Analysis Of Static Strength And Fatigue Life For Tube Trailer Cylinders

In recent years, as the growth of the energy consumption and the serious environment problems, usage of natural gas increases fast all over the world. Piping transportation is suitable for natural gas between places far away for each other while the transportable pressure vessels are more suitable for transportation within a limited district. A tube trailer is a kind of convenient natural gas transportation equipment, and is widely used in many countries. In this article, the static strength of a tube trailer cylinder is studied under internal pressure and gravity, and fatigue analysis is conducted consequently. Research in this subject is of a certain benefit for the safety of the tube trailers.A widely selected size of the cylinder in the practice is used in this paper and the static structural analysis is conducted with internal pressure and a combined load of internal pressure and gravity by using the finite element analysis software ANSYS. The results indicate that the main body of the cylinder, which is far away form the ends, is of a relatively low stress while the two ends of the cylinder which is connected with the flanges are suffering from high stress concentration. But even the stresses on the two ends are still lower than the yield stress of the material, that is, the strength of the cylinder is enough for the internal pressure and the gravity. Inertial loads will exist when the tube trailer is traveling on the roads. In order to find out the safety state of the cylinder while transportation, stress analysis by using ANSYS is done on conditions that inertial loads are mentioned. Analysis shows that stresses on the end of the cylinder are higher than the yield stress of the material and fatigue risk exists. Three axial inertial loads which is the radial direction, axial direction and the circumferential direction are used in the analysis, and the results show that the magnitude of the combined vector of the three axial inertial loads is the key variable for the stress of the cylinder and the stress is nearly increases proportionally to the magnitude of the vector.The lower six natural frequencies of the cylinder are obtained by ANSYS, and the corresponding proper moving speeds of the vehicle are suggested to be not over 120km/s2 by following. Fatigue lives under variation of the internal pressure are calculated and proved to be safe for the cylinder within the service cycle, although the cylinders are not working under infinite fatigue life. Fatigue lives under inertial loads are also be analyzed and a proper inertial load, which is normal to the axial direction of the cylinder is suggested no more than 18m/s2. Otherwise, the cylinder will be on the risk of failure of fatigue.