Numerical Studies on Re-rounding Behaviour of API 5L X46 Grade Steel Pipes Subjected to Internal Pressure

Pipelines are the backbone of oil and gas industry. They carry oil and gas which imparts internal pressure on the pipeline. These pipelines are also subjected to mechanical impacts during commissioning and in-service. Due to these impacts, pipes are dented. The dents re-round when the impacting object is removed. This re-rounding occurs due to elastic response of the material and the internal pressure from the operating condition. API 5L X46 grade steel is one of the most commonly used grades of steel in oil and gas industry. Numerical studies were carried out on API 5L X46 grade steel pipes to understand the effect of re-rounding by using a general purpose finite element software ABAQUS. Dents of spherical shape were imparted. Two different dent sizes were considered in proportion to the outer diameter of the pipe. Diameter of indenters were 0.25 times and 0.4 times the outer diameter of the pipe. Indentation forces of 90 kN and 105 kN were used for the dent formation. Dent depths proportional to the outer diameter of the pipe (10% and 12.5% of the outer diameter) were considered for re-rounding studies. Under commissioning condition, dents were imparted without internal pressure. Under in-service condition, internal pressure was applied and dents were imparted. Non-linear static analysis was carried out for the piping components containing dent. From the numerical studies, for the combination of above parameters, various responses were obtained. Re-rounding deformation at the center of the dent was obtained. The numerically obtained dent depth at predetermined loads were compared with the experimental values for validation. Strain values were captured around the dents. The results of this study gave confidence in planning further experimental studies.