Predicting the Fatigue Life of Long Dents in Petroleum Pipelines

2002 ◽  
Author(s):  
Adam J. Rinehart ◽  
Peter B. Keating
Keyword(s):  
Fatigue Life ◽  
Fatigue Behavior ◽  
Contact Region ◽  
Laboratory Data ◽  
Prediction Method ◽  
Fatigue Cracking ◽  
Local Stress ◽  
Fatigue Damage Accumulation ◽  
Bending Stresses ◽  
Life Predictions

A full scale experimental study has demonstrated that long, unrestrained pipeline dents typically experience fatigue cracking in the dent contact region and have significantly shorter fatigue lives compared to other dent types studied. Furthermore, these dents often fully reround under normal pipeline operating pressures, making them difficult to reliably detect and assess using existing depth-based approaches. Several conditions unique to the dent contact region accelerate fatigue damage accumulation and are considered in a case-specific long dent fatigue life prediction method. First, the contact region develops significant bending stresses that contribute to a higher rate of fatigue crack growth. Second, history dependent, thru-thickness residual bending stresses that may have a significant influence on fatigue behavior are present in the contact region as a result of plastic deformation associated with dent formation and subsequent rebounding. A method for predicting the fatigue life of long dents that accounts for these factors is presented here and is used to analyze specific cases for which laboratory data is available. Nonlinear finite element modelling of the dent life cycle, including the indentation and rebounding phases, is used to determine local stress range behaviors and residual stress distributions. The application of appropriate fracture mechanics based models of fatigue is discussed and demonstrated. Fatigue life predictions are made on a case by case basis for situations studied in the laboratory so that the validity and accuracy of the approach presented here may be studied.

Fatigue Life Prediction for Short Dents in Petroleum Pipelines

2002 ◽  
Author(s):  
Adam J. Rinehart ◽  
Peter B. Keating
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Propagation ◽  
External Force ◽  
Life Prediction ◽  
Fatigue Behavior ◽  
Contact Region ◽  
Fatigue Cracking ◽  
Fatigue Life Prediction ◽  
Crack Initiation Life

Pipeline dent fatigue behavior has been shown to be strongly dependent upon dent length and external force dent restraint characteristics. Full-scale laboratory tests have shown that short dents that are unrestrained by an external force typically experience fatigue cracking in the dent periphery outside of the dent contact region. A fatigue life prediction method for short dents is presented here. In order to assess method accuracy, predictions are made for cases in which fatigue life has been measured experimentally. The predictions account for both crack initiation life and crack propagation life. Stress concentration values used in the predictions are determined using finite element modelling on a case-by-case basis for comparison purposes. Appropriate crack initiation life estimates, stress intensity factor predictions, and crack propagation models are taken from existing literature. Predicted and measured fatigue lives are compared for the cases studied.

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.

Laboratory Comparison of Permanent Deformation and Fatigue Behavior of Neat, Polymer, and Rubber-Asphalt Binders

2019 ◽  
Vol 2673 (4) ◽  
pp. 524-532
Author(s):  
Felipe F. Camargo ◽  
Kamilla Vasconcelos ◽  
Liedi L. Bernucci
Keyword(s):  
Fatigue Life ◽  
Life Prediction ◽  
Fatigue Behavior ◽  
Permanent Deformation ◽  
Asphalt Binder ◽  
Fatigue Cracking ◽  
Fatigue Life Prediction ◽  
Polymer Modification ◽  
Neat Polymer ◽  
Percentage Recovery

