Study on creep-fatigue evaluation procedures for high-chromium steels—Part I: Test results and life prediction based on measured stress relaxation

2008 ◽  
Vol 85 (6) ◽  
pp. 406-422 ◽  
Author(s):  
Yukio Takahashi
Keyword(s):  
Stress Relaxation ◽  
Life Prediction ◽  
Test Results ◽  
High Chromium ◽  
Evaluation Procedures ◽  
Chromium Steels ◽  
Measured Stress ◽  
Creep Fatigue ◽  
Fatigue Evaluation

Development of 2012 Edition of JSME Code for Design and Construction of Fast Reactors: (4) Creep–Fatigue Evaluation Method for Modified 9Cr–1Mo Steel

2013 ◽  
Author(s):  
Shigeru Takaya ◽  
Yuji Nagae ◽  
Tai Asayama
Keyword(s):  
Evaluation Method ◽  
Time To Failure ◽  
Test Results ◽  
Fast Reactors ◽  
Material Test ◽  
Creep Fatigue ◽  
Summation Rule ◽  
Fatigue Evaluation ◽  
Failure Life ◽  
Design And Construction

This paper describes a creep–fatigue evaluation method for modified 9Cr–1Mo steel, which has been newly included in the 2012 edition of the JSME code for design and construction of fast reactors. In this method, creep and fatigue damages are evaluated on the basis of Miner’s rule and the time fraction rule, respectively, and the linear summation rule is employed as the failure criterion. Investigations using material test results are conducted, which show that the time fraction approach can conservatively predict failure life if margins on the initial stress of relaxation and the stress relaxation rate are embedded. In addition, the conservatism of prediction tends to increase with time to failure. Comparison with the modified ductility exhaustion method, which is known to have good failure life predictability in material test results, shows that the time fraction approach predicts failure lives to be shorter in long-term strain hold conditions, where material test data is hardly obtained. These results confirm that the creep–fatigue evaluation method in the code has implicit conservatism.

Accuracy and Margin in Creep-Fatigue Evaluation for Modified 9Cr-1Mo Steel

2007 ◽  
Author(s):  
Yukio Takahashi
Keyword(s):  
Stress Relaxation ◽  
Nuclear Power ◽  
Creep Damage ◽  
Assessment Method ◽  
Fatigue Tests ◽  
Simple Method ◽  
Component Design ◽  
Creep Fatigue ◽  
Grade 91 ◽  
Fatigue Evaluation

Modified 9Cr-1Mo steel (ASME SA-213, Grade 91) is regarded as a promising candidate for structural materials in some of the nuclear power generation plants considered in Generation-IV project. If it is used at high temperature conditions, consideration of creep-fatigue interaction in addition to simple creep rupture is needed in component design. The author has been conducting many creep-fatigue tests for the steel at temperatures between 550°C and 650°C in order to search for a suitable creep-fatigue assessment method. It was found that creep damage at failure estimated by applying the time fraction approach to measured stress relaxation data strongly depended on the test temperature and became quite small at 550°C. However, application of calculated stress relaxation brought about the increase of creep damage over the linear damage summation line. Furthermore, addition of design factors significantly increased the values of creep and fatigue damages, making margin against failure quite large. A new definition of creep damage as a ductility consumer in strain based approach gave a simple method to estimate creep damage more properly and stably with a much smaller sensitivity on the stress relaxation behavior.

Development of Creep-Fatigue Evaluation Method for Modified 9Cr-1Mo Steel

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Shigeru Takaya ◽  
Yuji Nagae ◽  
Tai Asayama
Keyword(s):  
Evaluation Method ◽  
Time To Failure ◽  
Test Results ◽  
Design Factor ◽  
Design Procedures ◽  
Material Test ◽  
Creep Fatigue ◽  
Summation Rule ◽  
Fatigue Evaluation ◽  
Failure Life

This paper describes a creep–fatigue evaluation method for modified 9Cr-1Mo steel, which has been newly included in the 2012 edition of the Japan Society of Mechanical Engineers code for design and construction of fast reactors (JSME FRs code). In this method, creep and fatigue damages are evaluated on the basis of Miner's rule and the time fraction rule, respectively, and the linear summation rule is employed as the failure criterion. The conservativeness of this method without design factors was investigated using material test results, and it was shown that the time fraction approach can conservatively predict failure life if margins on the initial stress of relaxation and the stress relaxation rate are embedded. In addition, the conservatism of prediction tends to increase with time to failure. Comparison with the modified ductility exhaustion method, which is known to have good failure life predictability in material test results, shows that the time fraction approach predicts failure lives to be shorter in long-term strain hold conditions, where material test data are hardly obtained. These results confirm that the creep–fatigue evaluation method in the JSME FRs code has implicit conservatism in addition to explicit margins in the design procedures such as design factor.

