damage Model 88 5.3.3 Creep-Fatigue Damage Model 90 5.4 Statiatical Damage Calculation for Steam Turbine 91 5.4.1 Statistical Characterization of Creep-Fatigue Damage Data 91 5.4.2 Creep Damage Calculation with Steady State Stress 94 5.4.3 Fatigue Damage Calculation with Transient Strain 95 5.5 Mode-Dependent Multiple Damage Interaction Model 100 5.5.1 Estimation of Damage Interaction Parameters 100 5.5.2 Validation of Mode-Dependent Model 101 5.5.3 Effect of Mode-dependence Effects on Multiple Damage 104 5.5.4 Case Study : Risk Assessment 108 5.6 Summary and Discussion 111 Chapter 6 Conclusions 113 6.1 Contributions and Impacts 113 6.2 Suggestions for Future Research 116 References 119 국문 초록 142Docto

Computational Methods for Failure Analysis and Life Prediction

This conference publication contains the presentations and discussions from the joint UVA/NASA Workshop on Computational Methods for Failure Analysis and Life Prediction held at NASA Langley Research Center 14-15 Oct. 1992. The presentations focused on damage failure and life predictions of polymer-matrix composite structures. They covered some of the research activities at NASA Langley, NASA Lewis, Southwest Research Institute, industry, and universities. Both airframes and propulsion systems were considered

Gas Turbines

This book is intended to provide valuable information for the analysis and design of various gas turbine engines for different applications. The target audience for this book is design, maintenance, materials, aerospace and mechanical engineers. The design and maintenance engineers in the gas turbine and aircraft industry will benefit immensely from the integration and system discussions in the book. The chapters are of high relevance and interest to manufacturers, researchers and academicians as well

Hot section components life usage analyses for industrial gas turbines

Industrial gas turbines generally operate at a bit stable power levels and the hot section critical components, especially high pressure turbine blades are prone to failure due to creep. In some cases, plants are frequently shut down, thus, in addition to creep low cycle fatigue failure equally sets in. Avoiding failure calls for proper monitoring of how the lives of these components are being consumed. Efforts are thus being made to estimate the life of the critical components of the gas turbine, but, the accuracy of the life prediction methods employed has been an issue. In view of the above observations, in this research, a platform has been developed to simultaneously examine engine life consumption due to creep, fatigue and creep-fatigue interaction exploiting relative life analysis where the engine life calculated is compared to a reference life in each failure mode. The results obtained are life analysis factors which indicate how well the engine is being operated. The Larson-Miller Parameter method is used for the creep life consumption analysis, the modified universal slopes method is applied in the low cycle fatigue life estimation while Taira's linear accumulation method is adopted for creep-fatigue interaction life calculation. Fatigue cycles counting model is developed to estimate the fatigue cycles accumulated in any period of engine operation. Blade thermal and stress models are developed together with a data acquisition and pre-processing module to make the life calculations possible. The developed models and the life analysis algorithms are implemented in PYTHIA, Cranfield University's in-house gas turbine performance and diagnostics software to ensure that reliable simulation results are obtained for life analysis. The developed life analysis techniques are applied to several months of real engine operation data, using LM2500+ engine operated by Manx Utilities at the Isle of Man to test the applicability and the feasibility of the methods. The developed algorithms provide quick evaluation and tracking of engine life. The lifing algorithms developed in this research could be applied to different engines. The relative influences of different factors affecting engine life consumption were investigated by considering each effect on engine life consumtion at different engine operation conditions and it was observed that shaft power level has significant impact on engine life consumption while compressor degradation has more impact on engine life consumption than high pressure turbine degradation. The lifing methodologies developed in this work will help engine operators in their engine conditions monitoring and condition-based maintenance