What Is a Ductile Iron Pipe?

Ductile iron pipe refers to a pipe that is cast by using no. 18 or more cast iron with a nodulizing agent and then centrifuged at a high speed by a centrifugal nodular cast iron machine. Mainly used for the transportation of tap water, it is the ideal choice for tap water pipelines.

In 1947, the British H. Morrogh discovered that when cerium was added to the hypereutectic gray cast iron so that the content was more than 0.02wt%, the graphite was spherical. In 1948, the United States APGanganebin et al. Pointed out that when magnesium was added to cast iron and then fertilized with ferrosilicon, spherical graphite was obtained when the residual magnesium content was greater than 0.04 wt%. Since then, large-scale industrial production of ductile iron has begun. The history of the use of cast iron pipes can be traced back to the water line of about 21.14Km from the Seine to Versailles in the suburbs of Paris in 1668. 300 years have passed. Except for the repair and replacement of some pipes and joints, the main body is still in use.

Status and Prospects of Ductile Iron Pipes in China

China's ductile iron pipe industry started in the early 1990s, and developed rapidly with the strong support of the China Urban Water Supply Association. After nearly 30 years of practical use, its safety and practicability have been generally recognized by the water supply industry. The annual output has reached 2.2 million tons, which is 11 times that of 1990. As China is a country with insufficient water resources, there are more than 600 cities with water shortages and more than 200 cities with severe water shortages. The water supply and water saving business is still in the ascendant. Ductile iron pipes have broad development prospects. ^[1]

Ductile iron pipe is a type of cast iron pipe. In terms of quality, the spheroidization level of the cast iron pipe is controlled to be 1-3 (spheroidization rate> 80%), so the material itself is mechanical

Ductile iron pipe is a type of cast iron, an alloy of iron, carbon and silicon. Graphite in nodular cast iron exists in the form of spheroids. Generally, the size of graphite is 6-7 grades, and the spheroidization grade of the cast pipe is controlled to 1-3 grades (spheroidization rate 80%). The properties have been better improved, with the nature of iron and the properties of steel. The annealed ductile iron pipe has good metallographic structure with ferrite and a small amount of pearlite.

Ductile iron pipe is mainly called

Minimum tensile strength: 420 / Mpa

Minimum yield strength: 300 / Mpa, minimum elongation 7%

Standard: GB / T13295-2013, ISO2531-2009

Caliber: DN80-DN2600

1.Trench excavation

The bottom width of the groove should be calculated as follows: B = D1 + 2 (b1 + b2)

Where: Bexcavation width at the bottom of the pipeline trench (mm) D1outer edge width of the pipeline structure (mm) b1width of the working surface on one side of the pipeline (mm) b2support width on one side of the pipeline (mm)

Groove support

The design is based on factors such as trench soil, groundwater, slotted section, and load conditions. It is required to be firm and reliable, to prevent landslides, and support not to hinder the downpipe and stabilize the pipe.

3. T-junction pipes should be provided with pieres at vertical or horizontal turns. The size of the pier should be determined by calculation based on factors such as pipe diameter, corner, and working pressure.

4. When transporting drinking water, the pipeline should not pass through the area polluted by poisons. If it must be passed, protective measures should be taken.

5. Nodular cast iron pipelines with socket connections must be calculated to set up pier, see National Building Standard Design Atlas 10S505 "Flexible Interface Water Supply Pipe Pier".

6. The outer anti-corrosion coating of ductile cast iron pipe should be selected according to the soil conditions of the pipe to be coated with galvanized and epoxy asphalt coating or higher requirements.

7. After the pipeline is installed and the pressure test is qualified, it should be washed with low chloride ion water and sterilized with 0.03% potassium permanganate solution.

1.Asphalt paint coating

Asphalt paint coatings are used to transport gas pipelines. Pre-heating the pipe before painting can improve the adhesion of asphalt paint and accelerate drying.

2. Cement mortar lining + special coating

This internal anti-corrosion measure is suitable for pipelines that transport sewage, which can improve the corrosion resistance of the inner lining.

3. Epoxy coal tar coating

Epoxy coal pitch coating is suitable for both gas pipelines and sewage pipelines. It is a two-component coating with high adhesion and a very smooth surface

4, epoxy ceramic lining

Epoxy ceramic lining is suitable for sewage pipes and gas pipes, but due to the difficulty of manufacturing process and high cost, it has certain limitations in use. Epoxy ceramic lining has high adhesion and smoothness and is a good anti-corrosion coating.

5.Aluminate cement coating or sulfate cement coating

These two special cement coatings are suitable for the internal corrosion protection of ductile iron pipes for sewage pipelines, and improve the ability to resist the erosion of acid and alkali components in sewage.

6, polyurethane coating

It is a new type of green special coating developed to meet the needs of environmental protection. It has good wear resistance and corrosion resistance. ^[3]