# The Influence of Axial Compressive Stress and Internal Pressure on a Pipeline Network: A Review
## 4 Effects of Axial Compressive Stress
### Detrimental Effects
For instance, a square defect with a 50% corrosion defect depth had a ductility displacement value of 5.4 mm, while a rectangular defect (3.5 times wider in the circumferential extent) had a ductility displacement value of only 2.9 mm. Finally, since the pipe material was highly ductile, only wrinkling failure mode occurred, and none failed due to rupture. Similar buckling with wrinkling but without rupture behavior was also observed by [PERSON] et al. [56], albeit without the influence of internal pressure. [PERSON] et al. [56] noted that the buckling behavior for deep corrosion, \(d/t=0.8\), was much more severe compared to those with medium depth corrosion, \(d/t=0.5\). This was indicated by a much lower collapse moment for pipes with \(d/t=0.8\) than those with \(d/t=0.5\). In cases where the axial compressional load is significantly large, failure modes such as buckling and wrinkling may occur. An FEA to assess the corrosion damage of pipelines subjected to combined internal pressure and external loading revealed that applying axial compressive stress and internal pressure caused buckling. This was prominent for pipes with shallow corrosion defects where the failure could be governed by global instability or buckling at the corrosion defect section of the pipe instead of rupture failure. The FEA model simulated API 5L X42 Grade B, X65, X80, and X100 pipelines subjected to defect depths ranging from 20% to 80% of the pipe wall thickness. Two sets of length and width dimensions were used, one being 8\(t\) by 2\(t\) with the other being 8\(t\) by 8\(t\). Referring to Figure 4, the pipes subjected to combined loads (internal pressure and axial compressive stress) above the failure locus were expected to fail via buckling, while those below were expected to remain safe [57]. A full-scale burst test on ASTM A333 Gr.6 pipeline material, which is commonly used as the secondary piping system of a nuclear power plant, showed that axial compressive forces subjected to corrosion defect region resulted in buckling failures [58]. The experiment included a four-point bending moment test that generated axial tensile and axial compressional forces. At the same time, the internal conditions of the pipeline were varied to be with or without internal pressure. Buckling failure can only occur before the onset of plastic deformation, and this behavior tends to happen with pipes with a relatively large diameter to full wall thickness ratio. Furthermore, the full-scale burst test proved that the length of corrosion defects, when subjected to external forces, influ  
Figure 4: In total, 457.2 mm (18 inch) Diameter Pipe with an 80% Deep Axial Groove—Internal Pressure versus Bending Moment Failure Locus [57]. Figure 3: Outward bulge buckling at the corrosion defect region [21]. The pipe is prone to cracking failure with the increase in corrosion defect length and the decrease in internal pressure. However, an increase in the corrosion defect width decreased the susceptibility of cracking and shifted the failure behavior to ovalization. This trend can be conceptually visualized in Figure 5[58]. This further proved that the corrosion defect length significantly affects the failure pressure of a pipe subjected to internal pressure and external loads. For compressional forces, the amount of pipe deformation depended on the corrosion defect's length and width. The study also summarized that, for short axial defects, tensile stress is the dominant force for failure, while for extended defects, compressive stress becomes the dominant force for failure [58]. [PERSON] et al. [31] investigated the possibility of bending collapse before any onset of rupture. Bending collapse is indicated by a zero slope of the moment versus the deflection curve. Bending collapse is due to a combination of progressive softening of the pipe wall through yielding, wrinkling, and ovalization. This softening behavior of the material is also supported by the work by [PERSON] et al. [35], who found that it occurs when the maximum moment is achieved.