Analysis On Sleeve Repair For Pipelines With Crack

Pipelines are widely used in industrial production process. Defects such as corrosion, unavoidable scratch, welding cracks, slag are common in pipelines in service. If the defects are not timely repaired, they would seriously affect the safety of pipelines. Sleeve repairs technology are widely used in service, and it can repair most of the pipeline defects. The safety evaluation of pipeline repair can adopt FAD diagram based on the J-integral. However, there are few research about the calculation method of J-integral after sleeve repairs. In addition, local collapse of pipelines are found under sleeve repairs. The structure cause of this phenomenon is not fully explained in literature work. This paper used ANSYS software to establish various pipeline crack model under sleeve repairs, The J-integral and crack arrest factor F of the crack are calculated under different conditions. At the same time a pipeline containing through wall cracks under external pressure was established. Influence of cracks on the pipeline stability was studied. The specific contents and conclusions of this paper are as follows:(1) A model of J-integral calculation of pipeline with axial crack was established, the modeling and calculation method was verified. At the same time, the stress calculation model of sleeve repair was established. Results showed that the modeling and calculation method is reasonable.(2)A model of pipeline with axial crack under sleeve repairs was established. The J-integral and crack arrest factor F of different crack form (through wall and part-through wall), loading type, sleeve parameters and pipeline parameters was calculated. The results showed that moment has nothing to do with pipeline with axial crack. There is no danger in pipeline with axial through wall crack under sleeve repair. Decreasing the gap between sleeve and pipeline has an extraordinary effect when using sleeve to repair pipeline with axial part-through wall crack.(3) A model of pipeline with circumference crack under sleeve repairs was established. The J-integral and crack arrest factor F of different crack form (through wall and part-through wall), loading type, sleeve parameters and pipeline parameters was calculated. The results showed that increasing the length of sleeve has an extraordinary effect when using sleeve to repair pipeline with circumference crack. Particularly, decreasing the gap between sleeve and pipeline has an extraordinary effect when using sleeve to repair pipeline with circumference part-through wall crack. (4) A model of pipeline containing through wall cracks or local thinning under external pressure was established. The influence of defects on the stability of pipelines was studied. Analysis of the mechanism of local collapse was conducted. The results showed that the axial crack has little effect on the stability of the pipeline. The circumference crack and local thinning seriously affect the stability of pipeline. The method of avoiding the break was gave at the last.