Numerical-experimental analysis of the process of delivering a repair system by a bypass pig to a hard-to-reach place of the pipeline

<ns3:p>Analysis of gas-dynamic processes occurring during the delivery of a repair system through a pipeline by a bypass pig to a local defect located in a hard-to-reach place behind an elbow. Determination of the patterns of influence of the axial hole diameter in the bypass pig on the pressure drop and the driving force acting on it. Investigation of the conditions under which bypass pigs become stuck in the elbows of the pipeline and assessment of the risk of overloading the repair system components during their delivery.The methodological basis of the study is grounded on the combination of CFD modelling of gas-dynamic processes and laboratory experimental tests of the interaction between the bypass pig and the airflow during the delivery of a repair system through a pipeline containing an elbow to a local wall defect. Numerical and experimental results were compared for model verification.As the bypass pig’s axial hole diameter decreases, the pressure drop and the driving force acting on it increase significantly. For a hole diameter of 6 mm, the driving force reaches 170.8 N, which provides a large pulling force for moving the repair system, but creates a risk of flexible tube damage when the pig stops directly behind the local wall defect until the air supply from the compressor is shut off. For an axial hole diameter of 14 mm, the driving force decreases to 6.6 N, making it impossible to pass through pipeline elbows. The optimal solution is to select the maximum possible hole diameter that still ensures sufficient driving force for pig motion while meeting the strength limitations of the repair system components.Although it has been established that when the diameter of the axial hole in the bypass pig exceeds 10.5 mm, the driving force becomes insufficient to overcome pipeline elbows (for example, at 14 mm the pig gets stuck), the quantitative criteria of the minimum required pressure drop remain undefined. To determine them, further studies of the contact interaction between the bypass pig made of elastic material and the pipe wall in curved sections are necessary. At small axial hole diameters (for example, 6 mm), the tensile force in the flexible tube of the repair system can reach 170 N, creating a risk of its damage or failure. To assess the operability of the flexible tube under such loads, it is advisable to perform strength calculations based on the mechanics of deformable solids.The results obtained in this study have practical significance for the development of in-line repair technologies of pipeline networks in hard-to-reach places, particularly behind fittings such as elbows. The work provides a foundation for the development and implementation of practical methodologies for selecting the design parameters of bypass pigs and the operating modes of the pipeline during the delivery of repair systems to hard-to-reach places.The results of CFD modelling and laboratory experiments were combined to establish the features of the process in which a bypass pig pulls a repair system through a pipeline with an elbow. The influence of the bypass pig’s axial hole diameter on the pressure drop and the driving force acting on it was determined, and the risks of pigs with large axial hole diameters getting stuck in elbows were demonstrated.</ns3:p>