# The Influence of Axial Compressive Stress and Internal Pressure on a Pipeline Network: A Review
## 4 Effects of Axial Compressive Stress
### Detrimental Effects  
Axial compressive stress due to thermal expansion results in Euler-bar buckling. The peak bending moment corresponds to the maximum point of the bending moment-curvature relationship. This peak is triggered by the development of wrinkling and bulging of the pipe at the compressive side of the specimen [30]. [PERSON] et al. [54] found that the initiation of wrinkling always coincides with the maximum bending moment. The initiation of wrinkling is where the non-uniform deformation begins. Non-uniform deformation is determined when the strain in the region of wrinkle increases faster than the strain away from the wrinkle. The maximum bending moment decreases with the decrease in the material hardening ability and an increase in the outer diameter to thickness ratio. A study conducted by [PERSON] et al. [49] revealed wrinkling where the pipe showed an excessive loss in bending stiffness during the application of compressive bending loads before the rupture of the pipe. Wrinkling is said to occur when the peak moment is achieved. A zero slope indicates this peak moment at the moment versus the deflection behavior. It is directly affected by the wall loss in the maximum bending region and the magnitude of the internal pressure, axial compression (or tension), and axial bending. [PERSON] et al. (1998) [48] conducted 20 full-scale tests on X65, which is 60 feet in length with 48-inch diameter pipe sections with a 0.462-inch wall thickness, to further study this detrimental effect. For each wrinkling test, only a moderate temperature difference (equal to 75 \({}^{\circ}\)F) was investigated. This value reflects the reduction in transported crude temperature observed over the pipeline's lifetime and since the initiation of full-scale testing. The sequence of load application for each test was designed to simulate a pipe in service. Wrinkling was produced in test cases exhibiting extreme depths and general corrosion where the major dimension was oriented in the hoop direction. Close examination of the results for these cases, as reported in [PERSON] et al. [55], showed that the wrinkling instability point strongly corresponded to the depth and width of corrosion defect parameters and the initial pressure and temperature differential applied. [PERSON] et al. [48] found that corrosion defects might cause a reduction in the hoop buckling capacity of the pipe. This is because buckling, defined as an equilibrium problem, occurs when the external loads subjected to the pipe are higher than or equal to the internal resistance over the cross-section. The external loads here refer to the axial compression acting on the cross-section. Amplification of the external stress occurs due to imperfections such as initial deflection from the circular shape and the axial compression stress acting on the pipe wall. This amplification of external stress is not be affected by local corrosion defects unless the dimensions of the corrosion defects are very wide and deep. Experimental research by [PERSON] and [PERSON] [21] on API 5L X46 steel pipes with artificially machined single corrosion defects subjected to 20% and 40% of \(p_{y}\) while being subjected to axial compressive stress found that the load capacity (the ability to withstand axial compressive force) started to decrease due to the initiation and growth of wrinkling at the corrosion defect region. The wrinkle was noted to be an outward bulge-type local buckle at the pipe wall, as shown in Figure 3. The load capacity was the lowest for pipes with 50% corrosion defect depths (compared to 25% corrosion defect depths) as the wall thickness had been severely compromised. In addition to reducing the load-carrying capacity, larger corrosion defect depths presented lower ductility, which is determined through the lower displacement at the maximum load. For corrosion defects that were wider in the circumferential direction, the load-carrying capacity and ductility were considerably lower.