### Abstract

The development of surface breaking flaws on the external surface of tubular components is a complex function of material properties, environment, and, applied/residual stresses. Variation in these factors results in uncertainty in the shape of flaw that can develop, particularly when the material in question has a complex heterogeneous microstructure. Flaw geometry has a direct effect on the stress/strain fields around the crack-tip and hence on the critical value of internal pressure required to cause failure.

Down-hole tubular components in oil and gas wells have developed surface breaking flaws which have led to their catastrophic failure. A time-variant reliability analysis has been carried out to examine the effect of crack geometry and internal pressure on the probability of production tubular failure. A limit state function was developed using a Finite Element model to convert internal pressure into an estimate of the time-varying integral at the crack-tip of idealised semi-elliptical flaws. A range of crack lengths and depths were examined and the up-crossing rate used in conjunction with the Poisson assumption to estimate the probability of failure for each configuration. The results demonstrate the important effect of crack geometry uncertainty on the probability of failure and the need to develop better understanding of the mechanisms that generate such flaws in the complex alloys used in down-hole components.

Down-hole tubular components in oil and gas wells have developed surface breaking flaws which have led to their catastrophic failure. A time-variant reliability analysis has been carried out to examine the effect of crack geometry and internal pressure on the probability of production tubular failure. A limit state function was developed using a Finite Element model to convert internal pressure into an estimate of the time-varying integral at the crack-tip of idealised semi-elliptical flaws. A range of crack lengths and depths were examined and the up-crossing rate used in conjunction with the Poisson assumption to estimate the probability of failure for each configuration. The results demonstrate the important effect of crack geometry uncertainty on the probability of failure and the need to develop better understanding of the mechanisms that generate such flaws in the complex alloys used in down-hole components.

Original language | English |
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Title of host publication | Proceedings of 4rth Asranet Colloquium |

Subtitle of host publication | 25-27th June, Athens, Greece |

Editors | P. Das |

Publication status | Published - 25 Jun 2009 |

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## Cite this

Renton, N. C., Deans, W. F., & Baker, M. J. (2009). The Effect of Crack Geometry on Time-Variant Reliability of Tubular Components. In P. Das (Ed.),

*Proceedings of 4rth Asranet Colloquium: 25-27th June, Athens, Greece*