Creep and Fatigue Behavior in Micro-alloyed Steels – A Review

2014 ◽  
Vol 33 (1) ◽  
pp. 1-12 ◽  
Author(s):  
A. Raj ◽  
B. Goswami ◽  
A.K. Ray
Keyword(s):  
High Temperature ◽  
Power Plants ◽  
Heating Temperature ◽  
Coal Dust ◽  
Fatigue Behavior ◽  
Control Process ◽  
Microalloyed Steels ◽  
High Temperature Strength ◽  
Creep Fatigue ◽  
Accelerated Creep

AbstractThis is a study of microalloyed steels for power plants and reactors. Components operate at coal dust fire temperature or thermal states of reactors, prone to creep during its service. This is to assess remaining life after passage of valuable life by variation in microstructure, e.g. cavity formation. Precipitation at the sub-grain boundaries and grain interior has increased high temperature strength. Coarsening of these appears at the end of life. Variation of heat treatment like spheroidising in place of solutionizing has been responsive to deteriorate performance. Dislocation interplay with precipitate has been acceptable while interaction among dislocations to forest dislocation has been unacceptable. Dislocation assisted nucleation of precipitates of fine size has been found to strengthen steel by thermo-mechanical control process with in greater heating temperature and lower finish rolling temperature. High temperature performance of materials has been assessed by creep, accelerated creep, creep-fatigue and fatigue performances. Increasing temperature for increasing efficiency has correlated the phase transformation of steel. Fatigue performances have been included in creep properties of materials when intermittent shut down–shut up schedules are operated, e.g. peaking power plants.

scholarly journals Synthesis and Evaluation of Ceramic Materials. High Temperature Strength and Creep-Fatigue Behavior of Ceramics.

1995 ◽  
Vol 44 (501) ◽  
pp. 710-714
Author(s):  
Masato MURATA ◽  
Wataru TAKAHARA ◽  
Yoshihiko MUKAI ◽  
Jun-ichi SATO ◽  
Takeshi DEGUCHI
Keyword(s):  
High Temperature ◽  
Fatigue Behavior ◽  
Ceramic Materials ◽  
High Temperature Strength ◽  
Creep Fatigue

Component Low Cycle Fatigue Behavior Based on Standard Calculation Procedure and Non-Linear FEA

2017 ◽  
Author(s):  
Jürgen Rudolph ◽  
Adrian Willuweit ◽  
Steffen Bergholz ◽  
Christian Philippek ◽  
Jevgenij Kobzarev
Keyword(s):  
Power Plants ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Hybrid Approach ◽  
Combined Cycle ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Constitutive Material Model ◽  
Standard Design ◽  
Creep Fatigue

Components of conventional power plants are subject to potential damage mechanisms such as creep, fatigue and their combination. These mechanisms have to be considered in the mechanical design process. Against this general background — as an example — the paper focusses on the low cycle fatigue behavior of a main steam shut off valve. The first design check based on standard design rules and linear Finite Element Analysis (FEA) identifies fatigue sensitive locations and potentially high fatigue usage. This will often occur in the context of flexible operational modes of combined cycle power plants which are a characteristic of the current demands of energy supply. In such a case a margin analysis constitutes a logical second step. It may comprise the identification of a more realistic description of the real operational loads and load-time histories and a refinement of the (creep-) fatigue assessment methods. This constitutes the basis of an advanced component design and assessment. In this work, nonlinear FEA is applied based on a nonlinear kinematic constitutive material model, in order to simulate the thermo-mechanical behavior of the high-Cr steel component mentioned above. The required material parameters are identified based on data of the accessible reference literature and data from an own test series. The accompanying testing campaign was successfully concluded by a series of uniaxial thermo-mechanical fatigue (TMF) tests simulating the most critical load case of the component. This detailed and hybrid approach proved to be appropriate for ensuring the required lifetime period of the component.

