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The purpose of this paper is to demonstrate the theoretical relationship between the layout of four‐sensor dynamic acoustic array tracking system and systematic observation accuracy, and provide an algorithm to determine the optimal arrangement of four‐sensor acoustic array and an indicator to evaluate acoustic array system measurement accuracy.

In the present paper, the measurement principle of the four‐sensor dynamic acoustic array tracking system is analyzed, and the system observation model and the conversion relationship between models are established. Subsequently, the optimization algorithm for the four‐sensor dynamic acoustic array is deduced, the theoretical optimal arrangement of the four‐sensor dynamic acoustic array tracking measurement system is obtained based on the optimal position dilution of precision function (PDOPF) of 2D target, and the static experimental study on sound‐source bearing estimation is designed. The theoretical results are compared with the experimental results of the present study.

The measurement accuracy of the four‐sensor dynamic acoustic array tracking system is largely dependent on the layout of the acoustic sensor. Theoretical studies and experimental results demonstrated that an optimal PDPOF can be used to analyze the rationality of the layout. It can also serve as an indicator for the layout of the four‐sensor dynamic acoustic array tracking system.

The PDOPF value is presented as an indicator for the evaluation of the four‐sensor dynamic acoustic array systematic observation accuracy based on theoretical analysis. The feasibility of the indicator and the rationality of the sensor layout in practical engineering application are verified through experimental studies on sound‐source bearing estimation. The higher the PDOPF value is, the lower the accuracy of the system will be.

The purpose of this paper was to investigate the corrosion behaviour of API X65 pipeline steel in the simulated CO₂/oil/water emulsion using weight loss technique, potentiodynamic polarization technique and characterization of the corroded surface techniques.

The weight loss analysis, electrochemical study and surface investigation were carried out on API X65 pipeline steel that had been immersed in the CO₂/oil/water corrosive medium to understand the corrosion behaviour of gathering pipeline steel. The weight loss tests were carried out in a 3L autoclave, and effects of temperature, CO₂ partial pressure, water cut and flow velocity on the CO₂ corrosion rate of API X65 pipeline steel were studied. Electrochemical studies were carried out in a three-electrode electrochemical cell with the test temperature was 60°C, and the CO₂ partial pressure was 1 atm by recording open circuit potential/time and potentiodynamic polarization characteristics. The surface and cross-sectional morphologies of corrosion product scales were characterized using scanning electron microscopy. The phases of corrosion product scales were investigated using X-ray diffraction.

The results showed that water cut was the main controlling factor of API X65 steel corrosion under the conditions of CO₂/oil/water multiphase flow, and it had significant impact on corrosion morphology. In the case of higher water cut or pure water phase, general corrosion occurred on the steel surface. While water cut was below 70 per cent, corrosion morphology transformed into localized corrosion, crude oil decreased corrosion rate significantly and played a role of inhibitor. Crude oil hindered the corrosion scales from being dissolved by corrosive medium and changed dimension and accumulation pattern of the crystal grain, thickness and structure of the corrosion scales; thus, it influenced the corrosion rate. The primary corrosion product of API X65 steel was ferrous carbonate, which could act as a protective film at low water cut so that the corrosion rate can be reduced.

The results can be helpful in selecting the suitable corrosion inhibitors and targeted anti-corrosion measures for CO₂/oil/water corrosive environment.