A comprehensive comparative analysis of ductile iron pipes and steel pipes with different materials is carried out in this article, and a preliminary analysis of the actual engineering economic comparison results of generally buried pipelines is provided.
1. Making a comprehensive performance comparison of ductile iron pipes and steel pipes
In the economic comparison of buried pipelines, 3PE anticorrosive steel pipes and ductile iron pipes are mainly compared. The economy of general projects is compared from three perspectives, namely labor, materials, and machinery. Generally, the comprehensive unit price is used for the direct comparison in the pricing process.
2. Making a comparison of the properties of the two materials
Ductile iron pipes and steel pipes are both metal pipes, and the performance difference between the two is mainly manifested in the difference in mechanical properties and anti-corrosion properties. Globular graphite can be obtained for nodular cast iron by adding a spheroidizing agent to improve the performance of cast iron. Its characteristic is that the hardness of the base material and the welding heat-affected zone is good, so it can withstand damage caused by a higher external force. In terms of anti-corrosion, the anti-corrosion performance of cast iron pipelines is superior, and no additional protection methods are required. The anti-corrosion performance of steel pipelines mainly depends on the anti-corrosion layer outside the pipeline and the sacrificial anode protection after the pipeline is laid.
Table 1 A performance comparison of two kinds of materials
| |
Ductile iron pipes |
Steel pipes |
| Anti-corrosion performance |
Being excellent |
There is a danger of corrosion protection and treatment of welding seams at the joint part in a humid environment. |
| Service lives |
Long service lives |
According to corrosion |
| Fire risks |
Low (non combustion-supporting materials) |
Low (non combustion-supporting materials) |
| Installation |
Socket ends, fast installation speeds, and heavy materials making it difficult to transport and hoist |
Slow welding, a lot of smoke, and difficult transportation and lifting |
| Influence of hydraulic interference |
Flexible interface with good adaptability |
The rigid interface being affected |
| The influence of expanding with heat and contract with cold |
The socket end being able to offset the influence |
Requiring an expansion joint |
3. Making a comparison of economic performance of general buried pipelines
Centrifugal cast iron pipes are easy and fast to install, and they are not affected by ambient temperatures, making them more suitable for sudden operations. Through an analysis and comparison, it can be seen from the comparison of comprehensive unit prices that PE pipes are suitable for pipes with a diameter less than 200 mm, while centrifugal ductile iron pipes are suitable for pipes with a pipe diameter 200 mm or over.
From the perspective of earthwork, earthwork includes excavation of trenches, backfilling, and disposal. The overall workload is not much different whether anti-corrosion seamless steels or PE pipes are used. In the installation stage of the pipeline, the budget of using seamless steel pipes is greater than that of using PE pipes. It should be pointed out that because the anti-corrosion steel pipes need to be subjected to the X-ray inspection for quality control, the engineering cost is relatively high. In terms of the electrical protection of seamless steel pipes, whether it is anode protection or anti-corrosion inspection fees, it is also a great cost. For PE pipes, no electrical protection is required. Generally, the method of electronic markers plus guide markers is used, and the overall cost is reduced by nearly 25 times.
By comparing the economic performance of the different materials, it can be seen that in the medium and low-pressure gas pipelines, PE pipes are suitable for pipelines below DN200. Centrifugal ductile iron pipes are applicable for pipelines with sizes between DN200 and DN400. 3PE anticorrosion steel pipes are good for pipelines with sizes above DN400. Although the old gray cast iron pipes have been eliminated, the performance of the new centrifugal ductile iron pipes can meet the engineering requirements and has the possibility of surpassing steel pipes in terms of anti-corrosion performance. Centrifugal ductile iron pipes have cheaper prices than steel pipes and PE pipes based on the price of centrifugal ductile iron pipes in other regions. Therefore, whether the centrifugal ductile iron pipe can become a gas pipeline in Beijing again is still a question.
