Which is better for ductile iron pipes and steel pipes to be corrosive in the same soil? Why?

The steel pipe is a little corrosion-resistant, and if it is ductile iron, it can be a little more corrosion-resistant than steel. Ordinary ductile iron is not corrosion-resistant.

Ductile iron pipes are more resistant to corrosion.

The corrosion resistance of ductile iron in various environments is mainly determined by its composition and microstructure. Each element in the composition of cast iron has an impact on its corrosion resistance, and carbon, silicon, manganese, phosphorus, and sulfur are the elements that must exist in cast iron.

1) Carbon (c).

The higher the amount of carbon, the higher the amount of graphite and cementite in its tissue. The cathode area increases, and the hydrogen evolution reaction accelerates. The rate of corrosion in non-oxidizing acids accelerates with increasing carbon content.

In oxidizing acids, the cathode components graphite and cementite make the alloy easy to change to a blunt state, and the corrosion rate decreases. In a neutral solution, the cathode is depolarized by oxygen, and the change in carbon content has no significant effect on the corrosion rate.

2) Silicon element (Si).

Ductile iron usually contains 1 3 of silicon. When the silicon content reaches about 4, the corrosion resistance of cast iron can be appropriately increased. When the silicon content reaches more than 14, the corrosion resistance of cast iron will be significantly improved.

However, the increase of silicon content will make the mechanical properties of cast iron become very poor, when the silicon content is greater than 16, cast iron will become very brittle, difficult to process, therefore, the silicon content in cast iron is generally controlled within 14 16.

The addition of silicon can form a dense SiO2 protective film on the surface of cast iron, which has high resistivity and high chemical stability, preventing further corrosion of cast iron by corrosive media.

The addition of silicon can also passivate the base metal in the cast iron structure, that is, the anode area, increase the electrode potential, and effectively improve the chemical corrosion resistance and electrochemical corrosion resistance of cast iron.

3) Manganese (MN).

Manganese and silicon are in the usual content range (Mn, Si

1 2 ), does not affect the corrosion resistance of cast iron.

4) Sulfur (s).

Sulfur reacts with iron and manganese to form sulfides that precipitate in a separate phase, which acts as cathode inclusions and accelerates corrosion (especially in acidic solutions).

5) Phosphorus (P).

Phosphorus ( does not change the corrosion resistance of cast iron in neutral media and atmospheric conditions, but in some media, such as unconcentrated inorganic acid solutions, the phosphorus content increases, promoting the hydrogen evolution reaction, resulting in a decrease in corrosion resistance.

In general, the effect of the above elements on the corrosion resistance of cast iron is not obvious in the normal content range. In order to improve the corrosion resistance of cast iron, alloying elements such as Ni, Cr, Si, Cu and Al are usually added to cast iron; Elements such as Ti (titanium) and V (vanadium) are also occasionally added as alloying elements. The addition of these elements, either alone or in combination, has a great effect on improving the corrosion and heat resistance of cast iron.

What is the specific content of the anti-corrosion treatment of ductile iron pipes, the following Zhongda Consulting will answer for you.

1.Asphalt paint coating.

Asphalt paint coating is used in pipelines to transport gas. Preheating the tube before painting can improve the adhesion of the asphalt paint and speed up drying.

2.Cement mortar lining + special coating.

This internal anti-corrosion measure is suitable for pipes transporting sewage, and the slag caution can improve the corrosion resistance of the lining.

3.Epoxy coal pitch coating.

The epoxy coal asphalt coating is suitable for both gas and sewage pipelines. It is a two-component beam coating with high adhesion and a very smooth surface.

4.Epoxy ceramic lining.

Epoxy ceramic lining is suitable for sewage pipes and gas pipelines, but due to the difficult manufacturing process and high cost, Zhijing has certain limitations in use. The epoxy ceramic lining has a high adhesion and finish and is an excellent anti-corrosion coating.

5.Aluminate cement coating or sulfate cement coating.

Both of these 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, with good wear resistance and corrosion resistance.

1. The concept is different

Machine-made cast iron pipe is a flexible interface drainage cast iron pipe produced by centrifugal pouring process, and the interface is generally W-type clamp type or A-type flange socket type.

Ductile iron pipe refers to the pipe made by high-speed centrifugal casting of centrifugal ductile iron machine after adding nodularizing agent to cast molten iron above No. 18, referred to as ball tube, ductile iron pipe and ductile cast pipe. It is mainly used for the transportation of tap water, and is an ideal material for tap water pipelines.

2. The performance is different

Ductile iron pipes are a type of cast iron, which is an alloy of iron, carbon, and silicon. Graphite in ductile iron is in the form of spheroids, the size of the general graphite is 6-7 grades, and the quality requires the nodularization grade of the cast pipe to be controlled as 1-3 grades, so the mechanical properties of the material itself have been well improved, with the essence of iron, the properties of steel. The annealed ductile iron pipe has a metallographic structure of ferrite and a small amount of pearlite, and the mechanical properties are good.

