Strength Analysis And Fatigue Study Of Low Temperature LNG Tanker

Various liquefied gases are becoming more and more common in modern practical industrial production and applications.It is also a common practice to use a moving pressure vessel for transport.A transport tanker is a typical moving pressure vessel that transports liquefied gas.Liquefied natural gas(LNG)has characteristics such as flammable,explosive and other liquefied gases,along with the increasing tonnage of transportation monomer,the adaptability of large-scale LNG transportation tankers to different roads,and the regulation of extreme operating conditions,Become an urgent common issue in the industry.This thesis mainly analyzes and evaluates the stress intensity of the key parts of the tank during the transportation process,and at the same time analyzes the tank body fatigue.At present,there are some shortcomings in the conventional design methods used in tanks for low-temperature LNG tankers.The design process is not detailed enough and is too conservative.The design often focuses only on the stationary state of LNG tankers,but ignores the emergency in the actual transportation process.Extreme conditions such as braking,sharp turns,and road conditions.These extreme conditions have a certain influence on the structural strength of key parts of the tank.Besides,in the conventional fatigue design of cryogenic LNG tanks,there is no clear standard for the calculation of the fatigue life of the tank.First of all,according to the national standards and specifications,a simple description of the structural design of the SDY9401GDY low-temperature LNG tanker tanks,while finishing the traditional design of the LNG tank design.At the same time,according to the two-dimensional drawing of the low-temperature LNG transportation tanker,a 3D geometric model of the tank of the LNG tanker was established in the 3D modeling software SolidWorks,and then the 3D model was introduced into the finite element analysis software ANASYS Workbench.Based on actual experience and research results of previous generations,a preliminary determination was made that the stress concentration areas in the extreme transport processes of LNG tankers are the compression surfaces of the surface and the support area in the transition zone of the head end.These dangerous areas are one of the most direct causes of failure of LNG tankers during transportation.Secondly,according to the results of the finite element analysis,the maximum stress intensity of the tank body under these four conditions is the same as our initial judgment,which is the area within and outside the transition zone of the inner cylinder and the head.The cylinder joint and the outer cylinder support area.Under such extreme transport conditions,high stress regions are present in the inner surface of the inner cylinder of the can body in a local area near the sliding end support edge.According to the stress classification method,the stress intensity of the tank body is checked,and its structural strength reaches the strength requirement.Therefore,this indicates that the tank is mainly affected by the internal pressure and has little effect on the inertial load.Finally,due to the different structure of the inner and outer cylinders of the tanker and the different alternating loads,different fatigue calculation methods were determined.When fatigue cylinder strength calculations are performed on the outer cylinder of the tanker,the cumulative damage cost coefficient is calculated according to the basic idea of JB4732-1995"Steel Pressure Vessel-Analytical Design Standard".The calculation results show that the cumulative damage coefficient of the outer cylinder of the tanker is 0.074,which is much less than 1,and it can be seen that the fatigue strength of the outer cylinder meets the requirements;using ANASYS Workbench finite element software,according to the ASME boiler and pressure vessel Based on the design criteria,the elasto-plastic hypothesis and the calculation method of the Miner cumulative fatigue analysis theory were used to calculate and calculate the fatigue life of the most stressed parts of the cryogenic LNG transport tank.The results show that after the cycle of10~6times,the minimum number of cycles obtained is 1.2117×10~4times,and the tank car body takes four hours as a cycle period to calculate the cylinder inside the tank of the low-temperature LNG transportation tanker.The service life under the same conditions is 6.058,which is about 6 years.