Piping system elbow study is the most important part in all fields of hydrocarbons transportation which presents the behaviour of circumferential crack at elbow extrados. The effect of geometry of adhesive and patch in the crack elbow is important in pipeline safety. This study shows the details for along the direction of the circumferential elbow crack by three dimensional (FEM) which is used to determine the stress intensity factor at 90° elbow for two cases: firstly, without patch and

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... y, repaired with composite patch. This method allows to predict the behaviour of cracked elbow through the analysis of crack propagation under the internal different pressures taking into consideration the operating conditions. The geometry and nature of composite patch proved that the increase of patch thickness leads to decrease the SIF from 7 MPa.m1/2 to 6.15 MPa.m1/2. It can be concluded that the repairing by composite materials leads to reduce the stress intensity factor with patch which not only can augment the lifetime of pipeline but also decreasing the costs and the pollution.