The service life of the machine-made cast iron pipe exceeds the life expectancy of the building, excellent seismic performance, can be applied to the seismic fortification of high-rise buildings, and the flexible connection of flange gland and rubber ring or lined rubber ring and stainless steel clamp is adopted, with good sealing, allowing swing in the range of 15 degrees without leakage.

Metal type centrifugal casting, cast iron pipe wall thickness is uniform, the structure is dense, the surface is smooth, there are no sand holes, slag inclusion and other casting defects. The rubber interface suppresses noise and is irreplaceable for the quietest pipe, creating the most comfortable living environment.

3. Different uses

Cast iron pipes are suitable for building drainage, sewage, civil engineering, road drainage, industrial wastewater, and agricultural irrigation pipelines; Cast iron pipes can be applied to large pipeline axial expansion displacement and transverse deflection deformation; Cast iron pipes are suitable for use in areas with a intensity of less than 9 degrees.

Graphite cast iron pipe is mainly called centrifugal ductile iron pipe, which has the essence of iron, the performance of steel, excellent anti-corrosion performance, good ductility performance, good sealing effect, easy installation, mainly used in municipal, industrial and mining enterprises water supply, gas transportation, oil transportation, etc. It is the first choice for water supply pipes, and it has a high cost performance.

There are some differences in materials and properties between ductile iron pipes (also known as ductile iron pipes or ductile iron pipes) and ordinary cast iron pipes:

1.Material composition: The base material of ductile wheels and cast iron pipes and ordinary cast iron pipes is cast iron, but ductile graphite particles are added to the ductile iron pipes. These particles give ductile iron pipes better toughness and tensile strength.

2.Performance characteristics: ductile iron pipes have better mechanical properties than ordinary cast iron pipes.

Ductile iron pipes have high bending strength and good impact toughness, and can withstand large deformation and external impact without being easy to break. Ordinary cast iron pipes, on the other hand, are brittle, and have relatively low tensile strength and impact toughness.

3.Corrosion resistance: There are also differences in the corrosion resistance of ductile iron pipes and ordinary cast iron pipes.

Due to the ductile graphite particles in the ductile iron pipe and the special treatment, it has good corrosion resistance and is suitable for use in some special environments and conditions. Ordinary cast iron pipes may corrode in some corrosive mediators.

4.Production process: The manufacturing process of ductile iron pipes is relatively complex and requires nodular ink treatment. This process involves the addition of a nodularizing agent and heat treatment to form a spherical graphite particle structure. Ordinary cast iron pipes do not have this process step.

Many people will confuse ductile iron pipes with ordinary cast iron pipes, so what is the difference between ductile iron pipes and ordinary cast iron pipes? Next, I will introduce it to you.

1. The definition is different

Ordinary cast iron pipe is a flexible interface drainage cast iron pipe produced by centrifugal casting process, and ductile iron pipe refers to the pipe made by high-speed centrifugal casting of centrifugal ductile iron machine after adding nodularizing agent to cast molten iron above No. 18.

2. The use is different

Ordinary cast iron pipes are suitable for building drainage, sewage, civil engineering, road drainage, industrial wastewater, etc., and ductile iron pipes are mainly used for water supply, gas transportation, oil transportation and so on in municipal, industrial and mining enterprises.

Do the smart ductile iron pipes on the market need to be separately anti-corrosion pro! Hello, I am glad to answer for you<> the ductile iron pipe on the market is Qi Xing's demolition of high jujubes, whether it does not need to be separately anticorrosive, the characteristics of ductile iron are not perishable and not easy to deform, so if there are special requirements, there is no need to do separate anti-corrosion treatment. Ductile iron pipe external anti-corrosion 1

Technical requirements for anti-corrosion layer: (1) The coating should have good adhesion with the ductile iron pipe; (2) Corrosion resistance of chemical media (including acid and alkaline soil and acid atmosphere); (3) Good mechanical and physical properties (hardness, wear resistance, flexibility); (4) Good weather resistance in the open air (including humid climate and strong ultraviolet rays); (5) Resistant to microorganisms, insects and rodents. (6) The buried part should be resistant to plant root penetration.

2.The selection of anti-corrosion layer epoxy coal asphalt anti-corrosion layer anti-corrosion materials and structures shall comply with: "Technical Standard for Epoxy Coal Asphalt Anti-corrosion Layer of Buried Steel Pipelines" (SY T0447-96) "Code for Construction and Acceptance of Epoxy Coal Asphalt Anti-corrosion Layer of Buried Steel Pipelines" (SY) 4047-90) "Code for Construction and Acceptance of Water Supply and Drainage Pipeline Engineering" (GB50268-97) 1) Before the ductile iron pipe is used for anti-corrosion construction, sandblasting and rust removal should be used until the ductile iron pipe exposes the metallic luster, which should reach (GB T8923-1988).

