In the long-term and continuous operation process of UGS injection-production well, the outer casing joint of the oil string is prone to failure. This causes gas to enter into the annular space between the casing and string forming the gas-liquid two-phase, leading to the issue of cavitation of the string. Therefore, herein, the string cavitation caused by the gas leakage in UGS gas well during the injection and production process is analyzed through electrochemical measurements and image characterization. The results show that the pipe string had no corrosion characteristics during the long time of injection and production owing to the action of corrosion inhibitor and passivation film of 13 Cr. During the 24 h experiment, when the leakage pressure reached 5 MPa, the pipe string was mainly layered corrosion. When the pressure increased to 10 MPa, the formation and rupture of gas bubbles on the metal surface led to the destruction of two protective films, and clear cavitation pits appeared on the metal surface. Greater the pressure, more prominent was the cavitation effect.

Solid concentration changes may affect the solid-liquid flow of the axial flow pump in the polypropylene loop reactor, accompanied with unstable operations (e.g., axial power fluctuation). The influencing factors and formation mechanisms of axial power fluctuation were analysed. After that, to discuss the influences of energy allowance of the mixture media in the loop reactor, the internal flow status of the pump under different solid volume fractions were compared. Then a head-correction strategy of operating control with single invert was proposed, to smooth the axial power fluctuation of the axial flow pump. Results demonstrate that viscosity of the mixture media is positively related, whereas the head of the axial flow pump is negatively correlated with solid concentration. Besides, head-correction curves can effectively regulate the off-design operation of pump under different solid volume fractions, with the energy allowance and the axial power fluctuation reduced in the loop reactor and the pump. Researches provide important references for the analysis of internal flow status and the solution of axial power fluctuation of the axial flow pump in the polypropylene loop reactor.