The role of spin-orbit effects in the mobility of N+ ions moving in a helium gas at low temperature

The mobility of N+ ions in ground-state helium gas at very low temperature is examined with explicit inclusion of spin–orbit coupling effects. The ionic kinetics is treated theoretically with the three-temperature model. The N+–He interaction potentials, including spin–orbit coupling, are determined using high-level ab initio calculations. Then, the classical and quantal transport cross sections, both needed in the computation of the mobility coefficients, are calculated in terms of the collisional energy of the N+–He system. The numerical results, at temperature 4.3 K, show the spin–orbit interactions have negligible effect on the mobility coefficients

Failure analysis of biocomposite sandwich pipe under internal pressure – Application for high pressure gas transportation pipelines MEDGAZ

In this paper, analytical and 3D numerical models are developed to investigate the mechanical behavior of sandwich pipe under internal pressure loading. The suggested models provide an exact solution for stresses, strains and displacement on the sandwich pipe, which is made of epoxy material for the core layer and reinforced materials with an alternate-ply for the skin layers. The aim of this analysis is to evaluate the potential applications of jute and pineapple leaf fiber (PALF) bio-fibers in order to replace glass synthetic fibers generally employed in sandwich pipes. In this subject, a failure analytical analysis was developed using TSAI-WU criterion. The results of stress, strain and displacement distribution through the thickness are presented for the analytical and numerical models. The comparison between the both models results show a very good agreement. In order to increase the rigidity of a biocomposite sandwich and reduce the gap compared with a synthetic sandwich, a gradual reinforcing of layer numbers was chosen, which permitted the best behavior. The ultimate pressure and safety factors obtained by increasing biocomposite layers are significant for composite transportation pressure pipelines, especially for sandwich pipe based on PALF/epoxy.This work has been funded partially by the DGRSDT, Algeria and Portuguese national funds of FCT/MCTES (PIDDAC) through the base funding from the UIDB/00690/2020 (CIMO) research unit.info:eu-repo/semantics/publishedVersio

Assessment of corroded API 5L X52 pipe elbow using a modified failure assessment diagram

Pipe elbows (bends) are considered critical pressurized components in the piping systems and pipelines due to their stress intensification and the effect of bend curvature. They are prone and hence more exposed to different corrosion failure modes than straight pipes. Late detection of such elbow damages can lead to different dangerous and emergency situations which cause environmental disasters, pollution, substantial consumer losses and a serious threat to human life. A comprehensive safety and reliability assessment of pipe elbows, including usage of prediction models, can provide significant increases in the service life of pipelines. It is well known that the limit pressure is an important parameter to assess the piping integrity. In this paper, the integrity assessment of damaged pipeline elbows made of API 5L X52 steel was done within the framework of numerical modeling using the finite element method (FEM) and finite element analysis (FEA). The evaluation of numerically FEM modeled limit pressure in the corroded elbow containing a rectangular parallelepiped-shaped corrosion defect with rounded corners at the intrados section was done and compared to different codes for calculating limit pressure. Moreover, the area with the corrosion defects with different relative defect depth to wall thickness ratios was FEM modeled at the intrados section of the pipe elbow where the highest hoop stress exists. The results showed that the codes for straight pipes could not be applied for the pipe elbows due to the significantly higher error in the obtained limit pressure value compared with numerically FEM obtained results. However, the results for modified codes, adapted for the pipe elbow case using the Goodall formula for calculation of the hoop stress in pipe elbows with defects are pretty consistent with the numerical FEA results. The notch failure assessment diagram (NFAD) was also used for the straight pipe and pipe bends with different corrosion defect depth ratios, while the obtained critical defect depth ratios further highlighted the criticality of pipe elbows as an essential pipeline component

Numerical study of semi-elliptical cracks in the critical position of pipe elbow

Pipelines are considered as a major tool to transport hydrocarbons due to its important role in transporting fluids taking into account the operating conditions. Despite the importance of the elbow which considered as a critical part in the pipelines, the repeated failures and defects became a dangerous and enormously costly issue. In this numerical study, the Fluid-Structure Interaction (FSI) analysis was carried out using Ansys software. This work is divided into four main parts: the first part focused on studying and comparing the effect of bending radius of pipe elbow on the maximum of Von-Mises stress values for each radius with the yield stress of the steel of the pipe. The second part focused on the creation of a semi-elliptical crack for different locations along the elbow angles to show the critical position compared to the stress intensity factors. In the third part, the semi-elliptical crack angle orientation was studied at the critical position to estimate the critical angle. In the last part, the failure assessment diagram (FAD) was used to show the critical crack depth ratios at a critical position and a critical angle

