PSI - Issue 22

Abdelkader Guillal et al. / Procedia Structural Integrity 22 (2019) 201–210 Author name / Struc ural Integrity Procedia 00 (2019) 000 – 0 0

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Fig 8. Evolution of sensitivity to mean value of random variables for LSF 2

Although, it can be concluded from the above analysis of crack shape influence that initial crack dimension ( a, c ) have a significant influence on predicted fatigue lifetime. The sensitivity analysis shows that the nature of dominant random variables depend on the considered failure mode, the efforts conducted to reduce the uncertainties of input parameters should take in consideration the scenario of failure with high probability of occurrence. Conclusion A probabilistic model based on Linear Elastic Fracture Mechanic has been used to evaluate the variation of reliability index of pipeline with semi elliptical crack on the surface under fatigue loading. A sensitivity analysis in term of mechanical model, failure mode and random input parameters based the probabilistic model has been addressed. Based on the above results, several conclusions can found as follow: 1. Constant shape ratio assumption can lead to an underestimation of fatigue life of component. 2. The variation of shape ratio depends on the initial shape and the assumed crack growth rate in deep and surface point. 3. The effect of variation of shape factor modeled using Newman assumption is clear in finale stage of propagation but has a low effect on failure probability of pipeline with semi elliptical surface crack. 4. Despite the disagreement about the physical base of Paris law parameters correlation, reliability calculation is influenced by the assumed correlation state. A high negative correlation has been showed great influence on the reliability analysis results. The assumed correlation should reflect fairly the reality. 5. The failure mode has a great effect on the reliability analysis; the importance of each random variable is influenced by the assumed failure mode. ANDERSON, T. L. 2017. Fracture mechanics: fundamentals and applications , CRC press. BEN SEGHIER, M. E. A., BETTAYEB, M., CORREIA, J., DE JESUS, A. & CALÇADA, R. 2018. Structural reliability of corroded pipeline using the so - called Separable Monte Carlo method. The Journal of Strain Analysis for Engineering Design, 53(8) , 730 - 737. BENSEGHIER, M. E. A., KESHTEGAR, B., CORREIA, J. A., LESIUK, G. & DE JESUS, A. M. 2019. Reliability analysis based on hybrid algorithm of M5 model tree and Monte Carlo simulation for corroded pipelines: Case of study X60 Steel grade pipes. Engineering Failure Analysis, 97 , 793 - 803. BENSEGHIER, M. E. A., KESHTEGAR, B. & ELAHMOUNE, B. 2018. Reliability analysis of low, mid and high - grade strength corroded pipes based on plastic flow theory using adaptive nonlinear conjugate map. Engineering Failure Analysis, 90 , 245 - 261. BS7910, B. S. 2000. Guidance on methods for assessing the acceptability of flaws in metallic structures. British Standards Institution . CARPINTERI, A. & PAGGI, M. 2007. Are the Paris’ law parameters dependent on each other? Fracture and Sturtural Integrity, 1 , 10 - 16. CHAHARDEHI, A., BRENNAN, F. P. & HAN, S. 2010. Surface crack shape evolution modelling using an RMS SIF approach. International Journal of Fatigue, 32 , 297 - 301. CORTIE, M. B. & GARRETT, G. G. 1988. On the correlation between the C and m in the paris equation for fatigue crack propagation. Engineering Fracture Mechanics, 30 , 49 - 58. EL AMINE, M., SEGHIER, B., BETTAYEB, M., BOUALI, E. & GACEB, M. 2017. Probabilistic approach evaluates reliability of pipelines with corrosion defects. Oil and Gas Journal, 115 , 64 - 68. References