Important Effects in Environmentally Assisted Fatigue (EAF) of Austenitic and Ferritic Steel Components Including Welds and Their Consideration in a Fatigue Assessment Concept

2019 ◽  
Author(s):  
Jürgen Rudolph ◽  
Matthias Herbst ◽  
Armin Roth ◽  
Christian Swacek ◽  
Tim Schopf
Keyword(s):  
Fatigue Life ◽  
Influencing Factors ◽  
Hold Time ◽  
Life Time ◽  
Operating Conditions ◽  
Experimental Program ◽  
Cooperative Research ◽  
Fatigue Assessment ◽  
Fatigue Design ◽  
Improve Fatigue

Abstract The fatigue assessment of pressure boundary components is of importance for the aging management regarding safety and reliability in nuclear power plants with light water reactors. For the evaluation of cyclic loading conditions, different country specific design codes and standards are applied to consider various mechanical and thermal loadings as well as geometrical and material effects. Those different influencing factors have also to be taken into account in the fatigue design curves. Current state of the art methods account for life time influencing factors such as temperature, surface finish, stress multi-axiality and loading history by the application of reduction factors for fatigue lives (penalty respectively margin factors) determined from fatigue design curves which are derived from laboratory test data. Other effects, such as environmental effects or hold times, are often considered with high levels of conservatism or are not taken into account at all. On the one hand, this may lead to non-conservative predictions of the materials fatigue behavior, while on the other hand, there are often large discrepancies between calculated fatigue life and practical experience from power plant operation, where the operating experience reveals much higher fatigue lifetimes as their predictions based on laboratory tests and conservative consideration of major influencing factors (plastification by Ke-factors, Environmentally Assisted Fatigue (EAF) by FEN-factors) in the calculation approach. Therefore, Framatome GmbH, Erlangen, and the Material Testing Institute MPA Stuttgart currently conducting a cooperative research program which aims to improve the understanding of environmental and loading effects as well as of welds on fatigue life time and to improve fatigue lifetime assessment methods in the framework of the well established engineering approach. Based on the results of a previous research project of the same project partners, an experimental program is performed to investigate the effect of loading parameters and hold times on environmentally assisted fatigue (EAF). Experiments on specimens of ferritic and austenitic stainless steels and austenitic stainless steel welds as well as component tests are performed under laboratory and operating conditions to improve fatigue assessment and serve to bridge the gap between specimen behavior and component fatigue in operation. Emanating from previous and ongoing cooperative research projects, the experimental results will contribute to the proposal of an engineering fatigue assessment concept, allowing more specific differentiation in the influencing factors for component fatigue life prediction. Furthermore, hold time effects are simulated based on further developed material models.

Proposal for an Improved Engineering Fatigue Lifetime Assessment Concept

2016 ◽  
Author(s):  
Jürgen Rudolph ◽  
Paul Wilhelm ◽  
Armin Roth ◽  
Matthias Herbst ◽  
Matthias C. Kammerer ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Influencing Factors ◽  
Experimental Results ◽  
Life Assessment ◽  
Experimental Program ◽  
Materials Testing ◽  
Assessment Procedure ◽  
Fatigue Lifetime ◽  
Fatigue Assessment ◽  
Fatigue Life Assessment

