Investigation On Fatigue Life And Ultimate Pressure Of Ultra-high Pressure Tubular Reactor

With the development of industry and technology,the ultra-high pressure vessels and the use of ultra-high pressure technology are more important.As an important production equipment of high-pressure low-density polyethylene,the ultra-high pressure tubular reactor is operated under the complex and harsh working conditions.The operation comditions are at high temperature,ultra high pressure and with corrosion.If the ultra-high pressure tubular reactor explodes or leaks will cause serious casualties and significant economic loss.At present,most of our ultra-high pressure tubular reactors have entered the final term of design life.In order to ensure the safety of production and personnel and property safety,the fatigue life and ultimate pressure analysis of the ultra-high pressure tubular reactor is of great significance.In this paper,the actual UHP tubular reactor,with service life of 19 years,is taken as the research object.Based on the mechanical properties test,fatigue test and blasting test,combined with theoretical analysis and ANSYS finite element simulation,the fatigue life and ultimate pressure of UHP tubular reactor were investigated.Furthermore,the fatigue life and ultimate pressure of UHP tubular reactors containing defects such as cracks were further investigated.The main contents are as follows:(1)A bilinear isotropic hardening model was adopted to analyze the stress of UHP tubular reactor,and the optimal autofrettage pressure calculation formula was derived.The optimal autofrettage pressure of the UHP tubular reactor was 652 MPa.Based on the theoretical analysis and ANSYS finite element analysis,the law of the equivalent stress changes prior and post the autofrettage treatment were investigated.The effect of autofrettage treatment on the safety of UHP tubular reactor were quantitatively analyzed by using safety factor.(2)Based on the stress-life method,the fatigue life of UHP tubular reactor is analyzed.The results show that the fatigue life of the UHP tubular reactor may be increased to 11.02 times of the original with 630 MPa autofrettage treatment,and increased to 12.65 times of the orginal with 652 MPa optimum autofrettage treatment.The maximum error of finite element simulation and theoretical analysis is 6.2%.The fatigue life and residual stress decay of UHP tubular reactor were tested by 12 000 cycles under simulated actual working conditions.(3)The blasting test of the UHP tubular reactor is then carried out,and the experimental results show that the ultimate pressure of the UHP tubular reactor is 957.40 MPa,and the maximum error of theoretical calculation and finite element simulation are 1.2% and 1.1% respectively,which proves the feasibility and accuracy of finite element simulation analysis of the ultimate pressure.(5)The fatigue life and ultimate load of UHP tubular reactor with cracks were analysed.Based on the fracture mechanics method,the fatigue life of UHP tubular reactor with initial crack was theoretically analyzed.The influence of crack direction and dimension on fatigue life and ultimate load were further explored by finite element simulation.The results show that the axial crack is more danger than the circumferential crack,and the crack depth has a more significant influence on the fatigue life and ultimate pressure of the UHP tubular reactor.From the example analysis of the defective small tube,the error of fatigue life is within 2.84~4.49% by finite element simulation and theoretical analysis,which proves the feasibility and accuracy of the analysis the fatigue life of defective equipment.In this paper,the fatigue life and ultimate load of the UHP tubular reactor were investigated,and the influence of crack on fatigue life and ultimate pressure was analyzed.It may provide basis for the safe operation and evaluation of the UHP tubular reactor,which is of certain engineering application and academic reference values.