Sensitivity of Estimated Tube Life to Material Property Variation

1983 ◽  
Vol 105 (1) ◽  
pp. 73-79 ◽  
Author(s):  
I. Berman ◽  
M. S. M. Rao
Keyword(s):  
Material Property ◽  
Failure Modes ◽  
Creep Damage ◽  
Cycle Number ◽  
Property Variation ◽  
Life Evaluation ◽  
Creep Fatigue ◽  
Incoloy 800 ◽  
Solar Receiver ◽  
Tube Life

The estimated tube life of the Incoloy 800 tubes of a solar receiver panel under nonaxisymmetric loading is compared for various material property assumptions. The basis of each life evaluation is an elastic-creep analytical study of up to 20 load cycles. The effect on tube life of a variation in the creep rate for the failure modes of creep ratcheting and creep fatigue is studied in some detail. As shown for these elastic-creep conditions, the creep damage and mean diametral strain accumulations per cycle decrease linearly over the calculated 20 cycles when plotted against cycle number on a log-log scale. The predictions of total creep damage and mean diametral strain in 10,000 cycles based on the extrapolated log-log scale curve are substantially lower than the predictions based on multiplication of the change in value of the 20th day of operation by 10,000. A limited evaluation of the effects of variations in other material parameters is also made.

Structural Design and Life Assessment of a Molten Salt Solar Receiver

1985 ◽  
Vol 107 (3) ◽  
pp. 258-263 ◽  
Author(s):  
T. V. Narayanan ◽  
M. S. M. Rao ◽  
G. Carli
Keyword(s):  
Molten Salt ◽  
Structural Integrity ◽  
Life Assessment ◽  
Fatigue Life Assessment ◽  
Life Evaluation ◽  
Creep Fatigue ◽  
Asme Code ◽  
Safety And Reliability ◽  
Solar Receiver ◽  
Commercial Size

This paper discusses the structural integrity and creep-fatigue life assessment of a commercial size molten salt solar central receiver. The life evaluation is based on criteria that are a modified version of ASME Code Case N-47. These criteria are deemed conservative enough to provide a reasonable level of safety and reliability, and yet not so conservative as to impose severe economic penalties on the receiver. The justification for these criteria and their application to the receiver are discussed in detail.

Fatigue and Creep-Fatigue Life Evaluation of U-Shaped Bellows

1992 ◽  
Vol 114 (3) ◽  
pp. 280-291 ◽  
Author(s):  
K. Tsukimori ◽  
T. Yamashita ◽  
M. Kikuchi ◽  
K. Iwata ◽  
A. Imazu
Keyword(s):  
Fatigue Life ◽  
Evaluation Method ◽  
Strain Range ◽  
Creep Damage ◽  
Fatigue Tests ◽  
Reliable Operation ◽  
Life Evaluation ◽  
Creep Fatigue ◽  
Fatigue Life Evaluation ◽  
Rational Evaluation

For the reliable operation of bellows under cyclic loadings at high temperatures, a rational evaluation method of life of bellows would be needed. Authors investigated simplified analysis methods for fatigue and creep-fatigue life prediction of U-shaped bellows considering inelasticity as well as various geometrical nonuniformity such as thickness and shape of convolutions. A conservative evaluation method of the strain range is developed, introducing three strain range amplification factors for nominal elastic strain range. Creep and relaxation behaviors of bellows are studied. Consequently, a new evaluation method of creep damage fractions is proposed which depends upon the relation between primary and secondary stresses. Fatigue and creep-fatigue tests are conducted and the validity of the present methods is discussed.

scholarly journals Some issues in creep-fatigue research

2021 ◽  
pp. 1-13
Author(s):  
Isamu Nonaka
Keyword(s):  
Fatigue Life ◽  
Elevated Temperatures ◽  
Creep Damage ◽  
Design Guidelines ◽  
Evaluation Procedures ◽  
Life Evaluation ◽  
Creep Fatigue ◽  
Fatigue Life Evaluation ◽  
Summation Rule ◽  
Loading Modes

In the component operated at elevated temperatures, the life evaluation should be made in consideration of both creep and fatigue (creep-fatigue) such as the linear damage summation rule. However, the concept of creep-fatigue life evaluation has not spread well in the industry. In order to consider the reason, a series of past creep-fatigue research was surveyed, namely experimental methods, life evaluation procedures and strength design guidelines. As a result, it was revealed that the mechanism of creep-fatigue interaction has not been fully clarified yet, which results in obscuring the necessity of creep-fatigue life evaluation. The necessity of creep-fatigue life evaluation was reviewed and consequently it proved to be necessary in two cases. One is the case where the creep-fatigue interaction is significant for some kinds of material, loading modes and temperatures. The other is one where the amount of creep damage is almost the same as that of fatigue damage even though the creep-fatigue interaction is insignificant.