Fatigue life assessment for pressurized components in nuclear power plants (NPPs) is an essential part of the aging management (AM) ensuring safe and long term operation (LTO). For fatigue life assessment different codes and standards provide a variety of methodologies with variable complexity. Major fatigue life influencing factors such as temperature, surface finish, multiaxiality, loading history and others are often considered in a more or less global way by combined overall reduction factors covering multiple mechanisms together. Other effects such as the environment or hold times are often considered not at all or otherwise with high levels of conservatism resulting in large discrepancies between calculated fatigue life and practical experience from power plant operation. In order to reduce this inadequacy a more accurate fatigue lifetime assessment concept including individual fatigue life influencing factors in a mechanistic manner is required. Nevertheless, these amendments are to fit into the existing basic engineering approach of design against fatigue failure as it is implemented in nuclear standards and design codes. In the framework of an ongoing three years German cooperation R&D project with participation of the Materials Testing Institute MPA University of Stuttgart and AREVA GmbH (Erlangen) it is the aim to both improve the state of the art based on an experimental program for some of the main fatigue life influencing factors and on the derivation of a practicable engineering fatigue assessment procedure. Within this fatigue assessment procedure the dominant fatigue life influencing factors are considered individually. The experimental program covers fatigue test results for austenitic and ferritic piping materials including a dissimilar metal weld. Within the testing program strain controlled fatigue tests were performed with and without hold-times in air and high temperature water environments. Smooth and notched specimens provide a database to study the influence of notches and multiaxiality. These results are used to state on the applicability of commonly used failure hypothesis like von Mises and Tresca in comparison to advanced fatigue damage parameters. In addition to constant amplitude strain controlled fatigue testing load spectra were investigated. Thereby fatigue cumulative damage models like Miner’s rule can be evaluated. This publication constitutes a follow-up to a previous paper [1] and targets at the presentation of experimental results in conjunction with potentials with an improved fatigue assessment concept. In addition the methodology of the concept is applied to experimental results on fatigue life assessments for piping materials published by other organizations. Requirements for further experimental investigations towards the verification of a closed concept are formulated.

The Influencing Factors and Assessment Rule of Fatigue Life of Shaft Based on Product Lifecycle Management

2007 ◽  
Vol 561-565 ◽  
pp. 2253-2256 ◽  
Author(s):  
You Tang Li ◽  
Ping Ma ◽  
Jun Tian Zhao
Keyword(s):  
Fatigue Life ◽  
Influencing Factors ◽  
Axial Stress ◽  
Assessment Method ◽  
Product Lifecycle Management ◽  
Product Lifecycle ◽  
Fatigue Design ◽  
Main Factors ◽  
Set Up ◽  
Lifecycle Management

Product lifecycle management is one of the main developmental aspects of advanced manufacturing technology. Anti-fatigue design is the key content in product lifecycle management. For designing the fatigue life of shaft exactly and determining the assessment method, the influencing factors must be realized roundly. The mechanical model of shaft is set up at first, and then the main factors that affect the fatigue life of shaft is discussed, the interrelations of the main factors and the framework are founded. The assessment equation of fatigue life for shaft is put forward and the influencing coefficient of multi-axial stress to fatigue life is analyzed. The results of this paper will establish the base of anti-fatigue and assessment life of shaft.

A Review of DNVGL-RP-F105 Fatigue Assessment Model or Why My Free Span Has Not Failed

2021 ◽  
Author(s):  
Mário Caruso
Keyword(s):  
Fatigue Life ◽  
Exposure Time ◽  
Vibration Analysis ◽  
Direct Reference ◽  
Assessment Model ◽  
Fatigue Assessment ◽  
Fatigue Design ◽  
Fatigue Model ◽  
Key Aspects

Abstract The objective of a free span fatigue assessment is to provide a rational criterion to evaluate the long-term integrity of a free spanning pipeline, to which DNVGL-RP-F105 was developed. The Recommended Practice has a long history. Guideline 14, the foundation document to it, was released in 1998. The guidelines of the DNVGL-RP-F105 were gradually adopted by the industry for free spans analysis, and even API 1111 makes direct reference to it. Today, DNVGL-RP-F105 is the de facto Vortex Induced Vibration analysis guide for all applications where small number of bending driven modes are expected to be excited, overstepping its original purpose of free spanning pipelines and providing guidance when no other source exists. With such a long history, it is easy to forget the basis for the Recommended Practice fatigue model and obtain results that do not match expectations. A prime example is when assessing a free span based on survey and the fatigue life capacity calculated following the Recommended Practice is much smaller than the actual exposure time. In this situation one may ask “why my free span has not failed?” and conclude that the Recommended Practice is either too over conservative or plainly wrong. This paper reviews some key aspects of the DNVGL-RP-F105 fatigue model and explore their implication to fatigue design and assessment. And it hopes to clarify why your free span has not failed even when you expected it to.

