Study On The Surface Creep Crack Growth Behavior Of C-tube Model Based On High Temperature Fracture Mechanics

With the increasingly prominent problems of energy shortage and environmental degradation,modern industrial equipment is developing towards the trend of high temperature and high pressure,increasing the risk of creep fracture failure of metal structures,which may cause serious losses,even disastrous consequences.In the process of transportation,installation and service,it is inevitable that there will be various crack defects on the outer surface of pipes and welds.However,the creep crack growth rate obtained by the CT specimen is too conservative,which leads to unnecessary maintenance or replacement of the in-service pipes,thus increasing the cost of equipment.In order to better study the creep crack growth behavior of the outer surface of high-temperature pressure-bearing pipe,this paper proposes a C-tube model which is more close to the actual working condition.The proposed model is further studied by means of simulation verification,experimental research and theoretical analysis.The main research contents include:(1)C-tube model simulation verification.Based on the step-by-step analysis method of ABAQUS,the C-tube axial crack model and the C-tube weld circumferential crack model are studied from four aspects: stress distribution,creep fracture parameter C*-integral value,creep crack growth behavior and creep crack growth time increment.The results are compared with the corresponding data of the circular pipe model to verify the feasibility of the proposed C-tube model.It lays a foundation for further research.(2)Experimental study on C-tube weld samples.By means of metallography,hardness,XRD and SEM,the changes of creep properties,prefabricated crack morphology and creep crack propagation behavior of C-tube weld specimens with different stress states were studied at 600? and 650?.The results show that high temperature and stress will increase the performance difference between the base metal and welding seam,resulting in the decline of the overall performance of the sample.The prefabricated crack mainly deforms and expands along the axial direction.Creep cracks mainly growth along grain boundaries,and the growth,aggregation and combination of creep voids are the main reasons for the crack growing forward.(3)Analysis of influencing factors of creep crack growth.The creep fracture parameter C*-integral value was calculated by finite element software ABAQUS,and then analyzes the influence of crack length,crack depth and loading stress on the creep growth behavior of axial crack and circumferential crack in the model The application of the proposed C-tube model to the study of creep crack growth on the outer surface of pipeline is further discussed and analyzed...