Overview of Proposed High Temperature Design Code Cases

2016 ◽  
Author(s):  
Peter Carter ◽  
T.-L. (Sam) Sham ◽  
Robert I. Jetter
Keyword(s):  
High Temperature ◽  
Yield Stress ◽  
Creep Damage ◽  
Cyclic Strain ◽  
Inelastic Strain ◽  
Cyclic Creep ◽  
Strain Accumulation ◽  
Temperature Dependent ◽  
Common Basis ◽  
Creep Fatigue

Proposals for high temperature design methods have been developed for primary loads, creep-fatigue and strain limits. The methodologies rely on a common basis and assumption, that elastic, perfectly plastic analysis based on appropriate properties reflects the ability of loads and stress to redistribute for steady and cyclic loading for high temperature as well as for conventional design. The cyclic load design analyses rely on a further key property, that a cyclic elastic-plastic solution provides an upper bound to displacements, strains and local damage rates. The primary load analysis ensures that the design load is in equilibrium with the code allowable stress, taking into account: i) The stress state dependent (multi-axial) rupture criterion, ii) The limit to stress re-distribution defined by the material creep law. The creep-fatigue analysis is focused on the cyclic creep damage calculation, and uses conventional fatigue and creep-fatigue damage calculations. It uses a temperature-dependent pseudo “yield” stress defined by the material yield and rupture data to identify cycles which will not cause creep damage > 1 for the selected life. Similarly the strain limits analysis bounds cyclic strain accumulation. It also uses a temperature-dependent pseudo “yield” stress defined by the material yield and creep strain accumulation data to identify cycles which will not cause average (membrane) inelastic strain > 1% for the design life. The paper gives an overview of the background and justification of these statements, and examples.

Structural Integrity Code and Regulatory Issues in the Design of High Temperature Reactors

2008 ◽  
Author(s):  
William J. O’Donnell ◽  
Amy B. Hull ◽  
Shah Malik
Keyword(s):  
High Temperature ◽  
Elevated Temperature ◽  
Structural Integrity ◽  
Cyclic Creep ◽  
Creep Rupture ◽  
Creep Fatigue ◽  
Asme Code ◽  
High Temperature Reactors ◽  
Gen Iv ◽  
Very High

Since the 1980s, the ASME Code has made numerous improvements in elevated-temperature structural integrity technology. These advances have been incorporated into Section II, Section VIII, Code Cases, and particularly Subsection NH of Section III of the Code, “Components in Elevated Temperature Service.” The current need for designs for very high temperature and for Gen IV systems requires the extension of operating temperatures from about 1400°F (760°C) to about 1742°F (950°C) where creep effects limit structural integrity, safe allowable operating conditions, and design life. Materials that are more creep and corrosive resistant are needed for these higher operating temperatures. Material models are required for cyclic design analyses. Allowable strains, creep fatigue and creep rupture interaction evaluation methods are needed to provide assurance of structural integrity for such very high temperature applications. Current ASME Section III design criteria for lower operating temperature reactors are intended to prevent through-wall cracking and leaking and corresponding criteria are needed for high temperature reactors. Subsection NH of Section III was originally developed to provide structural design criteria and limits for elevated-temperature design of Liquid-Metal Fast Breeder Reactor (LMFBR) systems and some gas-cooled systems. The U.S. Nuclear Regulatory Commission (NRC) and its Advisory Committee for Reactor Safeguards (ACRS) reviewed the design limits and procedures in the process of reviewing the Clinch River Breeder Reactor (CRBR) for a construction permit in the late 1970s and early 1980s, and identified issues that needed resolution. In the years since then, the NRC, DOE and various contractors have evaluated the applicability of the ASME Code and Code Cases to high-temperature reactor designs such as the VHTGRs, and identified issues that need to be resolved to provide a regulatory basis for licensing. The design lifetime of Gen IV Reactors is expected to be 60 years. Additional materials including Alloy 617 and Hastelloy X need to be fully characterized. Environmental degradation effects, especially impure helium and those noted herein, need to be adequately considered. Since cyclic finite element creep analyses will be used to quantify creep rupture, creep fatigue, creep ratcheting and strain accumulations, creep behavior models and constitutive relations are needed for cyclic creep loading. Such strain- and time-hardening models must account for the interaction between the time-independent and time-dependent material response. This paper describes the evolving structural integrity evaluation approach for high temperature reactors. Evaluation methods are discussed, including simplified analysis methods, detailed analyses of localized areas, and validation needs. Regulatory issues including weldment cracking, notch weakening, creep fatigue/creep rupture damage interactions, and materials property representations for cyclic creep behavior are also covered.