scholarly journals Fatigue and Corrosion Fatigue Life Assessment With Application to Autofrettaged Parts

2018 ◽  
Author(s):  
Volodymyr Okorokov ◽  
Donald MacKenzie ◽  
Yevgen Gorash
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Corrosion Fatigue ◽  
Local Stress ◽  
Life Time ◽  
Life Assessment ◽  
Cyclic Plasticity ◽  
Theoretical Modelling ◽  
Experimental Program ◽  
Low Carbon

This study investigates an effect of autofrettage on the fatigue and corrosion fatigue life of high pressure parts made from low carbon structural steel. To estimate the beneficial effect of autofrettage application, an extensive experimental program and advanced theoretical modelling are conducted and analyzed in this study. Accurate calculation of compressive residual stresses is achieved by application of a cyclic plasticity model which can precisely simulate a cyclic plasticity response of material. In terms of a fatigue life prediction methodology, a non-local stress based approach with a modified critical distance theory is used for prediction of the crack initiation stage providing conservative fatigue assessment. Because of the fact that the crack propagation stage can take a considerable part of the total life for autofrettaged parts, more accurate fatigue life calculation is performed by the use of a fracture mechanics approach. The total fatigue life time of autofrettaged parts is then calculated as a sum of the crack initiation and propagation stages.

Creep Fatigue Behavior and Damage Assessment for Mod 9 Cr 1 Mo Steel

2006 ◽  
Author(s):  
Marie-The´re`se Cabrillat ◽  
Lucien Allais ◽  
Michel Mottot ◽  
Bernard Riou ◽  
Claude Escaravage
Keyword(s):  
Fatigue Behavior ◽  
Hold Time ◽  
Pressure Vessels ◽  
Experimental Program ◽  
Design Rules ◽  
Fatigue Design ◽  
Internal Structures ◽  
Creep Fatigue ◽  
Grade 91 ◽  
Life Evaluations

Mod 9Cr-1Mo Steel (grade 91) is a material candidate for pressure vessels and some internal structures of Gas Cooled Reactors. Some of these structures will operate in the creep range and have to be designed relatively to creep-fatigue damage. In order to characterize the creep-fatigue behavior of this steel and to validate the creep fatigue design rules proposed in nuclear design codes (mainly RCC-MR and ASME), specific fatigue-relaxation (strain controlled during hold time) and creep-fatigue (stress controlled during hold time) tests have been carried out at CEA on this steel. All these tests are conducted at 550°C, but several loading conditions are considered and the influence of the position of hold time in the cycle (either in a tensile or a compressive state) is investigated. This paper presents the experimental program undertaken and describes the main results obtained. Then the creep-fatigue life evaluations are performed using creep-fatigue design rules and material data codified in RCC-MR and ASME and the predictions are compared to experimental results.

scholarly journals Characterization of Austenitic Stainless Steels with Regard to Environmentally Assisted Fatigue in Simulated Light Water Reactor Conditions

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 307
Author(s):  
Matthias Bruchhausen ◽  
Gintautas Dundulis ◽  
Alec McLennan ◽  
Sergio Arrieta ◽  
Tim Austin ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Fatigue Life ◽  
Elevated Temperature ◽  
Strain Rate ◽  
Power Plants ◽  
Research Effort ◽  
Hold Time ◽  
Strain Range ◽  
Austenitic Steels ◽  
Mean Strain

A substantial amount of research effort has been applied to the field of environmentally assisted fatigue (EAF) due to the requirement to account for the EAF behaviour of metals for existing and new build nuclear power plants. We present the results of the European project INcreasing Safety in NPPs by Covering Gaps in Environmental Fatigue Assessment (INCEFA-PLUS), during which the sensitivities of strain range, environment, surface roughness, mean strain and hold times, as well as their interactions on the fatigue life of austenitic steels has been characterized. The project included a test campaign, during which more than 250 fatigue tests were performed. The tests did not reveal a significant effect of mean strain or hold time on fatigue life. An empirical model describing the fatigue life as a function of strain rate, environment and surface roughness is developed. There is evidence for statistically significant interaction effects between surface roughness and the environment, as well as between surface roughness and strain range. However, their impact on fatigue life is so small that they are not practically relevant and can in most cases be neglected. Reducing the environmental impact on fatigue life by modifying the temperature or strain rate leads to an increase of the fatigue life in agreement with predictions based on NUREG/CR-6909. A limited sub-programme on the sensitivity of hold times at elevated temperature at zero force conditions and at elevated temperature did not show the beneficial effect on fatigue life found in another study.

