# The Influence of Axial Compressive Stress and Internal Pressure on a Pipeline Network: A Review
## 4 Effects of Axial Compressive Stress
### Detrimental Effects
Excessive ovalization of a pipe prevents the passage of inspection devices such as a PIG through the pipeline. The maximum allowable ovalization recommended in the SUPERB project is 5% [63]. A study by [PERSON] et al. [31] found that ovalization contributes to a loss of bending stiffness, which would eventually lead to bending collapse. [PERSON] and [PERSON] [30] found that failure modes such as bursting or fracture/plastic collapse would be dominant for pipes with a \(D/t<30\). This is because, for pipes with a \(D/t<30\), wrinkling only occurs at very high levels of pipe deformation. They added that bursting occurs when the pipe is subjected to axial compressive over-stress, resulting in excessive hoop strains, followed by external bulging accompanied by the thinning of the pipe and eventually bursting. [PERSON] and [PERSON] [64] and [PERSON] et al. [65] mentioned that, in terms of the pipe material, the burst pressure of a new pipe is weakly dependent on the yield strength; however, it is strongly dependent on the ultimate tensile strength and the burst failure is dominant for thick-pressured pipes. [PERSON] et al. [31] conducted a full-scale test on X65 steel pipe with artificially machined corrosion subjected to internal pressure and axial compressive stress. Axial compressive stress resulted in pipe bending and rupturing at the nominal compression side. The rupture failure was found to have been initiated within the corrosion defect with cracks running along the axial direction. This is due to the maximum strain being located within the corrosion defect and the cracks initiating and propagating in the axial direction due to the local plastic hoop strain being much more significant than the tensile plastic strain at the corrosion defect. Further parametric studies using FEA found that several failures were due to local ruptures. The FEA is also consistent with the results of the full-scale test where the rupture would begin at the corrosion defect on the nominal compression side in the presence of bending stress. Furthermore, failure due to rupture occurs for serious corrosion defects when subjected to relatively high internal pressure and axial compressive stress. It is generally known that an increase in the corrosion defect depth results in a significant decrease in the failure pressure. Similarly, for a pipe with constant corrosion depth, an increase in the corrosion defect length and width results in a lower failure pressure [31]. [PERSON] et al. [66] conducted 12 full-scale burst tests to develop the DNV-RP-F101 corrosion assessment method. The full-scale burst tests were conducted on X52-grade pipes. Test 5, Test 6, Test 7, and Test 9 were subjected to combined internal pressure and axial compressive forces with longitudinally and circumferentially aligned corrosion defects, while Test 10, Test 11, and Test 12 were subjected to combined internal pressure and axial compressive forces with groove corrosion defects. The results revealed that under compressive stress, axially oriented corrosion defects have a lower failure pressure than pipes with circumferentially oriented corrosion defects, despite the circumferential corrosion encompassing the entire diameter of the pipe. An example of a burst failure of an axially oriented defect is shown in Figure 8. In total, two out of the three pipes that had circumferentially oriented corrosion defects failed in a manner that the rupture occurred along the longitudinal direction. This exact failure behavior was also noted by other researchers [41; 67]. In a few cases, as noted by [PERSON] et al. [31], sufficient temperature increases, which results in high axial compressive stress, would cause the pipe to fail due to axial collapse. Axial collapse is the buckling of the pipe of a column specifically due to axial compressive stress. This type of buckling failure is often indicated by the zero slope of the axial load versus the midspan deflection curve.