1. General introduction
Vietnam is a hot and humid tropical country with a coastline of more than 3200 km stretching from North to South. This is the environmental condition that causes metal corrosion at a very high rate. According to survey data of Vietnam Association of Corrosion Science and Technology, the corrosion damage in our country is not less than 5% of GPD. Thus, it can be seen that the annual economic loss in our country is up to 20-25 billion USD due to corrosion, which is indeed a large loss. Corrosion damage in the world is also very large, in the US alone, this annual loss amounts to several hundreds of billions of dollars.
Therefore, the corrosion protection of metals to prolong the life of structures and equipment plays a very important role in the economy. To prevent metal corrosion, a variety of measures can be applied, including:
Selection of appropriate materials with high corrosion resistance in the working environment;
Using measures to change the corrosive aggressiveness of the environment, including the use of corrosion inhibitors;
Selection and use of coatings with long life, high mechanical strength;
In fact, the use of coating materials is a very popular, long-standing method and is an important measure in preventing metal corrosion. In some specific cases, such as underground buried pipelines and tanks, it is common to combine coating with electrochemical (cathode) protection. Open-air pipes and tanks are combined with coatings with corrosion inhibitors.
Therefore, the choice of protection measures must be considered carefully right from the design of the works. In other words, the choice of coating materials to protect against corrosion is especially important to determine the life of the building.
2. Conditions for metal corrosion to occur
The main cause of metal corrosion is the presence of both elements: water and oxygen.
Equipment, steel pipes (Fe-C) in contact with water (or steam) and oxygen gas often react:
3Fe + 4H2O = Fe3O4 (rust) + 4H2↑
3Fe + 2O2 = Fe3O4 (rust)
Or a redox reaction occurs in the electrolyte environment (soil with low resistance, acid, sword, salt …) and produces Fe3O4 nH2O (rust). This process generates a corrosion current and a faster rate of corrosion.
In some cases, steel corrosion even occurs in the absence of oxygen. Especially the sulphate corrosive form. Elemental sulfur is produced by microorganisms that decompose organic impurities.
3. Các dạng ăn mòn đường ống thép chôn ngầm
- Ăn mòn diện rộng: xảy ra với tốc độ đồng đều trên hầu hết các bề mặt trong suốt chiều dài đường ống. Hiện tượng này đối với các đường ống đã lâu năm hoặc các lớp phủ bảo vệ có tuổi thọ thấp và môi trường ăn mòn khá đồng đều.
- Ăn mòn cục bộ, rỗ: là trường hợp phản ứng ăn mòn cục bộ, phần lớn là do khuyết tật của lớp sơn hoặc lớp sơn phủ có độ bền cơ học thấp, bị hư hỏng trong quá trình lắp đặt gây trầy xước lớp sơn…
- Ăn mòn dạng mài mòn hay bào mòn cơ học: là trường hợp xảy ra mặt trong các đường ống, do các chất lỏng được vận chuyển gây ra các hiện tượng mài mòn của các hạt tạp chất đối với bề mặt đường ống.
- Ăn mòn dạng ứng suất: do quá trình đè nén, tải trọng nền đất, đá, cát… tác dụng làm biến dạng đường ống và kết hợp với các tác nhân ăn mòn gây ra.
4. Corrosion protection of buried pipelines
Underground pipelines when designed and installed usually require a minimum service life of more than 30 years. Maintenance and repair of underground pipes is a very expensive job and sometimes cannot be done due to site clearance conditions, deep underground, difficult to dismantle and replace… Therefore, any damage caused by Corrosion caused by the user is undesirable and can result in heavy economic loss. One of the preventive measures from the beginning is, the user or the designer must choose the most suitable coating, the highest mechanical and chemical resistance, the longest life …
Coatings for buried pipelines require the following characteristics:
High waterproofing ability (water, oxygen …)
Good electrical and electrical insulation
High adhesion to pipe surface
High mechanical and chemical resistance
Good impact resistance
Anti-scratch and wear-resistant, to protect from damage during handling, testing, transportation, installation and other site operations
Resistance to soil changes and thermal stress
High crack resistance
Currently, in the world different types of coatings are used to protect buried pipelines including:
Coal bitumen coating: coating used for a long time. Has the advantage of low cost, the disadvantage is low durability, low impact resistance, very easy to scratch during installation and contains toxic solvents. This type in the world today is very limited and rarely used.
