Safety Evaluation Of Engineering Defective Pipeline Based On VB

All the time, the safety assessment of pressure pipes is the focus. With the development of fracture mechanics, its application in safety assessment of defect structure becomes more and more widely. Obtaining the fracture parameters of defect structure by finite element method, and then carrying on the safety assessement of defect structure have been a popular method. At present, many scholars have made a large number of studies to simple structure’s fracture parameter by theoretical and analogy method, and summarize the relevant laws; However, for complex structure with cracks, such as elbows or tees, related research has not been launched intensively either theoretical solution or analog solution.Therefore, using the finite element analysis software ANSYS, establishs elbow model with many kinds of common cracks, and obtains the linear elastic fracture parameters——the stress intensity factor KI and the plastic parameters——limit load, then analyzes the influence factors of this two parameters. Finally, Base on Visual Basic technology, establishing the safety assessment expert system of defective pipeline. the following work have been done:(1) Using parametric language of ANSYS, builds straight pipe with axial half-through long crack or axial surface crack at inwall, and compares the finite element analog solution with the results of EPRI handbook. The results show that the stress intensity factor and limit load based on the finite element method are consistent with the literature results.(2) Exploring the easy way to create cracks by up-bottom method (substantive law), solving the spatial configuration and grid overlap difficulties from bottom-up method, and comparing new method with traditional methods to verify the new method’s correctness.(3) Calculating the SIFs and limit load of elbow with inwall ring crack、outerwall ring crack and through ring crack subjected to internal pressure and moment, and giving the fitting formula of typical structure affected by the internal pressure P、the moment M、the ratio of outer diameter and wall thickness Do/t、the ratio of crack depth and wall thickness a/t, the ratio of bend radius and outer diameter R/Do, the crack half-angle θ、the longitudinal crack angle θ1and the circumferential crack angle02.(4) Calculating the SIFs and limit load of elbows with through axial crack subjected to internal pressure and moment, And giving the fitting formula of typical structure affected by P、Do/t、R/Do、θ、θ1and θ2. (5) Base on the Visual Basic and database technology, programming the EPRI handbook(DUCTILE FRACTURE HANDBOOK), user can directly carry on theoretical calculation of fracture parameters; Making secondary development for the finite element software ANSYS to the crack that EPRI does not contain, achieves the finite element analogy calculation of fracture parameters; Finally, according to GB/T19624-2004, accomplishs the safety assessment expert system of defective pipeline.