# The Influence of Axial Compressive Stress and Internal Pressure on a Pipeline Network: A Review
## 4 Effects of Axial Compressive Stress
### Detrimental Effects
Furthermore, it was found that bending collapse typically occurs when the pipe is subjected to relatively low internal pressure. However, it does happen when subjected to relatively high internal pressure, assuming sufficiently large axial compressive stress is imposed. [PERSON] et al. [19] found that significantly large axial compressive stress resulted in buckling. An increase in corrosion defect width also results in a low maximum bending moment, while a decrease in corrosion defect width results in a steady increase in the maximum bending moment. [PERSON] and [PERSON] [58] examined the effect of the load-carrying capacity of pipelines with varying axial lengths subjected to external loads. Referring to Figure 6, the load-carrying capacity decreases as the corrosion defect length increases, regardless of the defect's width. The reduction in carrying capacity is due to buckling instability that occurred with the increase in the longitudinal extent of defects [59]. Figure 5: A conceptual visualization of the effects of the axial length of the corrosion defect area and internal pressure on pipe on the crack occurrence in the corrosion defect area is shown. Note that \(2\theta\) symbolizes the width of the defect [58]. [PERSON] et al. [60] found that under pure tensile and compressional loads, circumferentially oriented defects showed stronger interacting behavior than axially oriented defects. [PERSON] et al. [61] found that the axial extent of corrosion defects on plastic load limits is insignificant for pure bending forces (tension and compression). [PERSON] et al. [62] conducted an FEA to determine the effects of tensile and compressive strain on corrosion-affected pipelines. They found that a reduction in failure pressure occurred regardless of the presence of tensile or compressive strain. In addition, the failure pressure reduction increased as the tensile or compressive force intensity increased. Figure 7 shows that the plastic deformation distribution (region in red), when subject to external forces, is distinctly greater than when no external forces were subjected. Through the FEA stress-strain fields, it is evident that the plastic deformation regions grow in prominence with increasing tensile or compressive forces. The behavior of plastic deformation for tensile or compressive forces is distinct. This is because the stress-strain fields expand along the hoop direction for tensile forces, thus moving away from the defect. Meanwhile, the stress-strain fields expand by surrounding the defect for compressive forces. These differences in behavior result in differences in the failure mechanism. Defects subjected to tensile force are highly likely to undergo failure  
Figure 6: Graph representing the varying axial defect length subjected to internal pressure and external forces and its effect on pipe load-carrying capacity [58]. Figure 7: Plastic deformation distribution on X80 grade steel pipe when subjected to no external strain (**left**), 0.2% tensile strain (**middle**), 0.2% compressive strain (**right**) [62]. due to circumferential cracking. On the other hand, defects subjected to compressive forces are highly likely to undergo failure due to the buckling or wrinkling effect [62]. [PERSON] et al. [62] also added that plastic failure due to external forces can be explained by the conversion of forces or energy. The application of external forces is usually converted to strain energy through lattice distortion, lattice movement, and many more. Since there is an increase in strain in the system, lower internal pressure is required to result in failure. In cases where corrosion defects are present, the plastic deformation region is significantly higher than that of an intact pipe. It is noteworthy that the presence of external forces often causes hardening behavior, which is supported by [62]. [PERSON] et al. [54] mentioned that another side effect of inward buckling is the ovalization of the pipe cross section.