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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under pressure and there is a temperature in the tubular structure. The maximum principal stress is the nominal strength value, which is 580 MPa. The damage assessment criterion is the maximum tensile strength (the maximum steel crack opening is 1 mm), the research on the impact of structural damage is limited to the different situation (bend angle and bend radius), Three-dimensional hex-dominated quadratic elements were used to mesh the pipe elbow. The ovalization and concentration of the forces that cause injury in these zones necessitate mesh refinement. This enables for a more accurate recording of maximal stresses and fracture initiation, the pipe elbow symmetry (one-semi) can be employed, Fig. 2,3,4 depicts the specimen's mesh and mesh refinement at the fracture tip area.

Fig2. Mesh details of region in elbows . Fig3. Mesh of elbow with internal defect Fig4.The typical FE mesh with Metallic patch.

2. RESULTS AND DISCUSSION Different methods of pipe elbow repair are used, such as replacing a pipe elbow with a different bend angle and bend radius to repair the cracked elbow at 0°, 10°, and 45°, and the other method is represented by laying down two types of patch on the pipe elbow damaged and it comes by repair by composite bonding and metallic patch. This analysis focuses on calculating the critical moment carried by the damaged pipe elbow using the finite element approach in order to forecast the behavior of the pipe elbow and the influence of this method on the enhancement of the critical moment carried by the pipe elbow. 2.1. Change the elbow with different angle The bend response at bending moment is initially linear and identical for all cases, and takes different values until the damage, presented in the Fig.5. (a, b, c). This difference is much more caused by the angle of the elbow. In the first position of default (position of 0°), increasing in the elbow angle on the [120° to 135°], increase the critical bend moment by [20% to 45% ]. The maximum values of the bend moment were localized in the straight pipe (90°+ 90°) and the difference was 38%. In another way, move to the elbow angle of (145° to 150°), the position of default decrease the critical moments from 11% to 25%, regarding the 90° elbow as reference. For the second position of default at 10°, the significant critical moment was for the angle of (90°+30°), with the gain of 55% of energy. For the another’s position, there were less than the original elbow in the marge of [9 -13%].By the way, and for the third position of default at 45°, the critical elbow moment for the angles 30°, 45°, 55°, 60° were 11% ,25% and 12%lessthan the reference elbow at 90°. The straight pipe gives a possibility on the increasing in the breaking energy by 48%. The critical moment is associated with local buckling at wall-thinned areas subjected to compressive stresses when the defect is located at the second position (angle 45°) of the original 90° elbow. The level of damage is not the same when the defect is located at 0° in the case of 30°elbowwhen compare with original 90° elbow for example, this is refer to the concentration of efforts on this area. It is found in Figure the same responses up to the critical moment with different levels for the five bends of 30°, 45°, 55°, 60°and 90°. The straight pipe and the 30°elbow allows a large deformation capacity; the same behavior can be seen for the different location of defect as defect at 10° and 45° except when the defect locate at 45° in 90° elbow.