Stress Intensity Factor And Pressure Bearing Capacity Of Cracked Pipelines With Internal Corrosion Defects

With the extension of oil and gas pipelines running time,the interior of the pipe will inevitably produce corrosion defect,and weaken the static and dynamic resistance of pipeline.Due to stress concentration,the corrosion defect is likely to have crack,and further affect the performance of the pipeline.Thesis mainly studied the change rules of stress intensity factor and pressure ability of pipelines that containing corrosion defects-crack,it has more practical meaning than single defect or crack.There were many studies on pipeline corrosion defects and cracks,but the research on corrosion defect-crack was very few.Based on corrosion mechanism of defects and the theory of fracture mechanics,this paper studied the influence rules of different parameters of different cracks on stress intensity factor and limit bearing capacity.The main work of this paper includes:1.The studies on corrosion defects-axial crack:The stress intensity factor of the defect-axial crack was calculated by finite element method.The results showed that:keeping other parameters unchanged,with the increase of the relative depth of axial crack,the magnitude of stress intensity factor was multi-defect-axial crack>single defect-axial crack>double defect-axial crack with the relative depth of axial crack;With the increase of the internal pressure of pipes,the relationship between the stress intensity factor was double defect-axial crack>single defect-axial crack>multiple defects-axial crack.2.The research on stress intensity factor of different corrosion defect-cracks:The finite element method was used to solve the stress intensity factor of three-dimensional pitting defects-radial crack and uniform corrosion defect ring crack?rectangular crack.The results showed that the stress intensity factor increased with the relative depth of the crack and the internal pressure of the pipeline increased,and decreased with the wall thickness of the pipe increased.3.The calculation of shape factor:According to the results of numerical simulation and the formula of stress intensity factor,the relationship between the shape factor and the crack relative depth and the pipe wall thickness was deduced,and the correctness of the form factor is verified.4.The research on pipeline pressure;Based on numerical simulation and local plastic failure criterion,the failure pressure of pipeline with corrosion defect-crack was calculated,And the critical depth of the crack under the same internal pressure,the failure pressure of the pipeline under the same depth.5.Evaluation method of pipeline bearing capacity:The failure pressure of crack with different length was calculated by different evaluation methods,the result of evaluation of DNV RP-F101 is relatively high.ASME B31G evaluation method is too conservative.The improved B31G method,RPA method,Choi regression formula and finite element method are close to each other and the evaluation of pipeline pressure capacity is more reliable.