PSI - Issue 41

Chaaben Arroussi et al. / Procedia Structural Integrity 41 (2022) 752–758 Author name / StructuralIntegrity Procedia 00 (2019) 000–000

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The crack orientation varies from one test to another based on the bending direction and the pipe bend angle. Other investigations such as that presented by Togler describe the failure of pipe bends and the crack orientation size and initiation point, Togler et al, [5].Straight and intact bends under internal pressure cases were studies for verification the failure of cracked bends by developing a finite element code for fracture modeling by degenerating shell elements[6].The variation of hoop stress around the circumference of the bend case at 45° location calculated using analytical calculations matched the numerically calculated values. The maximum stress range is located at the 12 o’clock location of the bend. The stress concentration factor (SCF) has been calculated for the fatigue damage life of pipe bends under internal pressure and minor bending by a proposed polynomial equation with calibrated constants using FEA, Weib et al[7]. The conclusion remarks note the increase in wall thickness will increase the axial force and the shell elements are not recommended for high pressure bends. The works of Shalaby and al [8]were focuses on the plastic deformation of the bend and the development of plasticity with the increase in bending moment and compared between the opening and closing cases. The relationship between the bending moment capacity and the internal pressure applied significantly distant the instability bending moment capacity far from the point where it reaches the maximum values. Mourad et al[9]did not address the issue of initial ovality and the models used could not account for it. The difference between bend opening and bend closing is discussed in [10]only in the on-plane bending in terms of yield strength, diameter and wall thickness. The bending moment of bends is derived from the bending moment of straight pipe with calibrated factors due to the stiffness of the bends. The objective of this study is to numerically evaluate the effect of bending load on the failure moment of different locally wall thinned elbows under a load-controlled in-plane bending load combined with internal pressure. The wall thinned is simulate as a semi-elliptical crack with a depth (a/t) = 0.2 and a length a/c = 0.4 or a different position in the intrados and extrados of elbow pipe. To achieve this, several numerical tests were conducted on elbow pipe, each with a different local wall-thinning defect, under combined internal pressure and a constant in-plane bending load in opening and closing mode, as well as under simple internal pressure. Only the closing mode is taking in account in this part of study. Proposal engineering solutions are making to evaluate the effect of load-controlled bending load on failure moment as well the replace of elbow pipe radius for different (R/D) , the angle rotation of elbow (α) and to repair the elbow by a rolling composite or local metallic patch. Finally, the impact of load-controlled in-plane bending on the safety margin against the bursting of wall-thinned elbows was investigated by comparing the numerical failure moments with the original proposal design. In this study, the reparation by two mode of repaired pipeline were used, firstly by change the damaged elbow by elbow of the same diameter with different angles or revisit always the same elbows with different radius of curvatures , secondly by composite or metallic patch . Fig 1,2,3,4 illustrates the geometrical characteristics. The elastoplastic behavior and strength characteristics and chemical component of material are recorded in Figure (5) and Table (1), (2). The bent element is connected to two straight pipes with a length of 960 mm. This length is sufficient to ensure that the bend area does not cause stress interference due to the load applied to the end of the linear member. It is assumed that there is no malfunction at the bend. The straight tube is used only to uniformly transmit the bending moment to the bend. Numerically, the bending moment load on the bend is obtained by rotating around the axis of the bend. A tubular structure with the following dimensions: diameter equal to 274 mm and thickness equal to 9.27 mm. For the five bending angles (30 °,45°, 55°,60 ° and straight pipe)and four bend radius (R=1D ,1.5D,3D,5D) contain a defect in three critical position are analyzed, To compare them with the 90° elbow , these bends are regularly subjected to a rotational displacement of 42 °. In order to cause only damage 1. X-FEM NUMERICAL SIMULATION 1.1. Geometrical and materials models