Fatigue cracking and rutting are among the major types of distresses to be considered in flexible pavement design. In this context, the choice of the asphalt binder plays a major role in both the fatigue behavior and permanent deformation resistance of the asphalt mixture. This study was conducted to assess the permanent deformation and fatigue behavior of a field-blended rubber-asphalt (CRMA) and compare the results with typical binders used in Brazil. The neat binder used for modification was also employed as a control and as a base for polymer modification (SBSA). The binders were evaluated using the multiple stress creep and recovery (MSCR) for permanent deformation behavior, and the time sweep (TST) and linear amplitude sweep (LAS) tests for fatigue behavior. Modification of the neat binder resulted in an increase in percentage recovery in the MSCR, whereas the percentage recovery for CRMA was the highest among the three binders at any given temperature. The non-recoverable creep compliance for the CRMA was lower than that exhibited by the neat and SBSA binders for both stress levels for the range of temperatures tested. Binder modification resulted in an improved fatigue behavior compared with the neat binder according to the TST and LAS, whereas rubber modification resulted in the best fatigue behavior. Fatigue life prediction by TST was consistently higher than fatigue life prediction in the LAS test, probably because different criteria were used for determining failure in each test (ranking of the binders remained constant regardless of the criteria used).

Analyses of Contact Pressure and Stress Amplitude Effects on Fretting Fatigue Life

2000 ◽  
Vol 123 (1) ◽  
pp. 85-93 ◽  
Author(s):  
K. Iyer ◽  
S. Mall
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Contact Pressure ◽  
Stress Amplitude ◽  
Normal Load ◽  
Contact Region ◽  
Local Stress ◽  
Fretting Fatigue ◽  
Element Analysis ◽  
Stress Ratios

Elastic-plastic finite element analyses of a cylinder-on-plate configuration, studied experimentally, were performed to provide an explanation for the decrease in fretting fatigue life with increasing contact pressure. Three values of normal load, namely 1338 N, 2230 N, and 3567 N, and three stress ratios (0.1, 0.5, and 0.7) were considered. Based on a previously determined dependency between contact pressure and friction coefficient, the effect of coefficient of friction was also evaluated. The deformation remained elastic under all conditions examined. Cyclic, interfacial stresses, and slips were analyzed in detail. The amplification of remotely applied cyclic stress in the contact region is shown to provide a rationale for the effect of contact pressure and stress amplitude on life. Comparisons with previous experiments indicate that the local stress range computed from finite element analysis may be sufficient for predicting fretting fatigue life. Further, the results suggest that the slip amplitude and shear traction may be neglected for this purpose.

Hysteresis Strain Energy Behavior of Al6061-T6 With Multi-Fatigue Load Levels as Applied to an Energy-Based Fatigue Life Prediction Method

2013 ◽  
Author(s):  
Todd Letcher ◽  
Sepehr Nesaei ◽  
Cody Auen ◽  
Matt Nielsen ◽  
Fereidoon Delfanian
Keyword(s):  
Fatigue Life ◽  
Strain Energy ◽  
Life Prediction ◽  
Prediction Method ◽  
Fatigue Life Prediction ◽  
Representative Specimen ◽  
Energy Behavior ◽  
Stress Levels ◽  
Single Stress ◽  
Life Predictions

Fatigue testing is a time and resource-consuming task. Historically, SN testing was conducted at many stress levels on simple representative specimen in order to determine an SN curve, which could then be used to design a component from the same type of material. Recently, an energy-based fatigue life prediction method has been in development. The goal of this method is to quickly determine a material’s fatigue characteristics using simple test procedures. The main theory behind the energy-based fatigue life prediction method is that the strain energy in a monotonic tensile test is equal to the cumulative hysteresis energy of a cyclic test. This theory has always been tested using a single stress level on each specimen. The hysteresis loop information was then used to make fatigue life predictions at other stress levels. Further testing has been done to learn more about the hysteresis energy behavior throughout the lifetime of a specimen, but only for a single stress value. In this study, several stress levels were tested on a single specimen. This new information will help make fatigue life predictions by completely removing the difficult and inconsistent process of determining experimental curve fit coefficients traditionally used in the energy-based fatigue life prediction method.

