Caliper pigs are widely used for measuring pipeline internal geometry and detecting anomalies, such as dents, wrinkles and flat spots. Due to its excellent transport capacity, caliper pig is more widely used in subsea gas pipelines than smart pig, such as Magnetic Flux Leakage (MFL) pig or Ultrasonic Test (UT) pig. In this article, the bouncing process of detection arm of caliper pig across convex defect is studied. And then, the influence of the collision between the detection arm and deformation defect, as well as the defect shape on the bounce, is discussed. Based on that, a bouncing theoretical model of the detection arm is developed for analyzing the bouncing phenomenon. Furthermore,the bouncing process that the detection arm moves across the convex defect with different velocities and different initial spring forces is studied by experimental method. The bouncing model calculation value is approximately equal with the experimental value, verifying the validity of the bouncing model. The bouncing model has a great significance for caliper pig evaluating the pipeline convex defect.

Polyethylene (PE) pipes are widely used in urban gas transportation due to their good toughness and corrosion resistance. Currently, the designed service life of a PE pipeline is 50 years, and some urban gas PE pipelines are approaching their service life. However, research on the aging assessment of PE pipelines is not complete, and it is impossible to effectively predict their aging status in service. Once urban gas PE pipelines are damaged, serious accidents may be caused. PE80 and PE100 pipelines are commonly used for urban gas, and improved accelerated aging tests were conducted considering different conditions of pressure, pipe diameter, and temperature. According to the experimental results, an aging life prediction method for PE pipes was constructed based on the Arrhenius formula considering multiple effect factors.

In order to control the running speed of the detector in the gas pipeline, the flow field calculation method of the detector in the gas pipeline under the discharge state is studied. Based on the operating principle of the detector in the gas pipeline, the model of the discharge hole of the detector is constructed by using the standard orifice flowmeter. Based on computational fluid dynamics theory, the application of computational fluid dynamics software ICEM CFD and provided ANSYS CFX to generate flow field model and a numerical simulation was carried out, with fluid flowing through the discharge of the flow field simulation, the discharge state of gas pipeline detector in flow field, achieved under different aperture of gas flowing through the standard orifice plate before and after the pressure field, velocity field of numerical analysis. The results show that using the standard hole as the detector model in the gas pipeline under the discharge state has certain guidance, and it is of certain significance to further study the velocity control problem of the detector in the gas pipeline.