Abstract

International audience; The safety of gas transportation pipelines under fatigue loading remains an important issue. The purpose of the present study is to better evaluate the fatigue crack growth (FCG) behavior by carrying out analysis/predictions and experiments in full-size pipeline steels. A full characterization was made using several samples of an X42 grade pipeline steel, to characterize the monotonic and the fatigue behavior. Fatigue tests on full-scale pipeline steels under pressure loading were performed. The potential drop (PD) method applied to pressurized pipes makes it possible to monitor and quantify both crack initiation and crack propagation. These tests served as a basis for numerical comparison. Crack propagation of the full-size pipeline steel was simulated by finit element analysis (FEA) using an adaptive re-meshing approach implemented as part of the Z-set/Zebulon software. Simulation allows predicting fatigue crack growth life on pipes using results of tests on specimens as an input.

Abstract

International audience; Tramway traffic may produce vibrations propagating in soil, which implies vibration annoyance for people living or working in neighbouring buildings. Thus vibration is one of the most important consequences to be considered when planning new lines. Dynamic performance evaluation of tramway tracks is required to validate or modify the existing means that reduce vibrations. This paper presents experimental and theoretical investigations of vibrations caused by passing tramways in Nantes, France. A method is proposed to predict ground-borne vibrations, so as to estimate a trouble gauge concerning, for example, the impact of a future tramway line. This method is applied and validated in comparison with in situ measurement data obtained previously.Numerous studies have been carried out on vibrations induced by surface railways, for example, Lefeuve-Mesgouez et al. [1], Picoux [2] and Sheng et al. [3]. In the case of a tramway line, a two-dimensional model can be used to predict the behaviour of the propagation analysis of the corresponding vibrations, considering a thin layer model for the soil and using exact dynamic stiffness matrices [4,5], expressed in the frequency-wave number domain for the layered ground and the half-space [6]. Note that other models can be applied to predict vibration propagation, such as boundary element formulations [7].In this paper, soil is characterized by measurements using the spectral analysis of surface waves, often called the SASW method. Here the usual two-station approach is used [8]. The objective is to accurately define shear moduli and layer thicknesses. Then the general Barkan relation [9] is applied to obtain the dispersion curve and the damping ratios. Soil characterisation needs further improvements using a complete inversion method such as Occam's algorithm [10]. Nonetheless this first approach, often called "equivalent depth approach" already gives sufficient soil profile information to model waves propagation.Numerical methods, such as the wavenumber matrix approach, can be used for the prediction of the soil response to a hammer impact, i.e. to obtain the transfer functions. An alternative solution is proposed: the method is based on the assumption that for each frequency, the vertical measured shear wave velocity corresponds to a homogeneous half-space [9]. The vibratory response is obtained by multiplying the load spectrum by the transfer function in order to obtain the whole contribution of tramway passage for each measurement point. Results are given in the time domain and compared with in situ measurements.

Abstract

Due to external interference, pipelines used for onshore as well as offshore operations can present dent and gouge defects. As such defects can seriously impair facilities’ integrity and performance, it is necessary to evaluate the strains in the vicinity of these defects. The development of non-destructive approaches to assess defects severity remains an issue in the pipeline industry. In the present study, micro-hardness - strain relationships are established for three steel grades of pipeline materials: API X52 modern, API X52 vintage and API X63 vintage. The micro-hardness – strain correlations of the three pipe materials are analyzed in order to verify if they can be described by a master curve. For that purpose, Notched Tensile (NT) tests are performed in Longitudinal (L) and Transverse (T) directions for each grade in order to reach high strain values (up to 70%). The relationship proposed by Tabor was improved with the introduction of three new parameters that allow considering actual material behavior.