2) The anti-corrosion requirements of the pipe body are special grade, one bottom four oil and two cloths, the glass cloth is 10 12 or 10 10 alkali wax-free glass cloth, and the acceptance of the anti-corrosion layer of the dry film thickness: aCheck the adhesion, cut a tongue-shaped incision with a knife, and tear the anti-corrosion layer at the incision forcefully, and the surface of the pipe is still covered with patent leather, and the metal surface should not be exposed.

b.EDM test, with DC EDM leak detector, 5kV voltage detection, to do not spark as qualified. 3. The outer wall of the exposed ductile iron pipe should be pretreated with decontamination and rust removal before anti-corrosion, so as to meet the SA21 grade 2 standard in the "Steel Surface Corrosion Grade and Rust Removal Grade Before Painting" (GB T8923-1988).

After the outer wall of the ductile iron pipe is rusted, the outer wall is coated with IPN8710-2C weather-resistant color and paint, and the coating structure is two bottoms and two sides, and the total thickness of the paint film (dry film). Ductile iron pipe anti-corrosion directly buried section ductile iron pipe anti-corrosion can use cement mortar (8 2mm), overhead section ductile iron pipe anti-corrosion using the Ministry of Health licensed drinking water coating, such as IPN8710-2B drinking water coating, etc., the coating structure is two bottoms and two sides, the total thickness of the paint film is 2160um, so that the surface is smooth, no falling off, no missing brush, no blistering, I hope my can help you <>

Do you have any other questions?

Ductile iron pipes must be treated with anti-rust treatment in the production process, and the finished products can be used directly after the production.

Ductile iron pipes are mainly produced by heating and annealing in the intermediate frequency furnace and then lined with cement for anti-corrosion on the outer wall, while machine-made cast iron pipes are not lined with cement.

The length of a single ductile iron pipe is 6 meters, and the wall thickness is large; The single length of the machine-made cast iron pipe is 3 meters, and the wall thickness is thin.

Ductile iron pipes are widely used in municipal water supply and drainage, rural drinking water and outdoor fire protection engineering; The main purpose of the machine-made cast iron pipe is high-rise drainage and sewerage in the city.

Ductile iron pipes are commonly connected with flexible sealing rings; Mechanism drain pipes are mainly W type and B type, clamp connection and mechanical connection, inner gasket sealing ring.

Ductile iron has high strength and strong plasticity. The tensile strength of ductile iron is twice that of gray cast iron, and the yield strength even exceeds that of cast steel. Therefore, the compressive strength of ductile iron drainage pipe is much higher than that of cast iron drainage pipe, which is buried in the ground and is not easy to be crushed by automobiles.

Comparison of the performance of ductile iron pipes and common cast iron pipes:

The manufacturing process of ductile iron pipe is to add alkaline earth metals such as magnesium and calcium to the raw materials of ordinary cast iron pipes or rare metals to cast them. The casting process of ductile iron pipe includes continuous casting, hot mold casting and water-cooled centrifugal casting, among which the water-cooled method is the most advanced technology in the world today, and the technical performance of ductile iron in different processes.

Compared with ordinary cast iron pipes, it not only maintains the corrosion resistance of ordinary cast iron pipes, but also has the advantages of high strength, good toughness, thin walls, light weight, impact resistance, large bending performance, and easy installation. Therefore, ductile iron pipes are not only widely used abroad, but also have been well promoted in China, in many areas of China, ductile iron pipes have been widely used in medium and small diameter water supply pipes;

Comparison of the performance of ductile iron pipe and steel pipe:

Steel pipes can be divided into seamed steel pipes and seamless steel pipes, and seamed pipes are generally used in the middle channel of water supply pipes. Compared with ductile iron pipes, steel pipes have the advantages of good toughness, high tensile strength, thin pipe walls, high pressure resistance, long pipes, and few interfaces, but the biggest disadvantage is poor corrosion resistance and high corrosion resistance. Therefore, in general, except for small-diameter pipes and special works (e.g. pipe jacking works;

Performance comparison of ductile iron pipe and prestressed reinforced concrete pipe:

Ductile iron pipes and prestressed reinforced concrete pipes (suitable for large-diameter pipes, the maximum diameter has exceeded 2000), with the following characteristics:

1) Energy saving, the main materials are sand and stone, which can be used locally.

2) Large weight, brittle texture, difficult cutting and chiseling, and relatively difficult construction.

3) The working pressure is 2O-40 lower than that of the ductile ink tube, which is 0 15-0 25MPa.

4) The maximum deflection angle is 1 5 degrees, while the maximum deflection angle of ductile iron pipe can reach 3 0 degrees, so the terrain adaptability of the prestressed reinforced concrete pipe is poor.

Performance comparison of ductile iron pipe and PVC plastic pipe:

Compared with ductile iron pipes, PVC pipes are characterized by smooth inner wall, light weight, corrosion resistance, good anti-scaling performance, low quality, etc., but there are also many shortcomings, mainly the following points:

1) Easy aging, thermal expansion and contraction, should not be exposed to sunlight for a long time, storage room temperature should not be greater than 40.

2) Low strength, poor compressive performance, improper construction is easy to cause deformation. ．

3) Poor rigidity, poor deflection, easy to cause leakage.