A New Approach to Fatigue Damage Modeling of Composite Laminates

2011 ◽  
Vol 338 ◽  
pp. 315-318 ◽  
Author(s):  
Peng Gang Mu ◽  
Xiao Peng Wan ◽  
Mei Ying Zhao
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Composite Laminates ◽  
Fatigue Behavior ◽  
Failure Criteria ◽  
Damage State ◽  
Damage Indices ◽  
Model Combining ◽  
Proposed Model ◽  
Fatigue Damage Accumulation

Fatigue damage of composites can be described by the residual stiffness and residual strength, and the same damage state can be described by the two mechanical parameters equivalently. Based on this assumption, a new pair of fatigue damage accumulation models are established to simulate fatigue behavior and predict the fatigue life of composites. Each of two equations contains three parameters and has the similar form, and the power function relationships between the two damage indices are constructed. The proposed model, combining with constant life diagrams and failure criteria are used to estimate the fatigue life of composites, and good agreement is observed between the present model and experimental results.

scholarly journals Fatigue Life Prediction of Umbilicals Considering Non-Linear Stress

2017 ◽  
Vol 24 (s2) ◽  
pp. 154-163 ◽  
Author(s):  
Lu Qingzhen ◽  
Yin Yuanchao ◽  
Yang Zhixun ◽  
Chen Jinlong ◽  
Yan Jun ◽  
...  
Keyword(s):  
Fatigue Life ◽  
South China Sea ◽  
Life Prediction ◽  
Accurate Result ◽  
Prediction Method ◽  
Local Stress ◽  
Fatigue Life Prediction ◽  
Wave Loads ◽  
Non Linear

Abstract The fatigue problem induced by wave loads and floater movements of dynamic umbilicals in deepwater is studied. The prediction method of the fatigue life is investigated by considering no-linear local stress due to contact and friction between components of the umbilical. A case study of a dynamic umbilical for 1500 meters depth in South China Sea was presented. The results showed that the more accurate result of the fatigue life was calculated by considering non-linear local stress. The fatigue life by considering local stress with the no-slip assumption was conservative. An obviously longer fatigue life was obtained by considering local stress with the full-slip assumption.

Fatigue life prediction method for contact wire using maximum local stress

2015 ◽  
Vol 29 (1) ◽  
pp. 67-70 ◽  
Author(s):  
Yongseok Kim ◽  
Kiwon Lee ◽  
Haochuang Li ◽  
Chang-Sung Seok ◽  
Jae-Mean Koo ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Life Prediction ◽  
Prediction Method ◽  
Local Stress ◽  
Fatigue Life Prediction ◽  
Contact Wire

scholarly journals LABORATORY FATIGUE MODELS FOR RECYCLED MIXES WITH POZZOLANIC CEMENT AND BITUMEN EMULSION / PUCOLANINIO CEMENTO IR BITUMINIŲ EMULSIJŲ MIŠINIŲ PERDIRBIMO LABORATORINIAI NUOVARGIO MODELIAI

2011 ◽  
Vol 17 (1) ◽  
pp. 98-107 ◽  
Author(s):  
Amir Kavussi ◽  
Fereidoon Moghadas Nejad ◽  
Amir Modarres
Keyword(s):  
Fatigue Life ◽  
Portland Cement ◽  
Ordinary Portland Cement ◽  
Resilient Modulus ◽  
Fatigue Behavior ◽  
Fatigue Cracking ◽  
Strain Level ◽  
Initial Stiffness ◽  
Bitumen Emulsion ◽  
Pozzolanic Cement

