# Response of Corroded Steel Pipeline Without and with CFRP Reinforcement to Reverse Fault Movement
## 4 Results and Analyses
### Mechanical Response of Corroded Pipeline Crossing Reverse Fault
#### 4.2.2 Mechanical Response of Pipeline with Corrosion at Football  
Figure 7 shows the axial strain diagrams at the top of the pipeline with different residual wall thicknesses when the corrosion occurs at the football at a distance L = 3.2 m from the fault plane and 0.9 m fault displacement. It is seen from Figure 7 that compared with the peak strain of a non-corroded pipeline, the peak strain is increased by 24%, 70%, and 99% for 0.9 t, 0.8 t, and 0.7 t pipelines, respectively. Meanwhile, the peak strain of the pipeline at the football increases by 126% from \(-\)0.0801 for the intact pipeline to \(-\)0.1817 for 0.6 t. When the pipe wall thickness is reduced by 10%, the strain in the corroded area changes dramatically, showing an irregular nonlinear growth trend.  
Figure 8 shows the von Mises stress diagram of the pipeline with different residual wall thicknesses when corrosion occurs at the football at a distance L = 3.2 m from the fault plane and 0.9 m fault displacement. It reveals that the deformation mode of the whole pipeline is consistent with the corrosion of the hanging wall pipeline; however, the difference is that the corrosion of the football pipeline has a significant effect on its section deformation. As the corrosion extent increases, the stress level of the corrosion area increases gradually compared with the surrounding area, and the deformation becomes more concentrated, resulting in large section deformation. Though the main failure mode of the pipeline, in this case, is still local buckling, the axial compressive strain makes it easier to reach the failure limit with the deepening corrosion.  
Figure 6: Stress diagram of the pipeline with corrosion at the hanging wall.  
Figure 7: The axial strain of the pipeline’s top with corrosion at the football. (**a**) The axial strain of the pipe’s top. (**b**) Enlarged image.  
For corrosion at the hanging wall, as the fault displacement increases, the failure mode of the pipeline changes from a single failure mode of local buckling to a double failure mode controlled by local buckling and tensile fracture. On the other hand, the corrosion at the footwall does not change the main failure mode of local buckling; however, the corrosion effect intensifies the local buckling. Thus, different corrosion positions have a significant amplification effect on the local strain of the pipeline. The strain response caused by corrosion at the footwall is larger than that caused by corrosion at the hanging wall.
Figure 10 shows the variation trend of pipeline peak ellipticity under different fault displacements. Figure 10 shows that the ellipticity of the pipeline increases as the fault displacement increases. When the fault displacement exceeds 0.9 m, the pipeline with different corrosion extents gradually presents an elliptic deformation failure.  
Table 5 shows the critical fault displacement of the pipeline with corrosion at the hanging wall. Taking 0.8 t as an example, when fault displacement exceeds 0.9 m, the hanging wall pipeline simultaneously has three failure modes: local buckling at the bottom, tensile fracture at the top, and elliptic deformation. The results demonstrate that when corrosion occurs at the hanging wall, the increasing corrosion extent will weaken the pipeline's resistance to tensile fracture and elliptic deformation. With the increase in fault displacement and corrosion extent, the failure mode of the hanging wall pipeline changes from single to multiple forms.