Fatigue Stress Evaluation at Shell-to-Bottom Joint With Double Plastic Hinge in Elevated Temperature Steel Tanks on Concrete Ring Walls

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Sridhar Sathyanarayanan ◽  
Seshu M. R. Adluri
Keyword(s):  
Elevated Temperature ◽  
Current Practice ◽  
Low Cycle Fatigue ◽  
Current Model ◽  
Plastic Hinge ◽  
Strain Range ◽  
Fatigue Cracking ◽  
Element Analysis ◽  
Fatigue Evaluation ◽  
Concrete Ring

The shell-to-bottom joint of hydrocarbon storage tanks is a critical location which may experience fatigue cracking and requires evaluation of the local cyclic stresses especially in the case of elevated temperature tanks. The fill/draw down cycle of the stored liquid causes low cycle fatigue near this joint and hence a fatigue evaluation is recommended. The peak alternating stress at this location, used to enter the fatigue curves is currently determined using a pseudo-elastic analysis that represents strain range due to inelastic deformations. API 650 employs beam on elastic foundation theory for this analysis. This theory is being used for tanks resting fully on earthen foundation as well as those on concrete ring wall. This paper studies the validity of using this theory for tanks with concrete ring wall foundation which are much more rigid compared to earthen foundations. Some of the difficulties in the current practice are highlighted. An alternative to the current model is presented for the determination of stresses in such tanks. The results are validated using finite element analysis. The results show that the current practice needs to be revised or rejustified in an alternative manner.

Modified Fatigue Stress at Shell-to-Bottom Joint of Steel Tanks on Ring Walls

2012 ◽  
Author(s):  
Sridhar Sathyanarayanan ◽  
Seshu M. R. Adluri
Keyword(s):  
Low Cycle Fatigue ◽  
Current Model ◽  
Strain Range ◽  
Element Analysis ◽  
Steel Tanks ◽  
Hydrocarbon Storage ◽  
Wall Foundation ◽  
Fatigue Evaluation ◽  
Failure Location ◽  
Concrete Ring

Shell-to-bottom joint of hydrocarbon storage tanks is a critical failure location which needs careful evaluation especially in the case of elevated temperature tanks. The fill/draw down cycle of the stored liquid causes low cycle fatigue near this joint and hence a fatigue evaluation is recommended. The peak alternating stress at this location, used to enter the fatigue curves is currently determined using a pseudo elastic stress that represents strain range due to inelastic deformations. For this, API 650 employs beam on elastic foundation theory. This theory is being used for tanks resting fully on earthen foundation as well as those on concrete ring wall. This paper studies the validity of using this theory for tanks with concrete ring wall foundation which are much more rigid compared to earthen foundations. Some of the difficulties in the current practice are highlighted. Alternatives to using the current model are derived to determine the stresses in such tanks. The results are validated using finite element analysis.

A Novel Fatigue Evaluation Approach with Direct Steady Cycle Analysis (DSCA) Based on the Linear Matching Method (LMM)

2019 ◽  
Vol 795 ◽  
pp. 383-388 ◽  
Author(s):  
Xiao Tao Zheng ◽  
Zhi Yuan Ma ◽  
Hao Feng Chen ◽  
Jun Shen
Keyword(s):  
Fatigue Life ◽  
Evaluation Method ◽  
Low Cycle Fatigue ◽  
Effective Strain ◽  
Strain Range ◽  
Matching Method ◽  
Evaluation Approach ◽  
Perfectly Plastic ◽  
Fatigue Evaluation ◽  
Linear Matching Method

The traditional Low Cycle Fatigue (LCF) evaluation method is based on elastic analysis with Neuber’s rule which is usually considered to be over conservative. However, the effective strain range at the steady cycle should be calculated by detailed cycle-by-cycle analysis for the alternative elastic-plastic method in ASME VIII-2, which is obviously time-consuming. A Direct Steady Cycle Analysis (DSCA) method within the Linear Matching Method (LMM) framework is proposed to assess the fatigue life accurately and efficiently for components with arbitrary geometries and cyclic loads. Temperature-dependent stress-strain relationships considering the strain hardening described by the Ramberg-Osgood (RO) formula are discussed and compared with those results obtained by the Elastic-Perfectly Plastic (EPP) model. Additionally, a Reversed Plasticity Domain Method (RPDM) based on the shakedown and ratchet limit analysis method and the DSCA approach within the LMM framework (LMM DSCA) is recommended to design cyclic load levels of LCF experiments with predefined fatigue life ranges.