Application of Damage Mechanics and Polynomial Chaos Expansion for Lifetime Prediction of High-Temperature Components Under Creep-Fatigue Loading

2020 ◽  
Author(s):  
Felix Koelzow ◽  
Muhammad Mohsin Khan ◽  
Christian Kontermann ◽  
Matthias Oechsner
Keyword(s):  
High Temperature ◽  
Power Plants ◽  
Damage Mechanics ◽  
Fatigue Loading ◽  
Probabilistic Methods ◽  
Lifetime Prediction ◽  
Model Parameters ◽  
Creep Fatigue ◽  
High Temperature Components ◽  
Mechanics Concepts

Abstract Several (accumulative) lifetime models were developed to assess the lifetime consumption of high-temperature components of steam and gas turbine power plants during flexible operation modes. These accumulative methods have several drawbacks, e.g. that measured loading profiles cannot be used within accumulative lifetime methods without manual corrections, and cannot be combined directly to sophisticated probabilistic methods. Although these methods are widely accepted and used for years, the accumulative lifetime prediction procedures need improvement regarding the lifetime consumption of thermal power plants during flexible operation modes. Furthermore, previous investigations show that the main influencing factor from the materials perspective, the critical damage threshold, cannot be statistically estimated from typical creep-fatigue experiments due to massive experimental effort and a low amount of available data. This paper seeks to investigate simple damage mechanics concepts applied to high-temperature components under creep-fatigue loading to demonstrate that these methods can overcome some drawbacks and use improvement potentials of traditional accumulative lifetime methods. Furthermore, damage mechanics models do not provide any reliability information, and the assessment of the resultant lifetime prediction is nearly impossible. At this point, probabilistic methods are used to quantify the missing information concerning failure probabilities and sensitivities and thus, the combination of both provides rigorous information for engineering judgment. Nearly 50 low cycle fatigue experiments of a high chromium cast steel, including dwell times and service-type cycles, are used to investigate the model properties of a simple damage evolution equation using the strain equivalence hypothesis. Furthermore, different temperatures from 300 °C to 625 °C and different strain ranges from 0.35% to 2% were applied during the experiments. The determination of the specimen stiffness allows a quantification of the damage evolution during the experiment. The model parameters are determined by Nelder-Mead optimization procedure, and the dependencies of the model parameters concerning to different temperatures and strain ranges are investigated. In this paper, polynomial chaos expansion (PCE) is used for uncertainty propagation of the model uncertainties while using non-intrusive methods (regression techniques). In a further post-processing step, the computed PCE coefficients of the damage variable are used to determine the probability of failure as a function of cycles and evolution of the probability density function (pdf). Except for the selected damage mechanics model which is considered simple, the advantages of using damage mechanics concepts combined with sophisticated probabilistic methods are presented in this paper.

Structural Evaluation With Elastic and Inelastic Analysis Methods on a High Temperature Storage Tank Subjected to Static and Dynamic Loadings

2020 ◽  
Author(s):  
Wen Wang ◽  
Xiaochun Zhang ◽  
Xiaoyan Wang ◽  
Maoyuan Cai
Keyword(s):  
High Temperature ◽  
Elevated Temperature ◽  
Molten Salt ◽  
Fatigue Damage ◽  
Storage Tank ◽  
Power Plants ◽  
Elastic Analysis ◽  
Inelastic Analysis ◽  
Analysis Methods ◽  
Creep Fatigue

Abstract The structural integrity of reactor components is very essential for the reliable operation of all types of power plants, especially for components operating at elevated temperature where creep effects are significant and where components are subjected to high-temperature alteration and seismic transient loading conditions. In this article, a molten salt storage tank in high temperature thorium molten salt reactor (TMSR) is evaluated according to ASME-III-5-HBB high temperature reactor code. The evaluation based on 3D finite element analyses includes the load-controlled stress, the effects of ratcheting, and the interaction of creep and fatigue. The thermal and structural analysis and the application procedures of ASME-HBB rules are described in detail. Some structural modifications have been made on this molten salt storage tank to enhance the strength and reduce thermal stress. The effects of ratcheting and creep-fatigue damage under elevated temperature are investigated using elastic analysis and inelastic analysis methods for a defined representative load cycle. In addition, the strain range and the stress relaxation history calculated by elastic and inelastic methods are compared and discussed. The numerical results indicate that the elastic analysis is conservative for design and a full inelastic analysis method for estimating input for creep-fatigue damage evaluation need to be developed.

