Robust Methods for Creep Fatigue Analysis of Power Plant Components Under Cyclic Transient Thermal Loading

2013 ◽  
Author(s):  
Yevgen Kostenko ◽  
Henning Almstedt ◽  
Konstantin Naumenko ◽  
Stefan Linn ◽  
Alfred Scholz
Keyword(s):  
High Temperature ◽  
Power Plant ◽  
Constitutive Model ◽  
Thermal Loading ◽  
Hold Time ◽  
Local Stress ◽  
Life Assessment ◽  
Heat Transfer Analysis ◽  
Turbine Component ◽  
Plant Components

The aim of this paper is to apply robust mechanisms-based material laws to the analysis of typical high-temperature power plant components during an idealized start-up, hold time and shut-down sequence under a moderate temperature gradient. Among others a robust constitutive model is discussed, which is able to reflect inelastic deformation, hardening/recovery, softening and damage processes at high temperature. The model is applied for a creep analysis of advanced 9–12%CrMoV heat resistant steels and calibrated in particular case against experimental data for 10%CrMoV steel type. For a steam temperature profile transient heat transfer analysis of an idealized steam turbine component is performed providing the temperature field. From the subsequent structural analysis with the inelastic constitutive model local stress and strain state variations are obtained. As an outcome a multi-axial thermo-mechanical fatigue (TMF) loading loop for one or several loading cycles can be generated. They serve as input for a fatigue life assessment based on the generalized damage accumulation rule, whose results come close to reality. In addition, the accuracy of a simplified method which allows a rapid estimation of notch stresses and strains using a notch assessment rule (NAR) [1] based on Neuber approach is examined.

scholarly journals Accelerated Creep Life Assessment of In-Service Power Plant Components

2019 ◽  
Vol 293 ◽  
pp. 03001
Author(s):  
Saud Hamad Aldajah ◽  
Mohammad Mazedul Kabir ◽  
Mohammad Y. Al-Haik
Keyword(s):  
High Temperature ◽  
Power Plant ◽  
Structural Integrity ◽  
Elevated Temperatures ◽  
Sem Analysis ◽  
Life Assessment ◽  
High Temperature Creep ◽  
Creep Life ◽  
Temperature Creep ◽  
Plant Components

Structural metals used in plant components are subject to aging from a combination of fatigue, creep, and corrosion. Exposure to elevated temperatures promotes creep. Aged metals lose toughness, or the ability to absorb energy at stress above the yield point and cannot endure an occasional high load without fracturing. Creep is one of the most critical factors for determining the structural integrity of components. The main objective of the current study is to assess the remaining creep life of various 20-year old power plant engineering components such as the high temperature fasteners. Due to time constraints, the approach followed in this study was to utilize the accelerated high temperature creep testing in addition to Scanning Electron Microscopy (SEM) analysis to assess the remaining life of 4 different samples. The accelerated high temperature creep tests were conducted at a stress level of 61 MPa and at a temperature of 1000°C for samples Sample 1 (original), Sample 2, Sample 3 and Sample 4; these samples were collected from different parts of the power plant. SEM analysis was carried out for all the samples. The results of the accelerated high temperature tests were compared to similar materials’ theoretical creep data using Larson Miller curve. The Larson Miller actual creep lives of the tested samples were much higher than the experimental ones, which suggest that the samples are critically aged. SEM analysis on the other hand, showed that all samples have high percentage of creep voids

Prediction of Stress Relaxation in Power Plant Components Based on a Constitutive Model

2017 ◽  
Author(s):  
Y. Kostenko ◽  
K. Naumenko
Keyword(s):  
Power Plant ◽  
Stress Relaxation ◽  
Constitutive Model ◽  
Evolution Equations ◽  
Material Behavior ◽  
Assessment Procedure ◽  
Reliable Prediction ◽  
Inelastic Material ◽  
Plant Components

Many power plant components and joint connections are subjected to complex thermo-mechanical loading paths under severe temperature environments over a long period. An important part in the lifetime assessment is the reliable prediction of stress relaxation using improved creep modeling to avoid possible integrity or functionality issues and malfunction in such components. The aim of this work is to analyze the proposed constitutive model for advanced high chromium steels with the goal of predicting stress relaxation over the long term. The evolution equations of the constitutive model for inelastic material behavior are introduced to account for hardening and softening phenomena. The material properties were identified for 9–12%CrMoV steels in the creep range. The model is applied to the stress relaxation analysis of power plant components. The results for long-term assessment, which are encouragingly close to reality, will be presented and discussed. An outlook on further developments of the model and assessment procedure is also provided.

Influence of a Variable in Time Heat Transfer Coefficient on Stresses in Model of Power Plant Components

2013 ◽  
Author(s):  
Jerzy Okrajni ◽  
Mariusz Twardawa
Keyword(s):  
Heat Transfer ◽  
Power Plant ◽  
Mechanical Behaviour ◽  
Power Plants ◽  
Thermal Loading ◽  
Computer Modelling ◽  
Temperature Fields ◽  
Fluid Medium ◽  
Stress Changes ◽  
Plant Components

The paper discusses the issue of modelling of strains and stresses resulting from heating and cooling processes of components in power plants. The main purpose of the work is to determine the mechanical behaviour of power plant components operating under mechanical and thermal loading. Finite element method (FEM) has been used to evaluate the temperature and stresses changes in components as a function of time. Temperature fields in the components of power plants are dependent, among parameters, on variable heat-transfer conditions between components and the fluid medium, which may change its condition, flowing inside them. For this reason, evaluation of the temperature field and the consequent stress fields requires the use of heat-transfer coefficients as time-dependent variables and techniques for determining appropriate values for these coefficients should be used. The methodology of combining computer modelling of the temperature fields with its measurements performed at selected points of the pipelines may be used in this case. The graphs of stress changes as a function of time have been determined for the chosen plant components. The influence of the heat transfer conditions on the temperature fields and mechanical behaviour of components have been discussed.