Verification of the Prediction Methods of Strain Range in Notched Specimens Made of Mod.9Cr-1Mo

2010 ◽  
Author(s):  
Masanori Ando ◽  
Yuichi Hirose ◽  
Shingo Date ◽  
Sota Watanabe ◽  
Yasuhiro Enuma ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Elevated Temperature ◽  
Low Cycle Fatigue ◽  
Strain Range ◽  
Fatigue Tests ◽  
Estimation Methods ◽  
Prediction Methods ◽  
Test Machine ◽  
Notched Specimens ◽  
Creep Fatigue

Several innovative prediction methods of strain range have been developed in order to apply to the Generation IV plants. In a component design at elevated temperature, ‘strain range’ is used to calculate the fatigue and creep-fatigue damage. Therefore, prediction of ‘strain range’ is one of the most important issues to evaluate the components’ integrity during these lifetimes. To verify the strain prediction method of discontinues structures at evaluated temperature, low cycle fatigue tests were carried out with notched specimens. All the specimens were made of Mod.9Cr-1Mo, because it is a candidate material for a primary and secondary heat transports system components of JSFR (Japanese Sodium Fast Reactor). Deformation control fatigue tests and thermal fatigue tests were performed by ordinary uni-axial push-pull test machine and equipment generating the thermal gradient in the notched plate by induction heating. Stress concentration level was changed by varying the notch radius in the both kind of tests. Crack initiation and propagation process during the fatigue test were observed by the digital micro-scope and replica method. Elastic and inelastic FEAs were also carried out to estimate the ‘strain range’ for the prediction of fatigue life. Then the ranges of several strain predictions and estimations were compared with the test results. These predictions were based on the sophisticated technique to estimate the ‘strain range’ from elastic FEA. Stress reduction locus (SRL) method, simple elastic follow-up method, Neuber’s rule method and the methods supplied by elevated temperature design standards were applied. Through these results, the applicability and conservativeness of these strain prediction and estimation methods, which is the basis of the creep-fatigue life prediction, is discussed.

Cyclic Plastic Deformation of a Circular Plate With Work Hardening

1984 ◽  
Vol 106 (4) ◽  
pp. 336-341
Author(s):  
R. Winter
Keyword(s):  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Nonlinear Behavior ◽  
Strain Curve ◽  
Strain Range ◽  
Cyclic Strain ◽  
Cyclic Stress ◽  
Cycle Fatigue ◽  
Stress Strain ◽  
Element Analysis

An experimental and theoretical study was performed of the nonlinear behavior of a simply supported flat circular aluminum plate under reversed cyclic central load. The application is for the analysis of cyclic stress and strain of structural components in the plastic range for predicting low-cycle fatigue life. The main purpose was to determine the relative accuracy of an elastic-plastic large deformation finite element analysis when the material properties input data are derived from monotonic (noncyclic) stress-strain curves versus that derived from cyclic stress-strain curves. The results showed that large errors could be induced in the theoretical prediction of cyclic strain range when using the monotonic stress-strain curve, which could lead to large errors in predicting low-cycle fatigue life. The use of cyclic stress-strain curves, according to the model developed by Morrow, et al., proved to be accurate and convenient.

Low-Cycle Fatigue Behavior of Small Slice Specimens of Zircaloy-4 at Elevated Temperature

2006 ◽  
Vol 324-325 ◽  
pp. 1241-1244 ◽  
Author(s):  
Li Xun Cai ◽  
Yu Ming Ye
Keyword(s):  
Elevated Temperature ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Cyclic Hardening ◽  
Cyclic Softening ◽  
Fatigue Tests ◽  
Uniaxial Strain ◽  
Transverse Strain ◽  
Test Results ◽  
Element Analysis

A series of strain fatigue tests were carried out on small bugle-like slice-specimens of Zr-4 alloy at 20 and 400. According to Elastic and Plastic Finite Element Analysis and assumption of local damage equivalence, a strain formula was given to transform transverse strain of the specimen to uniaxial strain. Based on the test results of the alloy and the strain transform formula, M-C (Manson-Coffin) models to be used for estimating uniaxial fatigue life of Zr-4 alloy were obtained. The results show that, the alloy mainly behaves as cyclic softening at 20 and as cyclic hardening at 400, and the elevated temperature can lead serious additional fatigue damage of the alloy and the effect of the elevated temperature impairs gradually with increasing of amplitude strain. A conclusion is helpful that prediction life by using M-C model based on traditional strain transform equation is quite conservative when uniaxial strain amplitude is less than 0.5%.

