Large oil and gas pipelines are prone to corrosion and leakage, so in-pipe inspection is necessary. In this article, we show a novel robot mechanism for long-distance pipeline inspection. The robot consists of three crawlers and electric putters, which can adjust their speed and radius independently. Independent adjustment and system self-checking of the robot are achieved through multiple sensors. To make the robot operate efficiently, we studied the influence of size parameters on the forces between the central body and crawler. Moreover, we investigated how to adjust the attitude of the robot through the differential speed of the three crawlers. Static and dynamic simulations of internal forces are presented. The primary experiments indicate that our robot can operate stably in a large steel pipe.

The effect of element sulphur on the performance of corrosion inhibitor in H 2 S/CO 2 gas field solution was investigated at different velocities. The morphology and composition of corrosion products were characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) methods. The results indicated that L360 QS steel surface suffered from sulphur-induced pitting corrosion at a low velocity due to insufficient sulphur-carrying fluid power. At high flow velocities, the steel surface is likely to be suffered high fluid power which can remove the inhibitor film and corrosion scales by the mechanical erosion effect. The sulphur corrosion mechanism model and the flow-induced corrosion model due to the high wall shear force have been proposed in the study. This work suggested that the gas production rate should be controlled at an acceptable level to guarantee the service safety of pipeline system.

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Effect of corrosion duration on C110 casing steel was investigated in the stimulated gas field solution containing both 1 MPa CO2 and 1.5 MPa H2S at 90 °C by using a high temperature autoclave. And the corrosion rate prediction model was established based on the corrosion duration effect. In addition, effect of stress on corrosion of steel was analyzed from the thermodynamics and electrochemistry theories, moreover, the casing corrosion life prediction model was established under three axis stress state with considering the influences of stress and corrosion effect. The results reveal that the corrosion rate of C110 casing steel decreases significantly as corrosion time increases, then gradually tends toward stability. In addition, the casing steel is subjected to load and corrosion solution, the thermodynamic activity and the electrochemical reaction potential are changed, ultimately aggravating the process of corrosion. Compared to corrosion time and wall thickness, the internal pressure is the main factor governing the casing corrosion. Therefore, it is suggested that the synergistic effects of corrosion time and stress should be considered in casing safety design and operation.