Epoxy-based paint: common epoxy paint system is commonly used, easy to apply. Disadvantages are poor impact resistance, brittle, easy to crack, not resistant to thermal shock. Epoxy life is not too high, usually from 10 years to 15 years.
Newtec is applying the advanced line of Epoxy ceramic for pipeline protection projects.
Prestressed concrete pipes D1500 and D1200 are manufactured by Prestressed Concrete Factory in District 9 – HCM to serve the supply of clean water in the city for the Vo Van Van – Nguyen Van Linh route. NEWTEC is a supplier and installer of high strength poly epoxy amine based coating by two-component hot spray technology that cures quickly within 20 minutes, high wear resistance, good permeability and flexibility. . (Has WHO NSF certification in the US.)
Polyethylene jacketing coating: used by wrapping the pipe outside, leaving many joints. The polyethylene cover may be damaged during installation. It softens at 80°C (176°F) and melts near 100 to 110°C (212 to 230°F). It is not possible to apply protective coating inside the pipeline. Therefore, the application of this type is limited.
Polyurea coating: has been widely used in the world since about 30 years ago. In Vietnam, it has been used to protect pipelines for more than 10 years. This is the perfect coating of the 21st century with many outstanding advantages compared to other coatings.
The VOC-free polyurea coating used for buried pipelines is an example of new coatings developed due to stringent regulatory requirements. These coatings are used for water and wastewater piping systems, oil and gas pipelines and industrial applications.
Polyurea nguyên chất được sử dụng để lót đường ống nước sạch, vì nó trơ, có khả năng chống chịu nước và không có lợi cho sự phát triển của vi sinh vật và vi khuẩn. Lớp phủ polyurea rất thích hợp cho các đường ống dẫn nước thải cũng như các hệ thống xử lý nước thải bởi khả năng chịu ăn mòn hóa chất và chịu mài mòn cơ học rất cao.
Polyurea coatings have the following advantages over other coatings:
- Polyurea cures fast (10-15 seconds) and ensures economy with high production rate and efficiency.
- Has high adhesion to steel, concrete…
- Polyurea has high impact resistance.
- The corrosion resistance of polyurea is very high.
- Polyurea is highly resistant to cracking.
- High tensile strength and high elasticity.
- Reduced hydraulic loss due to smoother inner surface of the pipeline.
- The long-term economic effect due to the reduction of aggressive wear is low.
- In the case of industrial pipes or sewage pipes, pipes can be attacked by chemicals such as chlorides, alkalis, acids… then polyurea has high chemical resistance, ensuring a long economic life. than.
Corrosion inside oil and gas pipelines occurs when the pipe surface reacts with a combination of contaminants (e.g. moisture, oxygen, carbon dioxide, chloride, and sulfur compounds) present in the pipeline. gas. Operating parameters such as gas temperature, flow rate and particle velocity are also important to prevent corrosion. Corrosion is also induced and sustained by microorganisms when nutrients are present on the inner pipe surface.
This corrosion can be minimized by following operating instructions for temperature, velocity and contaminant control parameters.
Polyurea coatings are used as an optimal solution to prevent corrosion of gas and oil pipelines.
- The choice of anti-corrosion measure or in other words the choice of a protective coating against corrosion for buried pipelines is especially important. In order to ensure economic and technical efficiency as well as to ensure the life of the project. Polyurea-based materials are today’s most optimal choice for long-term corrosion protection for buried pipelines. The lifespan of polyurea in the underground environment over 30 years will bring high economic benefits to the whole society and minimize the damage caused by corrosion.
- NEWTEC is a leading provider of solutions for coating materials and polyurea coatings in Vietnam. We always improve the technology and improve the quality management system of waterproof and anti-corrosion coating systems to protect the works of all investors to ensure long-term durability and the highest economic efficiency.
- For more information, please contact NEWTEC at:
Newtec Construction and Trading Joint Stock Company
Room 808, House N2B, Trung Hoa Urban Area – Nhan Chinh, Nhan Chinh, Thanh Xuan, Hanoi.
Phone number: 024 32252003 – 093 880 7536