Verification of the Estimation Methods of Strain Range in Notched Specimens Made of Mod.9Cr-1Mo Steel

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Masanori Ando ◽  
Yuichi Hirose ◽  
Shingo Date ◽  
Sota Watanabe ◽  
Yasuhiro Enuma ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Elevated Temperature ◽  
Low Cycle Fatigue ◽  
Strain Range ◽  
Fatigue Tests ◽  
Estimation Methods ◽  
Test Machine ◽  
Component Reliability ◽  
Notched Specimens ◽  
Creep Fatigue

Several methods of estimating strain range at a structural discontinuity have been developed in order to assess component reliability. In a component design at elevated temperature, estimation of strain range is required to evaluate the fatigue and creep-fatigue damage. Therefore, estimation of strain range is one of the most important issues when evaluating the integrity of a component during its lifetimes. To verify the methods of estimating strain range for discontinuous structures, low cycle fatigue tests were carried out with notched specimens. All the specimens were made of Mod.9Cr-1Mo steel, because it is a candidate material for a primary and secondary heat transport system components of Japan Sodium-cooled Fast Reactor (JSFR). Displacement control fatigue tests and thermal fatigue tests were performed by ordinary uniaxial push–pull test machine and equipment generating the thermal gradient in the notched plate by induction heating. Several notch radii were employed to vary the stress concentration level in both kinds of tests. Crack initiation and propagation process during the tests were observed by a digital microscope and the replica method to define the failure cycles. Elastic and inelastic finite element analyses were also performed to estimate strain range for predicting fatigue life. Then, these predictions were compared with the test results. Several methods such as stress redistribution locus (SRL) method, simple elastic follow-up (SEF) method, Neuber's law, and the procedures employed by elevated temperature design codes were applied. Through these comparisons, the applicability and conservativeness of these strain range estimation methods, which is the basis of the fatigue and creep-fatigue life prediction, are discussed.

scholarly journals Evaluation of Structural Behavior and Fatigue Performance of a KR-Type Rail Clip

2021 ◽  
Vol 11 (24) ◽  
pp. 12074
Author(s):  
Sang-Hyeok Kim ◽  
Xiao-Jun Fang ◽  
Yeun-Chul Park ◽  
Hyoung-Bo Sim
Keyword(s):  
Finite Element Analysis ◽  
Fatigue Cracking ◽  
Fatigue Performance ◽  
Structural Behavior ◽  
Stress Range ◽  
Element Analysis ◽  
Essential Components ◽  
The Finite Element Analysis ◽  
Train Operation ◽  
Fatigue Evaluation

Rail clips are essential components of rail fastening systems that clamp the rails to sleepers. Fatigue damage of rail clips has been recently reported in railway lines. However, there has been a lack of research investigating this fatigue issue. The KR-type rail fastening system has been recently developed and used in some domestic railways. This study aimed at evaluating the structural behavior and fatigue performance of the KR-type rail clip. The assembly test performed in the laboratory showed that the stresses induced in the rail clips after tightening, particularly at the stress concentration locations, exceeded the yield stress, indicating that the rail clip could be vulnerable to fatigue cracking when combined with the stress range during repeated trainloads. The finite element analysis results, which revealed a good correlation with the experiments, were used to evaluate the fatigue performance of the rail clip by adopting the modified Goodman fatigue criteria. The fatigue evaluation results indicated that when the vertical rail displacement during train operation exceeded 2 mm, the rail clips could potentially suffer from fatigue failure.

Examination of Factors in the Modified Rate Approach Method Under Various Conditions

2011 ◽  
Author(s):  
Yuichi Fukuta ◽  
Seiji Asada ◽  
Yuichiro Nomura ◽  
Hiroshi Kanasaki
Keyword(s):  
Fatigue Life ◽  
Elevated Temperature ◽  
Strain Rate ◽  
Fatigue Damage ◽  
Correction Factor ◽  
Strain Range ◽  
Approach Method ◽  
Fatigue Evaluation ◽  
Response To Temperature ◽  
Temperature Water

Fatigue life in elevated-temperature water is affected by water chemistry, temperature, and strain rate. To evaluate these effects, the environmental fatigue life correction factor was established. And to evaluate fatigue damage in actual plants where factors such as temperature and strain rate are not constant, the modified rate approach method was developed. In order to confirm the applicability of these methods, several tests were carried out under a condition in which strain rate changes in response to temperature and fatigue life could be evaluated with an accuracy of a factor of 3, but conservatism was observed. In this evaluation, conservatism of environmental fatigue prediction is studied. To minimize conservatism in environmental fatigue evaluation, four factors are examined. As a result of examination, we conclude that an improvement the environmental fatigue life correction factor and application of a strain range insensitive to the environment may reduce conservatism, and that investigation into the mechanism of reduction in fatigue life is necessary for further improvement.

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.

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