What types of steel are used in pipelines?

Date:2024-09-29Tags:
In the application of industrial pipelines, the choice of steel is crucial. Different types of steel have different physical and chemical properties, so when choosing the right material, the use environment and requirements of the pipeline need to be considered. This article will explore several common types of pipeline steel, including carbon steel, alloy steel, stainless steel, galvanized steel, and the manufacturing characteristics of seamless and seamed pipes.

1. Types of steel used in pipelines

1.1 Carbon steel

Carbon steels account for about 90% of the total production of steel pipes. They are composed of relatively few alloying elements and are generally weaker when used alone. Because their mechanical properties and machinability are sufficient, they may cost slightly less and may be more suitable for low-stress applications. The lack of alloying elements reduces the suitability of carbon steels for high-pressure applications and extreme conditions, so they become less durable under high loads. The main reason why carbon steels are preferred for pipelines may be their good ductility and the property of not bending under load. They are commonly used in the automotive and marine industries and oil and gas transportation. A500, A53, A106, A252 are carbon steel grades that can be used as sutures or seamless.

1.2 Alloy steel

The presence of alloying elements improves the mechanical properties of steel, so the pipe is more resistant to high stress applications and high pressures. The most common alloying elements are nickel, chromium, manganese, copper, etc., which are present in amounts of 1-50 weight percent. Different alloying elements in different quantities affect the mechanical and chemical properties of the product in different ways, so the chemical composition of the steel is also modified according to the application requirements. Alloy steel pipes are generally used under high loads and unstable conditions, such as in the oil and gas industry, refineries, petrochemicals, and chemical plants.

1.3 Stainless steel

Stainless steel can also be classified under the family of alloy steels. The main alloying element in stainless steel is chromium, which is present in amounts between 10-20 weight percent. The main purpose of adding chromium is to give the steel stainless steel properties by preventing corrosion. Stainless steel pipes are often used in extreme conditions where corrosion resistance and high strength are crucial, such as in the marine industry, water purification, medicine, and the oil and gas industry. 304/304L and 316/316L are grades of stainless steel that can be used in pipe production. While the 304 grade has great corrosion resistance and strength; the 316 series has lower strength due to its low carbon content and can be welded.

1.4 Galvanized Steel

Galvanized pipe is steel pipe that has been treated with zinc to prevent corrosion. The zinc coating prevents corrosive substances from corroding the pipe. It was once the most common type of pipe in water supply lines, but due to the labor and time required to cut, thread and install galvanized pipe, it is no longer widely used except for limited use during repairs. These types of pipes range from 12 mm (0.5 in) to 15 cm (6 in) in diameter. They are available in lengths of 6 m (20 ft). However, galvanized pipes for water supply can still be seen in larger commercial applications. An important disadvantage of galvanized pipe is its service life of 40-50 years. Although the zinc coating covers the surface and prevents external substances from reacting with the steel and corroding it, the pipe may begin to corrode from the inside if the substance being transported is corrosive. Therefore, it is crucial to control and upgrade galvanized steel pipes in a specific period.

2 .Pipeline Types

According to the manufacturing method, pipes can be divided into two categories: seamless pipes and seamed pipes. Seamless pipes are formed in one go during the rolling process, while seamed pipes require a welding process after rolling. According to the seam geometry, seamed pipes can be divided into two categories: spiral welded and straight welded. Although there is controversy about whether seamless pipes are superior to seamed steel pipes, both seamless and welded pipe manufacturers can produce steel pipes with high quality, high reliability and corrosion resistance. When determining the type of pipe, the main focus should be on application specifications and cost aspects.

2.1 Seamless pipes

Seamless pipes are usually manufactured using a complex process, starting with drilling holes in the billet and then passing through cold drawing and cold rolling processes. In order to control the outer diameter and wall thickness, the size of seamless pipes is more difficult to control than welded pipes, and cold working can improve mechanical properties and tolerances. The most significant advantage of seamless pipes is that thick-walled pipes can be produced. Since seamless pipes have no welds, they are considered to have better mechanical properties and corrosion resistance than seamed pipes. In addition, the ovality or roundness of seamless pipes is also better. They are generally suitable for use in extreme environmental conditions such as high loads, high pressures and high corrosion.
 Seamless pipes

2.2 Seam pipes

Welded steel pipes are made of steel plates that are welded and rolled into a tube. The manufacturing process usually involves stretching hot billets or flat steel strips and pressing the edges together. Although the tolerances of seam pipes are tighter, the wall thickness is usually thinner, the delivery time is short and the cost is lower, so it is more advantageous in some applications. However, the weld may become a potential weak point where cracks may extend and cause the pipe to fail, so special attention should be paid to the treatment of the inner and outer surfaces of the pipe during the production process.

3. Summary

When choosing a suitable pipe material, it is necessary to comprehensively consider the characteristics of various types of steel and their applicability. Carbon steel, alloy steel, stainless steel and galvanized steel each have their own advantages and are suitable for different applications. Seamless pipes and seam pipes have their own advantages in performance and cost according to their manufacturing processes and characteristics. Understanding the characteristics of these materials will help make more informed choices in practical applications.

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