The TransAlta High-Energy Piping Program—A Five-Year History

2000 ◽  
Vol 123 (1) ◽  
pp. 65-69 ◽  
Author(s):  
Marvin J. Cohn,
Keyword(s):  
Creep Damage ◽  
Analytical Techniques ◽  
High Energy ◽  
Management Plan ◽  
Piping System ◽  
Engineering Consulting ◽  
Piping Systems ◽  
Creep Fatigue ◽  
Sustained Loads ◽  
Selection Of

In 1995, the High-Energy Piping Strategic Management Plan (HEPSMP) was initiated at TransAlta Utilities Corporation (TAU) for the three generating facilities. At that time, it was recognized that several of the piping systems were exhibiting signs of creep relaxation, with some hangers bottomed or topped out online and/or offline. Previous hanger adjustment attempts were not always adequate. The program workscope included: 1) hot and cold piping system walkdowns, 2) selection of high-priority girth weld inspection locations, 3) examination of critical weldments, 4) weld repairs where necessary, 5) adjustments or modifications of malfunctioning steam line hangers, and 6) recommended work for future scheduled outages. Prior to 1996, examination locations were limited to the traditional locations of the terminal points at the boiler and turbine, with reexaminations occurring at arbitrary intervals. Since the terminal points are not necessarily the most highly stressed welds causing service-related creep damage, service damage may not occur first at the pre-1996 examined locations. There was a need to maximize the safety and integrity of these lines by ensuring that the highest risk welds were identified and given the highest priority for examination. An engineering consulting company was selected to prioritize the highest risk weldments for each piping system. This risk-based methodology included the prediction and evaluation of actual sustained loads, thermal expansion loads, operating loads, multiaxial stresses, creep relaxation, and cumulative creep life exhaustion. The technical process included detailed piping system walkdowns and application of advanced analytical techniques to predict and rank creep/fatigue damage for each piping system. TAU has concluded that the program has met its objective of successfully prioritizing inspection locations. The approach has also resulted in reducing the scope and cost of reexaminations. Phases 1 and 2 evaluations and examinations have been completed for all units. Results of some of the important aspects of this program are provided as case history studies.

Estimation of Creep-Fatigue Damage Through Indentation Test Method

2011 ◽  
Author(s):  
Raghu V. Prakash
Keyword(s):  
Tensile Properties ◽  
Fatigue Damage ◽  
Indentation Test ◽  
Creep Damage ◽  
Test Method ◽  
Specimen Preparation ◽  
Creep Fatigue ◽  
Critical Components ◽  
The Cost

Creep, creep-fatigue damage is often estimated through in-situ metallography, tensile testing of specimens. However, these methods require specimen preparation which includes specimen extraction from critical components. Automated ball indentation testing has been used as an effective tool to determine the mechanical properties of metallic materials. In this work, the tensile properties of materials subjected to controlled levels of damage in creep, creep-fatigue is studied. It is found that the tensile properties such as yield strength and UTS deteriorates with creep damage, whereas the same specimens show an improved UTS values (at the cost of ductility) when subjected to creep-fatigue interactions.

Creep-Fatigue Damage and Crack Initiation for a Mod 9Cr-1Mo Structure With Weldments

2007 ◽  
Author(s):  
Hyeong-Yeon Lee ◽  
Se-Hwan Lee ◽  
Jong-Bum Kim ◽  
Jae-Han Lee
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Fatigue Damage ◽  
Hold Time ◽  
Fatigue Crack Initiation ◽  
Creep Damage ◽  
Steel Specimen ◽  
Structural Test ◽  
Creep Fatigue ◽  
Creep Fatigue Crack

A structural test and evaluation on creep-fatigue damage, and creep-fatigue crack initiation have been carried out for a Mod. 9Cr-1Mo steel structural specimen with weldments. The conservatisms of the design codes of ASME Section III subsection and NH and RCC-MR codes were quantified at the welded joints of Mod.9Cr-1Mo steel and 316L stainless steel with the observed images from the structural test. In creep damage evaluation using the RCC-MR code, isochronous curve has been used rather than directly using the creep law as the RCC-MR specifies. A y-shaped steel specimen of a diameter 500mm, height 440mm and thickness 6.35mm is subjected to creep-fatigue loads with two hours of a hold time at 600°C and a primary nominal stress of 30MPa. The defect assessment procedures of RCC-MR A16 guide do not provide a procedure for Mod.9Cr-1Mo steel yet. In this study application of σd method for the assessment of creep-fatigue crack initiation has been examined for a Mod. 9Cr-1Mo steel structure.

Reliability Analysis on a Turbine Disk Considering the Coupling of Multiple Failure Modes

2018 ◽  
Author(s):  
Dianyin Hu ◽  
Ying Shi ◽  
Xi Liu ◽  
Rongqiao Wang
Keyword(s):  
Reliability Analysis ◽  
Failure Modes ◽  
Low Cycle Fatigue ◽  
Single Mode ◽  
Turbine Disk ◽  
Coupling Scheme ◽  
Multiple Failure Modes ◽  
Creep Fatigue ◽  
Turbine Disks ◽  
Complex Structural

Current probabilistic design methods mainly focus on single mode of failure, under the consideration on random variables including geometry, loading, and material properties. However, due to the complex structural characters and unevenly distributed temperature, turbine disks are always undergoing multiple potential failure modes, which should be effectively evaluated under a coupling scheme in reliability analysis. To this end, a collaborative response surface method involving multiple potential modes was established, aligning individual failure modes that were precisely evaluated via linear heteroscedastic regression analysis. To validate our model, reliability assessment was conducted on a turbine disk in turbo-shaft engine, where the coupling failure including low cycle fatigue and creep-fatigue was considered. This method can be an effective tool in the evaluation of reliability analysis involving multiple failure modes.

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