Stress State Of The Overall Multilayered Pressure Vessel Research

The integrated multilayer-wrapped high pressure vessel is a kind of multilayer-wrapped high pressure vessel without the thick circumferential welding seam among cylinder. The inner cylinder is firstly spliced to the required length, then, the flange or the head can be weld on the two ends. The layers can be wrapped along with the full length one by one. When the overall length of the inner cylinder is well wrapped and welded and worn smooth, the second layer will be wrapped until specified thickness. The circumferential welding seams of each layer can be staggered mutually, and the longitudinal welding seams of layers can be also staggered at some angle by this kind of wrapping method. With the advantage of no thick circumferential welding seam among cylinder, the integrated multilayer-wrapped high pressure vessel may only leak, and may not burst out. This kind of vessels has been widely accepted and used. They have been widely used in the industry of petroleum, chemical, and metallurgy and so on, such as the ammonia separator, ammonia synthetical tower, and urea synthetical tower. As a device under static-pressure, the integrated multilayer-wrapped high pressure vessel has been investigated as to the stress status in the vessel wall when there exists no gap or perfect contact between layers by analytical theory. Many significant features and stress law have been discovered, which provides the theoretical basis about the design, manufacture and application of the vessel. The stress status of the wrapped vessels has not been well investigated when there exists gaps between layers and/or the vessel under dynamic pressure. It is important to systemically and completely investigate the stress status in the vessel wall as to the strength calculation, optimization design and safety operation.In the dissertation, the stress state of the cylinder of the integrated multilayer-wrapped high pressure vessel with gaps existing between layers subjected to steady-state pressure or dynamic pressure have been analyzed by theoretical method and numerical simulation, and the stress state of the connecting zone of the spherical head and the cylinder of the integrated multilayer-wrapped high pressure vessel has been analyzed by numerical simulation. The main work and the conclusions as to the integrated multilayer-wrapped high pressure vessel are as following: (1) The wrapped cylinder's stress state analysis by analytical theory. Based on the elastic theoretical hypothesis, the stress state of the cylinder of the integrated multilayer-wrapped vessel with gaps existing between layers subjected to steady-state pressure and different support conditions have been analyzed and summarized, and the stress theoretical calculation formulas of the cylinder of the integrated multilayer-wrapped high pressure vessel with gaps existing between layers subjected to dynamic pressure have been obtained, and comparison analysis of the stress state of the inner cylinder of the integrated multilayer-wrapped vessel with or without gaps existing between layers subjected to steady-state pressure or dynamic pressure have been carried out. The theoretical analysis results show that the stress of the vessel inner wall loaded with steady-state pressure increase with the size of gap increasing. For the vessel with uniform gap between two successive layers, the non-uniform gap can be equivalent to the uniform gap according to the principle of deformation equivalent, and comparison analysis of the stress of inner wall before and after deformation equivalent has been carried out. Taking some two wrapped vessel for instance, by calculating the stress state of a uniform gap and a non-uniform gap existing between the adjacent layers, it is shown that the stress value of the inner wall after the equivalent from non-uniform gap as a uniform gap is smaller than the value by the method of the average strain or the finite element analysis., but the differences are small enough.(2) The wrapped cylinder's stress state analysis by numerical simulation. For the cylinder of the integrated multilayer-wrapped vessel far away from the end connecting zone, a stress state analysis model of the cylinder has been established by using ANSYS contact unit, and numerical simulation for the stress state of the cylinder of the integrated multilayer-wrapped high pressure vessel with or without gaps existing between layers subjected to steady-state pressure or dynamic pressure have been carried out, and which are compared with the theoretical calculation results. The results show that numerical results are consistent to those of the theoretical solutions, indicating that the interlayer contact analysis method in the paper is right.(3) The end connecting zone's stress state analysis by numerical simulation. According to the interlayer contact model of the cylinder, a finite element contact analysis model of the end connecting zone of the spherical head and the cylinder of the integrated multilayer-wrapped high pressure vessel has been established. The stress state of the end connecting zone with the laddered connecting structure has been analyzed by using ANSYS software based on contact units as to the multilayer cylinder, and on solid units as to the spherical head. The results are compared with that of the non-multilayered structure with the same size, and the results show that the distribution of the stresses along inner and outer surfaces of the two kinds of structures are similar, and the stresses are obviously concentrated at the connecting zone, and the maximum axial stress is higher than the maximum circumferential stress, but apart the maximum stresses position, the stress attenuate rapidly. The strength of the end connecting zone has been evaluated, and the results show that the stress strength of the connecting zone is enough.