Creep Fatigue Interactions in a 1 CrMo V Steel

1976 ◽  
Vol 190 (1) ◽  
pp. 319-330 ◽  
Author(s):  
E.G. Ellison ◽  
A.J.F. Paterson
Keyword(s):  
Plastic Strain ◽  
High Strain ◽  
Creep Behaviour ◽  
Creep Damage ◽  
Cyclic Creep ◽  
Creep Data ◽  
Creep Tests ◽  
Brittle Transition ◽  
Creep Fatigue ◽  
Cyclic Plastic Strain

Static and cyclic creep tests have been carried out on a 1 Cr Mo V steel at 565 °C. In addition, the effects of prior high strain fatigue on subsequent creep behaviour has been studied. A well defined ductile/brittle transition was noted which was unaffected by the type of load controlled cycle. The material softened under cyclic plastic strain and no experimental evidence was obtained which indicated that fatigue and creep damage interacted in a load controlled test to give rise to unexpectedly short lives. The conclusion derived is that “softened creep” data should be used in predictions of deformation and rupture behaviour, and that the use of virgin creep data can give rise to substantial errors.

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.

A Plasticity Model for Cyclic Strain Accumulation

1971 ◽  
Vol 38 (4) ◽  
pp. 869-874 ◽  
Author(s):  
T. M. Mulcahy
Keyword(s):  
Cyclic Strain ◽  
Cyclic Creep ◽  
Plasticity Model ◽  
Strain Accumulation ◽  
Structural Elements ◽  
Load Cycling ◽  
Accumulation Phenomenon ◽  
Stress States

A general plasticity model is developed which is able to predict a cyclic strain accumulation phenomenon, sometimes called cyclic creep. To assess the consequences of the phenomenon for nonhomogeneous stress states, simple forms of the model are used in the analysis of two idealized structural elements. Very large stresses are found to develop for continued load cycling.

Investigation of Cyclic Creep Behavior and Life Prediction Method of Notch Specimen During High Temperature Fatigue

2008 ◽  
Author(s):  
Zhichao Fan ◽  
Xuedong Chen ◽  
Heng Jiang ◽  
Jie Dong
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Creep Behavior ◽  
Life Prediction ◽  
Low Cycle Fatigue ◽  
Prediction Method ◽  
Creep Damage ◽  
Cyclic Creep ◽  
High Temperature Stress ◽  
The Mean

Cyclic creeps can bring to additional damage, resulting in shorter fatigue lives, so the effects of fatigue damage and cyclic creep damage should be taken into account in the life prediction. In this case, the mean strain rate model based on ductility exhaustion theory can be adopted. An engineering structure inevitably has some stress concentration area. As to this situation, by high temperature low cycle fatigue tests with different notch sizes, cyclic creep behavior is investigated and compared with that of smooth specimens in this paper. The results indicate that, due to existence of notch, the cyclic creep deformation is restricted within a little range around notch and cannot spread widely, so the fatigue strength of notch specimens increases. Based on the ductility dissipation theory and effective stress concept of continuum damage mechanism (CDM), the mean displacement rate at half life is acted as control parameter, and a high temperature multi-axial fatigue life prediction method is proposed in this paper. The prediction results show that all test data are within ±2.0 error factor, which is better than that of axial maximum stress method. This method has simple form and fewer constants, can be used to predict high temperature stress-controlled fatigue life whatever smooth or notch specimens.

A Framework of Integrated Creep-Fatigue Modeling

2009 ◽  
Author(s):  
X. Wu ◽  
S. Yandt ◽  
Z. Zhang
Keyword(s):  
Fatigue Crack ◽  
Polycrystalline Material ◽  
Creep Damage ◽  
Inelastic Strain ◽  
Grain Boundary Sliding ◽  
Deformation Mechanisms ◽  
Final Fracture ◽  
Creep Fatigue ◽  
Boundary Sliding ◽  
Life Consumption

A framework of integrated creep-fatigue (ICF) modeling is proposed based on the deformation decomposition rule that the total inelastic strain (in a polycrystalline material) consists of intragranular deformation (ID) and grain boundary sliding (GBS). With consideration of the respective deformation mechanisms, the resulting constitutive laws are given in 3D tensor forms such that fatigue damage (ID) and creep damage (GBS) are represented in different strain spaces, respectively. Then, the creep-fatigue life consumption can be evaluated using a physics-based formula that captures the intricate interaction between a propagating fatigue crack and distributed creep damage, leading to final fracture.

