# Safety Analysis and Condition Assessment of Corroded Energy Pipelines under Landslide Disasters
## 4 Results and Discussion
### Effect of Corrosion Location  
To study the impact of different circumferential positions, the top of the pipeline is set at 0\({}^{\circ}\) with an angle interval of 30\({}^{\circ}\). Using a corrosion depth of 0.25\(t\) and a length of 20 cm, a circumferential corrosion model is constructed in the middle of the landslide area. The equivalent stress is extracted for the landslide displacement of 0.8 m, as shown in Figure 10. For corrosion positioned at angles of 90\({}^{\circ}\), 120\({}^{\circ}\), 150\({}^{\circ}\), 270\({}^{\circ}\), and 300\({}^{\circ}\), the maximum equivalent stress is observed at the corrosion site. In contrast, when the corrosion is at other circumferential angles, the maximum equivalent stress manifests near the sliding face, specifically within the range of 105\({}^{\circ}\) to 120\({}^{\circ}\). Under this displacement, the pipeline with corrosion at all positions except for at 300\({}^{\circ}\) exceeds the allowable stress of 499 MPa and fails. Notably, the stress in the pipeline corroded at 90\({}^{\circ}\), 120\({}^{\circ}\), and 150\({}^{\circ}\) surpasses the yield stress of 555 MPa, indicating a yield state. Even the pipeline with corrosion at 300\({}^{\circ}\) is on the verge of failure and should not be overlooked. Figure 11 shows the maximum equivalent stress across different circumferential corrosion angles under varied displacements; angles at 0\({}^{\circ}\), 30\({}^{\circ}\), 180\({}^{\circ}\), 210\({}^{\circ}\), 240\({}^{\circ}\), 270\({}^{\circ}\), 300\({}^{\circ}\), and 330\({}^{\circ}\) first experience a minor stress decrease before increasing with displacement;  
Figure 10: Stress for different circumferential corrosion positions of the pipeline. Figure 9: Distribution of limit displacement and safety range. Conversely, other angles display a consistent increase in stress with displacement. The observed trends stem from the interplay between the internal pressure and displacement loads. Initially, in specific locations, the dominant internal pressure causes a stress reduction with minor displacements. However, as the dragging effect of the landslide on the pipeline intensifies, surpassing the internal pressure effect, the circumferential stress begins to increase. When the corrosion defect is located at 300\({}^{\circ}\), its stress curve is notably lower than in other conditions, indicating the maximum equivalent stress remains at the corroded site. Analyzing the trends in stress changes, the circumferentially corroded pipelines can be categorized into three scenarios:  
* An initial decrease followed by a consistent growth rate (at 0\({}^{\circ}\), 30\({}^{\circ}\), 180\({}^{\circ}\), 210\({}^{\circ}\), 240\({}^{\circ}\), 270\({}^{\circ}\), and 330\({}^{\circ}\)). * An initial decrease then a gradual increase (at 300\({}^{\circ}\)). * Continuous growth (at 60\({}^{\circ}\), 90\({}^{\circ}\), 120\({}^{\circ}\), and 150\({}^{\circ}\)). Figure 12 shows the stress profile for defects positioned from 0\({}^{\circ}\) to 330\({}^{\circ}\) under landslide displacements ranging from 0.2 m to 1 m. Stress concentration is evident at the corrosion site. With increasing displacement, stress rises in the circumferential positions of the pipeline. At a given displacement, the stress at the defect angular position does not follow a uniform trend. The site of maximum stress can differ from the actual corrosion defect, influenced by the angular position and landslide displacement. Figure 11: Variation in equivalent stress with displacement for different defect angles: (a) 0-150\({}^{\circ}\) and (b) 180–330\({}^{\circ}\). Figure 12: Stress distribution in the pipeline with varying landslide displacement across different angular directions. While stress outcomes differ across angular positions and landslide displacements, the areas between the slide-facing and its opposite side exhibit subdued stress variations. This underscores the engineering rationale behind prioritizing monitoring stress in the slide-facing and slide-backing areas of the pipeline.