Dynamics and Speed Control of Instrumented Pipeline Inspection Gauge in Gas Pipelines

Instrumented pipeline inspection gauges (IPIGs) are used to carry out in-line inspection of the pipelines transporting petroleum cargo. The inspection of the pipelines carrying high-speed gas needs the speed of the tool to be maintained within a specified band to produce an optimum result. It can only be achieved by introducing an effective bypass vane with a motor controller in the tool commonly known as the speed control mechanism. The mechanism controls the tool speed at a desired set value without affecting the throughput. The reported information on the effect of flow transients on the motion of the tool inside the pipelines and its control is limited in the open domain. The challenge lies in the effective design of the speed control mechanism for an IPIG tool to address the transients envisaged during the motion of the tool inside the pipeline. A computational fluid dynamics (CFD) code, based on the method of characteristics, and a control algorithm have been developed to numerically simulate the IPIG motion with a set of actual gas pipeline data. Transients incorporated in the analysis include a sudden increase in inlet flow rate and abrupt closing/opening of the bypass vane. Tool dynamics have also been studied at different openings of the vane angles in order to observe the steady-state behavior following an initial disturbance. The theoretical analysis of this initial transient is of considerable interest. The peak-to-peak speed fluctuation experienced by the IPIG is found to be inversely proportional to the local average speed of gas and directly proportional to the dynamic friction per unit area. The suitably scaled peak-to-peak speed fluctuation has been analytically correlated with the vane angle opening. The simulation results conform to the actual field data and achieve the desired speed control of the tool.