scholarly journals Development of Simplified Model Test Methods for Creep-Fatigue Evaluation

2019 ◽  
Author(s):  
Y. Wang ◽  
B. Jetter ◽  
M. C. Messner ◽  
T.-L. Sham
Keyword(s):  
Model Test ◽  
Evaluation Method ◽  
Test Methods ◽  
Simplified Model ◽  
Test Results ◽  
Interaction Diagram ◽  
Creep Fatigue ◽  
Fatigue Evaluation ◽  
Creep Regime ◽  
Further Development

Abstract The Simplified Model Test (SMT) approach is an alternative creep-fatigue evaluation method that no longer requires the use of the damage interaction diagram, or D-diagram. The reason is that the combined effects of creep and fatigue are accounted for in the test data by means of a SMT specimen that is designed to replicate or bound the stress and strain redistribution that occurs in actual components when loaded in the creep regime. However, creep-fatigue experiments on SMT key feature articles are specialized and difficult to perform by the general research community. In this paper, two innovative SMT based creep-fatigue experimental methods are developed and implemented. These newly-developed SMT test methods have resolved all the critical challenges in the SMT key feature article testing and enable the potential of further development of the SMT based creep-fatigue evaluation method into a standard testing method. Scoping test results on Alloy 617 and SS 316H using the newly developed SMT methods are summarized and discussed. The concepts of the SMT methodology for creep-fatigue evaluation are explained.

Development of High Chromium Steel for SFR in Japan and Creep-Fatigue Assessment of the Welded Joint

2008 ◽  
Author(s):  
Takashi Wakai ◽  
Nobuhiro Isobe ◽  
Shingo Date ◽  
Tai Asayama ◽  
Shigenobu Kubo
Keyword(s):  
Fatigue Strength ◽  
Grain Boundaries ◽  
Welded Joints ◽  
Ferritic Steel ◽  
Welded Joint ◽  
Assessment Procedure ◽  
Test Results ◽  
Strength Assessment ◽  
High Chromium ◽  
Creep Fatigue

This paper describes the provisional material specifications of the high chromium (Cr) ferritic steel for the Sodium cooled Fast Reactor (SFR) and development of creep-fatigue assessment procedure for the welded joint made of the steel. Based on the test results, it was revealed that tungsten (W) should be diminished to achieve better creep-fatigue strength and toughness after long term aging at elevated temperature. Metallurgical examinations using a scanning electron microscope showed that W precipitated on the grain boundaries as “Laves phase” during aging process. The toughness of the steel which contained much W might be degraded by such coarse precipitations on the grain boundaries. As a result, provisional specifications of the high Cr ferritic steel for SFR pipes and tubes were proposed. Creep-fatigue strength assessment procedure for the welded joints made of the steels was also investigated. An assessment procedure using 2-element model was proposed and verified by comparing with some creep-fatigue test results. The creep-fatigue lives observed in the experiments were well predicted by the proposed assessment procedure, but the failure of the welded joints really occurred in the heat affected zone (HAZ) in some creep-fatigue tests. Since the HAZ was not taken into account in the procedure, there were obviously some rooms for improvement. Creep-fatigue failure mechanisms of the welded joint must be investigated and the characteristics of the HAZ must be formulated for more precise creep-fatigue strength assessment.

Study on Type-IV Damage Prevention in High-Temperature Welded Structures of Next-Generation Reactor Plants: Part I — Fatigue and Creep-Fatigue Behavior of Welded Joints of Modified 9Cr-1Mo Steel

2006 ◽  
Author(s):  
Yukio Takahashi
Keyword(s):  
Welded Joints ◽  
Power Plants ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Premature Failure ◽  
High Chromium ◽  
Type Iv ◽  
Chromium Steels ◽  
Creep Fatigue ◽  
New Generation

High-chromium ferritic steels, such as modified 9Cr-1Mo steel, are regarded as candidate structural materials for new generation nuclear power plants and reliable design methods need to be developed. Of particular importance is prevention of premature failure, commonly referred to as type-IV failure, in softened regions of the heat-affected zones as several incidents of type IV failures of high-chromium steels in the fossil power plants have been reported. As part of the work aimed at developing design method for high-chromium steels applicable to new generation reactor plants, strain-controlled fatigue and creep-fatigue tests were conducted for welded joints of modified 9Cr-1Mo steel plate mainly at 550°C and 600°C. Failure typically occurred in the base metal in the pure fatigue tests but type-IV failure in the heat-affected zone occurred in most of the creep-fatigue tests where a large life reduction due to strain hold was observed. Life prediction method of the welded joint under creep-fatigue loading condition was studied based on these results.

Sign in / Sign up

Export Citation Format

Share Document