Theoretical determination of the potassium far-wing photoabsorption spectra

This theoretical work reports full quantum-mechanical analysis of the potassium far-wing photoabsorption spectra. The accuracy of the adopted K2 potential-energy curves and transition dipole moments is established by computing the vibration-rotation levels and the radiative lifetimes of the excited molecular states and by determining the variation law with temperature of the diffusion coefficient of atomic K(4p) in a ground potassium gas. The pressure-broadening calculations revealed that the photoabsorption spectra have, in the temperature range 850-3000 K, a satellite structure characterized by the presence of three peaks around 718.7 nm in the blue wings and 1048.1 and 1100.8 nm in the red wings. This theoretical work could in particular point out the occurrence in the blue wing of a satellite originating from the bound-free B←X transitions near 731.5 nm. All these results agree quite well with the experimentally measured values

Probabilistic analysis of corroded pipeline under localized corrosion defects based on the intelligent inspection tool

A methodology is developed in this paper to estimate the time-dependent reliability of a pipeline in Algeria, which is in exploitation from 1981 and with internal and external localized corrosion defects detected in 2009. A probabilistic approach was applied to a pipeline made of API 5L X60 steel for the long-distance transportation of natural gas (55 km), which crossing several geo-graphical reliefs in different country areas. The analysis was carried out by taking into con-sideration the potential stochastic variables altering drastically the reliability of the pipeline, i.e., dimensions of the localized corrosion defects, their locations, and distribution, and the corrosion rate. The correlations between the pipeline spatial corrosion defects distribution and their di-mensions, obtained by using an intelligent inspection tool are used to analyze the actual in-service corrosion attack rate and for enhancement of the accuracy of the reliability assessment. The failure scenario was considered as the moment when the pipeline operating pressure exceeds the failure pressure defined analytically in accordance with different commonly used standards. The assessment of the reliability index of the corroded pipeline subjected to internal pressure and the failure probability was done. The detailed reliability analysis is carried out by using the second order reliability method (SORM) for the basic random variables with different prob-abilistic density within a nonlinear limit state function. The latter is based on the limit analysis of the failure pressure model for different standards and the numerical analysis using the finite element method and ANSYS software

The synergistic effects of hydrogen embrittlement and transient gas flow conditions on integrity assessment of a precracked steel pipeline

We are reporting in this study the hydrogen permeation in the lattice structure of a steel pipeline designed for natural gas transportation by investigating the influence of blending gaseous hydrogen into natural gas flow and resulted internal pressure values on the structural integrity of cracked pipes. The presence of cracks may provoke pipeline failure and hydrogen leakage. The auto-ignition of hydrogen leaks, although been small, leads to a flame difficult to be seen. The latter makes such a phenomenon extremely dangerous as explosions became very likely to happen. In this paper, a reliable method is presented that can be used to predict the acceptable defect in order to reduce risks caused by pipe failure due to hydrogen embrittlement. The presented model takes into account the synergistic effects of transient gas flow conditions in pipelines and hydrogen embrittlement of steel material due to pressurized hydrogen gas permeation. It is found that blending hydrogen gas into natural gas pipelines increases the internal load on the pipeline walls due to overpressure values that may be reached in a transient gas flow regime. Also, the interaction between transient hydrogen gas flow and embrittlement of API 5L X52 steel pipeline was investigated using Failure Assessment Diagram (FAD) and the results have shown that transient flow enhances pipeline failure due to hydrogen permeation. It was shown that hydrogen embrittlement of steel pipelines in contact with the hydrogen environment, together with the transient gas flow and significantly increased transient pressure values, also increases the probability of failure of a cracked pipeline. Such a situation threatens the integrity of high stress pipelines, especially under the real working conditions of hydrogen gas transportation

Theoretical investigation of the pressure broadening D 1 and D 2 lines of cesium atoms colliding with ground-state helium atoms

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