Finite Element Analysis and Full Scale Testing of Composite Repairs on Wrinkle Bends in Pipelines
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In the United States wrinkle bending was a common construction technique used in constructing gas transmission pipelines until the mid-1950s. However, this construction process causes severe geometry changes in the pipeline that generates areas of stress concentration. In a high strain and low pressure cycle environment, these stress concentrations have resulted in failures, typically due to bending and axial forces associated with shifting terrain and lack of sufficient pipe support. Different techniques have been studied and examined to mitigate wrinkle bend’s destructive effects on pipeline integrity. Applying composite repair materials has been proven as one of the most reliable and efficient technologies to repair different pipeline defects, including wrinkle bends. This paper examines a composite repair installation technique for wrinkle bends through the use of finite element analysis (FEA) and full-scale spool testing. A 26-inch (650mm) diameter, 0.281-inch (7.14mm) original wall thickness, Grade X52 steel pipe with wrinkle bends was removed from service. A non-linear kinematic hardening material model was developed and calibrated for X52 steel and elastic-plastic FEA was implemented to evaluate the stress-strain response of a wrinkled pipe subjected to cyclic bending loading and constant internal pressure. Full-scale tests were performed on the pipe removed from service to validate the effects of composite repair materials in enhancing the fatigue life of wrinkled pipes. Fatigue experiments demonstrated a significant enhancement in fatigue life by a factor of safety of 12.5 by applying the composite repair method. At the present time, there are numerous wrinkle bends that remain in the existing U.S. gas transmission pipeline system. Although there have not been an extensive number of failures associated with wrinkle bends in comparison to other pipeline anomalies such as corrosion and mechanical damage, concerns do exist that served as the basis for this study.
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