Schematic of the FAD.

Schematic of the FAD.

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Crack defects in the girth welds of pipelines have become an important factor affecting the safe operation of in-service oil pipelines. Therefore, it is necessary to analyze the factors affecting the safe operation of pipelines and determine the ultimate load during pipeline operation. Based on the failure assessment diagram (FAD) method described...

Contexts in source publication

Context 1
... stress and material analyses, the FAD method takes the fracture ratio Kr and load ratio Lr as two important decisive factors. As can be seen in Figure 1, for a given circumferential welded structure with cracks, the corresponding Kr and Lr values can be calculated, and the evaluation point A (Lr, Kr) in the diagram can be obtained. The final evaluation result can be determined based on the spatial relationship between the evaluation point and the failure assessment curve. ...
Context 2
... the above section, it can be seen that, the thinner the wall thickness, the higher the risk of cracks in the pipe; accordingly, the Ø813 × 11 mm pipeline girth weld crack risk is the highest. Consequently, in this section, the results of the Ø813 × 11 mm pipeline girth weld with 25 mm × 2.5 mm cracks with different material properties under an axial load of 0.9 times the minimum yield strength are analyzed ( Figure 10). ...
Context 3
... to the results shown in Figure 10a,b, under the same tensile strength, the lower the yield strength, the higher the corresponding cutoff value, and the wider the envelope range of the failure assessment curve. The increase range is concentrated mainly in the plastic deformation area. ...
Context 4
... to Figure 10c,d, under the same yield ratio, the higher the tensile strength of steel, the wider the envelope range of the corresponding failure evaluation curve. Moreover, the higher the fracture ratio of the evaluation point, the wider the envelope range of the evaluation curve, which can provide a larger safety margin. ...
Context 5
... effect of the crack depth ratio on the ultimate axial load was analyzed based on the evaluation results without and with 1 mm pipe misalignment under a fixed crack length-to-cycle ratio of 0.01 ( Figure 11). ...
Context 6
... effect of crack perimeter ratio on the ultimate axial load was analyzed based on the evaluation results without and with 1 mm pipe misalignment under a fixed crack depth ratio of a/B = 0.3. According to Figure 12, the larger the crack length-to-cycle ratio, the lower the ultimate axial tensile load that the girth welded joint can withstand. In addition, the Option 2 evaluation was less conservative than the Option 1 evaluation; thus, the ultimate axial load under the Option 2 evaluation was higher than that under the Option 1 evaluation. ...
Context 7
... to effects related to the welding environment, labor conditions, and other factors, girth welded joints often have misalignments. By controlling the maximum and minimum crack size, the effects of wall thickness and misalignment on the ultimate axial load were analyzed and the results are presented in Figure 13. ...
Context 8
... to Figure 14, under the same tensile strength, the higher the yield ratio of the steel, the lower the ratio of ultimate axial load to yield strength that the girth weld can withstand. This is more apparent when the crack size is small, and the effect of the yield ratio on the ultimate axial load weakens with increasing crack size. ...
Context 9
... can be observed in the prediction error diagram of the PSO-SVR model ( Figure 15), the error between most prediction results and finite element calculation results was less than 10%. As can be seen in Table 3, the correlation coefficients of the two models were higher than 99%, and the predicted results were found to be in good agreement with the numerical simulation ones, indicating that the proposed model has high prediction accuracy and reliability. ...

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