A Unified Constitutive Model With Optimized Parameters for Base and Diffusion Bonded Alloy 800H

2020 ◽  
Author(s):  
Heramb P. Mahajan ◽  
Tasnim Hassan
Keyword(s):  
Elevated Temperature ◽  
Power Plant ◽  
Nuclear Power Plant ◽  
Constitutive Model ◽  
Nuclear Power ◽  
Parameter Determination ◽  
Alloy 800H ◽  
Inelastic Analysis ◽  
Creep Fatigue ◽  
Plant Components

Abstract Current ASME Section III, Division 5 code provides elastic, simplified inelastic and inelastic analysis options for designing nuclear power plant components for elevated temperature service. These analyses methods may fail to capture the complex creep-fatigue response and damage accumulation in materials at elevated temperatures. Hence, for analysis and design of the nuclear power plant components at elevated temperature, a full inelastic analysis that can simulate creep-fatigue responses may be needed. Existing ASME code neither provides guidelines for using full inelastic analysis nor recommends the type of constitutive model to be used. Hence, a unified rate-dependent constitutive model incorporating a damage parameter will be developed, and its parameters for base metal will be determined. In addition, a full inelastic analysis methodology using this model to analyze the creep-fatigue performance of components for nuclear power applications will be developed. Base metal 800H (BM800H) data are collected from literature to determine constitutive material model parameters. The parameter determination methodology for a constitutive model is discussed. The optimized parameter set for BM 800H at different temperatures will be presented in the paper. Recommendations are provided on the constitutive model selection and its parameter determination techniques. In the future, this work will be continued for diffusion bonded Alloy 800H (DB800H) material, and obtained parameters will be compared.

Online Creep-Fatigue Monitoring of Cyclic Operation in a Coal-Fired Power Plant

2017 ◽  
Author(s):  
Stan T. Rosinski ◽  
Kent Coleman ◽  
Mario Berasi ◽  
Curt Carney ◽  
Ulrich Woerz ◽  
...  
Keyword(s):  
High Temperature ◽  
Power Plant ◽  
Fatigue Damage ◽  
Power Plants ◽  
Transfer Functions ◽  
Stress Transfer ◽  
Operating Conditions ◽  
Element Analysis ◽  
Thermal Transients ◽  
Plant Components

Coal-fired power plants are often required to cycle extensively and operate relatively infrequently due to power market conditions and an increasingly broad deployment of renewable energy. This cyclic (start-stop and/or fast ramp rate) operation can result in accumulation of fatigue damage, particularly in thick-walled components such as high temperature headers that experience the greatest thermal transients. In addition, components exposed to high temperature and pressure experience creep damage over time. Tracking the accumulation of creep and fatigue damage can aid in life management of these components. EPRI developed the Creep-FatiguePro™ system to monitor the accumulation of creep and fatigue damage in plant components while considering component geometry and the ongoing changes in operating conditions (temperatures, pressures and flow rates). The software requires a configuration process to define stress transfer functions for damage analysis and often involves performing a finite element analysis for each component geometry. Although accurate, this process can be time-consuming, especially if a large number of components are to be monitored. In a recent application of this system at the As Pontes power plant in Spain, a simple closed form analytical solution was used in the configuration process in order to more rapidly obtain the stress transfer functions. For direct interaction with the plant’s data historian, the software was also modified to support connection to the plant data system. Results using the two configuration approaches will be compared and recommendations made for future use in monitoring creep and fatigue damage in power plant components.

Fatigue Assessment of Nuclear Power Plant Components Subjected to Thermal Cyclic Loading

2009 ◽  
Author(s):  
Kai Bauerbach ◽  
Michael Vormwald ◽  
Ju¨rgen Rudolph
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Nuclear Power ◽  
Thermal Loading ◽  
Hysteresis Loops ◽  
Plastic Behavior ◽  
Loading Conditions ◽  
Material Parameters ◽  
Structural Loading ◽  
Plant Components

Thermal loading conditions of nuclear power plant components cause local stress-strain hystereses. For the fatigue life prediction of nuclear power plant components under thermal cyclic and structural loading a new method based on the local strain approach is to be presented. This method involves finite-element simulations as well as the experience gathered from lifetime assessment methods based on short crack models. The local stresses and strains are obtained from coupled-field FE-analyses. The calculation of the hysteresis-loops relies on appropriate material models and experimentally verified temperature-dependent material parameters in order to describe the elasto-plastic behavior of the material as realistically as necessary. Due to the temperature dependence of the material parameters the resulting hysteresis loops are of non-conventional shapes and similar to those observed under multiaxial nonproportional structural loading. Hence, fatigue methodologies developed for non-proportional loading conditions during the past years bear good prospects for successful application under non-isothermal loading conditions.

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