## 4 Results
### Parametric Study Using the Artificial Neural Network-Based Equation  
A parametric study was conducted to investigate the effects of material property, defect depth, defect length, and longitudinal compressive stress on the remaining strength of corroded pipelines with single corrosion defects. The middle-to-high strength pipelines considered in this study were X52, X65, and X80. Figure 9 shows the effect of defect depth on failure pressure for corroded pipelines with 0.0 and 0.7 \(\sigma_{c}/\sigma_{y}\) longitudinal compressive stress when the defect length was fixed at 0.8 \(l/D\) and defect width was fixed at 10 \(w/t\). Figure 9 shows that the X80 trendline presented the highest failure pressure on average, followed by X65 and X52. The trendlines demonstrate the same behaviour, whereby the failure pressure of the corroded pipeline linearly decreases with an increase in defect depth, and the introduction of longitudinal compressive stress significantly reduced the failure pressure. For trendlines with no longitudinal compressive stress, the average failure pressure reduction rates per 0.1 \(d/t\) of the X52, X65, and X80 pipelines were \(-\)8.51%, \(-\)8.87%, and \(-\)9.70%, respectively. For trendlines with 0.7 \(\sigma_{c}/\sigma_{y}\), the average failure pressure reduction rates per 0.1 \(d/t\) of the X52, X65, and X80 pipelines were \(-\)5.51%, \(-\)4.85%, and \(-\)6.92%, respectively. It can be observed that the average reduction rate for failure pressure was reduced when \(\sigma_{c}/\sigma_{y}\) increased from 0.0 to 0.7. However, the failure pressure of the corroded pipe subjected 0.7 \(\sigma_{c}/\sigma_{y}\) was still significantly lower than 0.0 \(\sigma_{c}/\sigma_{y}\) (\(-\)23.99% on average). The trendlines of the same material type exhibited similar behaviour, whereby the failure pressure of 0.2 \(d/t\) defects between 0.0 and 0.7 \(\sigma_{c}/\sigma_{y}\) was reduced by almost half when the defect depth was 0.8 \(d/t\). Similar trends were observed for defect lengths of 0.2, 0.4, 1.0, and 1.2 \(l/D\). Figure 10 shows the effect of defect depth on the failure pressure of corroded pipelines with 0.2 and 1.2 \(l/D\) defect lengths when the longitudinal compressive stress was 0.4 \(\sigma_{c}/\sigma_{y}\). The trendlines of Figure 11 show that the failure pressure of the corroded pipelined linearly decreases with increasing defect depth, albeit not as steep as the trendlines in Figure 9. For trendlines with 0.2 \(l/D\), the average failure pressure reduction rates per 0.1 \(d/t\) of the X52, X65, and X80 pipelines were \(-\)4.29%, \(-\)3.94%, and \(-\)6.11%, respectively. For trendlines with 1.2 \(l/D\), the average failure pressure reduction rates per 0.1 \(d/t\) of the X52, X65, and  
Figure 9: Failure pressure against normalised defect depth, with 0.0 and 0.7 normalised longitudinal compressive stresses for X52, X65, and X80. X80 pipelines were \(-\)7.93%, 8.38%, and \(-\)8.33%, respectively. A comparison of shallow and deep corrosion defects showed that the average failure pressure reduction rate increased when \(l/D\) increased from 0.2 to 1.2. This shows that increasing defect length of deeper corrosion defects could lower the failure pressure of a corroded pipeline (by \(-\)21.94% on average). Similar trends were also observed for longitudinal compressive stresses of 0.0, 0.2, 0.5, and 0.7 \(\sigma_{c}/\sigma_{y}\). Figure 11 shows the effect of longitudinal compressive stress on failure pressure for a corroded pipeline with 0.2 and 0.8 \(d/t\) normalised defect depths when the defect  
Figure 11: Failure pressure against normalised longitudinal compressive stress with 0.2 and 0.8 normalised defect depths for X52, X65, and X80. Figure 10: Failure pressure against normalised defect depth with 0.2 and 1.2 normalised defect lengths for X52, X65, and X80. length was fixed at 0.8 \(l/D\) and defect width was fixed at 10 \(w/t\). The trendlines in Figure 11 demonstrate the same trend across all three types of material for both shallow and deep corrosion defects.