Computational Investigation of Composite Repair Materials Preventive Effects on Wrinkle Bends Fatigue Failure

Wrinkle bending was a vintage technique in pipeline construction for aligning pipe sections. However, this process causes severe geometry changes over the pipeline structure and thus stress concentrations are developed. These stress concentrations have the potential to cause catastrophic pipeline failure due to internal pressure cycles, seismic effects and temperature changes. Different techniques have been studied and examined to mitigate the destructive effects that wrinkle bends pose to pipeline integrity. Composite repair methods and materials have been proven as one of the most reliable and efficient technologies to repair different pipeline defects. Designing an economical composite repair for a wrinkled pipe with proper performance requires precise design considerations. Finding an economical balance can be achieved multiple ways, such as performing experimental tests or applying analytical formulas and procedures. Each of these two methods has its own drawbacks: cost, errors and time can prevent accurate experimental tests and poor accuracy. Applicability of suggested analytical design equations can render certain analyses useless. To technically and economically improve the design and application processes of composite repair systems for wrinkle bends, elastic finite element analysis (FEA) was performed. The FEA analysis was conducted to study the effects of applying composite repairs on the elastic stress concentration factor of the wrinkle section of a Grade X52 carbon steel pipe. Moreover, a nonlinear kinematic hardening material model was developed and calibrated for this same steel. An elastic-plastic FEA was implemented to evaluate the stress-strain response of a wrinkled pipe subjected to a cyclic bending loading and constant internal pressure. Different strain based fatigue life estimation approaches were used to estimate the fatigue life enhancement achieved by utilizing a proprietary composite repair installation method.