Reliability Study of Metal Bellows in Low-Temperature High-Pressure Liquid Carbon Dioxide Transportation Systems: Failure Mechanism Analysis

In order to meet the harsh working environment and complex and changeable stress conditions, the low-temperature and high-pressure liquid carbon dioxide conveying system used in oil extraction will choose metal bellows for transportation. In this paper, the bellows in an accident section are investigated and observed by the working environment and characterization methods such as macroscopic analysis, metallographic analysis, EDS component analysis, fracture scanning electron microscopy analysis, and related mechanical performance test methods. The failure mechanism of the accident is preliminarily judged, and the unidirectional fluid–structure coupling model and the standard k-ω turbulence model are used as the calculation models for subsequent simulation. Combined with Fluent finite element simulation analysis, it is verified that the failure is caused by a welding defect, the maximum stress of the metal bellows under normal conditions is less than its own yield strength, and the material can work normally. When the welding crack is greater than 2 mm, the strength of the workpiece weld will be reduced, and the stress concentration has exceeded the yield strength that the workpiece can bear, causing failure fracture at the welding defect part. Combined with ANSYS simulation of accident defects, compared with bellows without defects, the stress at the crack will increase with the increase in the inlet flow velocity and decrease with the increase in temperature, and the flow rate will have a greater influence on it. Therefore, in actual working conditions, the stiffness and fatigue life of the conveying system can be improved by appropriately reducing the liquid flow rate and increasing the temperature. It provides a reference for the future application research of bellows and the research on bellows fracture failure.