Background for New Revision of DNV-RP-C203 Fatigue Design of Offshore Steel Structures

2010 ◽  
Author(s):  
Inge Lotsberg
Keyword(s):  
Steel Structures ◽  
Electronic Version ◽  
Fatigue Assessment ◽  
Fatigue Design ◽  
Different Types ◽  
Background Material ◽  
Made In

The DNV-RP-C203 Fatigue Design of Offshore Steel Structures is being used by a number of different companies for fatigue assessment of different types of structures. This has resulted in questions to DNV about background for the different sections in the document. It is therefore important that the basis for this document is open to the industry. Quite a lot of the background material has also been published earlier at conferences and in journals. In some situations it has been found that the content can be improved to better suite the industry. The document is presented in an electronic version making revisions easy. Therefore it has been revised several times since the last official presentation of a revision in 2005. The present paper gives an overview of the most significant changes made in the document since the 2005 revision. Some of these changes are already included in the present version of DNV-RP-C203. The remaining changes will be included in a revision dated 2010.

Fatigue Behaviour of Dented Pipes Under Internal Pressure: A Numerical-Experimental Approach

2018 ◽  
Author(s):  
Mario A. Polanco-Loria ◽  
Håvar Ilstad
Keyword(s):  
Fatigue Life ◽  
Internal Pressure ◽  
Fatigue Behavior ◽  
Crack Depth ◽  
Fatigue Behaviour ◽  
Experimental Methodology ◽  
Experimental Program ◽  
Metal Loss ◽  
Life Predictions ◽  
Dent Depth

This work presents a numerical-experimental methodology to study the fatigue behavior of dented pipes under internal pressure. A full-scale experimental program on dented pipes containing gouges were achieved. Two types of defects were studied: metal loss (plain dent) and sharp notch. Both defects acting independently reduce the fatigue life performance but their combination is highly detrimental and must be avoided. We did not find a severity threshold (e.g. dent depth or crack depth) where these defects could coexist. In addition, based on numerical analyses we proposed a new expression for stress concentration factor (SCF) in line with transversal indentation. This information was successfully integrated into a simple fatigue model where the fatigue life predictions were practically inside the window of experimental results.

scholarly journals Multiaxial fatigue study on steel transversal attachments under constant amplitude proportional and non-proportional loadings

2018 ◽  
Vol 165 ◽  
pp. 16007
Author(s):  
Martin Garcia ◽  
Claudio A. Pereira Baptista ◽  
Alain Nussbaumer
Keyword(s):  
Fatigue Life ◽  
High Strength ◽  
Fatigue Tests ◽  
Multiaxial Fatigue ◽  
Life Assessment ◽  
Experimental Program ◽  
Proportional Loading ◽  
Load Carrying ◽  
Stress States ◽  
Experimental Values

In this study, the multiaxial fatigue strength of full-scale transversal attachment is assessed and compared to original experimental results and others found in the literature. Mild strength S235JR steel is used and an exploratory investigation on the use of high strength S690QL steel and the effect of non-proportional loading is presented. The study focuses on non-load carrying fillet welds as commonly used in bridge design and more generally between main girders and struts. The experimental program includes 33 uniaxial and multiaxial fatigue tests and was partially carried out on a new multiaxial setup that allows proportional and non-proportional tests in a typical welded detail. The fatigue life is then compared with estimations obtained from local approaches with the help of 3D finite element models. The multiaxial fatigue life assessment with some of the well-known local approaches is shown to be suited to the analysis under multiaxial stress states. The accuracy of each models and approaches is compared to the experimental values considering all the previously cited parameters.

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