# Safety Analysis and Condition Assessment of Corroded Energy Pipelines under Landslide Disasters
## 4 Results and Discussion
### Effect of Corrosion Dimension  
The corrosion defect is located on the pipeline side facing the landslide. Corrosion depths from 0.10\(t\) to 0.40\(t\) and lengths between 10 cm and 30 cm are considered. This study investigates the influence of the corrosion depth on equivalent stress variations for different defect lengths across displacements ranging from 0 m to 1 m. Figure 6a reveals a stress concentration at the location of the corrosion defect generating the maximum equivalent stress. A distinctive zone of stress fluctuation is evident in the central region facing the slide, while both the edge and central part on the opposite side of the pipeline to the slide also show distinct stress zones. Three salient phenomena emerge based on the findings from Figure 6b-f:  
* Given a constant corrosion length and depth, with increasing landslide displacement, the maximum equivalent stress in the pipeline notably rises, stabilizing close to the yield stress of 555 MPa. * Given a constant corrosion length and landslide displacement, an increase in the corrosion depth significantly elevates the maximum equivalent stress in the pipeline. * Given a constant corrosion depth and landslide displacement, the corrosion length positively correlates with the maximum equivalent stress in the pipeline, albeit the correlation magnitude is not pronounced. Figure 7 illustrates the stress distributions in the pipeline affected by varying corrosion lengths and landslide displacements with a set corrosion depth of 0.25\(t\). As shown in Figure 7a, the corrosion length has a limited impact on the maximum equivalent stress of the pipeline. The stress variation curves closely overlap when the corrosion length exceeds 20 cm. When the corrosion length is short, its weakening effect on the pipeline is also limited as the length increases, resulting in a larger corroded area, which ironically affects the stress concentration, leading to a slower trend in the stress increase. Using an allowable stress of 499 MPa as the pipeline failure criterion, with a corrosion depth of 0.25\(t\), the limit  
Figure 6: Stress curves for pipelines with varying corrosion lengths and depths: (**a**) schematic of the model; (**b**) 10 cm corrosion length; (**c**) 15 cm corrosion length; (**d**) 20 cm corrosion length; (**e**) 25 cm corrosion length; and (**f**) 30 cm corrosion length. and landslide displacements corresponding to corrosion lengths ranging from 10 cm to 30 cm are 0.47 m, 0.44 m, 0.42 m, 0.41 m, and 0.40 m.  
For a corrosion length of 20 cm in the axial and circumferential analyses of the pipeline, Figure 7b shows the midpart of the pipeline as the most susceptible location under the landslide effect. As the landslide displacement increases, the difference in the equivalent stress between the central section and its adjacent areas diminishes. This trend can be attributed to the reduced impact of displacement once the corroded part of the pipeline achieves its yield stress, while the stress in the non-corroded sections continues to rise. As the shear action from the landslide edge on the pipeline intensifies, the equivalent stress at the edge increases from 252 MPa to 340 MPa. The axial distribution of pipeline stress transitions from an initial single peak to a tri-peak configuration, and the stress area near the edge peak value continually expands. This pattern is consistent with observations under non-corroded conditions. As shown in Figure 7c, based on the circumferential distribution, stress concentration occurs only at the corrosion site. It exceeds equivalent stresses in other circumferential locations of the pipeline when the displacement load is minimal. As the displacement load increases, stresses in both the slide-facing and slide-backing areas of the pipeline rise. However, the distribution does not display symmetrical patterns either horizontally or vertically.