In 1947, H. Morrogh discovered that when cerium was added to hypereutectic gray cast iron, the graphite was spherical when its content was above 0.02wt%. In 1948, A. P. Ganganebin et al. pointed out that spherical graphite was obtained when magnesium was added to cast iron and then inoculated with ferrosilicon when the residual magnesium content was more than 0.04wt%. Since then, nodular cast iron began to produce on a large scale. The use history of ductile iron pipes can be traced back to about 21.14 km of water pipeline from Seine River to Versailles in the suburbs of Paris in 1668. With the passage of 300 years, the main body of ductile iron pipes is still in use except for the maintenance and replacement of department pipes and joints.
The present situation and prospects of nodular cast iron pipes in China have been compiled in this section. China's nodular cast iron pipes industry started in the early 1990s and developed rapidly with the strong support of China Urban Water Supply Association. After nearly 20 years of practical use, its safety and practicability have been generally recognized by the water supply industry. In 2008, the annual output in China reached 2.2 million tons, 11 times that in 1990. Because our country is short of water resources, there are more than 600 water-deficient cities and more than 200 severe water-deficient cities. Water supply and water-saving undertakings are in the ascendant. Ductile iron pipe has a broad development prospect.
Advantages and disadvantages of the compilation of this paragraph:
Strengths:
In medium and low pressure pipeline network, ductile iron pipe has the advantages of safe and reliable operation, low damage rate, convenient construction and maintenance, and excellent anti-corrosion function.
Disadvantages:
In high-pressure pipeline network, generally not used, low pressure resistance. Because the pipe body is relatively bulky, machinery must be used in installation.
Manufacturers of the Compilation Section
The largest ductile iron pipe in China produces 1.5 million tons of ductile iron pipe annually and 50,000 tons of supporting pipe fittings. The product has been successfully applied to the key national and local engineering projects such as Taiyuan Yellow River Diversion Project, Lanzhou Yellow River Diversion Project, Nanjing Jiangning Water Supply Project, Xi'an City Water Environment Management Phase II Project, Baoji City Emergency Water Supply Project and so on. It has won the popularity of users with excellent quality and good service. Accreditation is recognized as the leading enterprise in the industry in China.
In addition, Maanshan Saint-Gobain, Shanxi Xuanshi, Jincheng Xinhuan and other manufacturers in the industry also have considerable strength. Saint-Gobain is the world's largest ductile iron pipe brand; Xuanshi, Xinhuan and other manufacturers are located in Jincheng, Shanxi Province, near Handan, Jincheng has always been a renowned forging town in the sea.
Key points of construction and installation in this compilation section:
1. Trench excavation
The width of groove bottom should be calculated as follows: B = D1 + 2 (b1 + b2)
In the formula, the excavation width at the bottom of the groove of B-pipeline (mm) D1-the outer edge width of pipeline structure (mm) b1-the working face width at the side of pipeline (mm) b2-the support width at the side of pipeline (mm)
2. Groove support
According to the factors such as soil quality, groundwater, slotted section, load premise, etc., the design should be firm and reliable, so as to prevent collapse and support from obstructing the lower pipe and stabilizing pipe.
3. The T-joint pipeline should be supported at the turning point in the vertical or horizontal direction. The size of the pier should be determined by calculation according to the factors such as pipe diameter, rotation angle and working pressure.
4. When transporting drinking water, the pipeline should not pass through the toxic contaminated area. If necessary, protective measures should be taken during the transit period.
5. All socketed ductile iron pipes must be supported by calculation. See National Building Standard Design Atlas 03SS505 "Flexible Joint Pipeline Piers".
6. External anti-corrosion coatings for ductile iron pipes should be galvanized and epoxy asphalt coatings or coatings with higher requirements according to the soil conditions of the piping site.
7. After the pipeline is installed and the pressure test is qualified, it is advisable to wash with low chloride ion water and disinfect with 0.03% potassium permanganate solution.
