International audienceThe aim of this paper is to propose a lifetime prediction method for threaded connections. The example discussed here is a drillstring connection used in the oil and gas industry. The method is based on a mechanical analysis performed either with finite elements or a closed-form solution described in a companion paper, and a fatigue analysis using the Dang Van criterion which has been extended to finite life domain. The mechanical analysis provides the stabilized stress path and the fatigue analysis provides the fatigue life. Fatigue tests have been performed on small scale threaded connections in order to validate the methodology. The comparisons with the predictions show the difficulties to estimate the fatigue life on structures presenting high stress gradient due to scale effects

In the design of flexible pipelines for offshore field developments, the determination of the pipe resistance while subjected to external pressure and bending is very important in deepwater and is now required by the ISO and API standards. One of the critical failure modes being associated with this type of loads is the hydrostatic collapse. The collapse value of flexible pipe is calculated with a model validated with over 200 tests performed on all possible pipe constructions. This model has an analytical basis, and has been established in the past, leading to a fast and straightforward use. In order to address the bent collapse failure mode, Technip and IFP have therefore developed and improved over the past few years an analytical calculation model, based on the collapse model for straight pipes. The purpose of this paper is to present this design methodology and its validation. The modelling principles of the collapse calculation of straight flexible pipes are firstly presented, along with the main hypotheses. The adaptation to the case of curved pipes is detailed in the sequel of the paper. Many types of flexible pipe samples have been tested up to collapse both in straight and curved configurations. The results of these tests have been used to validate this model. In the paper, several tests results will be presented and compared with the calculations. This model is effective, of straightforward use, and has been certified by a third party. It allows Technip to optimize the flexible pipe design in particular for ultra-deep water applications, where external pressure resistance is very important.

International audienceThe aim of this paper is to present an alternative solution to the finite element method for the determination of the elastic stress field for an axi-symmetric notched tube under tension and bending loadings. The proposed solution is an extension of the work of Filippi and Lazzarin (2004) [8] to tubular specimens. It provides the stress field distribution along the notch bisector. A good agreement was found between the solution proposed in the present paper and the results from a finite element analysis. A sensitivity analysis is performed to establish the domain of validity of the solution with respect to the dimensions of the notched tube

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