# Safety Analysis of Buried Corrosion-Defect Gas Pipeline in Ceramic Soil Layer Under Blasting Action
## 5 Analysis of the Safety Factor of Pipeline Under Different Working Conditions  
With the acceleration of urbanization, blasting operations are becoming more and more frequent in urban construction. However, the vibration effect of blasting may pose a potential safety threat to nearby buried pipelines, especially corroded and defective gas pipelines. In order to evaluate the safety of pipeline under blasting vibration, the concept of a safety factor is introduced, that is, the ratio of the maximum stress of pipeline to its yield stress. Studying the variation law of the safety factor under different elastic moduli, pipeline thicknesses, and defect lengths provides a theoretical basis for the safety design and maintenance of gas pipeline.  
According to the specification \"Code for Design of Gas Pipeline Engineering\" (GB50251-2015) [24], the effective stress of ball mill cast-iron pipeline should meet the following:  
\[\sigma_{e}\leq 0.90\sigma_{s} \tag{15}\]  
In the formula, \(\sigma_{s}\) is the minimum yield strength specified in the pipe standard, in MPa. According to China's code on \"ductile iron pipes, fittings and accessories for water and gas pipelines\" (GB-T 13295-2008) [25], in this experiment, the ductile iron pipe \(\sigma_{s}\) is 300 MPa. It is calculated that \([\sigma]=270\) MPa, because \(\sigma_{e}<[\sigma]\), so the pipeline material is not damaged, the pipeline is in a safe state, and according to the field test inspection, there is no obvious deformation and damage of the pipe body, so the above formula is reasonable.  
Under the same blasting parameters, the safety factor of the corrosive gas pipeline increases with the increase of the elastic modulus, as shown in Figure 13 and Table 5. In Figure 13, it seems that solid lines show the safety factor while dashed lines show maximum stress. Specifically, when the elastic modulus increases from 100 GPa to 200 GPa, although the maximum stress of the pipeline decreases, the safety factor increases from 1.28 to 1.92 due to the constant yield stress. This change shows that the pipeline with a higher elastic modulus has a more stable structure when bearing the same blasting vibration, and can better resist the generation of stress, thus improving the safety performance of the pipeline. On the other hand, the influence of pipeline thickness on the safety factor shows a reverse changing trend. Under the assumed data, as the thickness of the pipeline increases from 2 mm to 6 mm, although the maximum stress should theoretically decrease from 320 MPa to 140 MPa, the yield stress remains unchanged. Therefore, the safety factor should theoretically increase.  
In practice, attention should be paid to the real impact of the increase in thickness on the maximum stress. However, it should be emphasized that in the actual situation, with the increase of the thickness of the pipeline, its resistance to blasting vibration will be significantly enhanced, so as to effectively reduce the maximum stress and improve the safety factor. As for the defect length, its increase will lead to a significant increase in the maximum stress of the pipeline, thereby reducing the safety factor, which demonstrates the need for special vigilance.