scholarly journals Two-Stage Model for Fatigue Life Assessment of High Frequency Mechanical Impact (HFMI) Treated Welded Steel Details

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1318
Author(s):  
Boris Fuštar ◽  
Ivan Lukačević ◽  
Davor Skejić ◽  
Mladen Lukić
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
High Frequency ◽  
Life Assessment ◽  
Stage Model ◽  
Two Stage ◽  
Welded Steel ◽  
Mechanical Impact ◽  
Steel Grades ◽  
Critical Components

Welded steel details are critical components from the aspect of fatigue. Additional fatigue resistance can be achieved by the High-Frequency Mechanical Impact (HFMI) treatment. This treatment increases the crack initiation period by improving the weld geometry, introducing compressive residual stresses, and increasing the weld toe’s hardness. The study presented in this paper is based on the development and calibration of an Initiation–Propagation-based Two-Stage Model (TSM), which is, by the combination of different methods, suitable to separately consider crack initiation and crack propagation. It is shown that a TSM is able to predict the fatigue life of as-welded and HFMI-treated welded steel details, which is proven by comparing the calculated results with the results of tests on similar details given in the literature. A parametric study of the TSM is conducted for different steel grades in order to investigate the influence of steel strength and HFMI parameters on fatigue lives of a welded steel detail with longitudinal attachment.

scholarly journals Influence of the atmosphere corrosion on the fatigue life of welded T-joints treated by high frequency mechanical impact

2019 ◽  
Vol 16 ◽  
pp. 73-80 ◽  
Author(s):  
Vitalii Knysh ◽  
Sergii Solovei ◽  
Lyudmila Nyrkova ◽  
Illya Klochkov ◽  
Svіatoslav Motrunich
Keyword(s):  
Fatigue Life ◽  
High Frequency ◽  
T Joints ◽  
Mechanical Impact

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.

scholarly journals TWO‐STAGE‐MODEL FOR THE PROGNOSIS OF FATIGUE LIFE: APPLICATION TO BUTT WELDS

ce/papers ◽  
2019 ◽  
Vol 3 (3-4) ◽  
pp. 597-602
Author(s):  
Stefanie Röscher ◽  
Markus Knobloch
Keyword(s):  
Fatigue Life ◽  
Stage Model ◽  
Two Stage ◽  
Butt Welds

scholarly journals Fatigue life extension of existing welded structures via high frequency mechanical impact (HFMI) treatment

2021 ◽  
Vol 239 ◽  
pp. 112234
Author(s):  
Hassan Al-Karawi ◽  
Rüdiger U. Franz von Bock und Polach ◽  
Mohammad Al-Emrani
Keyword(s):  
Fatigue Life ◽  
High Frequency ◽  
Life Extension ◽  
Welded Structures ◽  
Mechanical Impact
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