## 4 Results
### Parametric Study Using the Artificial Neural Network-Based Equation
The failure pressure of pipelines with deep corrosion defects was significantly lower (on average \(-65.90\%\)) than the failure pressure of pipelines with shallow corrosion defects. This could be attributed to the higher stress concentration at the defect region for deeper corrosion defects. The failure pressure remained the same for longitudinal compressive stress of less than 0.4 \(\sigma_{c}/\sigma_{y}\) for shallow corrosion defects, and then the failure pressure decreases linearly beyond 0.4 \(\sigma_{c}/\sigma_{y}\). The failure pressure was not significantly reduced when the longitudinal compressive stress was increased in a pipeline with deep corrosion defects. Similar trends were observed for defect lengths of 0.2, 0.4, 1.0, and 1.2 \(l/D\). Figure 12 shows the effect of longitudinal compressive stress on failure pressure for a corroded pipeline with 0.2 and 1.2 \(l/D\) normalised defect depths when the defect length was 0.5 \(d/t\). The trendlines in Figure 12 demonstrate a similar pattern across all three types of material for both short and long corrosion defects. The failure pressure of long corrosion defects was lower (on average \(-25.00\%\)) than the failure pressure of short corrosion defects, though it was not as significant as that shown in the trendlines of Figure 11. Similar trends were also observed for defect depths of 0.2, 0.4, 0.6, and 0.8 \(d/t\). The effect of defect length on failure pressure for all three types of material is plotted in Figure 13, where the trendlines for 0.2 and 0.8 \(d/t\) defect depths are compared at a fixed defect width of 10 \(w/t\). Similar to the results shown in Figure 11, the failure pressure of a pipeline with deep defects was significantly lower (\(-66.91\%\) on average) than failure the pressure of pipeline with shallow defects. Based on the trendlines of Figure 13, the failure pressure generally linearly decreased before plateauing at 0.8 \(l/D\). For trendlines of 0.2 \(d/t\), the average failure pressure reduction rates per 0.1 \(l/D\) of the X52, X65, and X80 pipelines were \(-0.66\%\), \(-0.81\%\), and \(-1.03\%\), respectively. For trendlines with 0.8 \(d/t\), the average failure pressure reduction rates per 0.1 \(l/D\) of the X52, X65, and X80 pipelines were \(-2.17\%\), \(-1.84\%\), and \(-1.66\%\), respectively. The average failure pressure reduction rate increased from 0.2 to 0.8 \(d/t\), which indicates that defect depth impacted failure pressure. The failure pressure of a pipeline with shallow corrosion defects slightly decreased when the defect length increased, but failure pressure of a pipeline with deep defects increased  
Figure 12: Failure pressure against normalised longitudinal compressive stress with 0.2 and 1.2 normalised defect lengths for X52, X65, and X80. with the increasing defect length (up until the plateau point of 0.8 \(l/D\)). Similar trends were also observed for longitudinal compressive stresses of 0.0, 0.2, 0.5, and 0.7 \(\sigma_{c}/\sigma_{y}\). Figure 14 shows the effect of defect length on failure pressure for a corroded pipeline with 0.0 and 0.7 \(\sigma_{c}/\sigma_{y}\) normalised longitudinal compressive stresses when the defect depth was fixed at 0.5 \(d/t\). The trendlines in Figure 14 are similar to the trendlines in Figure 13, showing that failure pressure linearly decreased and then started to plateau at 0.8 \(l/D\). The failure pressure difference between 0.0 and 0.7 \(\sigma_{c}/\sigma_{y}\) was \(-\)20.79% on average. Longitudinal compressive stress did not influence the failure pressure as much as defect depth. Similar trends were also observed for defect depths of 0.2, 0.4, 0.6, and 0.8 \(d/t\). Figure 14: Failure pressure against normalised defect length with 0.0 and 0.7 normalised longitudinal compressive stresses for X52, X65, and X80. Figure 13: Failure pressure against normalised defect length with 0.2 and 0.8 normalised defect depths for X52, X65, and X80.