Abstract: Steel pipes and ductile iron pipes, as the first choice in the construction industry, have their own advantages and disadvantages. The economy of pipe engineering from the perspective of investment is analyzed, providing economic value reference for the comparison and selection of engineering pipes. For the Beijing area, when the pipe diameter is less than or equal to 800 mm, ductile iron pipes lined with cement mortar internal anticorrosive are more cost-effective after analysis; when the pipe diameter is greater than 800mm, steel pipes lined with cement mortar internal anticorrosive are more cost-effective. At the same time, it is proposed that the use of steel pipes lined with epoxy ceramic internal anticorrosive in the same project can effectively reduce construction investment.
At present, the most widely used pipes in water diversion and supply projects in China mainly include steel pipes, ductile iron pipes, glass steel pipes, PE pipes and PVC pipes. FRP pipes, PE pipes and PVC pipes have limited applications due to terrain adaptability, durability and product quality that are difficult to control. Steel pipes and ductile iron pipes have become favored by the construction industry.
Steel pipes have light weights and high strength, and are well adaptable to terrain. However, their internal and external anti-corrosion requirements are high and a large amount of joint welding work is required. Ductile iron pipes have good anti-corrosion performance and easy construction, but have poor terrain adaptability. The two kinds of pipes have their own advantages and disadvantages. Advantages and disadvantages of the two types of pipes from a technical point of view are not analyzed in this article, and only the economy of the project from the perspective of investment is analyzed, providing value reference for the comparison and selection of engineering pipes.
1. Unit price analysis of pipes based on pipe diameters
Carrying out a comparative analysis of the unit price of different pipes with the same pipe diameter and type of internal anti-corrosion form, aims to purely compare the cost of the pipe itself and analyze the unit price of the pipe, pipeline construction and installation.
1.1 Basic conditions of analysis
Combine the pipeline and internal anti-corrosion, and the names and specific definitions of each combination are as follows:
- S1, steel pipes coated with cement mortar internal anti-corrosion
- S2, grade K9 ductile iron pipes coated with cement mortar internal anti-corrosion, 3S3, steel pipes with epoxy ceramic internal anti-corrosion, 4S4, grade K9 ductile iron pipes lined with epoxy ceramic internal anti-corrosion
The comparative analyzed price is based on Cost Information of Construction Project in Beijing in October 2018. The wall thickness of the steel pipe involved in the article is set according to the operating conditions such as design working pressure of 0.7 MPa and a distance of 3m from the top outer wall to the ground. See the Table 1 for details.
Table 1 Wall thickness of steel pipes
| Pipe diameter/mm |
500 |
600 |
700 |
800 |
900 |
1000 |
1100 |
1200 |
1300 |
1400 |
1500 |
| Wall thickness/mm |
7 |
7 |
8 |
8 |
9 |
9 |
10 |
10 |
11 |
11 |
12 |
1.2 Analysis of the unit price of pipes
According to the Figure 1, from the perspective of the unit price of pipes, it is concluded that:
(1) Under the condition of a cement mortar internal anti-corrosion coating, when the pipe diameter is less than 800 mm, the unit price of steel pipes is higher than that of ductile iron pipes; when the pipe diameter is greater than 800 mm, the unit price of ductile iron pipes is significantly higher.
(2) Under the condition of the epoxy ceramic internal anti-corrosion coating, the unit price of steel pipes in the research range is significantly lower than that of ductile iron pipes, and the bigger the pipe diameter becomes, the more the difference is.
(3) When the pipe diameter is less than 800 mm, ductile iron pipes coated with cement mortar internal anti-corrosion are the most cost-effective; when the pipe diameter is greater than 800 mm, the steel pipe coated with cement mortar internal anti-corrosion is the most cost-effective. If there are other requirements, you can compare steel pipes coated with epoxy ceramic anti-corrosion and ductile iron pipes lined with cement mortar internal anti-corrosion and choose a better one.
Figure 1 Unit prices of pipes based on pipe diameters
(4) The ductile iron pipe coated with epoxy ceramic internal anticorrosive is less cost-effective.
1.3 Unit price analysis of pipeline construction and installation
Figure 2 Construction and installation unit price statistics based on pipe diameters
According to the Figure 2, from the perspective of the unit price of pipeline construction and installation, it is concluded that:
(1) Under cement mortar internal anti-corrosion conditions, when the pipe diameter is less than 800 mm, the unit price of steel pipe construction is basically the same as that of ductile iron pipe construction; when the pipe diameter is greater than 800 mm, the unit price of steel pipe construction is significantly lower than that of ductile iron pipe construction.
(2) Under the condition of the epoxy ceramic internal anti-corrosion coating, the unit price of steel pipe construction in the research range is significantly lower than that of the ductile iron pipe construction; the bigger the pipe diameter becomes, the more different it is.
(3) When the pipe diameter is less than 800 mm, you can compare steel pipes with cement mortar internal anticorrosive coatings and ductile iron pipes coated with cement mortar internal anticorrosive, and then select a better one; when the pipe diameter is greater than 800 mm, the steel pipe coated with cement mortar internal anticorrosive has the better cost performance. If there are higher anti-corrosion requirements, steel pipes with epoxy ceramic internal anti-corrosion have more advantages.
(4) The ductile iron pipe with epoxy ceramic internal anticorrosive coating has a lower cost performance.
1.4 Summary
Both the unit price of pipes and pipeline construction reflect the same laws: (1) When the pipe diameter is small (less than or equal to 800 mm), the ductile iron pipe has more economic advantages, and the ductile iron pipe with cement mortar internal corrosion is the most cost-effective; when the pipe diameter is large (greater than 800 mm), the steel pipe has more economic advantages, and the steel pipe with cement mortar anti-corrosion coatings has the best cost performance. (2) Steel pipes are more suitable when epoxy ceramics are required due to higher internal anti-corrosion requirements. 