Study In Mechanical Behavior Of Pipelines With Defect

Pipeline transportation is the important way of petroleum transportation all long. Crack is one of the major failure reason witch may exist in the pipelines because of the inner and outer factors. So the study for the mechanical performance of pipelines with cracks has important significance for the decisiones of the function, servicing and replacing of the pipelines.The paper adopts the large-scale finite element analysis software ANSYS to establish surface crack of thin-walled pipe model and get the calculation and analysis of fracture parameters and the plastic limit loads in-depth discussion and research.The main content of this paper are as follows:(1)Adopts entity modeling method to establish the axial and annular surface crack pipe mechanics behavior analysis model tentatively, including crack defects model and load model. Prepare command flow with parametric language to calculate necessary results accurately in the appropriate scope for parameter settings.(2)Explore brittle fracture and elastic-plastic fracture failure criterion and its application conditions. The criterion for brittle fracture basically has energy balance theory and the stress intensity factor theory. The research for elastic-plastic fracture mechanics mainly is J integral criterion witch is the most effective method for elastic-plastic fracture mechanics analysis.(3)The stress intensity factor K1of surface crack about thin-walled pipe is calculated with finite element analysis method based on the theoretical basis of fracture mechanics, and the influential factors of the stress intensity factor are analysed. The shape coefficients for deepest point and surface crack point of stress intensity factor are calculated according to the existing handbook of stress intensity factor witch makes the stress intensity factor about thin-walled pipe systematically.(4)The crack angle will be as variable for plastic J integral expression of plastic solution considering the lack of EPRI engineering method. The plastic J integral will be solved according to the stress intensity factor and the existing database based on the equivalent remote stress method, witch is more accurate and easier for engineering application.(5)Based on the plastic limit theory, induces the plastic limit analysis methods and engineering plastic limit load criteria,and determine the finite element method. (6)The plastic limit load of thin-wall pipe is solved with a new nonlinear finite element analysis method—stopping point method, witch is based on the plastic limit analysis theory.(7)Combined with the failure assessment technology, Pipeline failure behaviour is evaluated according to the analysis about plastic limit load and fracture parameters.