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.

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.

A Study on Fatigue and Creep-Fatigue Life Assessment Using Cyclic Thermal Tests With Mod.9Cr-1Mo Steel Structures

2012 ◽  
Author(s):  
Masanori Ando ◽  
Hiroshi Kanasaki ◽  
Shingo Date ◽  
Koichi Kikuchi ◽  
Kenichiro Satoh ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Temperature Distribution ◽  
Crack Initiation ◽  
Thermal Loading ◽  
Life Assessment ◽  
Estimation Methods ◽  
Short Term ◽  
Cyclic Thermal Loading ◽  
Fatigue Life Assessment ◽  
Creep Fatigue

In a component design at elevated temperature, fatigue and creep-fatigue is one of the most important failure modes, and fatigue and creep-fatigue life assessment in structural discontinuities is important issue to evaluate structural integrity of the components. Therefore, to assess the failure estimation methods, cyclic thermal loading tests with two kinds of cylindrical models with thick part were performed by using an induction heating coil and pressurized cooling air. In the tests, crack initiation and propagation processes at stress concentration area were observed by replica method. Besides those, finite element analysis (FEA) was carried out to estimate the number of cycles to failure. In the first test, a shorter life than predicted based on axisymmetric analysis. Through the 3 dimensional FEA, Vickers hardness test and deformation measurements after the test, it was suggested that inhomogeneous temperature distribution in hoop direction resulted in such precocious failure. Then, the second test was performed after improvement of temperature distribution. As a result, the crack initiation life was in a good agreement with the FEA result by considering the short term compressive holding. Through these test and FEA results, fatigue and creep-fatigue life assessment methods of Mod.9Cr-1Mo steel including evaluation of cyclic thermal loading, short term compressive holding and failure criterion, were discussed. In addition it was pointed out that the temperature condition should be carefully controlled and measured in the structural test with Mod.9Cr-1Mo steel structure.

Comparison of Thermo-Mechanical Fatigue Life Assessment Methods for Coke Drums

2010 ◽  
Author(s):  
Jorge A. Penso ◽  
Radwan Hazime
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Stress Analysis ◽  
Elastic Stress ◽  
Life Assessment ◽  
Structural Stress ◽  
Vast Number ◽  
Delayed Coking ◽  
Oil Refineries ◽  
Mechanical Fatigue

Assessing the life of coke drums is a challenge many refineries have faced since the delayed coking process was introduced in oil refineries. Delayed coking units are among the refinery units that have higher economical yields. Welds play an important role in the life of these vessels. Cracking and bulging occurrences in the coke drums, most often at the weld areas, characterize the history of the operation of delayed coking units. Thermo-mechanical fatigue is the most common cause for cracking in coke drums. Although coke drums constitutes a classical example of thermo-mechanical fatigue there are several other oil processes that are affected by this mechanism. Hence the findings from this work could be useful for other applications. Other possible application examples include mixing points of hot and cold streams, coal gasifiers, and steam generating equipment. There are a vast number of models and methods for estimating the thermo-mechanical fatigue life of engineering components subjected to thermal and mechanical loads. In this work, focus is placed on comparing some of the commonly used methods including: • API 579 methods: - Elastic stress analysis and equivalent stress; - Elastic-plastic stress analysis and equivalent strain; - Elastic stress analysis and structural stress. • Creep-fatigue crack initiation using R5 Volume 2/3. • Non-linear isothermal fatigue analysis using maximum shear strain amplitude with Morrow mean stress correction. In this study, a Finite Element (FEA) model is used to estimate the cyclic stresses and strains for the skirt-to-bottom head attachment weld. The model includes details of the geometry, material properties, boundary conditions, and loads. The results from the FEA are post-processed using the fatigue methods listed above. Lastly, a parametric study on the most important process variables is performed. The results of this work indicate that the predictions of the number of cycles to crack initiation are not significantly different between various crack initiation methods, but they are significantly different when compared with the structural stress method (a through-thickness crack). Thus, the thermo-mechanical fatigue algorithm selection should be based on the assessment goals and service conditions. The parametric analysis showed that the life of the drum is strongly influenced by the switch temperature and quench rates with lower switch temperatures and faster quench rates negatively impacting the life of the drum.

Corrosion Fatigue Evaluation of Austenitics Stainless Steels: The New Proposal to the Czech Standard in the Area of Nuclear Power Plants Type WWER

2013 ◽  
Author(s):  
Libor Vlcek
Keyword(s):  
Fatigue Life ◽  
Corrosion Fatigue ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Residual Life ◽  
Low Cycle Fatigue ◽  
Life Assessment ◽  
Technical Documentation ◽  
Primary Water

In the Czech Republic the NTD A.M.E. (Normatively Technical Documentation of Association of Mechanical Engineers) standard [1] is recommended by the State Office for Nuclear Safety for assessment of components and piping in the nuclear power plants of WWER type. So far the fatigue life assessment is based on fatigue design curves or mathematical formulas which are based on experimental tests in air environment conditions only. The present paper is dealing with the new proposal of Czech approach in the area of corrosion fatigue interaction. Based on original Russian works the environmental aspects were taken into account for the case of fatigue life evaluation. The aim of this work is to clarify the main idea of the new proposal of appropriate part of NTD A.M.E. residual life section. In the frame of primary water corrosion fatigue interaction not only theoretical background, but also low-cycle fatigue tests in primary water are presented.

StrainLife: Efficient Fatigue Life Data Generation for an Enhanced Ageing Assessment of Metallic Components

2018 ◽  
Author(s):  
Klaus Heckmann ◽  
Jürgen Sievers ◽  
Tim Schopf ◽  
Xaver Schuler ◽  
Ruth de Acosta ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Water Environment ◽  
Operation Time ◽  
Life Time ◽  
Fatigue Tests ◽  
Hot Water ◽  
Life Assessment ◽  
Data Generation ◽  
Operational Conditions ◽  
Piping Systems

Pressurized pipes in hot water environment are subject to ageing mechanisms such as fatigue and environmental-assisted fatigue. These ageing effects limit the in-service time of components due to the possibility of crack formation, initiation and growth. Furthermore, uncertainties in life time assessment evolve as a consequence of increased scattering and resulting deviations in material properties. The lack of appropriate information requires safety-oriented design and conservative margins in the acceptable operation time. In this contribution, investigations on methods for an improved assessment of fatigue life assessment based on microstructural aspects (specifically in the view of piping systems) are presented. The focus is on the metastable austenitic steel AISI 347 (X6CrNiNb18-10) under boiling water reactor operational conditions. In addition to strain-controlled fatigue tests and the hysteresis information, microstructural characterizations of the damage evolution are performed. Fatigue tests are equipped with magnetic and resistometric sensors to measure a different kind of material response correlated with the damage states. The information obtained is used for an improved derivation of fatigue life evaluations of piping systems. The StrainLife approach and its specific instrumentation is proposed and discussed. In this approach, the number of strain-controlled fatigue tests is basically reduced by an order of magnitude when compared to traditional procedures. A software tool (as a module of the structural analysis code PROST) has been developed to assist users in evaluating and incorporating the respective data and to derive the subsequent fatigue life curves. As an outlook, further development is addressed to transfer the methodology to the assessment of residual fatigue life of components being exposed to ageing in operation.

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