Numerical Study and Optimization of Speed Control Unit for Submarine Natural Gas Pipeline Pig

The speed control of a pipeline inspection gauge (PIG) directly affects the quality of the comprehensive inspection of submarine pipelines. However, the mechanism of the gas flow behavior in a pipeline under the influence of a pig speed control valve is not well understood. In this study, the driving differential pressure of a pig was modeled based on the building block method and numerical simulations. For the first time, the influence of the pressure and flow rate of the gas in a pipeline on the torque of the speed control valve opening process was studied. The results show that when the opening angle of the speed control valve increased from 4.5° to 22°, the gas differential pressure reduced from 1325 to 73 kPa, realizing a 94.5% pressure reduction. In addition, the torque of the bypass valve increased from 7.7 to 2470 Nm during the closing process. The pressure and flow rate increases were directly correlated with increased torque. The established experimental system for torque measurement confirmed the numerical analysis results. By clarifying the law of torque variation, this study provides theoretical guidance for the structural design and control scheme of a pig speed control unit.