SIE ASME-NH Program for the Structural Integrity Evaluations of a LMR Subjected to Elevated Temperature Operations

2006 ◽  
Author(s):  
Gyeong-Hoi Koo ◽  
Jae-Han Lee
Keyword(s):  
High Temperature ◽  
Elevated Temperature ◽  
Structural Integrity ◽  
Creep Damage ◽  
Pressure Vessels ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Ratcheting Strain ◽  
Creep Fatigue

In this paper, SIE ASME-NH (Structural Integrity Evaluation by ASME-NH) program, which has a computerized implementation of the details for ASME Pressure Vessels and Piping Code Section III Subsection NH rules including the time-dependent primary stress limits, total accumulated creep ratcheting strain limits, and the creep-fatigue limits for the reactor structures subjected to elevated temperature operations, are described with their detailed application procedures. Using this code, the selected high temperature structures which are subjected to two cycle types are evaluated and the sensitivity studies for the effects of the time step size, primary load, numbers of a cycle, normal temperature on the creep damage evaluations and the effects of the load history on the creep ratcheting strain calculations are investigated. From the selected applications, it is verified that the developed SIE ASME-NH Program is an easy user interface program and it can be an effective tool for the high temperature structural integrity evaluations of LMR.

An online monitoring method for creep-fatigue life consumption with real-time damage accumulation

2021 ◽  
pp. 105678952095425
Author(s):  
Hui Hong ◽  
Zhenwei Cai ◽  
Weizhe Wang ◽  
Yingzheng Liu
Keyword(s):  
High Temperature ◽  
Real Time ◽  
Evaluation Method ◽  
Creep Damage ◽  
Evaluation Methods ◽  
Damage Evaluation ◽  
Monitoring Method ◽  
Creep Fatigue ◽  
Rainflow Counting ◽  
Life Consumption

Online damage evaluation based on monitored complex cyclic loadings has become an important technique for reliability assessment, especially in high-temperature environments where creep occurs in addition to fatigue. Accuracy and rapidity of calculation are basic requirements for online damage evaluation methods. However, current creep damage evaluation methods seldom consider the fluctuation in stress, which leads to inaccuracy in life-consumption estimates. In addition, traditional cycle-counting methods are not applicable to online use. In this study, an online creep-fatigue damage evaluation method is proposed that accounts for the creep behavior that occurs under fluctuating loads. The cycle-counting method is modified from a rainflow-counting algorithm; it broadens the counting of half-cycles and adopts a new equivalent temperature in the stress-strain response calculation. The proposed method is explained in detail and demonstrated with a case study. The application of this method to a high-temperature, high-pressure pipe demonstrates its online applicability and accuracy. A time-matching algorithm is developed to display the damage evolution in real time, thus revealing the link between the incremental damage and the current load conditions, and yielding an intuitive demonstration of a given component’s state of health.

Simplified Inelastic Analysis in Helical Coil Heat Exchanger Design

1980 ◽  
Vol 102 (3) ◽  
pp. 558-562
Author(s):  
C. E. Richard
Keyword(s):  
Creep Damage ◽  
Cyclic Creep ◽  
Helical Coil ◽  
Heat Exchanger Design ◽  
Inelastic Analysis ◽  
Allowable Stresses ◽  
Creep Fatigue ◽  
Time Test ◽  
Coil Heat Exchanger ◽  
Short Time

A simplified, inelastic analysis of helical coil tubing for high-temperature applications is described. Elastically calculated operating stresses are compared with inelastic estimates of allowable cyclic creep/fatigue stresses. The technique of simplifying and analyzing the operating cycles to determine acceptable creep damage levels has general application. The allowable stresses represent the greatest uncertainty in the method, and tests are required to improve their accuracy. A method of utilizing short-time test data to determine allowable stresses for reactor lifetimes of 30 to 40 years is proposed.

Design Study of a Superheater Header Subjected to Cyclic and High Temperature Loading

2007 ◽  
Author(s):  
Jinhua Shi
Keyword(s):  
High Temperature ◽  
Fatigue Damage ◽  
Creep Damage ◽  
Operating Conditions ◽  
Design Code ◽  
Life Study ◽  
Interaction Diagram ◽  
Design Life ◽  
Time To Rupture ◽  
Creep Fatigue

A typical superheater header in a power station is normally subject to high pressure and high temperature loading. Due to increasing fuel prices, many stations especially gas fired power stations are operated cyclically to increase flexibility and to reduce the running costs. Accordingly, new design of heat recovery steam generators (HRSGs) has been required to undertake cyclic operations. For a base load superheater header, the design life is dominated by material creep properties (time to rupture). However, for a header subjected to two shift cyclic operating conditions, fatigue damage could be increased significantly. Therefore, creep-fatigue interaction should be considered. In this paper, a creep-fatigue design life study of a typical HRSG superheater header has been conducted under various cyclic conditions. Creep stresses for the header are calculated using a reverse design code method, and the creep damage is then obtained based on the time to rupture data. Meanwhile, fatigue calculations are carried out using the methodology given in a new European boiler design code BS EN 12952. The results of creep and fatigue damage obtained are presented in a creep-fatigue interaction diagram shown in ASME III Section NH (former N47 Case) for comparisons. After a brief discussion of the results, a conclusion is drawn.

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