In recent years, due to technical and economical advantages, the production of pozzolanic cements have considerably extended. In the case of asphalt recycling, using Pozzolonic cements has several advantages. Lower initial stiffness and less shrinkage microcracks than Ordinary Portland Cement (OPC) are some benefits of pozzolanic cements which may reduce the probability of occuring premature cracking in recycled layer. In this reserach in order to investigate the effects of I (PM) pozzolanic cement on the fatigue cracking of recycled mixes with bitumen emulsion and develope fatigue models for these mixes, extensive indirect tensile fatigue and resilient modulus tests were performed at different temperatures and curing times. Test results showed that at high strain levels I (PM) cement specimens have superior fatigue behavior than OPC specimens. Furthermore, the effects of I (PM) cement on fatigue life of recycled mixes related to the initial strain level. Therefore a boundary strain level was determined. Above the boundary strain level, adding cement caused a reduction in fatigue life, whereas below that level the reverse was true. Finally based on laboratory testing results distinct models were established for different boundary strain levels. Santrauka Pastaraisiais metais dėl techninių ir ekonominių veiksnių pucolaninio cemento gamyba gerokai padidėjo. Pucolaninio cemento naudojimas perdirbant asfaltą turi keletą pranašumų. Mažesnis pradinis standumas ir mažiau mikroįtrūkių nei įprastame portlandcementyje (Ordinary Portland Cement, OPC) – tai keletas pucolaninio cemento pranašumų, galinčių sumažinti priešlaikinio plyšių atsiradimo tikimybę perdirbamame sluoksnyje. Šiuo moksliniu tyrimu siekiama ištirti I (PM) pucolaninio cemento poveikį nuovargio plyšių atsiradimui perdirbamuose bituminių emulsijų mišiniuose ir sukurti šių mišinių nuovargio modelius. Buvo atlikti išplėstiniai netiesioginio tempimo nuovargio ir elastingumo modulių bandymai, esant skirtingoms temperatūroms ir džiūvimo laikui. Bandymų rezultatai parodė, kad esant aukštam įtempimo lygiui I(PM) cemento bandiniai yra atsparesni nuovargiui nei portlandcemenčio (Ordinary Portland Cement, OPC) bandiniai. Be to, perdirbtų mišinių iš I (PM) cemento tvarumas yra artimas pirminiam įtempimo lygiui. Todėl buvo nustatytas ribinis įtempimo lygis. Viršijus ribinį įtempimo lygį ir įmaišius cemento tvarumas sumažėja, o esant žemesniam įtempimo lygiui buvo gautas priešingas rezultatas. Galiausiai remiantis tyrimais buvo nustatyti atskiri modeliai skirtingiems ribiniams įtempimo lygiams.

The fatigue behavior of polymeric sulfur-modified asphalt mixtures subjected to freeze-thaw conditioning

2019 ◽  
pp. 089270571988998 ◽  
Author(s):  
Amir Kavussi ◽  
Mehdi Azarnia ◽  
Pooyan Ayar ◽  
Makan Pedram
Keyword(s):  
Fatigue Life ◽  
Fatigue Behavior ◽  
Fatigue Cracking ◽  
Crumb Rubber ◽  
Asphalt Mixtures ◽  
Experimental Results ◽  
Moisture Sensitivity ◽  
Modified Asphalt ◽  
Freeze Thaw ◽  
Brittle Behavior

Abundance, affordability, and also the usability of sulfur as a part of the binder are the main reasons for using this additive in asphalt mixtures. However, lack of proper adhesion and brittle behavior of sulfur-modified asphalt mixtures could make them susceptible to moisture damage and fatigue cracking. In this regard, anti-stripping agents and some polymers like crumb rubber may be used to overcome these types of distresses. This research aimed at investigating the effects of polymeric sulfur and crumb rubber on the moisture sensitivity and fatigue behavior of asphalt mixtures. To this end, asphalt mixtures were subjected to 1 and 3 freeze-thaw cycles. Then, an indirect tensile fatigue test was carried out. Moreover, the response surface method (RSM) was used to assess the interaction between various parameters in samples containing polymeric sulfur and crumb rubber. Results showed that with an increase in polymeric sulfur content, the fatigue life was reduced and the moisture sensitivity was increased. Additionally, the RSM was found to be effective in ranking parameters influencing the performance of asphalt mixtures. According to the experimental results, a crumb rubber-modified binder could improve the fatigue life of the polymeric sulfur-modified mixture up to 70%. Furthermore, experimental results and RSM analysis indicated that crumb rubber would be more effective in higher numbers of freeze-thaw cycles and raised temperatures, in which polymeric sulfur-modified asphalt mixtures are probably prone to moisture damages (i.e. the lack of adequate cohesion and adhesion).

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