## 3 Mechanical Analysis of Inner Wall of Buried Non-Corroded Pipeline in Seasonal Frozen Soil Region
### One-Way Analysis of Extreme Variance for Orthogonal Design Method Result Data  
According to the corrosion parameters in Table 3 of orthogonal design and simulated by ABAQUS finite element software, the residual strengths of 25 pipelines were calculated, and the simulated data were collated and analyzed with the mathematical statistics method, as shown in Table 4.  
Figure 14: Mises equivalent stress variation curves in the corrosion zone. Figure 15: The Mises equivalent stress curve when the corrosion zone is located on the side (9 o’clock) of the inner wall of the pipeline: (**a**) The corrosion length is greater than 600 mm and the corrosion width is greater than 50 mm; (**b**) The corrosion length is greater than 900 mm and the corrosion width is greater than 50 mm. According to Table 4 analysis:  
1. When the corrosion length was constant, the residual strength curve became steeper and steeper as the depth-thickness ratio of the corrosion defects in buried pipelines increased from 15% to 80%, as shown in Figure 16a; the relative decrease rate of residual strength of buried corrosion defect pipeline gradually increased, as shown in Table 5. In addition, the average residual strength of the pipeline changed from 24.840 MPa to 10.414 MPa, which was reduced by 14.426 MPa. The numerical fluctuation was about 2 times the corrosion length and 8 times the corrosion width, indicating that the corrosion depth was the main factor affecting the residual strength of the pipeline. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{3}{c}{**Results of the Simulation**} & \multicolumn{5}{c}{**Analysis of Results Data**} \\ \hline \multirow{3}{*}{**Number**} & **Residual** & \multirow{3}{*}{**Number**} & **Residual** & \multicolumn{2}{c}{**A**} & **B** & **C** \\ \cline{3-8}  & **Strength** & & **Strength** & & **Corrosion Depth** & & **Corrosion Length** & **Corrosion Width** \\ \hline
1 & 25.69 & 14 & 16.10 & & 124.200 & 110.710 & 85.110 \\
2 & 25.43 & 15 & 15.43 & & 114.180 & 93.170 & 94.210 \\
3 & 25.09 & 16 & 20.93 & T & 92.320 & 87.110 & 86.820 \\
4 & 24.08 & 17 & 13.43 & & 61.910 & 78.160 & 91.160 \\
5 & 23.91 & 18 & 11.22 & & 52.070 & 75.530 & 87.380 \\
6 & 25.22 & 19 & 8.81 & & & & \\
7 & 23.31 & 20 & 7.52 & & 24.840 & 22.142 & 17.022 \\
8 & 22.19 & 21 & 17.12 & & 22.836 & 18.634 & 18.842 \\
9 & 21.77 & 22 & 10.72 & t & 18.464 & 17.422 & 17.364 \\
10 & 21.69 & 23 & 9.85 & & 12.382 & 15.632 & 18.232 \\
11 & 21.75 & 24 & 7.40 & & 10.414 & 15.106 & 17.476 \\
12 & 20.28 & 25 & 6.98 & & & \\
13 & 18.76 & & & R & 14.426 & 7.036 & 1.820 \\ \hline \hline \end{tabular} In Table 4, A, B and C denote corrosion depth, corrosion length and corrosion width (mm) respectively; T denotes the sum of the data of each level factor for each factor; t denotes the average value of the data of each level factor; R denotes the range of the average value of the data of each level factor, and its value indicates the degree of influence of the factor on the residual strength (MPa) of the defect pipeline.  
\end{table} 
Table 4: Analysis of extreme variance of the resultant data. Figure 16: Residual strength curve of buried corroded pipeline: (**a**) Different corrosion depths; (**b**) Different corrosion lengths. 1. When the corrosion depth was constant, the corrosion length increased from 100 mm to 600 mm, as shown in Figure 16b, the residual strength curve also becomes steeper and steeper. The residual strength of the buried pipeline with internal corrosion defects decreased gradually, and the average residual strength of the pipeline changed from 22.142 MPa to 15.632 MPa, which was reduced by 6.51 MPa. However, when the corrosion length increased from 600 mm to 900 mm, the relative reduction rate of residual strength decreased gradually, as shown in Table 6. At this time, the average residual strength of the pipeline changed from 15.632 MPa to 15.106 MPa, only reduced by 0.526 MPa. In conclusion, the corrosion length had a great effect on the residual strength of the pipeline.