The Stress Analysis And Load Optimization Of CNG Storage And Transportation Equipment

With the research and development and application of compressed natural gas (CNG) automobile, gas storage wells and composite cylinders, as compressed natural gas storage and transportation equipment, have been massively promoted and applied. But people find a lot of problems in the process of using and testing gas wells and composite cylinders, which will often reduce the safety performance of the gas wells and composite cylinders. In order to improve their safety performance, relevant researchers have made a lot of research work in recent years and their research results have solved many practical problems. But now there are many problems to be solved. Therefore, the study of gas storage wells and composite cylinders is of great necessity.Casing and coupling are the main pressure parts of gas storage well, and they are connected by screw threads, the make-up torque has great influence on the quality of screw threads connection. This paper applies finite element analysis method to establish a corresponding mechanical model and stress analysis.The effects of make-up torque on the strength and fatigue properties of gas well casing pipe and coupling was discussed; A calculating method to calculate the make-up torque was porposed;The optimization of make-up torque of gas storage well was achieved by combined the make-up torque calculation formula and the related standard. The analysis results show that the make-up torque with its interference lapsin the range of0to3laps has greater influence on the connection strength of gas storage well and less influence on the fatigue properties; if the screw threads between casing pipe and coupling is between1.5to2.8laps, it will meet the request of make-up torque; if it is above2laps, the screw threads will in the best condition.With the liner and composite material layers of composite cylinders apply two kinds of materials varying greatly in its mechanical properties, making the stresses along the wall unevenly distributed. After autofrettage, the stress distribution of the composite cylinder tends to be uniform, and gives full play to the high strength quality of carbon fiber, improves the overall fatigue performance of composite cylinders.This paper takes a fully wrapped composite cylinder whose volume is140L, and working pressure is35MPa as an example of autofrettage analysis, and the optimzation of autofrettage pressure was achieved. The analysis results indicate that before autofrettage, parts of the composite cylinder liner has entered the plastic stress state; the maximum Mises stress of composite layer is far less than the tensile strength of carbon fibers; the superior performance of the carbon fiber has not been fully played,and the fatigue life will be greatly reduced; After autofrettage, stress distribution on liner can be improved, fiber properties are brought into full play and its fatigue life is greatly improved; the optimal autofrettage pressure of full-wrapped composite cylinders with its working pressure of35MPa is64.4MPa.