Prediction of Failure Pressure in Pipelines with Localized Defects Repaired by Composite Patches

In recent years, fibrous composite materials have been used to repair pipelines in combination with commonly employed standards such as ASTM B31G and ASTM PCC2. Reinforcement and repair of pipelines without interruption are the advantages of these new methods. Pipe repair by composite patches with considering various types of surface damages and crack has been investigated in many previous works. In the present paper, a comprehensive model has been developed to predict the critical pressure for several defect types in static pressure loading condition using the ABAQUS finite element software. The effect of various defect patterns in API X65 Grade steel pipes is investigated by a ductile damage criterion. The obtained results are assessed using available experimental data. The first ply failure theory is employed to predict failure in composite patches. The effects of boundary conditions are considered using a semi-infinite element. The results generated from finite element simulations are compared with those from ASTM PCC2 standard. Moreover, the required minimum patch thickness for different live internal pressures is proposed. The extended finite element method is also applied to study the effect of patch layer thickness on crack propagation. The effect of initial crack angle on the critical internal pressure with and without patch is investigated too. The results indicate that the z symmetric boundary conditions are appropriate for pipelines. The estimation of the burst pressure using a ductile damage criterion is shown to be in good agreement with experimental data and ASME B31G. Furthermore, the estimated values for patch layer thickness obtained by the present approach agree well with ASME PCC2 standard. The obtained results also clearly indicate that using composite patches has no considerable influence on prevention of crack propagation.