Failure Mechanisms of High Temperature Components in Power Plants

2000 ◽  
Vol 122 (3) ◽  
pp. 246-255 ◽  
Author(s):  
R. Viswanathan ◽  
J. Stringer
Keyword(s):  
High Temperature ◽  
Power Plants ◽  
Failure Mechanisms ◽  
Laboratory Data ◽  
Broad Perspective ◽  
Section Size ◽  
Creep Fatigue ◽  
Ultimate Failure ◽  
High Temperature Components ◽  
Utility Deregulation

The principal mechanisms of failure of high temperature components include creep, fatigue, creep-fatigue, and thermal fatigue. In heavy section components, although cracks may initiate and grow by these mechanisms, ultimate failure may occur at low temperatures during startup-shutdown transients. Hence, fracture toughness is also a key consideration. Considerable advances have been made both with respect to crack initiation and crack growth by the above mechanisms. Applying laboratory data to predict component life has often been thwarted by inability to simulate actual stresses, strain cycles, section size effects, environmental effects, and long term degradation effects. This paper will provide a broad perspective on the failure mechanisms and life prediction methods and their significance in the context utility deregulation. [S0094-4289(00)00103-1]

Development of Guideline for Prediction of Inelastic Strain for Creep-Fatigue Evaluation

2013 ◽  
Author(s):  
Osamu Watanabe ◽  
Ken-ichi Kobayashi ◽  
Kyotada Nakamura
Keyword(s):  
High Temperature ◽  
Power Plants ◽  
Inelastic Strain ◽  
Local Area ◽  
Stage Of Development ◽  
Inelastic Analysis ◽  
Design Changes ◽  
Creep Fatigue ◽  
High Temperature Components ◽  
Fatigue Evaluation

Cyclic thermal and mechanical loads are frequently applied to power plants during their service lives due to the regular operation of start-up and shutdown. Design or actual lives of these high temperature machines and structures have been mainly dominated by the creep-fatigue failure life. Since most of these failures happen at limited local area, namely, it may happen at the geometrical or material discontinuities in structures or components, the detail inelastic analyses with a conservative margin are required at the design and maintenance. However, much time and colossal effort should be avoided at the stage of development to reduce the total cost of designing because the design changes many times until the final configuration is fixed. Many materials in the high temperature components are subjected to inelastic behaviors; plastic or creep strain always cause in the components. In the computational analyses such as Finite Element Analyses, constitutive equations of both plasticity and creep affect analytical results. Neuber’s rule is employed in the present design code to achieve the simplified design of component but its result sometimes provides more conservative margin. Stress Redistribution Locus (Hereinafter denoted as SRL) method is a simplified inelastic analysis and was developed in Japan. ETD committee in HPI has studied its applicability to basic problems and actual components.

Creep-Fatigue Damage Evaluation of Grade 91 Steel Using Interrupt Creep Fatigue Test

2018 ◽  
Author(s):  
Uijeong Ro ◽  
Jeong Hwan Kim ◽  
Hoomin Lee ◽  
Seok Jun Kang ◽  
Moon Ki Kim
Keyword(s):  
Fatigue Damage ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Fatigue Behavior ◽  
Fe Model ◽  
Testing Method ◽  
Creep Fatigue ◽  
Grade 91 ◽  
Grade 91 Steel

The Sodium Fast-cooled Reactor (SFR), are generation IV nuclear power plants, have a target operating temperature of 550°C which makes creep-fatigue behavior more critical than a generation III nuclear power plants. So it is important to understand the nature of creep-fatigue behavior of the piping material, Grade 91 steel. The creep-fatigue damage diagram of Grade 91 steel used in ASME-NH was derived using a conventional time-fraction testing method which was originally developed for type 300 stainless steels. Multiple studies indicate that the creep-fatigue damage diagram of Grade 91 steel developed using this testing method has excessive conservatism in it. Therefore, an alternative testing method was suggested by separating creep and fatigue using interrupted creep tests. The suggested method makes it possible to control creep life consumption freely which was difficult with the previous method. It also makes it easier to observe the interaction between creep and fatigue mechanisms and microstructural evolution. In conclusion, an alternative creep-fatigue damage diagram for Grade 91 steel at 550°C was developed using an interrupt creep fatigue testing method and FE model simulation.

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